To see the other types of publications on this topic, follow the link: Octahedral structure.
Journal articles on the topic 'Octahedral structure'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Octahedral structure.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Burns, Peter C. "The crystal structure of szenicsite, Cu3MoO4(OH)4." Mineralogical Magazine 62, no. 04 (1998): 461–69. http://dx.doi.org/10.1180/002646198547837.
Full textAbstract:
Abstract The crystal structure of szenicsite, Cu3MoO4(OH)4, orthorhombic, a = 8.5201(8), b = 12.545(1), c = 6.0794(6) Å, V = 649.8(2) Å3, space group Pnnm, Z = 4, has been solved by direct methods and refined by least-squares techniques to an agreement index (R) of 3.34% and a goodness-of-fit (S) of 1.11 for 686 unique observed [|F| ⩾ 4σF] reflections collected using graphite-monochromated Mo-Kα X-radiation and a CCD area detector. The structure contains three unique Cu2+ positions that are each coordinated by six anions in distorted octahedral arrangements; the distortions of the octahedra are due to the Jahn-Teller effect associated with a d 9 metal in an octahedral ligand-field. The single unique Mo6+ position is tetrahedrally coordinated by four O2− anions. The Cu2+ϕ6 (ϕ: unspecified ligand) octahedra share trans edges to form rutile-like chains, three of which join by the sharing of octahedral edges to form triple chains that are parallel to [001]. The MoO4 tetrahedra are linked to either side of the triple chain of Cu2+ϕ6 octahedra by the sharing of two vertices per tetrahedron, and the resulting chains are cross-linked through tetrahedral-octahedral vertex sharing to form a framework structure. The structure of szenicsite is closely related to that of antlerite, Cu3SO4(OH)4, which contains similar triple chains of edge-sharing Cu2+ϕ6 octahedra.
2
Colombo, F., J. Rius, O. Vallcorba, and E. V. Pannunzio Miner. "The crystal structure of sarmientite, Fe23+ (AsO4)(SO4)(OH)·5H2O, solved ab initio from laboratory powder diffraction data." Mineralogical Magazine 78, no. 2 (2014): 347–60. http://dx.doi.org/10.1180/minmag.2014.078.2.08.
Full textAbstract:
AbstractThe crystal structure of sarmientite, Fe23+ (AsO4)(SO4)(OH)·5H2O, from the type locality (Santa Elena mine, San Juan Province, Argentina), was solved and refined from in-house powder diffraction data (CuKα1,2 radiation). It is monoclinic, space group P21/n, with unit-cell dimensions a = 6.5298(1), b = 18.5228(4), c = 9.6344(3) Å, β = 97.444(2)º, V = 1155.5(5) Å3, and Z = 4. The structure model was derived from cluster-based Patterson-function direct methods and refined by means of the Rietveld method to Rwp = 0.0733 (X2 = 2.20). The structure consists of pairs of octahedral-tetrahedral (Fe−As) chains at (y,z) = (0,0) and (½,½), running along a. There are two symmetry-independent octahedral Fe sites. The Fe1 octahedra share two corners with the neighbouring arsenate groups. Both individual chains are related by a symmetry centre and joined by two symmetry-related Fe2 octahedra. Each Fe2 octahedron shares three corners with double-chain polyhedra (O3, O4 with arsenate groups; the O8 hydroxyl group with the Fe1 octahedron) and one corner (O11) with the monodentate sulfate group. The coordination of the Fe2 octahedron is completed by two H2O molecules (O9 and O10). There is also a complex network of H bonds that connects polyhedra within and among chains. Raman and infrared spectra show that (SO4)2− tetrahedra are strongly distorted.
3
Schwendtner, Karolina, and Uwe Kolitsch. "Octahedral As in M + arsenates – architecture and seven new members." Acta Crystallographica Section B Structural Science 63, no. 2 (2007): 205–15. http://dx.doi.org/10.1107/s0108768106054942.
Full textAbstract:
Arsenates with arsenic in octahedral coordination are very rare. The present paper provides an overview of all known M + arsenates(V) containing octahedrally coordinated arsenic (M + = Li, Na, K, Rb, Cs, Ag) and the crystal structures (determined from single-crystal X-ray diffraction data) of the following seven new hydrothermally synthesized members belonging to six different structure types, four of which are novel: LiH2As3O9, LiH3As2O7, NaHAs2O6-type KHAs2O6, KH3As4O12 and isotypic RbH3As4O12, CsAs3O8 and NaH2As3O9-type AgH2As3O9. The main building unit of these compounds is usually an As4O14 cluster of two edge-sharing AsO6 octahedra sharing two apical corners each with two AsO4 tetrahedra. The different connectivity between these clusters defines the different structure types. The novel CsAs3O8 structure, based on a derivative of the As4O14 cluster, is the most condensed of all these M + arsenates, with an O/As ratio of only 2.67 compared with values of 2.75–3.5 for the remaining members. This is achieved through polymerization of the cluster derivatives to infinite chains of edge-sharing AsO6 octahedra. The [4]As/[6]As ratio drops to only 0.5. All but two of the protonated title compounds show protonated AsO6 octahedra. Hydrogen bonds range from very strong to weak. An analysis of bond-length distribution and average bond lengths in AsO6 octahedra in inorganic compounds leads to an overall mean As—O distance for all known AsO6 octahedra (with R factors < 0.072) of 1.830 (2) Å.
4
Balić-Žunić, Tonči, Martha G. Pamato, and Fabrizio Nestola. "Redetermination and new description of the crystal structure of vanthoffite, Na6Mg(SO4)4." Acta Crystallographica Section E Crystallographic Communications 76, no. 6 (2020): 785–89. http://dx.doi.org/10.1107/s2056989020005873.
Full textAbstract:
The crystal structure of vanthoffite {hexasodium magnesium tetrakis[sulfate(VI)]}, Na6Mg(SO4)4, was solved in the year 1964 on a synthetic sample [Fischer & Hellner (1964). Acta Cryst. 17, 1613]. Here we report a redetermination of its crystal structure on a mineral sample with improved precision. It was refined in the space group P21/c from a crystal originating from Surtsey, Iceland. The unique Mg (site symmetry \overline{1}) and the two S atoms are in usual, only slightly distorted octahedral and tetrahedral coordinations, respectively. The three independent Na atoms are in a distorted octahedral coordination (1×) and distorted 7-coordinations intermediate between a `split octahedron' and a pentagonal bipyramid (2×). [MgO6] coordination polyhedra interchange with one half of the sulfate tetrahedra in <011> chains forming a (100) meshed layer, with dimers formed by edge-sharing [NaO7] polyhedra filling the interchain spaces. The other [NaO7] polyhedra are organized in a parallel layer formed by [010] and [001] chains united through edge sharing and bonds to the remaining half of sulfate groups and to [NaO6] octahedra. The two types of layers interconnect through tight bonding, which explains the lack of morphological characteristics typical of layered structures.
5
Beck, J., and F. Wolf. "Three New Polymorphic Forms of Molybdenum Pentachloride." Acta Crystallographica Section B Structural Science 53, no. 6 (1997): 895–903. http://dx.doi.org/10.1107/s0108768197008331.
Full textAbstract:
Three new polymorphic modifications of molybdenum pentachloride could be obtained by solvothermal syntheses in CCl4 and SbCl5 as solvents. The structures have been solved by single-crystal X-ray diffraction. The already known structure of monoclinic \alpha-MoCl5 (C2/m) is not isomorphous with \alpha-NbCl5 and is better derived from the closest packing of Cl atoms of the Sm type with molybdenum occupying 1/5 of the octahedral holes. The triclinic structure of \beta-MoCl5 (P\overline 1) can be derived from hexagonal closest packing. The orthorhombic structure of \gamma-MoCl5 (Pnma) and the monoclinic structure of \delta-MoCl5 (P21/c) can both be derived from double-hexagonal closest packing. All four forms of MoCl5 have in common the discrete Mo2Cl10 moieties built from edge-sharing double octahedra with the metal atoms displaced from the octahedron centres away from each other. The differences between the modifications lie in the different stacking sequences of the close-packed Cl-atom layers and the different occupation of the octahedral interstices. This is reflected in the group–subgroup relationships of the space groups of the closest packings and the molybdenum pentachlorides. X-ray powder diffraction shows that sublimed MoCl5 is a mixture of all four modifications in variable amounts and probably a further unknown form.
6
Martin, C. David, Yue Meng, Vitali Prakapenka, and John B. Parise. "Gasketing optimized for large sample volume in the diamond anvil cell: first application to MgGeO3and implications for structural systematics of the perovskite to post-perovskite transition." Journal of Applied Crystallography 41, no. 1 (2008): 38–43. http://dx.doi.org/10.1107/s0021889807050029.
Full textAbstract:
Structure models of MgGeO3post-perovskite (Cmcm) are presented, along with a structure survey, demonstrating that all perovskite, post-perovskite and CaIrO3-type structures (ABX3) have specific ranges of the volume ratio between cation-centered polyhedra (VA:VB). The quality of the reported diffraction data and MgGeO3structure models is enhancedviaimplementation of a new graphite gasket for the diamond anvil cell, which stabilizes a larger sample volume, improving powder statistics during X-ray diffraction, andviathe thermal insulation required to achieve ultra-high temperatures while laser-heating samples at pressures near 100 GPa. The structure survey supports the theory that the pressure–temperature conditions under which the perovskite/post-perovskite phase transition occurs can be estimated by extrapolating the change inVA:VBto a value of 4, which corresponds to a maximum tilt ofBX6octahedra in the perovskite structure (Pbnm) where inter-octahedral anion–anion distances match the average intra-octahedral anion–anion distance. Once these short inter-octahedral distances between anions are reached in the perovskite structure, further tilting of octahedra and decrease of theVA:VBratio does not occur, driving the transition to post-perovskite structure as pressure is increased.
7
Post, Jeffrey E., Peter J. Heaney, and Andreas Ertl. "Rietveld refinement of the ranciéite structure using synchrotron powder diffraction data." Powder Diffraction 23, no. 1 (2008): 10–14. http://dx.doi.org/10.1154/1.2836477.
Full textAbstract:
Rietveld refinement using synchrotron powder X-ray diffraction data of the ranciéite, Ca0.19K0.01(Mn4+0.91◻0.09)O2⋅0.63H2O, crystal structure reveals significant differences from that reported previously. The interlayer H2O molecules occupy sites halfway between the Mn,O octahedral sheets. The Mn sites in the octahedral sheets have 10% vacancies, and the mean Mn–O distance indicates that all Mn is tetravalent (Mn4+). The interlayer Ca cations are located above and below the Mn vacancies and are octahedrally coordinated to three O2 atoms in the octahedral sheet and three H2O molecules in the interlayer.
8
Kovac, Sabina, Predrag Dabic, and Aleksandar Kremenovic. "Crystal structure of K3EuSi2O7." Journal of the Serbian Chemical Society 86, no. 7-8 (2021): 663–72. http://dx.doi.org/10.2298/jsc210218026k.
Full textAbstract:
As part of research on the flux technique for growing alkali rare-earth elements (REE) containing silicates, tripotassium europium disilicate, K3EuSi2O7, was synthesized and characterized by single-crystal X-ray diffraction. It crystallizes in the space group P63/mcm. In the crystal structure of the title compound, one part of the Eu cations are in a slightly distorted octahedral coordination and the other part are in an ideal trigonal prismatic coordination environment. The disilicate Si2O7 groups connect four EuO6 octahedra and one EuO6 trigonal prism. Three differently coordinated potassium cations are located between them. Silicates containing the larger rare earth elements usually crystallize in a structure that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment.
9
Redhammer, Günther J., Haruo Ohashi, and Georg Roth. "Single-crystal structure refinement of NaTiSi2O6 clinopyroxene at low temperatures (298 < T < 100 K)." Acta Crystallographica Section B Structural Science 59, no. 6 (2003): 730–46. http://dx.doi.org/10.1107/s0108768103022018.
Full textAbstract:
The alkali-metal clinopyroxene NaTi3+Si2O6, one of the rare compounds with trivalent titanium, was synthesized at high temperature/high pressure and subsequently investigated by single-crystal X-ray diffraction methods between 298 and 100 K. One main difference between the high- and the low-temperature form is the sudden appearance of two different Ti3+—Ti3+ interatomic distances within the infinite chain of the TiO6 octahedra just below 197 K. This change can be seen as direct evidence for the formation of Ti—Ti singlet pairs in the low-temperature phase. Mean Ti—O bond lengths smoothly decrease with decreasing temperature and the phase transition is associated with a slight jump in the Ti—O bond length. The break in symmetry, however, causes distinct variations, especially with respect to the two Ti—Oapex bond lengths, but also with respect to the four Ti—O bonds in the equatorial plane of the octahedron. The TiO6 octahedron appears to be stretched in the chain direction with a slightly larger elongation in the P\bar 1 low-temperature phase compared with the C2/c high-temperature phase. Polyhedral distortion parameters such as bond-length distortion and octahedral angle variance suggest the TiO6 octahedron in P\bar 1 to be closer to the geometry of an ideal octahedron than in C2/c. Mean Na—O bond lengths decrease with decreasing temperature and the variations in individual Na—O bond lengths are the result of variations in the geometry of the octahedral site. The tetrahedral site acts as a rigid unit, which does not show pronounced changes upon cooling and through the phase transitions. There are neither large changes in bond lengths and angles nor in polyhedral distortion parameters, for the tetrahedral site, when they are plotted. In contrast with the C2/c → P21/c phase transition, found especially in LiMSi2O6 clinopyroxenes, no very large variations are found for the tetrahedral bridging angle. Thus, it is concluded that the main factor inducing the phase transition and controlling the structural variations is the M1 octahedral site.
10
Reinauer, F., and R. Glaum. "Ideal and Real Structure of Ti5O4(PO4)4: X-ray and HRTEM Investigations." Acta Crystallographica Section B Structural Science 54, no. 6 (1998): 722–31. http://dx.doi.org/10.1107/s0108768198003590.
Full textAbstract:
The crystal structure of pentatitanium tetraoxide tetrakis(phosphate), Ti5O4(PO4)4, has been determined and refined from X-ray diffraction single-crystal data [P212121 (No. 19), Z = 4, a = 12.8417 (12), b = 14.4195 (13), c = 7.4622 (9) Å (from Guinier photographs); conventional residual R 1 = 0.042 for 2556 Fo > 4σ(Fo ), R 1 = 0.057 for all 3276 independent reflections; 282 parameters; 29 atoms in the asymmetric unit of the ideal structure]. The structure is closely related to those of β-Fe2O(PO4)-type phosphates and synthetic lipscombite, Fe3(PO4)4(OH). While these consist of infinite chains of face-sharing MO6 octahedra, in pentatitanium tetraoxide tetrakis(phosphate) only five-eighths of the octahedral voids are occupied according to □3Ti5O4(PO4)4. Four of the five independent Ti4+O6 show high radial distortion [1.72 ≤ d(Ti−O) ≤ 2.39 Å] and a typical 1 + 4 + 1 distance distribution. The fifth Ti4+O6 is an almost regular octahedron [1.91 ≤ d(Ti−O) ≤ 1.98 Å]. Partial disorder of Ti4+ over the available octahedral voids is revealed by the X-ray structure refinement. High-resolution transmission electron microscopy (HRTEM) investigations confirm this result.
11
Bosi, Ferdinando. "Chemical and structural variability in cubic spinel oxides." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 75, no. 2 (2019): 279–85. http://dx.doi.org/10.1107/s2052520619002282.
Full textAbstract:
The empirical relations between cubic spinel oxides of different compositions were investigated using data from 349 refined crystal structures. The results show that the spinel structure is able to tolerate many constituents (at least 36) by enlarging and decreasing the tetrahedra and octahedra. This is reflected in a large variation in tetrahedral and octahedral bond distances. The oxygen positional parameter (u) may be regarded as a measure of the distortion of the spinel structure from cubic close packing or of the angular distortion of the octahedron. The distortion can best be explained in terms of ionic potential (IP), which merges the size and charge properties of an ion. Sterically induced distortion depends on ion size, whereas electrostatically induced distortion is caused by cation–cation repulsion across faces of tetrahedra and shared edges of octahedra. The strong correlations between the u parameter and the IP at the T and M sites are consistent with the main role played by the both charge and size. Large distortions (u ≫ 0.27) result in oxygen–oxygen distances of the octahedron shorter than 2.50 Å, which would lead to structural instability because of increased non-bonded repulsion forces between the oxygen atoms.
12
Hennings, Erik, Horst Schmidt, and Wolfgang Voigt. "Crystal structures of ZnCl2·2.5H2O, ZnCl2·3H2O and ZnCl2·4.5H2O." Acta Crystallographica Section E Structure Reports Online 70, no. 12 (2014): 515–18. http://dx.doi.org/10.1107/s1600536814024738.
Full textAbstract:
The formation of different complexes in aqueous solutions is an important step in understanding the behavior of zinc chloride in water. The structure of concentrated ZnCl2solutions is governed by coordination competition of Cl−and H2O around Zn2+. According to the solid–liquid phase diagram, the title compounds were crystallized below room temperature. The structure of ZnCl2·2.5H2O contains Zn2+both in a tetrahedral coordination with Cl−and in an octahedral environment defined by five water molecules and one Cl−shared with the [ZnCl4]2−unit. Thus, these two different types of Zn2+cations form isolated units with composition [Zn2Cl4(H2O)5] (pentaaqua-μ-chlorido-trichloridodizinc). The trihydrate {hexaaquazinc tetrachloridozinc, [Zn(H2O)6][ZnCl4]}, consists of three different Zn2+cations, one of which is tetrahedrally coordinated by four Cl−anions. The two other Zn2+cations are each located on an inversion centre and are octahedrally surrounded by water molecules. The [ZnCl4] tetrahedra and [Zn(H2O)6] octahedra are arranged in alternating rows parallel to [001]. The structure of the 4.5-hydrate {hexaaquazinc tetrachloridozinc trihydrate, [Zn(H2O)6][ZnCl4]·3H2O}, consists of isolated octahedral [Zn(H2O)6] and tetrahedral [ZnCl4] units, as well as additional lattice water molecules. O—H...O hydrogen bonds between the water molecules as donor and ZnCl4tetrahedra and water molecules as acceptor groups leads to the formation of a three-dimensional network in each of the three structures.
13
Fleet, M. E., and S. W. Knipe. "Structure of Magnesium Hydroxide Sulfate [2MgSO4.Mg(OH)2] and Solid Solution in Magnesium Hydroxide Sulfate Hydrate and Caminite." Acta Crystallographica Section B Structural Science 53, no. 3 (1997): 358–63. http://dx.doi.org/10.1107/s0108768197000104.
Full textAbstract:
Magnesium hydroxide sulfate [2MgSO4.Mg(OH)2; MHS] is tetragonal with a = 7.454 (1), c = 12.885 (2) Å, V = 716.0 Å3, space group P43212, Z = 4 and D x 2.774 g cm−3. The structure (single-crystal X-ray, R = 0.025, wR = 0.023) comprises spiral (43) single chains of corner-shared Mg(2) octahedra cross-linked by SO4 tetrahedra and face-shared Mg(1) octahedra. A linear ternary group of face-shared Mg octahedra [Mg(2)—Mg(1)—Mg(2)] alternates with an unoccupied octahedral position in rows along [\overline 110]. A crystal of MHS was grown hydrothermally (0.15 GPa, 673 K) from gold-bearing Mg—S—O—H fluid. The MHS structure, with Mg(1) octahedra sharing two octahedral faces with Mg(2) octahedra, revises the structure assumed for the complex solid solution magnesium hydroxide sulfate hydrate and the related ocean-floor mineral caminite [2MgSO4.xMg(OH)2.(2 − 2x)H2O; 0.5 < x < 1.0]. The substitution reaction appears to be Mg(1)2+ ⇋ 2H+. The H-substituted MHS structure is distinguished from that of kieserite (MgSO4.H2O), which has straight single chains of corner-shared Mg octahedra.
14
Saber, Muna, and Anton Van der Ven. "Lithium Intercalation Mechanisms in Wadsley-Roth Phases." ECS Meeting Abstracts MA2023-01, no. 2 (2023): 694. http://dx.doi.org/10.1149/ma2023-012694mtgabs.
Full textAbstract:
Wadsley-Roth crystallographic shear phases are complex inorganic compounds that intercalate alkali ions at a rapid rate, allowing for fast charging lithium-ion battery electrodes with high power densities. Wadsley-Roth crystallographic shear phases consist of mxn size blocks of corner-sharing octahedra. These mxn blocks of octahedra share edges with other blocks of corner sharing octahedra, thereby forming what are referred to as crystallographic shear planes. A variety of Wadsley-Roth phases have been synthesized with differing structural features including the size of the blocks of corner-sharing transition metal octahedra, transition metal chemistry, and disorder among the transition metal sites. Using first-principles statistical mechanics methods, we have predicted the electrochemical properties of PNb9O25, TiNb2O7, and Nb2O5 (Figure 1), three important Wadsley-Roth shear phases, to explore the interplay between crystal structure, transition metal chemistry, Li site preferences, and the voltage profile. The computational approach relied on a triptych of ab initio density functional theory calculations, cluster expansion methods and finite temperature Monte Carlo methods. The calculations provide insights about lithium site preferences, strain evolution[1], and electronic structure [2, 3] as a function of state of charge in representative Wadsley-Roth phases. For the PNb9O25 compound, we find that lithium prefers to initially fill pyramidal sites at the crystallographic shear planes. It is not until higher lithium concentrations that Li begins to fill window sites at the center of the 3 by 3 octahedral blocks. This inversion in Li-Va ordering is paired with an increase of crystallographic strain and a decrease in octahedral distortions. In contrast to PNb9O25, the TiNb2O7 compound, a commercialized Wadsley-Roth phase, is characterized by Ti-Nb disorder on the transition metal sublattice. We find that the Nb, due to its higher oxidation state, prefers octahedral sites that share fewer edges with neighboring octahedra, relegating the lower oxidation state Ti cations to octahedra at the block edges. First-principles calculations and Monte Carlo simulations predict that the lithium site stability is paired to the local transition metal chemistry and ordering, with Li preferring to fill sites coordinated by TiO6 octahedra. With the use of symmetry adapted collective displacement order parameters we uncover changes in octahedral distortions that differ between the TiO6 and NbO6 octahedra upon intercalation of lithium. Furthermore, we find a similar evolution in strain upon intercalation as is predicted for PNb9O25. To study the effect of octahedral block size on electrochemical properties of Wadsley-Roth phases, we performed an additional in-depth study on Nb2O5, a Wadsley-Roth structure with 4 by 4 corner-sharing octahedral blocks. Predictions for this phase indicate that the dilute limit Li site preference changes when increasing block sizes. Unlike TiNb2O7 and PNb9O25, which have 3 by 3 octahedral block structures, lithium window sites at the center of the block are stable in Nb2O5 at the dilute limit. We attribute this to differences in octahedral distortions in the 4 by 4 and 3 by 3 blocks. Our results indicate that there are a wide variety of structural and chemical levers with which to modify and further optimize the electrochemical properties of Wadsley-Roth phases. References Saber, M., Preefer, M.B., Kolli, S.K., Zhang, W., Laurita, G., Dunn, B., Seshadri, R. and Van der Ven, A., 2021. Role of Electronic Structure in Li Ordering and Chemical Strain in the Fast Charging Wadsley–Roth Phase PNb9O25. Chemistry of Materials, 33(19), pp.7755-7766. Preefer, M.B., Saber, M., Wei, Q., Bashian, N.H., Bocarsly, J.D., Zhang, W., Lee, G., Milam-Guerrero, J., Howard, E.S., Vincent, R.C. and Melot, B.C., 2020. Multielectron redox and insulator-to-metal transition upon lithium insertion in the fast-charging, Wadsley-Roth phase PNb9O25. Chemistry of Materials, 32(11), pp.4553-4563. Baek, S.W., Preefer, M.B., Saber, M., Zhai, K., Frajnkovič, M., Zhou, Y., Dunn, B.S., Van der Ven, A., Seshadri, R. and Pilon, L., 2022. Potentiometric entropy and operando calorimetric measurements reveal fast charging mechanisms in PNb9O25. Journal of Power Sources, 520, p.230776. Figure 1
15
Hohn, Frauke, Heinrich Billetter, Ingo Pantenburg, and Uwe Ruschewitz. "Ni(C2(COO)2)(H2O)4 · 2 H2O und Ni(C2(COO)2)(H2O)2: zwei Koordinationspolymere mit dem Acetylendicarboxylat-Dianion / Ni(C2(COO)2)(H2O)4 · 2 H2O and Ni(C2 (COO)2)(H2O)2: Two Co-ordination Polymers of the Acetylenedicarboxylate Dianion." Zeitschrift für Naturforschung B 57, no. 12 (2002): 1375–81. http://dx.doi.org/10.1515/znb-2002-1206.
Full textAbstract:
From a solution of Ni(CH3COO)2 ∙ 4 H2O and acetylenedicarboxylic acid in deionized water single crystals of Ni(C2(COO)2)(H2O)4 ∙ 2 H2O(P21/a, Z = 2, isotypic to Co(C2(COO)2)(H2O)4 ∙ 2 H2O) were obtained by slow evaporation of the solvent. In the solid state structure nickel is octahedrally surrounded by four water molecules and two oxygen atoms of the carboxylate anions. These octahedra are connected to chains by the dicarboxylates. Heating the hexahydrate to 100 °C in a stream of argon leads to Ni(C2(COO)2)(H2O)2 (C2/c, Z = 4, isotypic to Mn[C2(COO)2] ∙ 2 H2O). Here, the NiO6 octahedron is built by two water molecules and four oxygen atoms of the dicarboxylate ligands, which connect the Ni octahedra to a three-dimensional network. Thermoanalytical investigations show another mass loss at about 200 °C, which leads to non-crystalline products. Finally, at about 400 °C NiO is formed. Measurements of the magnetic susceptibilities result in the expected behaviour for Ni2+ in an octahedral co-ordination (3A2 ground state). The effective magnetic moment at room temperature is μeff = 3.20 μB.
16
Cooper, M. A., F. C. Hawthorne, and M. E. Back. "The crystal structure of khinite and polytypism in khinite and parakhinite." Mineralogical Magazine 72, no. 3 (2008): 763–70. http://dx.doi.org/10.1180/minmag.2008.072.3.763.
Full textAbstract:
AbstractThe crystal structure of khinite, Pb2+Cu2+3Te6+O6(OH)2, orthorhombic, a = 5.7491(10), b = 10.0176(14), c = 24.022(3) Å, V = 1383.6(4) Å3, space group Fdd2, Z = 8, Dcalc = 6.29 g/cm3, from the Empire mine, Tombstone, Arizona, USA, has been solved by direct methods and refined to R1 = 3.2% on the basis of 636 unique observed reflections. There is one distinct Te site occupied by Te and coordinated by six O atoms in an octahedral arrangement with a <Te–O> distance of 1.962 Å. typical of Te6+. There are three octahedrally-coordinated Cu sites, each of which is occupied by Cu2+ with <Cu–O> distances of 2.132, 2.151 and 2.308 Å, respectively. Each Cu octahedron shows four short meridional bonds (~1.95 Å) and two long apical bonds (2.46–2.99 Å) characteristic of Jahn-Teller-distorted Cu2+ octahedra. There is one distinct Pb site occupied by Pb and coordinated by six O atoms and two (OH) groups with a <Pb–O, OH> distance of 2.690 Å. TeF6 and CuΦ6 octahedra share edges and corners to form an [MΦ2] (where Φ = O, OH) layer of composition [TeCu3Φ8]. These layers stack along the c axis at 6 A intervals with Pb atoms between the layers. Identical layers occur in the structure of parakhinite, Pb2+Cu2+Te6+O6(OH)2, hexagonal, a = 5.765(2), c = 18.001(9) Å, V =518.0(4) Å3, space group P32, Z = 3, Dcalc = 6.30 g/cm3. It is only the relative stacking of the TeCu3Φ8 layers in the c direction that distinguishes the two structures, and hence khinite and parakhinite are polytypes.
17
Boffa Ballaran, Tiziana, Kanchana Kularatne, and Reidar Trønnes. "High-pressure structural behaviour of CaIrO3polymorphs." Acta Crystallographica Section A Foundations and Advances 70, a1 (2014): C267. http://dx.doi.org/10.1107/s2053273314097320.
Full textAbstract:
The two known polymorphs of CaIrO3 crystallize int the orthorhombic space groups Pbnm and Cmcm. These compounds have been the focus of much research in the Earth sciences community because they are isostructural with MgSiO3 perovskite and post-perovskite structures which are likely the most abundant minerals in the Earth's lower mantle. CaIrO3 post-perovskite is stable at ambient conditions and transforms at 1-3 GPa and at temperatures above 13500C to the CaIrO3 perovskite structure providing an ideal low pressure and low temperature analogue for the MgSiO3 perovskite to post-perovskite phase transformation which occurs at the extreme conditions of 125 GPa and 2500 K. However, in order to assess whether the CaIrO3 compounds can be used as analogues of MgSiO3 phases, a correct knowledge of their atomic structures and their response to changes in pressure and temperature is essential. In this study the structural behavior of both CaIrO3 polymorphs has been investigated using single-crystal X-ray diffraction at different pressures up to 10 GPa. The orthorhombic distortion of CaIrO3 perovskite derives from the cubic perovskite aristotype by tilting of the octahedral units. These tilts are very large and their variation with pressure is clearly different from the tilting reported for other Ca-oxide perovskites giving rise to a much stiffer structure. The CaIrO3 post-perovskite phase has a layered structure consisting of alternating sheets of Ca atoms and distorted IrO6 octahedra which share edges to form rows running parallel to [100]. With increasing pressure the octahedral tilting remains practically constant and compression of the post-perovskite structure occurs as a result of compression of Ca layers. With increasing temperature, instead, the octahedral tilting increases giving rise to smaller distances between oxygens of adjacent octahedra whose repulsion likely causes the transformation to the CaIrO3 perovskite structure.
18
Hönle, Wolfgang, and Arndt Simon. "Darstellung und Kristallstrukturen von LiGaBr4 und LiGaBr3/Preparation and Crystal Structure of LiGaBr4 and LiGaBr3." Zeitschrift für Naturforschung B 41, no. 11 (1986): 1391–98. http://dx.doi.org/10.1515/znb-1986-1113.
Full textAbstract:
Abstract The com pounds LiGaBr4 and LiGaBr3 are prepared by reaction of stoichiometric mixtures of LiBr and GaBr3 or GaBr2, respectively, in glass am poules at 250 °C. Single crystal X-ray studies show LiGaBr4 to be isotypic to LiAlCl4 containing GaBr4 tetrahedra arranged as in the structure of SnBr4 and Li+ ions filling octahedral voids [d̄(GaBr) = 232.5, d̄(Li -Br) = 280.3 pm]. LiGaBr, has to be formulated as Li2[Ga2Br6] and the Ga -Ga-bonded unit Ga2Br6 has an ecliptic conformation. The L i+ ions occupy octahedral voids, and the LiBr6 octahedra are linked via apices, [d(Ga -Ga) = 240.4, d̄(Ga -Br) = 238.9, d̄(L i-B r) = 281.1 pm]. The structures is compared with the structures of PuBr3, Re3B, FeB and Ga2I3, and the group-subgroup relationship with GdFeO3 is established.
19
Hawthorne, F. C., and M. A. Cooper. "The crystal structure of chalcoalumite: mechanisms of Jahn-Teller-driven distortion in [6]Cu2+-containing oxysalts." Mineralogical Magazine 77, no. 7 (2013): 2901–12. http://dx.doi.org/10.1180/minmag.2013.077.7.02.
Full textAbstract:
AbstractThe crystal structure of chalcoalumite, ideally Cu2+Al4(SO4)(OH)12(H2O)3, monoclinic, P21/n, Z = 4:a 10.228(3), b 8.929(3), c 17.098(6) Å, β 95.800(11)°, V 1553.6(1.5) Å3, has been refined to R1 = 3.08% for 4,022 unique observed (4σ) reflections collected on a Bruker D8 three-circle diffractometer equipped with a rotating-anode generator, multilayer optics and an APEX-II CCD detector. In the structure of chalcoalumite, there is one S site, tetrahedrally coordinated by four O anions, with <S–O> = 1.472 Å. There are four Al sites with site-scattering values in accord with occupancy by Al and <Al–O> distances of 1.898–1.919 Å. There is one Cu site occupied by Cu2+ and coordinated by six anions in the [4 + 2] arrangement typical for octahedrally coordinated Cu2+. The short <Cu–O> distance of 2.086 Å is in accord with the low degree of bond-length distortion of the Cu octahedron. There are 19 anion sites: 4 sites are occupied by O atoms that are bonded to the S cation, 12 sites are occupied by (OH) groups that bond to all octahedrally coordinated cations, and 3 sites are occupied by (H2O) groups that are held in the structure solely by hydrogen bonding. The structure of chalcoalumite consists of interrupted sheets of edge-sharing Al and Cu octahedra of the form [Cu2+Al4(OH)12]2+ that intercalate layers of (SO4) tetrahedra and (H2O) groups. Chalcoalumite is a member of the nickelalumite group.Cu2+ϕ6(ϕ = O2–, (OH)–, (H2O)0) octahedra show a wide range of bond-length distortion away from the holosymmetric arrangement, driven by spontaneous symmetry-breaking of the degenerate electronic ground-state in holosymmetric octahedral coordination. Here, we examine the structural mechanisms that allow large octahedron distortions of this type. There are two mechanisms: (1) coupling of (usually parallel) octahedron distortions to a vibrational phonon, inducing a (often ferroelastic) phase transition in M2+-Cu2+ solid-solutions; (2) cooperative orientational disorder, where bond topology (polyhedron linkage) allows large differences in bond lengths within polyhedra to accord with the valence-sum rule of bond-valence theory.
20
Jørgensen, J. E., W. G. Marshall, and R. I. Smith. "The compression mechanism of CrF3." Acta Crystallographica Section B Structural Science 60, no. 6 (2004): 669–73. http://dx.doi.org/10.1107/s010876810402316x.
Full textAbstract:
The structure of CrF3 has been studied in the pressure range from ambient to 9.12 GPa by time-of-flight neutron powder diffraction. Rietveld refinements of the crystal structure were performed in the space group R\overline 3 c for all the recorded data sets. It was found that volume reduction is achieved through rotation of the CrF6 octahedra and that the Cr—F—Cr bond angle decreases from 144.80 (7) to 133.9 (4)° within the investigated pressure range. Furthermore, a small octahedral strain was found to develop during compression. The octahedral strain reflects an elongation of the CrF6 octahedra along the c-axis direction. The zero-pressure bulk modulus B o and its pressure derivative B_o^{\prime} were determined to be B o = 29.2 (4) GPa and B^{\prime}_o = 10.1 (3).
21
Jupe, A. C., J. K. Cockcroft, P. Barnes, S. L. Colston, G. Sankar, and C. Hall. "The site occupancy of Mg in the brownmillerite structure and its effect on hydration properties: an X-ray/neutron diffraction and EXAFS study." Journal of Applied Crystallography 34, no. 1 (2001): 55–61. http://dx.doi.org/10.1107/s0021889800016095.
Full textAbstract:
Samples of pure (Ca2FeAlO5) and lightly doped (Ca2Fe0.95Al0.95Mg0.05Si0.05O5) brownmillerite have been synthesized. Synchrotron X-ray and neutron diffraction data have been collected so that the structures can be refined using, simultaneously, both diffraction data sets and known compositional information; this overcomes the problem of under-determinacy resulting from multi-occupation of the tetrahedrally and octahedrally coordinated sites in the structure. For the pure form, a 2.7:1 iron/aluminium preference for octahedral/tetrahedral (respectively) occupation is obtained. This trend is reflected also in the doped brownmillerite, though, because of the low level of Mg doping, the occupancy of Mg is only resolved through the additional use of Mg EXAFS (extended X-ray absorption fine structure) data, which shows that Mg displays a distinct octahedral site preference rather than a disordered occupation between the octahedral/tetrahedral sites. The consequences of Mg doping are then examined using time-resolved multi-angle energy-dispersive powder X-ray diffraction studies of the mineral undergoing hydration; this shows that the pure form is more active than the doped form.
22
Zhao, Hongyuan, Yongfang Nie, Dongyang Que, Youzuo Hu, and Yongfeng Li. "Improved Electrochemical Properties of LiMn2O4-Based Cathode Material Co-Modified by Mg-Doping and Octahedral Morphology." Materials 12, no. 17 (2019): 2807. http://dx.doi.org/10.3390/ma12172807.
Full textAbstract:
In this work, the spinel LiMn2O4 cathode material was prepared by high-temperature solid-phase method and further optimized by co-modification strategy based on the Mg-doping and octahedral morphology. The octahedral LiMn1.95Mg0.05O4 sample belongs to the spinel cubic structure with the space group of Fd3m, and no other impurities are presented in the XRD patterns. The octahedral LiMn1.95Mg0.05O4 particles show narrow size distribution with regular morphology. When used as cathode material, the obtained LiMn1.95Mg0.05O4 octahedra shows excellent electrochemical properties. This material can exhibit high capacity retention of 96.8% with 100th discharge capacity of 111.6 mAh g−1 at 1.0 C. Moreover, the rate performance and high-temperature cycling stability of LiMn2O4 are effectively improved by the co-modification strategy based on Mg-doping and octahedral morphology. These results are mostly given to the fact that the addition of magnesium ions can suppress the Jahn–Teller effect and the octahedral morphology contributes to the Mn dissolution, which can improve the structural stability of LiMn2O4.
23
Yang, Li. "Experimental-assisted design development for an octahedral cellular structure using additive manufacturing." Rapid Prototyping Journal 21, no. 2 (2015): 168–76. http://dx.doi.org/10.1108/rpj-12-2014-0178.
Full textAbstract:
Purpose – This paper aims to demonstrate the design and verification of a 3D reticulate octahedral cellular structure using both analytical modeling and additive manufacturing. Traditionally, it has been difficult to develop and verify designs for 3D cellular structures due to their design complexity. Design/methodology/approach – Unit cell modeling approach was used to model the octahedral cellular structure. By applying structural symmetry simplification, the cellular structure was simplified into a representative geometry that could be further designed with a standard beam theory. The verification samples were fabricated with EBM process using Ti6Al4V as materials, and compressive testing were performed to evaluate their properties. In addition, designs with different number of unit cells were investigated to evaluate their size effect. Findings – Explicit mechanical property design (including modulus and compressive strength) of the octahedral cellular structure was realized via parametric equations driven by geometrical designs and material types. In addition, it was verified both numerically and experimentally that the octahedral cellular structure exhibit unusual size effect, which is highly predictable. Unlike some of the other cellular structures, the octahedral cellular structure exhibits softening behavior when the number of unit cell increases between the sandwich skins, which could be explained by the upsetting effect commonly observed in bulk deformation processes. Originality/value – This paper established a more comprehensive understanding in the design of octahedral cellular structures, which could enable this type of structure to be designed for sandwich structures with higher fidelity. Therefore, this study not only demonstrated an efficient methodology to design 3D cellular structures using additive manufacturing, but also facilitated the development of design for an additive manufacturing theory.
24
Levin, Igor, Tammy G. Amos, Juan C. Nino, et al. "Crystal Structure of the Compound Bi2Zn2/3Nb4/3O7." Journal of Materials Research 17, no. 6 (2002): 1406–11. http://dx.doi.org/10.1557/jmr.2002.0209.
Full textAbstract:
The crystal structure of Bi2Zn2/3Nb4/3O7 was determined using a combination of electron, x-ray, and neutron powder diffraction. The compound crystallizes with a monoclinic zirconolite-like structure [C2/c (No.15) space group, a = 13.1037(9) Å, b = 7.6735(3) Å, c = 12.1584(6) Å, β = 101.318(5)°]. According to structural refinement using neutron diffraction data, Nb preferentially occupies six-fold coordinated sites in octahedral sheets parallel to the (001) planes, while Zn is statistically distributed between two half-occupied (5 + 1)-fold coordinated sites near the centers of six-membered rings of [Nb(Zn)O6] octahedra. The Nb/Zn cation layers alternate along the c-axis with Bi-layers, in which Bi cations occupy both eight- and seven-fold coordinated sites. The eight-fold coordinated Bi atoms exhibited strongly anisotropic thermal displacements with an abnormally large component directed approximately along the c-axis (normal to the octahedral layers).
25
Yang, Juan, Xin Zhang, Biao Liu, Wei Sun, and Ya-Xi Huang. "K2[FeII 3(P2O7)2(H2O)2]." Acta Crystallographica Section E Structure Reports Online 68, no. 6 (2012): i47—i48. http://dx.doi.org/10.1107/s1600536812021484.
Full textAbstract:
The title compound, dipotassium diaquabis(diphosphato)triferrate(II), K2[FeII 3(P2O7)2(H2O)2], was synthesized under solvothermal conditions. The crystal structure is isotypic with its Co analogue. In the structure, there are two crystallographically distinct Fe positions; one lies on an inversion center, the other on a general position. The first Fe2+ cation adopts a regular octahedral coordination with six O atoms, whereas the other is coordinated by five O atoms and a water molecule. The [FeO6] octahedron shares its trans-edges with an adjacent [FeO5(H2O)] octahedron; in turn, the [FeO5(H2O)] octahedron shares skew-edges with a neighbouring [FeO6] octahedron and an [FeO5(H2O)] octahedron, resulting in a zigzag octahedral chain running along [001]. The zigzag chains are linked to each other by the P2O7 diphosphate groups, leading to a corrugated iron diphosphate layer, [Fe3(P2O7)2(H2O)2]2−, parallel to (100). The interlayer space is occupied by K+ cations, which adopt an eight-coordination to seven O atoms and one water molecule from a neighbouring iron diphosphate layer. Thus, the K+ ions not only compensate the negative charge of the layer but also link the layers into a network structure.
26
Levin, Igor, and Leonid A. Bendersky. "Symmetry classification of the layered perovskite-derived A n B n X 3n+2 structures." Acta Crystallographica Section B Structural Science 55, no. 6 (1999): 853–66. http://dx.doi.org/10.1107/s0108768199005479.
Full textAbstract:
The effects of combinations of octahedral tilts on the symmetries of layered A n B n X 3n+2 structures were considered. Two complementary approaches were used to deduce the symmetries. The space groups associated with different tilt systems were determined for structures with different layer thicknesses (n values) and for structures with different layer stacking arrangements. For the most symmetrical tilts about the orthorhombic axes of the A n B n X 3n+2 structure, maximal group/subgroup relations were established. Comparison of these results with experimental data available in the literature suggests that the symmetries of most observed A n B n X 3n+2 compounds are fully determined by the tilt systems adopted by rigid BX 6 octahedra. The most common tilt system observed at room temperature is a combination of an in-phase tilt about an orthorhombic axis parallel to the pseudo-fourfold axis of the octahedron with a tilt about an orthorhombic axis perpendicular to the layers.
27
Barnes, Paris W., Michael W. Lufaso, and Patrick M. Woodward. "Structure determination of A 2 M 3+TaO6 and A 2 M 3+NbO6 ordered perovskites: octahedral tilting and pseudosymmetry." Acta Crystallographica Section B Structural Science 62, no. 3 (2006): 384–96. http://dx.doi.org/10.1107/s0108768106002448.
Full textAbstract:
The room-temperature crystal structures of six A 2 M 3+ M 5+O6 ordered perovskites have been determined from neutron and X-ray powder diffraction data. Ba2YNbO6 adopts the aristotype high-symmetry cubic structure (space group Fm\overline 3m, Z = 4). The symmetries of the remaining five compounds were lowered by octahedral tilting distortions. Out-of-phase rotations of the octahedra about the c axis were observed in Sr2CrTaO6 and Sr2GaTaO6, which lowers the symmetry to tetragonal (space group = I4/m, Z = 2, Glazer tilt system = a 0 a 0 c −). Octahedral tilting analogous to that seen in GdFeO3 occurs in Sr2ScNbO6, Ca2AlNbO6 and Ca2CrTaO6, which lowers the symmetry to monoclinic (space group P21/n, Z = 2, Glazer tilt system = a − a − c +). The Sr2 MTaO6 (M = Cr, Ga, Sc) compounds have unit-cell dimensions that are highly pseudo-cubic. Ca2AlNbO6 and Ca2CrTaO6 have unit-cell dimensions that are strongly pseudo-orthorhombic. This high degree of pseudosymmetry complicates the space-group assignment and structure determination. The space-group symmetries, unit-cell dimensions and cation ordering characteristics of an additional 13 compositions, as determined from X-ray powder diffraction data, are also reported. An analysis of the crystal structures of 32 A 2 MTaO6 and A 2 MNbO6 perovskites shows that in general the octahedral tilt system strongly correlates with the tolerance factor.
28
Lufaso, Michael W., and Patrick M. Woodward. "Prediction of the crystal structures of perovskites using the software program SPuDS." Acta Crystallographica Section B Structural Science 57, no. 6 (2001): 725–38. http://dx.doi.org/10.1107/s0108768101015282.
Full textAbstract:
The software program SPuDS has been developed to predict the crystal structures of perovskites, including those distorted by tilting of the octahedra. The user inputs the composition and SPuDS calculates the optimal structure in ten different Glazer tilt systems. This is performed by distorting the structure to minimize the global instability index, while maintaining rigid octahedra. The location of the A-site cation is chosen so as to maximize the symmetry of its coordination environment. In its current form SPuDS can handle up to four different A-site cations in the same structure, but only one octahedral ion. Structures predicted by SPuDS are compared with a number of previously determined structures to illustrate the accuracy of this approach. SPuDS is also used to examine the prospects for synthesizing new compounds in tilt systems with multiple A-site coordination geometries (a + a + a +, a 0 b + b +, a 0 b − c +).
29
King, Graham. "New examples of non-cooperative octahedral tilting in a double perovskite: phase transitions in K3GaF6." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, no. 5 (2020): 789–94. http://dx.doi.org/10.1107/s2052520620009695.
Full textAbstract:
The crystal structures of three polymorphs of K3GaF6 and the transition temperatures between these phases are reported for the first time. Synchrotron powder diffraction data clearly show that at 300 K α-K3GaF6 crystallizes in space group I41/a with lattice parameters of a = 19.1124 (3) Å, c = 34.4165 (6) Å, and Z = 80. The structure is based on the double perovskite but with two fifths of the GaF6 octahedra rotated by ∼45°. This phase remains stable until ∼460 K, above which it undergoes a transition to I4/m with lattice parameters of a = 13.6088 (4) Å, c = 8.6764 (3) Å, and Z = 10 at 485 K. β-K3GaF6 has a similar structure but with only one fifth of the GaF6 rotated by ∼45°. Above ∼510 K, the cubic Fm 3 m δ-K3GaF6 structure is stabilized, with a lattice parameter of a = 8.6649 (1) Å at 550 K. The F atoms have highly anisotropic displacement parameters which suggest dynamic octahedral tilting is occurring. This work expands the fairly small group of double perovskite compounds which display non-cooperative patterns of octahedral tilting.
30
Schwendtner, Karolina, and Uwe Kolitsch. "M + M 3+ 2As(HAsO4)6 (M + M 3+ = TlGa, CsGa, CsAl): three new metal arsenates containing AsO6 octahedra." Acta Crystallographica Section E Crystallographic Communications 74, no. 8 (2018): 1163–67. http://dx.doi.org/10.1107/s2056989018010721.
Full textAbstract:
The crystal structures of hydrothermally synthesized (T = 493 K, 7 d) thallium(I) digallium arsenic(V) hexakis[hydrogenarsenate(V)], TlGa2As(HAsO4)6, caesium digallium arsenic(V) hexakis[hydrogenarsenate(V)], CsGa2As(HAsO4)6, and caesium dialuminium arsenic(V) hexakis[hydrogenarsenate(V)], CsAl2As(HAsO4)6, were solved by single-crystal X-ray diffraction. The three compounds are isotypic and adopt the structure type of RbAl2As(HAsO4)6 (R\overline{3}c), which itself represents a modification of the RbFe(HPO4)2 structure type and consists of a tetrahedral–octahedral framework in which the slightly disordered M + cations are located in channels. The three new compounds contain AsO6 octahedra assuming the topological role of M 3+O6 octahedra. The As—O bond lengths are among the shortest As—O bond lengths known so far in AsO6 octahedra.
31
Klepp, Kurt O. "Darstellung und Kristallstruktur von Tl2TiS4 : Ein Perthiotitanat(IV) mit ∞1-[TiS42-]-Ketten Preparation and Crystal Structure of Tl2TiS4 : A Perthiotitanate(IV) with ∞1-[TiS42-]-Chains." Zeitschrift für Naturforschung B 40, no. 2 (1985): 229–34. http://dx.doi.org/10.1515/znb-1985-0214.
Full textAbstract:
Abstract Tl2TiS4 is orthorhombic, space group Pbca, with a = 22.176(7), b = 9.484(4), c = 6.3977(9) Å, Z = 8. The crystal structure was solved by direct methods and refined to a conventional R of0.058 for 704 reflections with I ≥3σ(I). The crystal structure is characterized by infinite perthioanions, ∞1-[TiS 4/2 (S2)2- ], which are separated by Tl+ -cations. The anion chains are built up by distorted octahedra which share two skew edges to form infinite cis-chains running along [001], The two unshared S-atoms of each octahedron are connected via a S -S-single bond of 2.10 Å length. The crystal structure is described as a mixed packing of TI-and S-atoms, composed of puckered TlS2 -layers, in which the Ti-atoms occupy the octahedral interstices. The relationship of the ∞1-[TiS42- -]-chains to the anionic groups of Cs2TiS3 is discussed.
32
Liu, Junhua, Xiaofei Gao, Wen Xiao, et al. "Controlled properties of perovskite oxide films by engineering oxygen octahedral rotation." JUSTC 53, no. 1 (2023): 1. http://dx.doi.org/10.52396/justc-2022-0101.
Full textAbstract:
Complex perovskite oxides exhibit extremely rich physical properties in terms of magnetism, electrical transport, and electrical polarization characteristics due to the competition and coupling of many degrees of freedom. The B-site ions and O ions in perovskite form six-coordinated octahedral units, which are connected at a common vertex toward the basic framework of the perovskite oxide, providing a crucial platform to tailor physical properties. The rotation or distortion of the oxygen octahedra will tip the competing balance, leading to many emergent ground states. To further clarify the subtle relationship between emergent properties and oxide octahedral behavior, this article reviews the structure of perovskite oxides, the characterization methods of oxygen octahedral rotation and the response of transport, electrical polarization and magnetism of several typical perovskite heterostructures to oxygen octahedral rotation modes. With knowledge of how to manipulate the octahedral rotation behavior and regulate the physical properties of perovskite oxides, rationally designing the sample manufacturing process can effectively guide the development and application of novel electronic functional materials and devices.
33
Schwendtner, Karolina, and Uwe Kolitsch. "Two new Rb–Ga arsenates: RbGa(HAsO4)2 and RbGa2As(HAsO4)6." Acta Crystallographica Section E Crystallographic Communications 74, no. 9 (2018): 1244–49. http://dx.doi.org/10.1107/s2056989018011180.
Full textAbstract:
The crystal structures of hydrothermally synthesized (T = 493 K, 7–9 d) rubidium gallium bis[hydrogenarsenate(V)], RbGa(HAsO4)2, and rubidium digallium arsenic(V) hexa[hydrogenarsenate(V)], RbGa2As(HAsO4)6, were solved by single-crystal X-ray diffraction. Both compounds have tetrahedral–octahedral framework topologies. The M + cations are located in channels of the respective framework. RbGa(HAsO4)2 crystallizes in the RbFe(HPO4)2 structure type (R\overline{3}c), while RbGa2As(HAsO4)6 adopts the structure type of RbAl2As(HAsO4)6 (R\overline{3}c), which represents a modification of the RbFe(HPO4)2 structure type. In this modification, one third of the M 3+O6 octahedra are replaced by AsO6 octahedra, and two thirds of the voids in the structure, which are usually filled by M + cations, remain empty to achieve charge balance.
34
Nolan, Annette L., Christine C. Allen, Robert C. Burns, Donald C. Craig, and Geoffrey A. Lawrance. "Monomeric and Dimeric Cobalt(III) Polyoxomolybdates: Crystal Structures and Cyclic Voltammetry of Na3 [H6CoMo6O24].8H2O and K6 [H4Co2Mo10O38].7H2O." Australian Journal of Chemistry 51, no. 9 (1998): 825. http://dx.doi.org/10.1071/c97218.
Full textAbstract:
The crystal structures of Na3 [H6CoMo6O24].8H2O and K6 [H4Co2Mo10O38].7H2O have been determined by X-ray diffraction. The monomer, Na3 [H6CoMo6O24].8H2O, is triclinic, space group P-1, a 6·451(1), b 10·866(2), c 10·922(2) Å, α 109·20(1), β 106·90(1), γ 95·43(1)°, V 676·3(2) Å3, Z 1, and the structure was solved to an R1 value of 0·0243 (wR2 0·0784) for 3761 independent observed reflections. The anion exhibits the well known Anderson structure with six octahedral MoO6 edge-sharing units surrounding the central ‘CoO6’ octahedron, with all metals in a common plane. The dimer, K6 [H4Co2Mo10O38].7H2O, is monoclinic, space group P21/c, a 11·795(5), b 11·626(2), c 29·731(13) Å, β 95·33(2)°, V 4059(3) Å3, Z 4, and the structure was solved to an R1 value of 0·0215 (wR2 0·1040) for 6546 independent observed reflections. The anion can be derived from the monomeric hexamolybdocobaltate(III) ion by removing one ‘MoO5’ unit (ignoring the hydrogen atoms) from each of two monomer anions, turning one 180° around a CoO6 octahedral diagonal, and joining them to create two CoO6 octahedra sharing an edge. Cyclic voltammetry shows that both anions are irreversibly reduced at low pH values (4·0–4·5), likely as a result of chemical reactions following the initial reduction steps. At higher pH values (4·5–5·4), a change in speciation occurs in both cases, most likely the result of the formation of less highly protonated species, which also display irreversible electrochemical behaviour.
35
Đorđević, Tamara, and Ljiljana Karanović. "An update on the mineral-like Sr-containing transition metal arsenates." Mineralogical Magazine 85, no. 3 (2021): 416–30. http://dx.doi.org/10.1180/mgm.2021.41.
Full textAbstract:
AbstractWe report on the crystal structures of three novel synthetic SrM-arsenates (M = Ni and Fe3+), isostructural or structurally related to the minerals from tsumcorite, carminite and brackebuschite groups. They were synthesised under mild hydrothermal conditions and further characterised using single-crystal X-ray diffraction (SXRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and Raman spectroscopy. SXRD and SEM-EDS yielded formulae: (I) SrNi2(AsO4)2⋅2H2O, (II) Sr1.4Fe3+1.6(AsO4)2(OH)1.6 and (III) SrFe3+(AsO4)(AsO3OH). All three structures are built up of slightly distorted MO6 octahedra and AsO4 tetrahedra that are linked by Sr2+ with different coordination geometries and hydrogen bonds. I represent a basic structure type typical for tsumcorite-group minerals (space group C2/m) while II has a new intermediate structure between carminite, PbFe3+2(AsO4)2(OH)2 and arsenbrackebuschite, Pb2Fe3+(AsO4)2(OH) (s.g. Pm). III is triclinic and adopts a new structure-type (s.g. P$\bar{1}$). The structure of I is built up of infinite linear edge-sharing NiO4(OH2)2 octahedral chains, extending along [010] and linked by AsO4 tetrahedra, SrO8 polyhedra and hydrogen bonds. The structure of II is characterised by the carminite-like FeO4(OH)2 octahedral chains and Edshammar-polyhedral chains, which involves SrO11 coordination polyhedra similar to that of PbO11 in arsenbrackebuschite. Both chains in II are aligned parallel to the b axis of the monoclinic unit cell and connected together by the arsenate AsO4 tetrahedra, SrO8 polyhedra and the hydrogen-bonding network. The compound III has a new type of crystal structure based on the unusual corrugated octahedral–tetrahedral-quadruple chains. These are made up of a central double-sided chain linked to two single-sided chains into a quadruple chain extended along the a axis. The chains in III are built up of FeO6 octahedra and AsO4 tetrahedra further linked to each other by shared vertices. The quadruple chains are interconnected by additional AsO4 tetrahedra forming a heteropolyhedral 3D open framework. Strontium atoms are situated in the two channels. The structural connections to related minerals and inorganic compounds are discussed.
36
Krivovichev, Sergey V., Taras L. Panikorovskii, Ayya V. Bazai, and Mikhail Yu Sidorov. "The Crystal Structure of Manganotychite, Na6Mn2(CO3)4(SO4), and Structural Relations in the Northupite Group." Crystals 13, no. 5 (2023): 800. http://dx.doi.org/10.3390/cryst13050800.
Full textAbstract:
The crystal structure of manganotychite has been refined using the holotype specimen from the Alluaiv Mountain, Lovozero massif, Kola peninsula, Russia. The mineral is cubic, Fd3¯, a = 14.0015(3) Å, V = 2744.88(18) Å3, Z = 8, R1 = 0.020 for 388 independently observed reflections. Manganotychite is isotypic to tychite and ferrotychite. Its crystal structure is based upon a three-dimensional infinite framework formed by condensation of MnO6 octahedra and CO3 groups by sharing common O atoms. The sulfate groups and Na+ cations reside in the cavities of the octahedral-triangular metal-carbonate framework. In terms of symmetry and basic construction of the octahedral-triangular framework, the crystal structure of manganotychite is identical to that of northupite, Na3Mg(CO3)2Cl. The transition northupite → tychite can be described as a result of the multiatomic 2Cl− → (SO4)2− substitution, where both chlorine and sulfate ions are the extra-framework constituents. However, the positions occupied by sulfate groups and chlorine ions correspond to different octahedral cavities within the skeletons of Na atoms. The crystal structure of northupite can be considered as an interpenetration of two frameworks: anionic [Mg(CO3)2]2− octahedral-triangular framework and cationic [ClNa3]2− framework with the antipyrochlore topology. Both manganotychite and northupite structure types can be described as a modification of the crystal structure of diamond (or the dia net) via the following steps: (i) replacement of a vertex of the dia net by an M4 tetrahedron (no symmetry reduction); (ii) attachment of (CO3) triangles to the triangular faces of the M4 tetrahedra (accompanied by the Fd3¯m → Fd3¯ symmetry reduction); (iii) filling voids of the resulting framework by Na+ cations (no symmetry reduction); and (iv) filling voids of the Na skeleton by either sulfate groups (in tychite-type structures) or chlorine atoms (in northupite). As a result, the information-based structural complexity of manganotychite and northupite exceeds that of the dia net.
37
Ling, Christopher D., Siegbert Schmid, Ray L. Withers, John G. Thompson, Nobuo Ishizawa, and Shunji Kishimoto. "Solution and refinement of the crystal structure of Bi7Ta3O18." Acta Crystallographica Section B Structural Science 55, no. 2 (1999): 157–64. http://dx.doi.org/10.1107/s0108768198011148.
Full textAbstract:
The structure of heptabismuth tritantalum octadecaoxide, Bi7Ta3O18, has been solved and refined using single-crystal X-ray diffraction data collected at a synchrotron source in conjunction with unit-cell and symmetry information derived from electron diffraction. The space-group symmetry is triclinic C1 but is very close to monoclinic C2/m. A twin component observed during data collection was successfully modelled in the refinement. The C2/m prototype fitted all the Rietveld-refinable features of a medium-resolution neutron powder diffraction pattern. The metal-atom array is approximately face-centred cubic (fluorite type), punctuated by regularly spaced displacement faults perpendicular to the [111]fluorite direction every 2.5 fluorite unit cells. The metal-atom populations and O-atom positions are fully ordered. The Ta5+ cations are octahedrally coordinated, with TaO6 octahedra forming columns. The remaining O atoms occupy distorted fluorite positions. The Bi3+ cations occupy octahedral, square pyramidal or trigonal prismatic sites within the O-atom array; strain in the latter coordination environment appears to be responsible for the lowering of symmetry from monoclinic to triclinic.
38
Redhammer, Günther J., Georg Roth, Georg Amthauer, and Werner Lottermoser. "On the crystal chemistry of olivine-type germanate compounds, Ca1 + x M 1 − x GeO4 (M 2+ = Ca, Mg, Co, Mn)." Acta Crystallographica Section B Structural Science 64, no. 3 (2008): 261–71. http://dx.doi.org/10.1107/s0108768108010434.
Full textAbstract:
Germanate compounds, CaMGeO4 with M 2+ = Ca, Mg, Co and Mn, were synthesized as single crystals by slow cooling from the melt or by flux growth techniques. All the compositions investigated exhibit Pnma symmetry at 298 K and adopt the olivine structure. The M2 site is exclusively occupied by Ca2+, while on M1 both Ca2+ and M 2+ cations are found. The amount of Ca2+ on M1 increases with the size of the M1 cation, with the smallest amount in the Mg compound (0.1 atoms per formula unit) and the largest in the Mn compound (0.20 atoms per formula unit), while in Ca2GeO4, also with olivine structure, both sites are completely filled with Ca2+. When compared with those of Ca silicate olivine, the lattice parameters a and c are distinctly larger in the analogous germanate compounds, while b has essentially the same values, regardless of the tetrahedral cation, meaning that b is independent of the tetrahedral cation. Structural variations on the octahedrally coordinated M1 site are largely determined by the size of the M1 cation, the average M1—O bond lengths being identical in Ca silicate and Ca germanate olivine. Increasing the size of the M1 cation induces an increasing polyhedral distortion, expressed by the parameters bond-length distortion, octahedral angle variance and octahedral quadratic elongation. However, the Ca germanate olivine compounds generally have more regular octahedra than the analogous silicates. The octahedrally coordinated M2 site does not exhibit large variations in structural parameters as a consequence of the constant chemical composition; the same is valid for the tetrahedral site.
39
Xu, Zhenyang, Francisco Restrepo, Junjing Zhao, Utpal Chatterjee, and Despina Louca. "Octahedral to tetrahedral bonding transitions in the local structure of phase change optical media Ge2Sb2Se5xTe5−5x with Se doping." AIP Advances 13, no. 4 (2023): 045005. http://dx.doi.org/10.1063/5.0133981.
Full textAbstract:
Random access memories utilize fast, reversible switching between ordered and disordered states of matter in phase change materials (PCMs) such as Ge2Sb2Te5−5x. The short-range structure in the disordered phase has been described either as (i) a network of Ge tetrahedra or (ii) Peierls distorted Ge/Sb octahedra. The PCM transition was investigated in bulk Ge2Sb2Se5xTe5−5x (GSST), in which amorphization sets in with Se doping (x ≈ 0.85) upon quenching. GSST has a hexagonal crystalline ground state with Ge/Sb octahedral coordination, but the phase change transition to the amorphous state that is only observed when the system is quenched brings a short-range structure with sharp, tetrahedrally coordinated Ge/Sb correlations and shortened bonds that are distinctly different from the expected octahedral pairing.
40
Pang, Wei Kong, Vanessa K. Peterson, Neeraj Sharma, Je-Jang Shiu, and She-huang Wu. "Structure of the Li4Ti5O12 anode during charge-discharge cycling." Powder Diffraction 29, S1 (2014): S59—S63. http://dx.doi.org/10.1017/s0885715614001067.
Full textAbstract:
The structural evolution of the “zero-strain” Li4Ti5O12 anode within a functioning Li-ion battery during charge–discharge cycling was studied using in situ neutron powder-diffraction, allowing correlation of the anode structure to the measured charge–discharge profile. While the overall lattice response controls the “zero-strain” property, the oxygen atom is the only variable in the atomic structure and responds to the oxidation state of the titanium, resulting in distortion of the TiO6 octahedron and contributing to the anode's stability upon lithiation/delithiation. Interestingly, the trend of the octahedral distortion on charge–discharge does not reflect that of the lattice parameter, with the latter thought to be influenced by the interplay of lithium location and quantity. Here we report the details of the TiO6 octahedral distortion in terms of the O–Ti–O bond angle that ranges from 83.7(3)° to 85.4(5)°.
41
Zhai, Yun, Sibo He, Lei Lei, and Tianmin Guan. "Mechanical property of octahedron Ti6Al4V fabricated by selective laser melting." REVIEWS ON ADVANCED MATERIALS SCIENCE 60, no. 1 (2021): 894–911. http://dx.doi.org/10.1515/rams-2021-0080.
Full textAbstract:
Abstract The stress shielding effect is a critical issue for implanted prosthesis due to the difference in elastic modulus between the implanted material and the human bone. The adjustment of the elastic modulus of implants by modification of the lattice structure is the key to the research in the field of implanted prosthesis. Our work focuses on the basic unit structure of octahedron Ti6Al4V. The equivalent elastic modulus and equivalent density of porous structure are optimized according to the mechanical properties of human bone tissue by adjusting the edge diameter and side length of octahedral lattice. Macroscopic long-range ordered arrangement of lattice structures is fabricated by selective laser melting (SLM) technology. Finite element simulation is performed to calculate the mechanical property of octahedron Ti6Al4V. Scanning electronic microscopy is applied to observe the microstructure of octahedron alloy and its cross section morphology of fracture. Standard compression test is performed for the stress–strain behavior of the specimen. Our results show that the octahedral lattice with the edge diameter of 0.4 mm and unit cell length of 1.5 mm has the best mechanical property which is close to the human bone. The value of equivalent elastic modulus increases with the increase in the edge diameter. The SLM technology proves to be an effective processing way for the fabrication of complex microstructures with porosity. In addition, the specimen exhibits isotropic mechanical performance and homogeneity which significantly meet the requirement of implanted prosthetic medical environment.
42
Drits, V. A., B. A. Sakharov, and A. Manceau. "Structure of Feroxyhite as Determined by Simulation of X-Ray Diffraction Curves." Clay Minerals 28, no. 2 (1993): 209–22. http://dx.doi.org/10.1180/claymin.1993.028.2.03.
Full textAbstract:
AbstractPowder X-ray diffraction (XRD) curves were calculated for the different structural models so far proposed for feroxyhite (δFeOOH). The influence on XRD features of different structural parameters, including site occupancy of Fe atoms, atomic coordinates, content and distribution of stacking faults, and dimension of coherent scattering domains, were considered. On the basis of agreement between experimental and simulated curves it is shown that δFeOOH is a mixture of feroxyhite proper and ultradispersed hematite in the 9 : 1 volume ratio. Feroxyhite proper consists of hexagonal close packing of anions containing 5% stacking faults. Iron atoms occupy only octahedral sites and are distributed in such a way that face-sharing filled octahedral pairs regularly alternate with vacant octahedral pairs along the c axis. This distribution of Fe atoms is quite similar to that established by Patrat et al. (1983), but in each pair, Fe atoms are displaced by the same value of 0.3 Å in opposite directions away from the centre of their octahedron. Nearest Fe-Fe distances calculated for the model proposed (2.88, 3.01, 3-39 and 3-73 Å) practically coincide with those found by EXAFS spectroscopy for the same sample (2-91, 3.04, 3.41 and 3.7-3.8 Å).
43
Röhr, Caroline. "K19Pb8O4(OH)3 und KPb: Ein Oxid-Hydroxid und eine Zintl-Phase mit [Pb4]4--Anionen / K 19Pb8O4(OH)3 and KPb: An Oxide-Hydroxide and a Zintl Phase with [Pb4]4- Anions." Zeitschrift für Naturforschung B 50, no. 5 (1995): 802–8. http://dx.doi.org/10.1515/znb-1995-0519.
Full textAbstract:
Abstract K19Pb8O4(OH)3 crystallizes in the cubic system with space group Fm3m (a = 1622.7(4) pm: Z = 4). KPb crystallizes with the NaPb structure type (tetragonal, space group 141/acd, a = 1153.2(6) pm. c = 1886.8(9) pm. Z = 32). The crystal structures of both compounds contain Zintl-anions [Pb4]4- as characteristic building units, which in the Zintl phase are separated by potassium cations only. The oxide-hydroxide contains additional anions O2- and OH- enclosed by potassium ions in an octahedral coordination. The oxygen centered octahedra form a three-dimensional network of clusters [(O/OH)6K19] (consisting of six octahedra [(O/OH)K6] sharing edges) and single octahedra [OK6] connected by common corners. Tlie [Pb4]4- tetrahedra occupy the voids within this framework.
44
Gonçalves, João N., Anthony E. Phillips, Wei Li, and Alessandro Stroppa. "First-Principles Study of Structure and Magnetism in Copper(II)-Containing Hybrid Perovskites." Crystals 10, no. 12 (2020): 1129. http://dx.doi.org/10.3390/cryst10121129.
Full textAbstract:
We report a first-principles study of hybrid organic–inorganic perovskites with formula [A]Cu(H2POO)3 (A = triazolium (Trz) and guanidinium (Gua), and H2POO− = hypophosphite), and [HIm]Cu(HCO2)3 (HIm = imidazolium cation, HCO2− = formate). The triazolium hypophosphite and the formate have been suggested as possible ferroelectrics. We study the fully relaxed structures with different magnetic orderings and possible phonon instabilities. For the [Trz]Cu hypophosphite, the Trz cation is shown to induce large octahedral distortions due to the Jahn-Teller effect, with Cu-O long-bond ordering along two perpendicular directions, which is correlated with antiferromagnetic ordering and strongly one-dimensional. We find that the structure is dynamically stable with respect to zone-center distortions, but instabilities appear along high symmetry lines in the Brillouin zone. On the other hand, for the [HIm]Cu formate, large octahedral distortions are found, with large Cu-O bonds present in half of the octahedra, in this case along a single direction, and correspondingly, the magnetism is almost two-dimensional.
45
Whittle, Thomas A., Siegbert Schmid, and Christopher J. Howard. "Octahedral tilting in the tungsten bronzes." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 71, no. 3 (2015): 342–48. http://dx.doi.org/10.1107/s2052520615008252.
Full textAbstract:
Possibilities for `simple' octahedral tilting in the hexagonal and tetragonal tungsten bronzes (HTB and TTB) have been examined, making use of group theory as implemented in the computer programISOTROPY. For HTB, there is one obvious tilting pattern, leading to a structure in space groupP63/mmc. This differs from the space groupP63/mcmfrequently quoted from X-ray studies – these studies have in effect detected only displacements of the W cations from the centres of the WO6octahedra. The correct space group, taking account of both W ion displacement and the octahedral tilting, isP6322 – structures in this space group and matching this description have been reported. A second acceptable tilting pattern has been found, leading to a structure inP6/mmmbut on a larger `2 × 2 × 2' unit cell – however, no observations of this structure have been reported. For TTB, a search at the special points of the Brillouin zones revealed only one comparable tilting pattern, in a structure with space-group symmetryI4/mon a `21/2 × 21/2by 2' unit cell. Given several literature reports of larger unit cells for TTB, we conducted a limited search along the lines of symmetry and found structures with acceptable tilt patterns inBbmmon a `21/22 × 21/2 × 2' unit cell. A non-centrosymmetric version has been reported in niobates, inBbm2 on the same unit cell.
46
Zhang, Nan, Lixia Ma, Luo Huang, Houyu Zhu, and Ruibin Jiang. "First-Principles Study of Stability and N2 Activation on the Octahedron RuRh Clusters." Catalysts 12, no. 8 (2022): 881. http://dx.doi.org/10.3390/catal12080881.
Full textAbstract:
The geometric and electronic structures of different octahedron RuRh clusters are studied using density functional theory calculations. The binding energy, electronic structure, and energy gap of the clusters have been obtained to determine the possible stable structures. The results show that the Ru4Rh2 cluster is the most stable structure which has D4h symmetry with the largest ionization potential, smallest affinity energy and larger energy gap. Furthermore, the information on adsorption and dissociation of multiple nitrogen molecules and the density of state for the octahedral Ru4Rh2 cluster is analyzed. The dissociation barrier of three nitrogen molecules further decreases to 1.18 eV with an increase in the number of N2 molecules. The co-adsorption of multiple N2 molecules facilitates the dissociation of N2 on the Ru4Rh2 cluster. The strong interaction between the antibonding orbital of N2 and the d orbital of the Ru4Rh2 cluster is illustrated by calculating and analyzing the results of PDOS, which stretches the N−N bond length and reduces the activation energy to dissociation. The antibonding orbital of the nitrogen molecule shows distinct and unique catalytic activity for the dissociation of the adsorbed nitrogen molecule on the octahedral Ru4Rh2 cluster.
47
Spiridonova, Tatyana S., Sergey F. Solodovnikov, Aleksandra A. Savina, et al. "Synthesis, crystal structures and properties of the new compounds K7–x Ag1+x (XO4)4 (X = Mo, W)." Acta Crystallographica Section C Structural Chemistry 73, no. 12 (2017): 1071–77. http://dx.doi.org/10.1107/s2053229617015674.
Full textAbstract:
Two new isostructural compounds, namely heptapotassium silver tetrakis(tetraoxomolybdate), K7–x Ag1+x (MoO4)4 (0 ≤ x ≤ 0.4), and heptapotassium silver tetrakis(tetraoxotungstate), K7–x Ag1+x (WO4)4 (0 ≤ x ≤ 0.4), have been synthesized and found to crystallize in the polar space group P63 mc (Z = 2) with the unit-cell dimensions a = 12.4188 (2) and c = 7.4338 (2) Å for K6.68Ag1.32(MoO4)4 (single-crystal data), and a = 12.4912 (5) and c = 7.4526 (3) Å for K7Ag(WO4)4 (Rietveld analysis data). Both structures represent a new structure type, with characteristic [K1(XO4)6] `pinwheels' of K1O6 octahedra and six XO4 tetrahedra (X = Mo, W) connected by common opposite faces into columns along the c axes. The octahedral columns are linked to each other through Ag1O4 tetrahedra along with the K2 and K3/Ag2 polyhedra, forming the polar rods (...Ag1O4–X1O4–empty octahedron–Ag1O4...). Ag1 is located almost at the centre of the largest face of its coordination tetrahedron and seems to have some mobility. The new structure type is related to the Ba6Nd2Al4O15 and CaBaSiO4 types, and to other structures of the α-K2SO4–glaserite family. The differential scanning calorimetry (DSC) and second harmonic generation (SHG) results show that both compounds undergo first-order phase transformations to high-temperature centrosymmetric phases.
48
Lufaso, Michael W., Paris W. Barnes, and Patrick M. Woodward. "Structure prediction of ordered and disordered multiple octahedral cation perovskites using SPuDS." Acta Crystallographica Section B Structural Science 62, no. 3 (2006): 397–410. http://dx.doi.org/10.1107/s010876810600262x.
Full textAbstract:
The software package SPuDS has previously been shown to accurately predict crystal structures of AMX 3 and A 1 − x A′ x MX 3 perovskites that have undergone octahedral tilting distortions. This paper describes the extension of this technique and its accuracy for A 2 MM′X 6 ordered double perovskites with the aristotype Fm\overline 3m cubic structure, as well as those that have undergone octahedral tilting distortions. A survey of the literature shows that roughly 70% of all ordered double perovskites undergo octahedral tilting distortions. Of the 11 distinct types of octahedral tilting that can occur in ordered perovskites, five tilt systems account for ∼97% of the reported structures. SPuDS can calculate structures for the five dominant tilt systems, Fm\overline 3m (a 0 a 0 a 0), I4/m (a 0 a 0 c −), R\overline 3 (a − a − a −), I2/m (a 0 b − b −) and P21/n (a − a − b +), as well as two additional tilt systems, Pn\overline 3 (a + a + a +) and P4/mnc (a 0 a 0 c +). Comparison with reported crystal structures shows that SPuDS is quite accurate at predicting distortions driven by octahedral tilting. The favored modes of octahedral tilting in ordered double perovskites are compared and contrasted with those in AMX 3 perovskites. Unit-cell pseudosymmetry in Sr- and Ca-containing double perovskites is also examined. Experimentally, Sr2 MM′O6 compounds show a much stronger tendency toward pseudosymmetry than do Ca2 MM′O6 compounds with similar tolerance factors.
49
Redhammer, Günther J., and Gerold Tippelt. "The crystal structure of KScP2O7." Acta Crystallographica Section E Crystallographic Communications 76, no. 9 (2020): 1412–16. http://dx.doi.org/10.1107/s2056989020010427.
Full textAbstract:
Single crystals of KScP2O7, potassium scandium diphosphate, were grown in a borate flux. The title compound crystallizes isotypically with KAlP2O7 in space-group type P21/c, Z = 4. The main building block is an {ScP2O11}9– unit, forming layers parallel to (001). These layers are stacked along [001] via common corners of octahedral and tetrahedral units to span up large heptagonal cavities that host the potassium cations with a coordination number of 10. The P—O—P bridging angle increases with increasing size of the octahedrally coordinated M III cation, as do the K—O distances within a series of KM IIIP2O7 compounds (M III = Al to Y with ionic radii r = 0.538 to 0.90 Å).
50
Nelson, Joey. "XANES reflects coordination change and underlying surface disorder of zinc adsorbed to silica." Journal of Synchrotron Radiation 28, no. 4 (2021): 1119–26. http://dx.doi.org/10.1107/s1600577521004033.
Full textAbstract:
Zinc K-edge X-ray absorption near-edge structure (XANES) spectroscopy of Zn adsorbed to silica and Zn-bearing minerals, salts and solutions was conducted to explore how XANES spectra reflect coordination environment and disorder in the surface to which a metal ion is sorbed. Specifically, XANES spectra for five distinct Zn adsorption complexes (Znads) on quartz and amorphous silica [SiO2(am)] are presented from the Zn–water–silica surface system: outer-sphere octahedral Znads on quartz, inner-sphere octahedral Znads on quartz, inner-sphere tetrahedral Znads on quartz, inner-sphere octahedral Znads on SiO2(am) and inner-sphere tetrahedral Znads on SiO2(am). XANES spectral analysis of these complexes on quartz versus SiO2(am) reveals that normalized peak absorbance and K-edge energy position generally decrease with increasing surface disorder and decreasing Zn–O coordination. On quartz, the absorption-edge energy of Znads ranges from 9663.0 to 9664.1 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On SiO2(am), the absorption-edge energy of Znads ranges from 9662.3 to 9663.4 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On both silica substrates, octahedral Znads presents a single K-edge peak feature, whereas tetrahedral Znads presents two absorbance features. The energy space between the two absorbance peak features of the XANES K-edge of tetrahedral Znads is 2.4 eV for Zn on quartz and 3.2 eV for Zn on SiO2(am). Linear combination fitting of samples with a mixture of Znads complex types demonstrates that the XANES spectra of octahedral and tetrahedral Znads on silica are distinct enough for quantitative identification. These results suggest caution when deciphering Zn speciation in natural samples via linear combination approaches using a single Znads standard to represent sorption on a particular mineral surface. Correlation between XANES spectral features and prior extended X-ray absorption fine structure (EXAFS) derived coordination environments for these Znads on silica samples provides insight into Zn speciation in natural systems with XANES compatible Zn concentrations too low for EXAFS analysis.