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Journal articles on the topic 'Polytypes'

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Published: 4 June 2021

Last updated: 1 February 2022

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1

Dawei, Meng, Wu Xiuling, Mou Tao, and Li Douxing. "Determination of six new polytypes in parisite-(Ce) by means of high resolution electron microscopy." Mineralogical Magazine 65, no. 6 (2001): 797–806. http://dx.doi.org/10.1180/0026461016560010.

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AbstractThe ultrastructures of parisite-(Ce) from a rare-earth mineral deposit of Sichuan Province, southwest China, have been observed and investigated by selected area electron diffraction (SAED) and high resolution electron microscopy (HREM). Six new polytypes 4H, 10H, 16H, 18R, 24R and 30R were determined in parisite-(Ce), as were their crystal structure types, subcell (a′c‴, a′c″, a′c′) and supercell (ac) parameters, reflection conditions, polytype features and probable space groups. The HREM studies revealed the complex polytypism in parisite-(Ce) whereby the six new polytypes, formed by

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2

Arakcheeva, Alla, Philip Pattison, Annette Bauer-Brandl, Henrik Birkedal, and Gervais Chapuis. "Cimetidine, C10H16N6S, form C: crystal structure and modelling of polytypes using the superspace approach." Journal of Applied Crystallography 46, no. 1 (2013): 99–107. http://dx.doi.org/10.1107/s0021889812048133.

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The H2 antagonist cimetidine forms many polymorphs, several of which have resisted structural analysis thus far. Using single-crystal X-ray measurements obtained from synchrotron radiation, the crystal structure of cimetidine form C has been solved. This layered structure crystallizes in space groupC2/cwith an unusually large lattice parameter,a= 82.904 Å. The thickness of each layerLis equal toa′ =a/6 = 13.82 Å, anda= 6a′ originates from a sixfoldLLLL′L′L′ sequence withLandL′ differing by 0.5b. This packing is reminiscent of polytypic stacking in metals. A (3 + 1)-dimensional superspace model

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3

Spear, K. E., A. W. Phelps, and W. B. White. "Diamond polytypes and their vibrational spectra." Journal of Materials Research 5, no. 11 (1990): 2277–85. http://dx.doi.org/10.1557/jmr.1990.2277.

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A series of diamond polytype structures are described and their IR and Raman vibrational modes predicted. The diamond polytypes are analogous to the well-known silicon carbide polytypes. The intermediate 6H diamond polytype was recently identified by single crystal electron diffraction of vapor precipitated diamond powder. In addition, end member polytypes of 3C (cubic diamond) and 2H diamond (hexagonal lonsdaleite) have been previously established, and polytypes such as 4H, 8H, 15R, and 21R diamond are predicted, but may be difficult to isolate and identify. The various diamond polytype struc

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4

Kader, Thomas, Paul Kautny, Berthold Stöger, and Johannes Fröhlich. "OD- and non-OD-polytypism of 9-(3-chloropyridin-4-yl)-9H-carbazole." Zeitschrift für Kristallographie - Crystalline Materials 232, no. 5 (2017): 375–84. http://dx.doi.org/10.1515/zkri-2016-2040.

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Abstract9-(3-Chloropyridin-4-yl)-9H-carbazole (1) crystallizes as polytypes made up of layers of one kind with P(c)21b symmetry, in which layer contacts are geometrically non-equivalent (non-OD polytypes). In both polytypes adjacent layers are related by a glide reflection with a plane parallel to (100). In polytype I (Ic2a), the intrinsic translation vector of the glide reflection is b/2. In polytype II (P21), the intrinsic translation vector is sc/2 with s=0.771. It is a polytype with a maximum degree of order (MDO) of a family of OD structures. Fragments of the second MDO polytype lead to s

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5

Luo, Huixia, Weiwei Xie, Jing Tao, et al. "Polytypism, polymorphism, and superconductivity in TaSe2−xTex." Proceedings of the National Academy of Sciences 112, no. 11 (2015): E1174—E1180. http://dx.doi.org/10.1073/pnas.1502460112.

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Polymorphism in materials often leads to significantly different physical properties—the rutile and anatase polymorphs of TiO2 are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer-stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effec

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Tsavdaris, Nikolaos, Kanaparin Ariyawong, Eirini Sarigiannidou, Jean Marc Dedulle, Odette Chaix-Pluchery, and Didier Chaussende. "Interface Shape: A Possible Cause of Polytypes Destabilization during Seeded Sublimation Growth of 15R-SiC." Materials Science Forum 806 (October 2014): 61–64. http://dx.doi.org/10.4028/www.scientific.net/msf.806.61.

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We report on the stabilization of 15R Silicon Carbide (15R-SiC) grown by seeded sublimation method. It was found that polytype transitions are directly related to the occurrence of facets on the grown crystals. Once a foreign polytype is formed, its propagation is governed mainly by the interface shape of the crystal and its evolution during growth. A concave crystal shape enhances the expansion of foreign polytypes, usually formed at the periphery of the crystal. Then, foreign polytypes can either overlap the original polytypes (constant concave crystal shape) or form inclusions (change to co

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7

Kaur, Harjeet. "Points to Ponder in the Study of Cadmium Iodide." International Letters of Chemistry, Physics and Astronomy 27 (February 2014): 1–5. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.27.1.

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During the growth of cadmium iodide crystals from solution, it has been observed that sometimes the crystal suddenly rotates. Probably, the convection currents are providing the force for the rotation. Mathematically, this force can be estimated and it must be greater than the van-der Walls force acting between adjacent sandwiches of cadmium iodide and can give rise to polytypic phase transformations. Further, studies of vacancies and the density measurements of various polytypes can help in understanding the phenomenon of polytypism better.

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8

Banerjee, Swastika, Jaehong Park, Cheol Seong Hwang, Jung-Hae Choi, Seung-Cheol Lee, and Swapan K. Pati. "Regulation of transport properties by polytypism: a computational study on bilayer MoS2." Physical Chemistry Chemical Physics 19, no. 32 (2017): 21282–86. http://dx.doi.org/10.1039/c7cp02973j.

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Being a member of the van der Waals class of solids, bilayer MoS<sub>2</sub>exhibits polytypism due to different possible stacking arrangements, namely, 2H<sub>c</sub>, 2H<sub>a</sub>and 3R-polytypes which in turn differentiates the transport preoperty of the polytypes.

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9

Pirouz, Pirouz. "Stress-Induced Phase Transformations in SiC." Microscopy and Microanalysis 4, S2 (1998): 548–49. http://dx.doi.org/10.1017/s1431927600022868.

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Tetrahedrally co-ordinated materials can undergo stress-induced structural transformations often under invariant plane strain conditions; examples of such transformations are twinning and polytypism. The structure of a tetrahedrally co-ordinated material, XY, may be considered in terms of an assembly of “normal”, Ti’and “twinned” tetrahedra, T'I’all connected to each other at their corners. In some of these materials, e.g. SiC, GaN or CdS, these corner-sharing tetrahedra may be connected to each other in different ways, giving rise to different polytypes. In this paper, a dislocation model for

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10

Menon, J., C. Suryanarayana, and G. Singh. "Polytypism in a decagonal quasicrystalline Al–Co phase." Journal of Applied Crystallography 22, no. 2 (1989): 96–99. http://dx.doi.org/10.1107/s0021889888011409.

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A decagonal quasicrystalline phase has been produced in rapidly solidified binary Al–14 to 25 at.% Co and ternary Al–20 at.% Co–5 at.% Si alloys. Observation of periodicity along one of the directions in the electron diffraction patterns has confirmed the decagonal nature of the phase. Variations in periodicity ranging from 4 to 16 Å suggest that a polytypism-like phenomenon occurs in these phases. By in situ hot-stage electron microscopy, it can be shown that one polytype transforms into another. Reasons for the formation and transformation of polytypes in decagonal quasicrystalline phases ar

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11

BIRMAN, JOSEPH L., and J. P. LU. "INTERACTING ORDER PARAMETER MODEL FOR INCREASED Tc IN POLYTYPES OF THE Cu-O SYSTEMS." Modern Physics Letters B 02, no. 11n12 (1988): 1297–302. http://dx.doi.org/10.1142/s0217984988001272.

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We introduce a simple phenomenological model with coupled order parameters for polytypes of multilayer copper-oxide systems. Polytypism increases the transition temperature from the [Formula: see text] of a single layer. For polytypes of a single layer of CuO2 we obtain the maximum T c of ~ 140 K using reasonable values of parameters.

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12

Merlino, Stefano, Cristian Biagioni, Elena Bonaccorsi, et al. "‘Clinobarylite’–barylite: order-disorder relationships and nomenclature." Mineralogical Magazine 79, no. 1 (2015): 145–55. http://dx.doi.org/10.1180/minmag.2015.079.1.12.

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Abstract'Clinobarylite', BaBe2Si2O7, was defined as a monoclinic dimorph of orthorhombic barylite. Subsequently, its crystal structure was also proved to be orthorhombic, differing from barylite in terms of the space group symmetry, Pmn21 instead of Pmnb, and in unit-cell dimensions. Through the order-disorder (OD) theory, the polytypic relationships between 'clinobarylite' and barylite are described. 'Clinobarylite' corresponds to the MDO1 polytype, with unit-cell parameters a = 11.650, b = 4.922, c = 4.674 Å, space group Pmn21; barylite corresponds to the MDO2 polytype, with a = 11.67, b = 9

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13

Köhl, Martin, Philipp Schroth, and Tilo Baumbach. "Perspectives and limitations of symmetric X-ray Bragg reflections for inspecting polytypism in nanowires." Journal of Synchrotron Radiation 23, no. 2 (2016): 487–500. http://dx.doi.org/10.1107/s1600577516000333.

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X-ray diffraction, possibly time-resolved during growth or annealing, is an important technique for the investigation of polytypism in free-standing nanowires. A major advantage of the X-ray diffraction approach for adequately chosen beam conditions is its high statistical significance in comparison with transmission electron microscopy. In this manuscript the interpretation of such X-ray intensity distribution is discussed, and is shown to be non-trivial and non-unique given measurements of the [111]cor [333]creflection of polytypic nanowires grown in the (111)cdirection. In particular, the d

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14

Kautny, Paul, Thomas Schwartz, Berthold Stöger, and Johannes Fröhlich. "An unusual case of OD-allotwinning: 9,9′-(2,5-dibromo-1,4-phenylene)bis[9H-carbazole]." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 73, no. 1 (2017): 65–73. http://dx.doi.org/10.1107/s2052520616018291.

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9,9′-(2,5-Dibromo-1,4-phenylene)bis[9H-carbazole] (1) crystallizes as a category I order–disorder (OD) structure composed of non-polar layers of one kind with B2/m(1)1 layer symmetry. The crystals are made up of the two polytypes with a maximum degree of order (MDO). The monoclinic MDO1 polytype (B21/d) possesses an orthorhombic B-centered lattice and appears in two orientations, which are related by reflection at (100). The orthorhombic MDO2 polytype (F2dd) has a doubled b-axis and appears in two orientations, which are related by inversion. The crystal structures of both polytypes were deter

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15

Arzig, Matthias, Michael Salamon, Norman Uhlmann, and Peter J. Wellmann. "Tracking of the Growth Interface during PVT-Growth of SiC Boules Using a X-Ray Computed Tomography Setup." Materials Science Forum 963 (July 2019): 14–17. http://dx.doi.org/10.4028/www.scientific.net/msf.963.14.

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A crystal comprising various polytype switches was analyzed in detail. A very flat temperature profile together with an on axis seed are used to increase the probability for the nucleation of foreign polytypes during growth. Formation of foreign polytype occurred from thin lamella propagating from the edge of the main facet to the crystal rim as well as from 2D nucleation. The evolution of the crystal surface during the growth time is visualized using in-situ X-Ray computed tomography. Two concurrent growth centers are identified in the beginning of the growth process. Nucleation and lateral g

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16

García-Vicente, Andrea, Adrián Lorenzo, Juan Morales, Emilia García-Romero, and Mercedes Suárez. "Field Spectroscopy Applied to the Kaolinite Polytypes Identification." Environmental Sciences Proceedings 6, no. 1 (2021): 16. http://dx.doi.org/10.3390/iecms2021-09353.

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A detailed characterization of a group of kaolin samples rich in some minerals of the kaolinite group was done. The mineralogical and structural characterization was conducted by X-ray diffraction (XRD) together with the study of the spectroscopy response in visible-near infrared and short wave (VNIR–SWIR), and the main objective was the determination of kaolinite polytypes. The XRD patterns group the samples according to the kaolinite polytype into five kaolinites, two dickites and six halloysites. Diagnostic peaks for kaolinite, dickite polytypes and halloysite were identified in the spectra

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17

Авров, Д. Д., А. Н. Горляк, А. О. Лебедев та ін. "Сравнительный эллипсометрический анализ политипов карбида кремния 4H, 15R, 6H, полученных модифицированным методом Лели в одном ростовом процессе". Письма в журнал технической физики 46, № 19 (2020): 28. http://dx.doi.org/10.21883/pjtf.2020.19.50041.18376.

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In this paper, we propose a model for the quantitative analysis of the dependence of the dielectric function of hexagonal silicon carbide polytypes on the photon energy in the range 0.0–6.5 eV. This model consists of the sum of two Tauc-Lorentz oscillators (main and minor) with a total band gap. This approach is used to describe the three hexagonal polytypes of silicon carbide 4H, 15R, 6H obtained in one growth process. Both C-faces and Si-faces of each polytype are analyzed. A number of conclusions have been made about the dependence of the oscillator parameters on the polytype hexagonality d

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18

VIGNOLES, GÉRARD L. "ITERATIONS OF THE SAWTOOTH MAP AS A DYNAMICAL MODEL FOR CVD/CVI SiC POLYTYPE GROWTH." International Journal of Bifurcation and Chaos 03, no. 05 (1993): 1177–94. http://dx.doi.org/10.1142/s0218127493000970.

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In order to describe silicon carbide polytype growth under CVD/CVI conditions, a dynamical model based on iterations of the sawtooth map has been studied. A two-parameter bifurcation diagram has been computed for a simple logistic-like family, and its structure has been studied in more detail by means of kneading theory and study of the skeleton. All the routes to chaos are shown to derive from the application of a central theorem involved in the construction of the skeleton. A comparison, under a combinatorial point of view, between this mathematical model and the reported data on known SiC p

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Ortiz, Angel L., Florentino Sánchez-Bajo, Francisco L. Cumbrera, and Fernando Guiberteau. "The prolific polytypism of silicon carbide." Journal of Applied Crystallography 46, no. 1 (2013): 242–47. http://dx.doi.org/10.1107/s0021889812049151.

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A worked example of polytypism is presented, aimed at assisting undergraduates in the learning and instructors in the teaching of this topic. In particular, this crystallography concept, not necessarily obvious for beginners, is illustrated pedagogically using to that end the model case of the prolific polytypism of silicon carbide (SiC). On the basis of concepts that are easily assimilated by students (i.e.simple topological constraints) this article first presents a unified description of the polytypism phenomenon in SiC that allows one to understand without difficulty the existence of its n

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Grice, J. D., and R. Rowe. "Hilgardite polytype distribution in Sussex, New Brunswick evaporite deposits." Mineralogical Magazine 78, no. 2 (2014): 235–52. http://dx.doi.org/10.1180/minmag.2014.078.2.02.

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AbstractHilgardite, Ca2B5O9Cl·H2O, has a zeolite-type framework structure consisting of cross-linked (010) layers of borate sheets having the fundamental building block (FBB) = 2Δ3☐:<Δ2☐>-<Δ2☐>. These layers are polar and the orientation, plus the number of layers in a sequence, determine the polytype. To date three hilgardite polytypes have been described: hilgardite-1A, -3A and -4M. A reliable means of polytype identification by micro X-ray powder diffraction (mXRPD) is outlined. Two polytypes are identified in the Sussex New Brunswick potash deposits: hilgardite-1A and -3A. Both

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21

Logunov, Mikhail, Vladimir Neverov, Bari Mamin, Denis Skvortsov, and Roman Sidorov. "Study of Nanoscale Inhomogeneities in Silicon Carbide Crystals via Small-Angle X-Ray Scattering." Materials Science Forum 858 (May 2016): 349–52. http://dx.doi.org/10.4028/www.scientific.net/msf.858.349.

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The structure of 4H-SiC and 6H-SiC monocrystals’ nanoscale defects was studied by the small-angle X-ray scattering (SAXS) method. Analysis of dispersion indicatrices has shown the presence of inhomogeneities in the form of linear fractals in silicon carbide crystals of 6H and 4H polytypes, mass fractals in 6H polytype and inhomogeneities partition’s fractal surface in 4H polytype.

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Cook, Nigel J., Cristiana L. Ciobanu, Wenyuan Liu, et al. "Polytypism and Polysomatism in Mixed-Layer Chalcogenides: Characterization of PbBi4Te4S3 and Inferences for Ordered Phases in the Aleksite Series." Minerals 9, no. 10 (2019): 628. http://dx.doi.org/10.3390/min9100628.

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Bi-Pb-chalcogenides of the aleksite series represent homologous mixed-layer compounds derived from tetradymite (Bi2Te2S). Considering tetradymite as composed of five-atom (Bi2Te2S) layers, the named minerals of the aleksite homologous series, aleksite (PbBi2Te2S2) and saddlebackite, (Pb2Bi2Te2S3) have been considered as phases formed by regular stacking of longer seven- and nine-atom layers. High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) imaging of thinned foils prepared in-situ on domains deemed homogeneous from electron probe microanalysis, STEM energy-d

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23

Pezoldt, Jörg. "Heteropolytypic Superlattices." Materials Science Forum 858 (May 2016): 278–82. http://dx.doi.org/10.4028/www.scientific.net/msf.858.278.

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Based on a Kronig-Penney model the electronic properties of heteropolytypic superlattices consisting of lamellas of 3C-and 4H-SiC polytypes with thicknesses below ten nanometers are analysed. Due to the large difference in the electron negativity and the resulting high barriers between the different polytypic lamellas an increased number of minizones compared to other materials are formed. The field strength for the appearance of the negative differential resistance in the heteropolytypic superlattice is lower than the critical fields in the silicon carbide polytypes.

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Ma, Chi, and George R. Rossman. "Complex Layer Stacking In Muscovite: A Hrtem Study." Microscopy and Microanalysis 5, S2 (1999): 152–53. http://dx.doi.org/10.1017/s1431927600014082.

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One-, two- and three-layer polytypes are common in muscovite (sheet silicate). Based on high-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM) examinations, we report in the discovery of complex 5-layer and 7- layer polytypes in natural muscovite for the first time (Fig. 1) and the implications of polytype transitions.Three main structures are found in muscovite crystals in a sample from Oreana, Nevada, which are 1M, 2M1, and a disordered structure often containing short-range ordered stacking sequences. On the scale of a few micrometers, muscovite oc

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Kogure, Toshihiro, and Massimo Nespolo. "A TEM study of long-period mica polytypes: determination of the stacking sequence of oxybiotite by means of atomic resolution images and Periodic Intensity Distribution (PID)." Acta Crystallographica Section B Structural Science 55, no. 4 (1999): 507–16. http://dx.doi.org/10.1107/s0108768199003845.

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In this study it is shown that the stacking sequences in long-period mica polytypes (including a rare example of a mixed-rotation polytype, with a 36-layer long periodicity) can be unambiguously determined using atomic resolution images recorded down two zone axes separated by 30° (e.g. [100] and [31¯0]) at the same area. Uniformity of these stacking sequences in a large area is further confirmed by the correspondence between computed and observed Periodic Intensity Distributions (PIDs) in electron diffraction patterns. The appearance of long-period polytypes containing layers with different o

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Capitani, Giancarlo. "Synchysite-(Ce) from Cinquevalli (Trento, Italy): Stacking Disorder and the Polytypism of (Ca,REE)-Fluorcarbonates." Minerals 10, no. 1 (2020): 77. http://dx.doi.org/10.3390/min10010077.

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Synchysite-(Ce) at Cinquevalli occurs as fine needles intergrown with quartz in quartz-dikes and in association with altered K-feldspar and oxidized chalcopyrite as major constituents. Synchysite-(Ce) [Ca1.00(Ce0.43La0.26Nd0.17Y0.07Pr0.04Sm0.02Gd0.01)Σ=1.00(CO3)2(F0.58(OH)0.42)], shows an overgrowth rim of bastnäsite-(Ce) [(Ce0.34La0.25Nd0.17Pb0.07C a0.06Y0.06Pr0.04S m0.02Gd0.01)Σ=1.00C O3(F0.75(OH)0.25)]. Unit cell refinement of synchysite (C2/c) and bastnäsite (P62c) led to a = 12.272(4), b = 7.100(2), c = 18.640(5) Å, β = 102.71(5)°, and a = 7.085(1), c = 9.746(2) Å, respectively. Polysomat

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Lumpi, Daniel, Paul Kautny, Berthold Stöger, and Johannes Fröhlich. "Crystal chemistry of layered structures formed by linear rigid silyl-capped molecules." IUCrJ 2, no. 5 (2015): 584–600. http://dx.doi.org/10.1107/s2052252515011665.

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The crystallization behavior of methylthio- or methylsulfonyl-containing spacer extendedZ,Z-bis-ene–yne molecules capped with trimethylsilyl groups obtained by (tandem) thiophene ring fragmentation and of two non-spacer extended analogs were investigated. The rigid and linear molecules generally crystallized in layers whereby the flexibility of the layer interfaces formed by the silyl groups leads to a remarkably rich crystal chemistry. The molecules with benzene and thiophene spacers both crystallized withC2/csymmetry and can be considered as merotypes. Increasing the steric bulk of the core

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Pezoldt, Jörg, and Volker Cimalla. "Imprinting the Polytype Structure of Silicon Carbide by Rapid Thermal Processing." Crystals 10, no. 6 (2020): 523. http://dx.doi.org/10.3390/cryst10060523.

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Silicon carbide is a material with a multistable crystallographic structure, i.e., a polytypic material. Different polytypes exhibit different band gaps and electronic properties with nearly identical basal plane lattice constants, making them interesting for heterostructures without concentration gradients. The controlled formation of this heterostructure is still a challenge. The ability to adjust a defined temperature–time profile using rapid thermal processing was used to imprint the polytype transitions by controlling the nucleation and structural evolution during the temperature ramp-up

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Britton, Doyle, Wayland E. Noland, and Kenneth J. Tritch. "Two new polytypes of 2,4,6-tribromobenzonitrile." Acta Crystallographica Section E Crystallographic Communications 72, no. 2 (2016): 178–83. http://dx.doi.org/10.1107/s2056989016000256.

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Three polymorphs of 2,4,6-tribromobenzonitrile (RCN), C7H2Br3N, two of which are novel and one of which is a redetermination of the original structure first determined by Carter & Britton [(1972).Acta Cryst.B28, 945–950] are found to be polytypic. Each has a layer structure which differs only in the stacking of the layers. Each layer is composed of molecules associated through C[triple-bond]N...Br contacts which formR22(10) rings. Two such rings are associated with each N atom; one with eachortho-Br atom. No new polytypes of 1,3,5-tribromo-2-isocyanobenzene (RNC) were found but a re-determ

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Guo, Deqi, J. Stephen Hartman, and Mary Frances Richardson. "Long-range shielding and NMR chemical shifts in silicon carbide polytypes." Canadian Journal of Chemistry 70, no. 3 (1992): 700–702. http://dx.doi.org/10.1139/v92-093.

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Despite an apparently successful empirical correlation, it is incorrect to ascribe variations in 29Si and 13C chemical shifts in silicon carbide polytypes to diamagnetic anisotropy effects Keywords: silicon carbide, long-range shielding, polytypism, MAS NMR.

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Mercier, Frédéric, and Shin Ichi Nishizawa. "Bulk and Surface Effects on the Polytype Stability in SiC Crystals." Materials Science Forum 717-720 (May 2012): 41–44. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.41.

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We investigated with ab initio calculations the 3C-, 6H-, 4H- and 2H-SiC polytypes. We discuss the geometry and the energetics of bulk and surface relaxed structures ((0001) Si face and the (000-1) C face surfaces). The polytype stability is discussed regarding the bulk and surface effects.

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Rodriguez-Horta, Edwin, Ernesto Estevez-Rams, Raimundo Lora-Serrano, and Reinhard Neder. "Close-packed structure dynamics with finite-range interaction: computational mechanics with individual layer interaction." Acta Crystallographica Section A Foundations and Advances 73, no. 5 (2017): 377–86. http://dx.doi.org/10.1107/s2053273317008968.

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This is the second contribution in a series of papers dealing with dynamical models in equilibrium theories of polytypism. A Hamiltonian introduced by Ahmad & Khan [Phys. Status Solidi B(2000),218, 425–430] avoids the unphysical assignment of interaction terms to fictitious entities given by spins in the Hägg coding of the stacking arrangement. In this paper an analysis of polytype generation and disorder in close-packed structures is made for such a Hamiltonian. Results are compared with a previous analysis using the Ising model. Computational mechanics is the framework under which the an

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Rowe, Ralph, Joel D. Grice, and Rémy S. Poulin. "Differentiating veatchite polytypes using X-ray powder diffraction." Powder Diffraction 29, no. 1 (2013): 69–75. http://dx.doi.org/10.1017/s0885715613000766.

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Veatchite polytypes were properly identified from several localities relying solely on micro powder diffraction data. Diagnostic differences in their respective calculated patterns gave reliable identification results when compared with measured data. This permitted the confirmation of co-existing veatchite-1A and -2M on the same specimen from the Billie Mine, Inyo County, California as flat elongated crystals (-1A) and flat rhombic plates (-2M), respectively. On the specimen from the Sterling Borax Mine (Lang), type-locality for veatchite-2M, the polytype veatchite-1A was confirmed from radia

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Zobetz, Erich. "Homometric polytypes." Crystal Research and Technology 29, no. 3 (1994): 379–85. http://dx.doi.org/10.1002/crat.2170290318.

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J.F., Banfield, and Kogure T. "Polytypic Constraints for Solid-State Layer Silicate Transformation Mechanisms Via Atomic-Resolution Transmission Electron Microscopy." Microscopy and Microanalysis 4, S2 (1998): 598–99. http://dx.doi.org/10.1017/s1431927600023114.

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Layer silicates are important and abundant minerals. Polytypic details can be determined directly from atomic-resolution images recorded down [010] of layer silicates such as chlorite (Fig. 1), serpentine, and micas using a transmission electron microscope with a point resolution of ∼ 0.2 nm. For chlorite, this involves determination of whether octahedral slants in the brucite-like interlayers and octahedral sheet of the tetrahedral - octahedral-tetrahedral (TOT) layers are the same or opposed, the (3 angle, and how the octahedral cations in the brucite-like interlayer are positioned relative

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Onoda, Mitsuko, Anne-Claire Dhaussy, and Yasushi Kanke. "Structural characterization of YV4O8: simultaneous analysis of coexisting polytypes and simulation of diffuse scattering for a stacking disorder model." Acta Crystallographica Section B Structural Science 59, no. 4 (2003): 429–38. http://dx.doi.org/10.1107/s0108768103010450.

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The structure of a crystal of newly synthesized YV4O8 was refined on the assumption that two polytypes and their respective twin forms intergrow. The model was expressed as a commensurate composite crystal with two types of subsystem: one is a V4O8 framework with rather large tunnels and the other consists of Y ions. In the tunnels, Y ions and vacancies are located at every second site in an ordered manner that is characteristic of each polytype. Refinement was performed using a high-dimensional formalism and all reflections from all domains. Diffuse streaks observed in the X-ray and electron

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Oleynik, G. S., and A. V. Kotko. "On the mechanism of formation of the granular structure and interfaces in self-reinforced aluminum nitride." Uspihi materialoznavstva 2021, no. 2 (2021): 63–71. http://dx.doi.org/10.15407/materials2021.02.063.

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Results of an investigation by scanning electron microscopy methods of the microstructure of self-reinforced aluminum nitride obtained on the basis of aluminum nitride powder and containing 3 mass.% oxygen by plasma-chemical synthesis in the temperature range 1700-2000 °C are presented. Initial aluminum nitride was represented by the wurtzite (2H) phase. Samples were obtained by free sintering in a nitrogen atmosphere. It was established that, during sintering of AlN in the indicated temperature range, three microstructural types of the material and six types of interfaces (three types of inte

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Давыдов, С. Ю. "Электронный спектр капсулированных монослоев: аналитические результаты". Письма в журнал технической физики 47, № 13 (2021): 52. http://dx.doi.org/10.21883/pjtf.2021.13.51124.18749.

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Green’s function method is used to find the dispersion low for a monolayer (ML) placed be-tween two crystalline slabs. Weak- and strong-coupling regimes are considered in details. For the systems graphene, hBN – metallic ML – SiC polytypes analytical expressions for the ML electron effective masses are obtained. It is shown that the effective mass decreases with the increase of the SiC polytype energy gap.

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Pezoldt, Jörg, and Andrei Alexandrovich Kalnin. "Wurtzite SiC Formation in Plastic Deformed 3C and 6H." Materials Science Forum 1004 (July 2020): 243–48. http://dx.doi.org/10.4028/www.scientific.net/msf.1004.243.

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Single side clamped 3C and 6H single crystal silicon carbide beams were elastic deformed using a special designed deformation stage in an electron microscope and subjected to high temperatures. The structural transitions occurring during the plastic relaxation process were recorded in situ in the electron microscope using reflection high energy electron diffraction in {110} azimuthal direction. For both polytypes, a polytype phase transition into the wurtzite silicon carbide polytype was observed independent on the surface polarity. The critical initial elastic deformation of the polytype phas

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Mokhov, E. N., M. V. Chukichev, A. D. Roenkov, G. V. Saparin, S. K. Obyden, and A. I. Ivanov. "Investigation of single crystals and epitaxial layers (EL) Of SiC by means of real color SEM technique." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (1990): 712–13. http://dx.doi.org/10.1017/s0424820100176691.

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Investigations were undertaken with SiC, a large-bandgap semiconductor material, that is rather promising for designing different optoelectronic devices. The characteristic feature of SiC is the availability of a large number of modifications, i.e. polytypes, strongly differing in the band-gap. The important problems that stand in the way of mastering SiC are the detectable doping of single crystals and epitaxial structures, the transformation of polytypes, and the structure of the intermediate layer. Crystals of SiC and its EL of 3C, 15R, 6H, 4H polytypes doped with N, Al, Ga and B were inves

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Seki, Kazuaki, S. Harada, and Toru Ujihara. "Bulk 3C-SiC Crystal by Top Seeded Solution Growth Method." Materials Science Forum 740-742 (January 2013): 311–14. http://dx.doi.org/10.4028/www.scientific.net/msf.740-742.311.

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In this paper, we review our researches on the high-quality 3C-SiC bulk crystal growth. The polytype control and the suppression of defects are essential in the growth 3C-SiC on hexagonal SiC seed crystals. The growth polytype of SiC is usually controlled by the inheritance of the seed crystal. In contrast, we established kinetic polytype control in which the preferential growth of 3C-SiC can be achieved by the difference in the growth rates depending on supersaturation for the polytypes. In the growth of 3C-SiC, double positioning boundaries (DPBs) are often formed by the existence of twinned

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Marinova, Maya, Alkyoni Mantzari, Ariadne Andreadou, and Efstathios K. Polychroniadis. "On the Polytypic Transformations in SiC." Journal of Nano Research 18-19 (July 2012): 89–96. http://dx.doi.org/10.4028/www.scientific.net/jnanor.18-19.89.

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In the present work we report on the polytypic transformations taking place in nanoscale dimensions within 6H-SiC crystals. The examined crystals were grown by Liquid Phase Epitaxy using a mixture of Si and Al as solvents. The study concentrated on the differences from the “correct” stacking order of the Si-C bilayers for 6H-SiC leading to the formation of other polytypes. A great variety of sequences was found, which resulted to the appearance of rare short and long period polytypes or individual lamellae having their “own” stacking inside the 6H-SiC matrix. These nanostructured faults which

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Leineweber, A., C. Wolf, P. Kalanke, et al. "From random stacking faults to polytypes: A 12-layer NiSn4 polytype." Journal of Alloys and Compounds 774 (February 2019): 265–73. http://dx.doi.org/10.1016/j.jallcom.2018.09.341.

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Frewin, Christopher L., Camilla Coletti, Christian Riedl, Ulrich Starke, and Stephen E. Saddow. "A Comprehensive Study of Hydrogen Etching on the Major SiC Polytypes and Crystal Orientations." Materials Science Forum 615-617 (March 2009): 589–92. http://dx.doi.org/10.4028/www.scientific.net/msf.615-617.589.

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A comprehensive study on the hydrogen etching of numerous SiC polytype surfaces and orientations has been performed in a hot wall CVD reactor under both atmospheric and low pressure conditions. The polytypes studied were 4H and 6H-SiC as well as 3C-SiC grown on Si substrates. For the hexagonal polytypes the wafer surface orientation was both on- and off-axis, i.e. C and Si face. The investigation includes the influence of the prior surface polishing method on the required etching process parameters. 3C-SiC was also studied grown in both the (100) and (111) orientations. After etching, the samp

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Medizadeh, V., and S. Mardix. "New ZnS polytypes." Acta Crystallographica Section C Crystal Structure Communications 42, no. 5 (1986): 518–19. http://dx.doi.org/10.1107/s0108270186095549.

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Suda, Jun, and Masahiro Horita. "Polytype Replication in Heteroepitaxial Growth of Nonpolar AlN on SiC." MRS Bulletin 34, no. 5 (2009): 348–52. http://dx.doi.org/10.1557/mrs2009.98.

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AbstractZinc-blende and wurtzite are the most common structures for binary compound semiconductors. Aluminum nitrides (AIN), one of the most promising materials for deep ultraviolet light-emitting diodes, have a wurtzite structure as an equilibrium phase due to its strong ionicity. Silicon carbide (SiC) is widely used as a substrate for heteroepitaxial growth of AlN, since SiC has a hexagonal structure whose lattice constant is close to that of AIN. Different from other compound semiconductors, SiC can have many different crystalline structures, called polytypism. Among various polytypes of Si

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Hao, Wenming, Yongsheng Liu, Alexandra Neagu, et al. "Core-Shell and Hollow Particles of Carbon and SiC Prepared from Hydrochar." Materials 12, no. 11 (2019): 1835. http://dx.doi.org/10.3390/ma12111835.

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The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (β-SiC) but also significant amounts of the 2H or the 6H polytypes (α-SiC) in the SiC.

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Ivády, Viktor, Bálint Somogyi, Viktor Zólyomi, et al. "Transition Metal Defects in Cubic and Hexagonal Polytypes of SiC: Site Selection, Magnetic and Optical Properties from Ab Initio Calculations." Materials Science Forum 717-720 (May 2012): 205–10. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.205.

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Relatively little is known about the transition metal defects in silicon carbide (SiC). In this study we applied highly convergent and sophisticated density functional theory (DFT) based methods to investigate important transition metal impurities including titanium (Ti), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo) and tungsten (W) in cubic 3C and hexagonal 4H and 6H polytypes of SiC. We found two classes among the considered transition metal impurities: Ti, V and Cr clearly prefer the Si-substituting configuration while W, Nb, and Mo may fractionally form a complex with carbon

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Zhitova, E. S., V. N. Yakovenchuk, S. V. Krivovichev, A. A. Zolotarev, Y. A. Pakhomovsky, and G. Yu Ivanyuk. "Crystal chemistry of natural layered double hydroxides. 3. The crystal structure of Mg,Al-disordered quintinite-2H." Mineralogical Magazine 74, no. 5 (2010): 841–48. http://dx.doi.org/10.1180/minmag.2010.074.5.841.

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AbstractTwo crystals of Mg, Al-disordered quintinite-2H (Q1 and Q2), [Mg4Al2(OH)12](CO3)(H2O)3, from the Kovdor alkaline massif, Kola peninsula, Russia, have been characterized chemically and structurally. Both crystals have hexagonal symmetry, P63/mcm, a = 3.0455(10)/3.0446(9), c = 15.125(7)/15.178(5) Å, V = 121.49(8)/121.84(6) Å3. The structures of the two crystals have been solved by direct methods and refined to R1 = 0.046 and 0.035 on the basis of 76 and 82 unique observed reflections for Q1 and Q2, respectively. Diffraction patterns obtained using an image-plate area detector showed the

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Luberda-Durnaś, Katarzyna, Marek Szczerba, Małgorzata Lempart, Zuzanna Ciesielska, and Arkadiusz Derkowski. "Layer stacking disorder in Mg-Fe chlorites based on powder X-ray diffraction data." American Mineralogist 105, no. 3 (2020): 353–62. http://dx.doi.org/10.2138/am-2020-6982.

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Abstract The primary aim of this study was the accurate determination of unit-cell parameters and description of disorder in chlorites with semi-random stacking using common X-ray diffraction (XRD) data for bulk powder samples. In the case of ordered chlorite structures, comprehensive crystallographic information can be obtained based on powder XRD data. Problems arise for samples with semi-random stacking, where due to strong broadening of hkl peaks with k ≠ 3n, the determination of unit-cell parameters is demanding. In this study a complete set of information about the stacking sequences in

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