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Relevant bibliographies by topics / Jahn-Teller distortion

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Academic literature on the topic 'Jahn-Teller distortion'

Author: Grafiati

Published: 4 June 2021

Last updated: 6 September 2023

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Journal articles on the topic "Jahn-Teller distortion"

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ZHANG, MINPING, and GUANGTAO WANG. "THE ORBITAL ORDERING OF THE CUBIC KCrF3." Modern Physics Letters B 26, no. 04 (February 10, 2012): 1150025. http://dx.doi.org/10.1142/s0217984911500254.

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The electronic, magnetic and orbital structures of KCrF 3 in the cubic phase are studied by first principles method. In the cubic phase, the three Cr - F bonds distance are equal. If the Jahn–Teller distortion is the origin of the orbital polarization, the orbital ordering would disappear. However, our theoretical calculations show that the orbital ordering exists even without the Jahn–Teller distortion. By studying how the orbital polarization changes with the electron correlation and the Jahn–Teller distortion, we found that the origin of the orbital polarization should be the electron correlation and the Jahn–Teller distortion can reinforced such polarization.

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Jung, Haeyoon, Jiyeon Kim, and Sooran Kim. "Phonon study of Jahn–Teller distortion and phase stability in NaMnO₂ for sodium-ion batteries." Journal of Applied Physics 132, no. 5 (August 7, 2022): 055101. http://dx.doi.org/10.1063/5.0086903.

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Cathode materials undergo various phase transitions during the charge/discharge process, and the structural transitions significantly affect the battery performance. Although phonon properties can provide a direct clue for structural stability and transitions, it has been less explored in sodium cathode materials. Here, using the first-principles calculations, we investigate phonon and electronic properties of various layered NaMnO2 materials, especially focusing on the dependency of the Jahn–Teller distortion of Mn3+. The phonon dispersion curves show that the O′3 and P′2 structures with the Jahn–Teller distortion are dynamically stable in contrast to undistorted O3 and P2 structures. The structural instability of O3 and P2 structures is directly observed from the imaginary phonon frequencies, as so-called phonon soft modes, whose corresponding displacements are from O atoms distorting along the local Mn–O bond direction in the MnO6 octahedra. This is consistent with the experimental stability and a structural transition with the Jahn–Teller distortion at the high Na concentration. The orbital-decomposed density of states presents the orbital redistribution by the Jahn–Teller distortion, such as eg-band splitting in both O′3 and P′2 system, and the stability of O′3 and P′2 is not sensitive to the electron–electron correlation. Our results demonstrate the importance of phonon analysis to further understand the structural stability and phase transitions in cathode materials.

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Tang, Fu Ling, F. C. Wan, X. Q. Dai, and W. J. Lu. "Atomic Simulation for Lattice Structure of La/SrMnO₃ Superlattice." Materials Science Forum 689 (June 2011): 49–57. http://dx.doi.org/10.4028/www.scientific.net/msf.689.49.

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We studied in detail the lattice transition and local lattice structure (including Jahn-Teller distortion) in LaMnO3/SrMnO3surperlattices by classical atomistic simulation. For a certain doping density, it is found that the superlattices with short modulation period have small lattice energies and larger differences among lattice parametersa,b/√2 andc. The average La-Mn (Mn3+-O) distance is larger than the average Sr-Mn (Mn4+-O) distance for all doping densities and superlattice configurations at certain doping density. The standard deviation of Mn-O bond lengths and Jahn-Teller distortion of MnO6octahedra have been calculated. Both the standard deviation and Jahn-Teller distortion of Mn3+O6octahedra in the superlattices are much smaller than those of Mn3+O6octahedra in LaMnO3, while Mn4+O6octahedra in the superlattices have the smallest lattice distortion, but larger than those in SrMnO3.

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Orii, Yuta, Masaki Kobayashi, Yuki Nagai, Kohei Atsumi, Daichi Tazaki, Satoshi Ehara, and Takashiro Akitsu. "Anisotropic strain and Jahn-Teller effect of chiral complexes and metal oxides." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C179. http://dx.doi.org/10.1107/s2053273314098209.

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For about a decade, we have systematically investigated thermally-accessible lattice strain and local pseudo Jahn-Teller distortion of [CuL2]3[M(CN)6]2·4H2O (L = (1R, 2R)-cyclohexanediamine; M = Cr, Co, and Fe). In mononuclear Cu(II) complexes, (pseudo) Jahn-Teller effect plays an important role in flexible distortion of crystal structures especially Cu(II) coordination environment. Beside Jahn-Teller distortion, we have dealt with some factors for example, metal substitution as bimetallic assemblies, chirality of ligands, and H/D isotope effect to vary intermolecular interaction and crystal packing. According to the course work using variable temperature PXRD, we have found that anisotropy of crystal strain distortion did not corporate with Jahn-Teller distortion around local coordination environment because of the discrepancy of the crystallographic axes and molecular alignment. In order to elucidate the anisotropic control of lattice strain and Jahn-Teller distortion closely, we have employed transition metal oxide with orthogonal or layered structures to prepare composite materials with the chiral metal complexes for discussion of thermally-accessible PXRD changes and IR shift due to adsorption. At first, we have employed chiral one-dimensional zig-zag Cu-Cr bimetallic assemblies and their oxides prepared by burining. Based on variable temperature XRD patterns, a linear correlation (lnK = a/T + b) of K (=d(T)-d(0)/d(T)) values, where d(T) and d(0) are spacing of lattice plane (d = nλ/(2sinθ)) at T K and 0 K (extrapolated), respectively, and its deviation from ideal correlation indicates degree of anisotropic lattice distortion of the composite materials. For example, we could observe LiMnO2, typical material of lithium ion battery, was enhanced anisotropic lattice strain along the b axis or the (011) plane added by [CuL2(H2O)2](NO3)2 complexes. Which may prevent from breaking down regular crystal structures during charge-discharge of secondary battery.

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Radin, Maxwell, Julija Vinckeviciute, Jonas Kaufman, John C. Thomas, and Anton Van der Ven. "The Coupling between Mechanics and Intercalation Chemistry in Layered Battery Materials." ECS Meeting Abstracts MA2018-01, no. 32 (April 13, 2018): 1946. http://dx.doi.org/10.1149/ma2018-01/32/1946.

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In addition to a change in lattice parameters, many materials also experience complex structural transformations upon intercalation. For example, many layered lithium and sodium oxides transform between the O3/O1/P3 stacking sequences, and Ni and Mn oxides often undergo transformations associated with collective Jahn-Teller distortions. Many questions remain about how these structural transformations affect battery performance, and in particular, how they affect cycle life limitations arising from fracture and mechanical damage. Here we present new models to capture the coupling between intercalation chemistry and mechanics arising from stacking-sequence changes and Jahn-Teller distortions. This includes first-principles simulations and mesoscale models to elucidate the thermodynamics and kinetics of stacking sequence changes, as well as analyses of how these transformations might result in irreversible changes to microstructure. Regarding the mechanics of Jahn-Teller distortions, we have developed anharmonic vibrational models to explore the transition from a collective distortion to a dynamic one in layered materials such as lithium nickel and manganese oxides (as well as their sodium analogues). Numerical simulations reveal how the interplay between the shape of the Jahn-Teller energy landscape and rigidity of the crystal impact the local structure and thermodynamic properties of the dynamically distorted phase.

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Kochelaev, B. I., E. Shilova, J. Deisenhofer, H. A. Krug von Nidda, A. Loidl, A. A. Mukhin, and A. M. Balbashov. "Orbital Order and Spin Relaxation in La0.95Sr0.05MnO3." Modern Physics Letters B 17, no. 10n12 (May 20, 2003): 469–77. http://dx.doi.org/10.1142/s0217984903005494.

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We analyze the temperature and angular dependence of the paramagnetic-resonance linewidth of La 0.95 Sr 0.05 MnO 3. The observed anisotropy can be well described by the crystal field contributions originated by the Jahn–Teller distortion. The critical behavior of the linewidth at the Jahn–Teller transition is found to be directly related with the orbital order.

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Tian, Lin, Ya-Sha Yi, Chui-Lin Wang, and Zhao-Bin Su. "E⊗e Jahn–Teller Effect in ${\rm C}_{70}^{3-}$ Systems." International Journal of Modern Physics B 11, no. 16 (June 30, 1997): 1969–78. http://dx.doi.org/10.1142/s0217979297001039.

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The electron–phonon interaction in C 70 anions is studied by making use of a lattice relaxation approach. We find there exists a Jahn–Teller effect in [Formula: see text] system, due to an extra electron being doped to the double degenerate [Formula: see text] state. As a result of this effect, the original D5h symmetry of the ground state becomes unstable, which causes distortion of the lattice configuration. The only symmetry maintained in the final state of the relaxation is the x–y plane reflection symmetry. We further find that besides the Jahn–Teller active [Formula: see text] modes, the non-Jahn–Teller active [Formula: see text] vibrations also contribute to the relaxation process. The [Formula: see text] components come from the nonlinear effect and are two or three orders smaller than those of the Jahn–Teller active modes. We suggest that the [Formula: see text] molecule is a promising Berry Phase candidate in this effective E⊗e Jahn–Teller system.

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Thangavel, Arumugam, Marika Wieliczko, Christopher Scarborough, Birger Dittrich, and John Bacsa. "An investigation of the electron density of a Jahn–Teller-distorted CrIIcation: the crystal structure and charge density of hexakis(acetonitrile-κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate." Acta Crystallographica Section C Structural Chemistry 71, no. 11 (October 13, 2015): 936–43. http://dx.doi.org/10.1107/s2053229615015739.

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In the crystal structure of the title homoleptic CrIIcomplex, [Cr(CH3CN)6](C24H20B)2·CH3CN, the [Cr(CH3CN)6]2+cation is a high-spind4complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single-crystal X-ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the CrIIcation away from idealized octahedral symmetry. The topological analysis of the asphericald-electron density about the CrIIcation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the CrIIcation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller-distorted six-coordinate complex.

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Engel, Nicholas, Sergey I. Bokarev, Alexandre Moguilevski, Azhr A. Raheem, Ruba Al-Obaidi, Tobias Möhle, Gilbert Grell, et al. "Light-induced relaxation dynamics of the ferricyanide ion revisited by ultrafast XUV photoelectron spectroscopy." Physical Chemistry Chemical Physics 19, no. 22 (2017): 14248–55. http://dx.doi.org/10.1039/c7cp01288h.

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Zarrabeitia, Maider, Elena Gonzalo, Marta Pasqualini, Matteo Ciambezi, Oier Lakuntza, Francesco Nobili, Angela Trapananti, et al. "Unraveling the role of Ti in the stability of positive layered oxide electrodes for rechargeable Na-ion batteries." Journal of Materials Chemistry A 7, no. 23 (2019): 14169–79. http://dx.doi.org/10.1039/c9ta02710f.

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Dissertations / Theses on the topic "Jahn-Teller distortion"

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Sacchetti, Andrea. "Effects of induced structural modifications in manganites and related compounds: the Jahn-Teller distortion of MnO_6 octahedra." Doctoral thesis, La Sapienza, 2005. http://hdl.handle.net/11573/917143.

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Abdul, Latiff Hawa Alima Binti. "Magnetic anisotropy and coercivity of tetragonally distorted spinel ferrite particles via the Jahn-Teller distortion and the magnetoelastic coupling." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY005.

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Cette étude propose l'idée des aimants dits de ferrite tétragonale en rendant la symétrie cristalline des ferrites de spinelle cubique afin d'améliorer l'anisotropie magnétique (et donc, d'améliorer la coercivité). Pour concrétiser cette idée, nous avons synthétisé des particules (Cu, Co) -ferrite à distorsion tétragonale et caractérisé systématiquement les propriétés magnétiques en conséquence avec leurs distorsions de réseau. Les facteurs intrinsèques et extrinsèques contribuant à la coercivité ont été étudiés. Pour élucider l'anisotropie magnétique, nous avons démontré un modèle de couplage physique de l'effet Jahn-Teller (JT) et de l'effet magnétoélastique (ME) au sein de la théorie phénoménologique. Ensuite, nous avons effectué une analyse de coercivité dans deux modèles généraux de coercivité afin de clarifier les paramètres de la microstructure contribuant au mécanisme d'inversion de la magnétisation. À partir de l'analyse du modèle magnétoélastique, nous avons démontré l'expression linéaire de l'anisotropie magnétique en utilisant le paramètre tétragonal obtenu à partir de la distorsion JT. Les valeurs du coefficient magnétoélastique pour Cu (B1Cu = 2 MJ / m3) et Co (B1Co = 40 MJ / m3) déduites de la courbe expérimentale étaient acceptables avec la valeur calculée pour le ferrite de cuivre en vrac (B1Cu en vrac = 4 MJ / m3) et le cobalt. ferrite (masse B1Co = 55 MJ / m3). Les résultats suggèrent que l’anisotropie magnétique peut être attribuée au couplage de la distorsion JT avec l’effet magnétoélastique de Co. Au lieu d’une augmentation indéfinie avec x, l’anisotropie magnétique Ku tend à atteindre une valeur de saturation en raison de la concurrence entre les effet magnétoélastique de Co et le JT de Cu. Entre le x tétragonal x = 0,1 et le x cubique = 0,2, les valeurs de Ku constantes d'anisotropie magnétique intrinsèque ne varient pas de manière aussi significative que la différence entre les champs de coercivité et d'anisotropie. La réduction des champs d'anisotropie supérieurs à x = 0,1 peut alors être attribuée à l'augmentation de l'aimantation spontanée. L'analyse de la coercivité au sein du modèle micromagnétique a révélé une contribution importante à la coercivité de la microstructure et de l'effet démagnétisant local. Le paramètre de microstructure αMM = 0,25 obtenu était une valeur classique de l'analyse micromagnétique, suggérant le départ du champ d'anisotropie avec ce facteur de réduction. Les facteurs démagnétisants locaux effectifs NeffMM d’environ 1,4 obtenus étaient plutôt importants, ce qui suggère un effet démagnétisant significatif. Dans l'analyse du modèle global (GM), les valeurs de NeffGM obtenues étaient were 0,38 pour l'échantillon x = 0,1. La valeur négative suggère la présence d'une interaction d'échange agissant efficacement en opposition à l'interaction dipolaire. En deçà de 100 K, une différence dans le modèle suggère l’idée d’un réchauffement local consécutif à l’activation thermique due au changement d’énergie Zeeman et à une dissipation de chaleur inefficace. Cet événement peut avoir conduit à la réduction du champ coercitif à une température suffisamment basse dans l'échantillon x = 0.1 en supposant que les grains sont fortement couplés en échange
This study proposes the idea of the so-called tetragonal ferrite magnets by rendering the crystal symmetry of the cubic spinel ferrites to enhance the magnetic anisotropy (and hence, enhance the coercivity). To realize this idea, we synthesized tetragonally distorted (Cu,Co)-ferrite particles and systematically characterized the magnetic properties accordingly with their lattice distortions. The intrinsic and extrinsic factors contributing to coercivity were investigated. To elucidate the magnetic anisotropy, we demonstrated a physical coupling model of the Jahn-Teller (JT) effect and the magnetoelastic (ME) effect within the phenomenological theory. Then, we performed coercivity analysis within two general models of coercivity to clarify the microstructure parameters contributing to the magnetization reversal mechanism. From the magnetoelastic model analysis, we demonstrated the linear expression of the magnetic anisotropy using the tetragonal parameter obtained from the JT distortion. The magnetoelastic coefficient values for Cu (B1Cu = 2 MJ/m3) and Co (B1Co = 40 MJ/m3) deduced from the experimental curve were agreeable with the value calculated for bulk copper ferrite (B1Cu bulk= 4 MJ/m3) and cobalt ferrite (B1Co bulk= 55 MJ/m3). The results suggests that the source of magnetic anisotropy can be attributed to the coupling of the JT distortion with the magnetoelastic effect of Co. Instead of an indefinite increase with x, the magnetic anisotropy Ku tends to reach a saturation value due to the competition between the magnetoelastic effect of Co and the JT effect of Cu. Between the tetragonal x = 0.1 and the cubic x = 0.2 samples, the intrinsic magnetic anisotropy constant Ku values do not vary as significantly compared to the difference in the coercivity and the anisotropy fields. The reduction of anisotropy fields above x = 0.1 then can be attributed to the increase in the spontaneous magnetization.The coercivity analysis within the micromagnetic model revealed significant contribution to the coercivity by the microstructure and the local demagnetizing effect. The microstructure parameter αMM = 0.25 obtained was a classical value in the micromagnetic analysis, suggesting the departure of anisotropy field with this reduction factor. The effective local demagnetizing factor NeffMM of about 1.4 obtained were rather large suggesting a significant demagnetizing effect. Within the global model (GM) analysis, the values of NeffGM obtained were －0.38 for the x = 0.1 sample. The negative value suggests the presence of an exchange interaction acting effectively in opposition to the dipolar interaction. Below 100 K, discrepancy in the GM suggests the idea of a local heating event following the thermal activation due to the change in Zeeman energy and ineffective heat dissipation. This event may have led to the reduction of coercive field at sufficiently low temperature in the x = 0.1 sample assuming the grains are strongly exchange-coupled

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Sparks, Taylor David. "Oxide Thermoelectrics: The Role of Crystal Structure on Thermopower in Strongly Correlated Spinels." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10243.

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This dissertation reports on the synthesis, structural and thermal characterization and electrical and thermal transport properties of a variety of strongly correlated spinels. General structure property relationships for electrical and thermal transport are discussed. However, the relationship between thermopower and features of the crystal structure such as spin, crystal field, anti-site disorder, and structural distortions are explored in depth. The experimental findings are reported in the context of improving existing oxide thermoelectric materials, screening for new materials or using thermopower as a unique characterization tool to determine the cation distribution in spinels. The need for improved n-type oxide thermoelectric materials has led researchers to consider mixed valence \((+3/+4)\) manganese oxides. Contrary to previous findings we report herein that the \(LiMn_2O_4\) compound reaches the relatively large n-type thermopower of \(-73 \mu V/K\) which is three times larger than the value observed in other manganese oxides, \(-25 \mu V/K\). The cause of this increase in thermopower is shown to be the absence of a Jahn-Teller distortion on the \(Mn^{3+}\) ions in \(LiMn_2O_4\). By avoiding this structural distortion the orbital degeneracy is doubled and the Koshibae et al.’s modified Heikes formula predicts a thermopower of \(-79 \mu V/K\) in good agreement with the experiment. Altering the \(Mn^{3+/4+}\) ratio via aliovalent doping did not affect the thermopower and is a second evidence of universal charge transport first reported by Kobayashi et al. The role of anti-site disorder was further examined in \(Fe_xMn_{1-x}NiCrO_4\) x=0, ½, ¾, 1 spinels but the effect on thermopower was inconclusive due to the presence of impurity phases. Next, the thermopower as a function of temperature in \(Co_3O_4\) was investigated as a means whereby the Wu and Mason’s 30 year old model for using thermopower to calculate cation distribution in spinels could be revisited. We report evidence that Wu and Mason’s original model using the standard Heikes formula and considering octahedral sites alone leads to a stoichiometrically inconsistent result at high temperatures. Alternate models are evaluated considering Koshibae et al.’s modified Heikes formula and accounting for tetrahedral site contributions. Furthermore, the effect of a possible spin state transition is considered.
Engineering and Applied Sciences

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Shang, Jing. "2D Magnetic and multiferroic materials: Fundamental physics and application exploration from theoretical simulation." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/227367/1/Jing_Shang_Thesis.pdf.

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This thesis aims to propose the feasible approaches to control and manipulate the magnetism in two-dimensional (2D) magnets through magnetoelectric coupling by using density functional theory (DFT) calculations. It is found that the goal can be achieved by building 2D magnetic-ferroelectric heterostructures or seeking for the multiferroic candidates. The effective manipulations of magnetic states are expected to not only provide new insights into the fundamental research, but also pave the solid foundations for the spintronic applications.

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Yun, Li Jeng, and 李政昀. "Jahn – Teller Distortion in metalloporphyrin oxidation." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/06211844561799457710.

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碩士
國立中興大學
化學系
94
Metalloporphyrin cation radical often reveals some unusual deformation which including the altered 16 atom inner ring and saddle or ruffle distortion. In 1989, Spiro etc figure out that the distortion comes from Jahn–Teller distortion which makes a1u and a2u mix. In 2002, Ghosh confirm that Jahn–Teller distortion makes the in plane distortion as long as the energy gap between a1u and a2u is less than 0.15eV. About the out of plane distortion, there is no clear explanation except the possibility of packing effect in crystal structure. By DFT calculation, we also confirm the oxidation of diamagnetic metalloporphyrin makes in plane distortion, and a1u and a2u mix. According to Pearson’s classification, it belongs to SOJT (Second order Jahn–Teller Distortion). For paramagnetic metalloporphyrin oxidation, our result reveals that copper porphyrin display out of plane deformation after oxidation. There is bonding interaction between dx2-y2 and a2u and lower energy. This is also a SOJT.

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Malguth, E. "Optical properties of transition-metal-doped GaN and ZnO for spintronics applications." Thesis, 2008. http://hdl.handle.net/10453/37253.

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University of Technology, Sydney. Faculty of Science.
Spin-based devices have the potential to take modern electronics and optoelectronics to the next level. So-called ‘spintronics’ exploit both the charge and the spin of an electron for data processing, transport and storage. A significant step towards the realisation of such devices would be to achieve room temperature ferromagnetic semiconductors. Theoretical works predict the possibility of room temperature ferromagnetism in the wide bandgap semiconductors GaN and ZnO doped with transition metals. The present models of spin-coupling in such dilute magnetic semiconductors require input in form of quantitative information on electronic states that arise from the introduction of transition metal ions into the host lattice. This work focuses on the detailed experimental investigation of such states in GaN and ZnO doped with different transition metals. A large array of Fe, Mn and Ni doped GaN and ZnO samples with different doping levels and n-type and p-type co-doping were intensively studied by a wide range of experimental techniques. The investigation of Fe doped GaP, GaAs and InP provided valuable insights into the transient shallow acceptor state constituted by a hole bound to Fe2+. The most significant results are summarised in the following: A comprehensive literature review is presented on the Fe centre in III-V and II- VI semiconductors. Experimental and theoretical data that have been obtained over a few decades were reviewed thoroughly unveiling common phenomena that can be generalised to other TMs. The positions of established Fe3+/2+ and Fe2+/1+ levels were summarised allowing for predictions on the positions of further charge transfer levels based on the internal reference rule. The Fe3+/4+ level has not been identified unambiguously in any of the studied materials. Detailed term schemes of the observed charge states in tetrahedral and trigonal crystal field symmetry are presented including fine structure, isotope effects and a dynamic Jahn-Teller effect. By means of cathodoluminescence experiments Ni and Fe doping of HVPE-grown GaN was found to promote the formation of inhomogeneous regions with increased donor density and enhanced luminescence efficiency. In these regions richly structured cathodoluminescence patterns are observed at the surface. By means of optical studies on high quality Fe doped GaN samples the electronic structure of Fe3+ and Fe2+ was established in great detail. The effects of spin-orbit interaction, of the axial distortion of the crystal held in hexagonal GaN and of the Jahn-Teller coupling were successfully investigated. Both the Fe3+ centre and the Fe2+ centre were found to be stabilised against a dynamic Jahn Teller effect by the trigonal symmetry of the wurtzite lattice. A bound state with a binding energy of 50±10 meV was identified as a hydrogenic state consisting of a hole localised at an Fe2+ centre. This [Fe2,h] state represents a transient shallow acceptor state. It could be described by effective-mass-theory revealing an effective Bohr radius of 1.5 nm which may enable a long-range spin interaction via overlapping wavefunctions at relatively low Fe doping. The position of the Fe3+/2+ acceptor level could be narrowed down to 2.863±0.005 eV above the valence band maximum. Acting as a deep acceptor Fe incorporation was shown to quench the intrinsic yellow luminescence of GaN by lowering the Fermi level and passivating native donor states. Implications concerning the internal reference rule are discussed. A deep understanding of the effective-mass-like state [Fe2+,h] could be obtained by temperature and stress dependent measurements on Fe doped GaP, GaAs and InP. Besides the ground state, the hole was observed in several excited hydrogenic states each involving different Fe2+ fine structure states. Particularly for the hydrogenic ground state, a weak exchange interaction was found between the hole Fe2+ core states. Due to finite p-d hybridisation of Fe orbitals with the valence band, a weaker binding energy was observed for the ground state than predicted by effective mass theory. Finally, with regard to the Fe3+ ground state, 6A1(S), in GaP and InP, the hyperfine structure level T8 was found to be above the T7 level. ZnO:Fe samples were prepared by Fe coating ZnO crystals, which were grown from the gas phase, and subsequent annealing under varying atmospheres. In these samples the internal Fe2+(5E—5T2) transition was observed for the first time at 395.7 meV by means of Fourier transform infrared transmission spectroscopy. This value is in good agreement with the general trend in III-V and II-VI materials that the (5E—5T2) energy rises with an increasing degree of ionicity and decreasing lattice constant. No axial symmetry was found for the Fe2+ centre which is unusual for wurtzite ZnO. Possible reasons are discussed taking into account a strong Jahn- Teller effect, the non-constant c/a-ratio of ZnO and a high concentration of defects. Moreover, Fe-defect complexes and local vibrational modes could be identified. A large array of GaN samples with varying Mn concentrations and n-type and p-type co-doping allowed for a systematic charge state tuning by shifting the Fermi level providing access to the oxidation states Mn2+, Mn3+ and Mn4+. The respective electronic structures were investigated by means of optical and magnetic techniques. The Mn3+ centre and Mn4+ centre showed clear effects of degradation of crystal quality as a result of Mn, Si and Mg doping. A strong tendency was demonstrated for the formation of Mn-Mg complexes. A photoluminescence structure found around 1 eV in Mg co-doped GaN:Mn samples was proven to originate from Mn4+ involved in such complexes. A resonant Stokes process by secondary excitation and stimulated hole transfer was established in these Mn-Mg complexes. The Mn3+/4+ donor and Mn3+/2+ acceptor levels were found 1.15 eV and 1.65 eV above the VB maximum, respectively, compensating n-type and p-type doping. As a consequence, there is no reasonable chance to achieve high carrier concentrations in GaN:Mn, a precondition for free-carrier-mediated spin-coupling. The results presented in this thesis contribute to the general understanding of transition-metal-related electronic states in III-V and II-VI semiconductors, particularly in GaN and ZnO. These new insights are valuable contributions to a targeted design of dilute magnetic semiconductors that will help to, one day, realise next- generation spintronic devices.

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Chakraborty, Tirthankar. "Magnetic, Electrical and Structural Properties of Doped Manganite, Ferrite and Nickelate Perovskites." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4150.

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Multifunctional materials with novel magnetic and electric properties have attracted intense research interest due to prospects in technological applications as well as understanding of fundamental physics. Perovskite materials with ABO3 structure belong to one of the most interesting and vastly studied families by virtue of their rich magnetic and electrical properties. In the present thesis, efforts have been made to investigate the magnetic, electrical, and structural properties of A and B-site doped perovskites. In the beginning, a general introduction to basic concepts of various physical phenomena are discussed. This is followed by a brief description of the various experimental methods employed including sample synthesis and single crystal growth. Fe3+ and Mn3+ have the same ionic radii in oxygen octahedra. However, Mn3+ is Jahn–Teller active, and the magnetic ground states of RFeO3 and RMnO3 are completely different. The evolution of structural and electrical properties with doping of Mn3+ ion in RFeO3 was investigated on a series of NdFe1-xMnxO3 (0≤x≤1) compounds. Despite similar ionic radii in Mn3+ and Fe3+, a large variation in the lattice parameters and a crossover from dynamic to static Jahn– Teller distortion were discernible. The magnitude of Fe/Mn–O–Fe/Mn bond angle on ab plane and activation energy corresponding to transport and dielectric relaxation (deduced by assuming the small polaron hopping (SPH) model) vary with doping in a characteristic manner which was attributed to changes in magnetic interaction. Effects of size mismatch at B-site were investigated by doping Mn-site with Ni cations in Ho2NiMnO6 compound. This induces B-site ordering which leads to double perovskite structure and ferromagnetic ordering at TC = 86 K. Ideal Curie–Weiss law fails to provide a reasonable fit in the paramagnetic region which follows a modified Curie–Weiss law. Such a deviation occurs due to presence of heavy rare earth element Ho. Griffiths phase pertaining to the Ni/Mn subsystem was ascertained. Two dielectric relaxations due to phononic and Maxwell–Wagner mechanisms were observed. The system has also been shown to be a potential magnetocaloric refrigerant. A solid solution of RFeO3 and RMnO3 offer much prospects due to its vastly different magnetic properties. A single crystalline phase is essential for such studies, and we were successful in growing single crystals of ErFe0.55Mn0.45O3 which order antiferromagnetically at 365 K with spin canting-induced weak ferromagnetic moment along c axis. Upon cooling, magnetization along c axis passes through zero at 266.4 K and becomes negative below this temperature and a spin reorientation occurs from Γ4(Gx, Ay, Fz) to Γ1(Ax, Gy, Cz) configuration in the temperature window of 255 to 258 K. Magnetic behavior is explained with spin configuration and interplay between net magnetization of individual Er and Fe/Mn sublattices which are oppositely coupled and have different temperature evolution. To observe the effect of A-site doping on RFeO3 perovskites, Ho0.5Dy0.5FeO3 single crystals were grown. Two spin reorientations of Fe magnetic sublattice were evident viz. Γ4(Gx, Ay, Fz) → Γ1(Ax, Gy, Cz) → Γ2(Fx, Cy, Gz) at temperatures of 49 and 26 K. As magnetic field along c axis increases, the sample resumes Γ4 state in place of Γ1 state. Along c axis, field- induced transition from Γ1 to Γ4 is feasible. Studies on hybrid organic-inorganic perovskite compounds have also been carried out on heterometallic [(CH3)2NH2]Mn0.5Ni0.5(HCOO)3 and [(CH3)2 NH2]Co0.5Ni0.5(HCOO)3 which were found to crystallize in trigonal space group R-3c at room temperature and order antiferromagnetically with weak ferromagnetism induced by spin canting at 17 and 8 K, respectively. Hydrogen bond ordering leads to spontaneous polarization and structural transition occurs from R-3c to Cc through mixed phase. This is reflected in impedance data also. Highlights of major findings in different chapters and a general conclusion to this study are presented at the end.

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Books on the topic "Jahn-Teller distortion"

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Launay, Jean-Pierre, and Michel Verdaguer. Basic concepts. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198814597.003.0001.

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The electronic structure of molecules is described, starting from qualitative Molecular Orbital (MO) theory. After the case of simple atoms and molecules, one treats molecular solids and develops the relation between Molecular Orbital theory and band theory. In both cases, one shows that the electronic structure can influence the geometrical structure, through Jahn–Teller effects or Peierls distortion. The effect of interelectronic repulsion, the central problem of Quantum Chemistry, is put in perspective by a synthetic presentation of different approaches: Hartree–Fock Self-Consistent Field with treatment of electron correlation, Valence Bond models, and finally Density Functional Theory methods (DFT). The last section is devoted to quantum tunnelling and its dynamical aspects.

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Book chapters on the topic "Jahn-Teller distortion"

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Zlatar, Matija, Jean-Pierre Brog, Alain Tschannen, Maja Gruden-Pavlović, and Claude Daul. "Density Functional Theory Study of the Multimode Jahn-Teller Effect – Ground State Distortion of Benzene Cation." In Vibronic Interactions and the Jahn-Teller Effect, 25–38. Dordrecht: Springer Netherlands, 2011. http://dx.doi.org/10.1007/978-94-007-2384-9_2.

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Khanna, S. N., B. K. Rao, P. Jena, and J. L. Martins. "Jahn-Teller Distortion, Hund’s Coupling and Metastability in Alkali Tetramers." In Physics and Chemistry of Small Clusters, 435–38. Boston, MA: Springer US, 1987. http://dx.doi.org/10.1007/978-1-4757-0357-3_61.

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Day, P., A. C. W. P. James, and J. R. G. Thorne. "Jahn-Teller Distortion of the 4T1(G) State Of MnCl4 2- in Cs3MnCl5." In Understanding Molecular Properties, 85–93. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3781-9_5.

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Kaplan, Michael D., and Benjamin G. Vekhter. "Mutual Influence of Distortive, Magnetic, and Electric Dipole Orderings in Jahn—Teller Elastics." In Cooperative Phenomena in Jahn—Teller Crystals, 189–266. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1859-4_4.

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Feiner, Louis Felix, and Andrzej M. Oles. "Dynamic Jahn-Teller Effect and Distortional Disorder in Manganites." In Open Problems in Strongly Correlated Electron Systems, 409–11. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0771-9_44.

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Klupp, G., and K. Kamarás. "Following Jahn–Teller Distortions in Fulleride Salts by Optical Spectroscopy." In Springer Series in Chemical Physics, 489–515. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03432-9_16.

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Reinen, Dirk, and Micheil Atanasov. "DFT Calculations of the “Lone Pair” Effect — A Tool for the Chemist to Predict Molecular Distortions?" In Vibronic Interactions: Jahn-Teller Effect in Crystals and Molecules, 83–95. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0985-0_9.

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Röhler, J., and A. Larisch. "Evidence for Jahn-Teller Distortions in Bi-Sr-Ca-Cu-O High-Tc Superconductors." In Springer Series in Solid-State Sciences, 152–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84345-7_29.

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Brouet, V., H. Alloul, S. Gàràj, and L. Forrò. "NMR Studies of Insulating, Metallic, and Superconducting Fullerides: Importance of Correlations and Jahn–Teller Distortions." In Fullerene-Based Materials, 165–99. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/b94382.

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Lüders, Martin, and Nicola Manini. "Jahn–Teller Distortions and Excitation Energies in." In Advances in Quantum Chemistry, 289–304. Elsevier, 2003. http://dx.doi.org/10.1016/s0065-3276(03)44018-5.

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Conference papers on the topic "Jahn-Teller distortion"

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Bietsch, W., J. Bao, A. Schilder, and M. Schwoerer. "The Jahn-Teller distortion of." In ELECTRONIC PROPERTIES OF NOVEL MATERIALS--SCIENCE AND TECHNOLOGY OF MOLECULAR NANOSTRUCTURES. ASCE, 1999. http://dx.doi.org/10.1063/1.59818.

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Kamarás, K. "Jahn-Teller distortion in Cs4C60 studied by vibrational spectroscopy." In STRUCTURAL AND ELECTRONIC PROPERTIES OF MOLECULAR NANOSTRUCTURES: XVI International Winterschool on Electronic Properties of Novel Materials. AIP, 2002. http://dx.doi.org/10.1063/1.1514073.

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Haritha, L., G. Gangadhar Reddy, and A. Ramakanth. "Influence of band Jahn-Teller distortion on the magnetoresistance in manganites." In SOLID STATE PHYSICS: PROCEEDINGS OF THE 57TH DAE SOLID STATE PHYSICS SYMPOSIUM 2012. AIP, 2013. http://dx.doi.org/10.1063/1.4791419.

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Tiwari, Vandana, Ajay Jha, Hong-Guang Duan, and R. J. Dwayne Miller. "Photoinduced Jahn-Teller distortion in crystals of Cu(I) phenanthroline complex." In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/up.2022.tu4a.49.

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We have studied the effect of lattice induced strained ligand geometry on the excited state dynamics of prototypical Cu(I) based photocatalyst in single crystals using fs-broadband transient absorption spectroscopy. Our results show faster intersystem crossing in crystals (~5 ps) as compared to the solution (~9 ps).

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Sundaresan, A. "Jahn–Teller distortion and magnetoresistance in Sr[sub 1−x]Ce[sub x]MnO[sub 3]." In Physics in local lattice distortions. AIP, 2001. http://dx.doi.org/10.1063/1.1363100.

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AHMED, M. A., and S. I. EL-DEK. "EVIDENCE OF JAHN-TELLER DISTORTION and PHASE SEPARATION IN Ca DOPED LaMnO3." In Proceedings of the Third International Conference on Modern Trends in Physics Research. WORLD SCIENTIFIC, 2011. http://dx.doi.org/10.1142/9789814317511_0010.

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Panda, Saswati, G. C. Rout, and S. N. Behera. "Instability and re-entrant behaviour of Jahn-Teller distortion due to induced magnetization in manganites." In FUNCTIONAL MATERIALS: Proceedings of the International Workshop on Functional Materials (IWFM-2011). AIP, 2012. http://dx.doi.org/10.1063/1.4736902.

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ABDEL-KHALEK, E. K., W. M. EL-MELIGY, E. A. MOHAMED, T. Z. AMER, and H. A. SALLAM. "STUDY OF THE RELATIONSHIP BETWEEN ELECTRICAL AND MAGNETIC PROPERTIES AND JAHN–TELLER DISTORTION IN R0.7Ca0.3Mn0.95Fe0.05O3 PEROVSKITES BY MÖSSBAUER EFFECT." In Proceedings of the Third International Conference on Modern Trends in Physics Research. WORLD SCIENTIFIC, 2011. http://dx.doi.org/10.1142/9789814317511_0013.

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Iwamura, Munetaka, Kunihiko Ishii, Satoshi Takeuchi, and Tahei Tahara. "The Hollow on the Excited-State Potential for Photo-induced `Jahn-Teller¿ Distortion of Copper Complexes Revealed by Ultrafast Spectroscopy." In 2007 Conference on Lasers and Electro-Optics - Pacific Rim. IEEE, 2007. http://dx.doi.org/10.1109/cleopr.2007.4391607.

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Capone, M. "Crucial role of Jahn–Teller distortions in LaMnO[sub 3]." In Physics in local lattice distortions. AIP, 2001. http://dx.doi.org/10.1063/1.1363103.

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Reports on the topic "Jahn-Teller distortion"

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Mitchell, J. F., D. N. Argyriou, and J. D. Jorgensen. Charge delocalization and structural response in layered La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}: Enhanced Jahn-Teller distortion in the metallic regime. Office of Scientific and Technical Information (OSTI), November 1996. http://dx.doi.org/10.2172/399708.

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