4,049 results on '"Soft modes"'
Search Results
2. Black holes decohere quantum superpositions.
- Author
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Danielson, Daine L., Satishchandran, Gautam, and Wald, Robert M.
- Subjects
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QUANTUM superposition , *BLACK holes , *QUANTUM theory , *DECOHERENCE (Quantum mechanics) , *QUANTUM gravity - Abstract
We show that if a massive body is put in a quantum superposition of spatially separated states, the mere presence of a black hole in the vicinity of the body will eventually destroy the coherence of the superposition. This occurs because, in effect, the gravitational field of the body radiates soft gravitons into the black hole, allowing the black hole to acquire "which path" information about the superposition. A similar effect occurs for quantum superpositions of electrically charged bodies. We provide estimates of the decoherence time for such quantum superpositions. We believe that the fact that a black hole will eventually decohere any quantum superposition may be of fundamental significance for our understanding of the nature of black holes in a quantum theory of gravity. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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3. Phase Diagram and Soft Modes Behavior TbFe3–xGax(BO3)4 Solid Solutions with Huntite Structure
- Author
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Krylov, A. S., Vtyurin, A. N., Gudim, I. A., Nemtsev, I. V., and Krylova, S. N.
- Published
- 2023
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4. Symmetry‐adapted pair distribution function analysis (SAPA): a novel approach to evaluating lattice dynamics and local distortions from total scattering data.
- Author
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Bird, Tobias A., Herlihy, Anna, and Senn, Mark S.
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DISTRIBUTION (Probability theory) , *LATTICE dynamics , *BARIUM titanate , *PHASE transitions , *LOSSY data compression , *DATA distribution - Abstract
A novel symmetry‐adapted pair distribution function analysis (SAPA) method for extracting information on local distortions from pair distribution function data is introduced. The implementation of SAPA is demonstrated in the TOPAS‐Academic software using the freely available online software ISODISTORT, and scripts for converting the output from ISODISTORT to a SAPA input file for TOPAS are provided. Finally, two examples are provided to show how SAPA can evaluate the nature of both dynamic distortions in ScF3 and the distortions which act as an order parameter for the phase transitions in BaTiO3. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
5. Fluctuations in the Dynamics of Glasses
- Author
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Castillo, Horacio [Ohio Univ., Athens, OH (United States). Department of Physics and Astronomy]
- Published
- 2015
- Full Text
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6. Soft Modes
- Author
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Leal Filho, Walter, Series Editor, Azul, Anabela Marisa, editor, Brandli, Luciana, editor, Lange Salvia, Amanda, editor, and Wall, Tony, editor
- Published
- 2021
- Full Text
- View/download PDF
7. Transformable Superisostatic Crystals Self-Assembled from Segment Colloidal Rods.
- Author
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Hu JD, Wang T, Lei QL, and Ma YQ
- Abstract
Transformable mechanical structures can switch between distinct mechanical states. Whether this kind of structure can be self-assembled from simple building blocks at microscale is a question to be answered. In this work, we propose a self-assembly strategy for these structures based on a nematic monolayer of segmented colloidal rods with lateral cutting. By using Monte Carlo simulation, we find that rods with different cutting degrees can self-assemble into different crystals characterized by bond coordination z that varies from 3 to 6. Among these, we identify a transformable superisostatic structure with pgg symmetry and redundant bonds ( z = 5). We show that this structure can support either soft bulk modes or soft edge modes depending on its Poisson's ratio, which can be tuned from positive to negative through a uniform soft deformation. We also prove that the bulk soft modes are associated with states of self-stress along the direction of zero strain during uniform soft deformation. The self-assembled transformable structures may act as mechanical metamaterials with potential applications in micromechanical engineering.
- Published
- 2024
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8. Dispersion Engineering by Hybridizing the Back-Folded Soft Mode of Monomode Elastic Metamaterials with Stiff Acoustic Modes.
- Author
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Groß MF, Schneider JLG, Chen Y, Kadic M, and Wegener M
- Abstract
In many cases, the hybridization of two or more excitation modes in solids has led to new and useful dispersion relations of waves. Well-studied examples are phonon polaritons, plasmon polaritons, particle-plasmon polaritons, cavity polaritons, and magnetic resonances at optical frequencies. In all of these cases, the lowest propagating mode couples to a finite-frequency localized resonance. Herein, the unusual metamaterial phonon dispersion relations arising from the hybridization of an ordinary acoustical phonon mode with a back-folded soft or easy phonon mode of a monomode elastic metamaterial are discussed. Conceptually, the single easy mode can have strictly zero wave velocity. In reality, its wave velocity is very much smaller than that of all other modes. Considering polymeric three-dimensional printed elastic monomode metamaterials at ultrasound frequencies, it is shown theoretically and experimentally that the resulting pronounced avoided crossing, with a frequency splitting comparable to the mid-frequency, leads to backward-wave behavior for the lowest band over a broad frequency range, conceptually at zero loss., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)
- Published
- 2024
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9. Influence of the Vibrational Modes from the Organic Moieties in 2D Lead Halides on Excitonic Recombination and Phase Transition.
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Moral, Raphael F., Germino, José C., Bonato, Luiz G., Almeida, Diogo B., Therézio, Eralci M., Atvars, Teresa D. Z., Stranks, Samuel D., Nome, René A., and Nogueira, Ana F.
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PHASE transitions , *LEAD halides , *MOIETIES (Chemistry) , *ELECTRONIC excitation , *EXCITON theory , *METAL halides , *POLARONS - Abstract
2D metal halide semiconductors have been intensively studied in the past few years due to their unique optical properties and potential for new‐generation photonic devices. Despite the large number of recent works, this class of materials is still in need of further understanding due to their complex structural and optical characteristics. In this work, a molecular‐level explanation for the dual band emission in the 2D (C4H9NH3)2PbI4 in its bulk form is presented, demonstrating that this feature is caused by a strong exciton–phonon coupling. Temperature‐dependent photoluminescence with Raman and IR spectroscopies reveals that vibrations involving the C‐NH3+ butylammonium polar head are responsible for this exciton–phonon coupling. Additionally, experimental shifts in the mean phonon frequencies coupled with the electronic excitation, combined with a theoretical model, show that these vibrational modes present a soft‐mode behavior in the phase transition of this material. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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10. Structural phase transition in TbFe2.5Ga0.5(BO3)4 single crystal.
- Author
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Krylov, A. S., Gudim, I. A., Krylova, S. N., Krylov, A. A., and Vtyurin, A. N.
- Subjects
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PHASE transitions , *RAMAN spectroscopy , *GALLIUM antimonide , *CONDENSATION - Abstract
The Raman spectra of the TbFe2.5Ga0.5(BO3)4 single crystal in the temperature range from 8 to 400 K have been observed. The condensation and restoration of the soft modes have been found. The soft modes are associated with the structural phase transition from the R32 phase to the P3121 phase. The behavior of the hard modes confirms the structural phase transition close to the tricritical point. The temperature of the structural phase transition T1 = 33 K is established. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
11. Soft modes in HoFe2.5Ga0.5(BO3)4 solid solution.
- Author
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Krylov, Alexander, Krylova, Svetlana, Gudim, Irina, and Vtyurin, Alexander
- Subjects
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MAGNETIC transitions , *SOLID solutions , *PHASE transitions , *MAGNETIC crystals , *RAMAN spectroscopy - Abstract
The condensation of two soft modes has been found when studying the Raman spectra of the solid solution HoFe2.5Ga0.5(BO3)4 in the temperature range from 7 to 350 K. The first high-temperature soft mode is associated with the structural phase transition from the R32 phase to the P3121 phase. The second soft mode is related to the reveal of the phonon-magnon interaction during magnetic ordering in the crystal. The temperatures of the structural phase transition T1 = 266 K and the magnetic phase transition T2 = 28 K are established. Experimentally interaction between the structural phase transition order parameter fluctuations and the magnetic order parameter fluctuations was found. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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12. Open and Anisotropic Soft Regions in a Model Polymer Glass
- Author
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Carlo Andrea Massa, Francesco Puosi, Antonio Tripodo, and Dino Leporini
- Subjects
polymer glasses ,vibrational dynamics ,soft modes ,molecular-dynamics simulations ,Organic chemistry ,QD241-441 - Abstract
The vibrational dynamics of a model polymer glass is studied by Molecular Dynamics simulations. The focus is on the “soft” monomers with high participation to the lower-frequency vibrational modes contributing to the thermodynamic anomalies of glasses. To better evidence their role, the threshold to qualify monomers as soft is made severe, allowing for the use of systems with limited size. A marked tendency of soft monomers to form quasi-local clusters involving up to 15 monomers is evidenced. Each chain contributes to a cluster up to about three monomers and a single cluster involves a monomer belonging to about 2–3 chains. Clusters with monomers belonging to a single chain are rare. The open and tenuous character of the clusters is revealed by their fractal dimension df<2. The inertia tensor of the soft clusters evidences their strong anisotropy in shape and remarkable linear correlation of the two largest eigenvalues. Owing to the limited size of the system, finite-size effects, as well as dependence of the results on the adopted polymer length, cannot be ruled out.
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- 2021
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13. Lattice stability, mechanical and thermal properties of a new class of multicomponent (Fe, Mo, W)6C η carbides with different atomic site configurations
- Author
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Yunxuan Zhou, Liujie Xu, Zulai Li, Jing Feng, Xiaoyu Chong, Yehua Jiang, Yang Lin, Shizhong Wei, and Fei Zhang
- Subjects
Materials science ,Process Chemistry and Technology ,chemistry.chemical_element ,Thermodynamics ,Soft modes ,Thermal expansion ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Carbide ,chemistry ,visual_art ,Materials Chemistry ,Ceramics and Composites ,Melting point ,visual_art.visual_art_medium ,Wyckoff positions ,Ceramic ,Anisotropy ,Carbon - Abstract
Transition metal carbides are candidates for high-temperature structural ceramics because of their high melting point, high hardness, and high strength. However, one challenge is overcoming their high intrinsic brittleness. In this study, we investigated a new class of (Fe, Mo, W)6C carbides, which have three Wyckoff positions for metallic atoms (16d, 32e, and 48f) and one Wyckoff position for carbon (16c). These different Wyckoff positions provide a great opportunity to optimize the mechanical properties by the partial replacement of atoms at each Wyckoff position to obtain high-entropy carbides. The current results show that the phonon spectra have no imaginary frequency when Fe occupies the 16d or 32e positions, but a soft mode is observed when Fe occupies 48f. (Fe, Mo, W)6C η carbides have a higher fracture toughness compared with those of M3C and MC carbides owing to their low carbon content (14.3 at.%). The mechanical anisotropy of (Fe, Mo, W)6C is weak, which is beneficial for increasing the damage tolerance. The thermal expansion coefficients of the (Fe, Mo, W)6C η carbides are predicted to be approximately (8.5–9.5) × 10−6 K−1 at 1400 K.
- Published
- 2022
14. The nature of the intermediate phase in K3Na(SeO4)2 crystals: three possible transition paths of the trigonal-monoclinic phase transition.
- Author
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Kitaev, Yu. E., Roginskii, E. M., and Zhandun, V. S.
- Subjects
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PHASE transitions , *MONOCLINIC crystal system , *DENSITY functional theory , *CRYSTAL defects , *PRIMITIVE cells (Crystallography) - Abstract
Three different transition paths of the phase transition from the high-symmetry trigonal P
m1 to the low-symmetry monoclinic phase C2/c in K3Na(SeO4)2 crystals have been analyzed using ab initio calculations based on the density functional theory (DFT) as well as programs and retrieval tools of the Bilbao Crystallographic server (BCS). We conclude that the intermediate state observed in experiments within 346-329 K temperature range consists of a mixture of two monoclinic phases C2/m and C2/c, both with the primitive cell doubled along the z-axis. Both monoclinic phases result from the softening of the double-degenerated zone-edge soft phonon . [ABSTRACT FROM AUTHOR] - Published
- 2018
- Full Text
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15. Emphanisis in Cubic (SnSe)0.5(AgSbSe2)0.5: Dynamical Off-Centering of Anion Leads to Low Thermal Conductivity and High Thermoelectric Performance
- Author
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Martin Etter, Umesh V. Waghmare, Moinak Dutta, Kanishka Biswas, and Koushik Pal
- Subjects
Condensed matter physics ,Phonon ,Chemistry ,Anharmonicity ,Pair distribution function ,General Chemistry ,Electronic structure ,Soft modes ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Thermal conductivity ,Thermoelectric effect ,Density functional theory - Abstract
The structural transformation generally occurs from lower symmetric to higher symmetric structure on heating. However, the formation of locally broken asymmetric phases upon warming has been evidenced in PbQ (Q = S, Se, Te), a rare phenomenon called emphanisis, which has significant effect on their thermal transport and thermoelectric properties. (SnSe)0.5(AgSbSe2)0.5 crystallizes in rock-salt cubic average structure, with the three cations occupying the same Wycoff site (4a) and Se in the anion position (Wycoff site, 4b). Using synchrotron X-ray pair distribution function (X-PDF) analysis, herein, we show the gradual deviation of the local structure of (SnSe)0.5(AgSbSe2)0.5 from the overall cubic rock-salt structure with warming, resembling emphanisis. The local structural analysis indicates that Se atoms remain in off-centered position by a magnitude of ∼0.25 A at 300 K along the [111] direction and the magnitude of this distortion is found to increase with temperature resulting in three short and three long M-Se bonds (M = Sn/Ag/Sb) within the average rock-salt lattice. This hinders phonon propagation and lowers the lattice thermal conductivity (κlat) to 0.49-0.39 W/(m·K) in the 295-725 K range. Analysis of phonons based on density functional theory (DFT) reveals significant soft modes with high anharmonicity which involve localized Ag and Se vibrations primarily. Emphanisis induced low κlat and favorable electronic structure with multiple valence band extrema within close energy concurrently give rise to a promising thermoelectric figure of merit (zT) of 1.05 at 706 K in p-type carrier optimized Ge doped new rock-salt phase of (SnSe)0.5(AgSbSe2)0.5.
- Published
- 2021
16. Ab Initio Calculation of Li-Sn System: Unraveling New Phases of Superconducting Materials with Increasing Compression
- Author
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Thong Leng Lim, S. K. Lai, Tiem Leong Yoon, and Yee Hui Robin Chang
- Subjects
Superconductivity ,Crystal ,symbols.namesake ,Materials science ,Condensed matter physics ,Fermi level ,Ab initio ,symbols ,Tetrahedron ,Density functional theory ,Soft modes ,Linear response function - Abstract
Stoichiometry, crystal compound, electronic attributes and superconductivity of compressed lithium-tin composites have been thoroughly studied using quantum mechanical genetic algorithm approach and the first principles computations based on density functional theory. Our simulations at moderate pressure (5-20 GPa) predict a complex convex hull diagram, with the following stable Li‑rich phases: I4/mmm-Li6Sn2, -Li7Sn2, -Li5Sn2, Ama2-Li4Sn2, -Li5Sn2, -Li6Sn2, C2/m-Li4Sn1, P21/m-Li6Sn2, -Li7Sn2 and Cmcm-Li4Sn2. Careful examination at their independent elastic parameters reveals sufficient mechanical stability in them. These phases are metallic system, with reasonably high electron concentration near to Fermi level or N(EF) that ranges from 0.6 to 2.4 states/eV cell. It is also interesting for us to observe soft modes and steep-flat energy bands at Fermi levels of Li6Sn2 structures which are stable throughout the pressure range. These features are prerequisites for superconducting behavior. Linear response function with Gaussian and tetrahedron methods reveals satisfactory superconducting transition temperature Tc (3.1 ~ 6.6 K) and Tc (2.1 ~ 2.4 K), respectively. Structural transition results for based elements Li and Sn agree well with literature thus signifying reliable prediction of intermediate phases.
- Published
- 2021
17. First-Principles Characterization of Surface Phonons of Halide Perovskite CsPbI3 and Their Role in Stabilization
- Author
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Liang Z. Tan and Ruo Xi Yang
- Subjects
Quenching ,Materials science ,Phonon ,Soft modes ,Condensed Matter::Materials Science ,symbols.namesake ,Strain engineering ,Chemical physics ,Phase (matter) ,Physical Sciences ,Chemical Sciences ,symbols ,General Materials Science ,Density functional theory ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Perovskite (structure) - Abstract
The stability of halide perovskites has been a long-standing issue for their real-world application. Approaches to improve stability include nanostructuring, dimensionality reduction, and strain engineering, where surfaces play an important role in the formation of a stable structure. To understand the mechanism we compute the lattice dynamics of the surface of CsPbI3 using density functional theory. We demonstrate, for the first time, that CsPbI3 crystals exhibit surface phonons that are localized on the outermost layers of the slabs, and we perform a complete symmetry characterization including an identification of the Raman/IR active modes. These surface phonons are present in the optically active cubic phase but are absent in the optically inactive "yellow" phase. Furthermore, we show that the surface suppresses bulk instabilities by hardening soft modes of the bulk cubic phase, resulting in phase stabilization and quenching of dynamical disorder. This study is fundamental for understanding the structural behavior of halide perovskite materials with high surface area-to-volume ratios, and for guiding stabilization strategies.
- Published
- 2021
18. Strain and temperature-dependent dielectric permittivity of cubic SrTiO3: Self-consistent phonon theory calculations
- Author
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Woon Ih Choi, Inkook Jang, Dae Sin Kim, and Jae Sik An
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Strain (chemistry) ,Phonon ,Dielectric permittivity ,General Physics and Astronomy ,02 engineering and technology ,Soft modes ,Self consistent ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Square (algebra) ,0103 physical sciences ,Curie temperature ,General Materials Science ,0210 nano-technology - Abstract
We examine the strain effect on the dielectric permittivity of cubic SrTiO3 (STO) with Self-Consistent Phonon (SCP) theory calculations. Despite the soft mode frequency overestimation with this theory scheme and workflow, our calculations predict the correct tendency of TO1 with respect to temperature and strain. We found that a uniform tensile strain leads to softer TO1 modes. In addition, the TO1 frequency drops suddenly to zero at a specific temperature in the presence of a ferroelectric transition. The square linear relation between TO1 and temperature is used to estimate the Curie Temperature (TC), and the STO dielectric permittivity calculated with the Lyddane-Sachs-Teller relation follows the Curie-Weiss (CW) law; which can also be used to determine another TC value. Results from both approaches are in good agreement with each other and show that TC increases significantly even when the applied tensile strain is only a few percent.
- Published
- 2021
19. Soft-mode dynamics in the ferroelectric phase transition of GeTe
- Author
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Yue Chen, Jiangtao Wu, Jan Peter Embs, Yanzhong Pei, Zezhu Zeng, Chen Wang, and Jie Ma
- Subjects
Phase transition ,Materials science ,Condensed matter physics ,Phonon ,Anharmonicity ,Interatomic potential ,02 engineering and technology ,Soft modes ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,Ferroelectricity ,Inelastic neutron scattering ,Computer Science Applications ,Condensed Matter::Materials Science ,QA76.75-76.765 ,Mechanics of Materials ,Modeling and Simulation ,0103 physical sciences ,TA401-492 ,General Materials Science ,Computer software ,010306 general physics ,0210 nano-technology ,Materials of engineering and construction. Mechanics of materials - Abstract
GeTe that exhibits a strong anharmonicity and a ferroelectric phase transition between the rhombohedral and cubic structures has emerged as one of the leading thermoelectric materials. Herein, combining molecular dynamics simulations and inelastic neutron scattering measurements, the lattice dynamics in GeTe have been investigated to reveal the soft-mode mechanisms across the phase transition. We have constructed a first-principles-based machine-learning interatomic potential, which successfully captures the dynamical ferroelectric phase transition of GeTe by adopting the neural network technique. Although the low-energy acoustic phonons remain relatively unaffected at elevated temperatures, the high-energy optical, and longitudinal acoustic phonons demonstrate strong renormalizations as evidenced from the vibrational phonon spectra, which are attributed to the large anharmonicity accompanying the phase transition. Furthermore, our results reveal a nonmonotonic temperature dependence of the soft-modes beyond the perturbative regime. The insight provided by this work into the soft-modes may pave the way for further phonon engineering of GeTe and the related thermoelectrics.
- Published
- 2021
20. Pecularities of antiferroelectric phase transitions in PbZr0.71Sn0.29O3 crystal investigated by Mössbauer effect.
- Author
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Podgórna, Maria, Żukrowski, Jan, Jankowska‐Sumara, Irena, Majchrowski, Andrzej, and Berent, Katarzyna
- Subjects
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ANTIFERROELECTRIC materials , *PHASE transitions , *LATTICE dynamics , *MOSSBAUER effect , *PHASE equilibrium , *MATHEMATICAL models - Abstract
The Mössbauer spectra of 119Sn in PbZr1-xSnxO3 compound were studied from 30 to 300°C with particular emphasis on the regions of phase transitions. Some changes of the Mössbauer spectrum near the phase transition temperatures were observed, as expected from the change in the crystal structure. The measurements also showed that the Mössbauer fraction considerably drops near the temperature of the phase displacive transition between two antiferroelectric phases (AFE1–AFE2), whereas this drop is considerably smaller at Curie point. Little difference was found in the center shift of the spectrum, indicating that the bonding character is not affected by the phase transitions. The obtained results were interpreted according to Dvorak’s suggestion that in antiferroelectrics the frequency over the entire optical branch may soften at particular phase transitions. According to the theory, the mode softening should manifest as a decrease in the Mössbauer–Lamb recoil-free fraction (f-factor) due to the increasing vibrational amplitude of the soft mode. Such softening was already observed in Raman scattering measurements in the PbZr1-xSnxO3 single crystals. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
21. Ferroelectric phase transitions in PbHPO4-type crystals
- Author
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Trilok Chandra Upadhyay and Muzaffar Iqbal Khan
- Subjects
010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,Phonon ,Physics::Optics ,Soft modes ,Condensed Matter Physics ,01 natural sciences ,Ferroelectricity ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,Electric field ,0103 physical sciences ,symbols ,Dissipation factor ,Dielectric loss ,Electrical and Electronic Engineering ,Hamiltonian (quantum mechanics) - Abstract
The statistical retarded double-time temperature-dependent Green’s function method and modified two sublattice pseudospin lattice coupled mode model Hamiltonian by adding phonon anharmonic interactions, extra spin–lattice interactions, direct spin–spin interaction and as well as an electric field terms have been used for the study of phase transition mechanism in PbHPO4-type crystals. The expressions for soft mode frequency, dielectric permittivity and dielectric loss tangent are derived for PbHPO4-type crystals. The modelled values of different physical parameters are fitted in the obtained theoretical expressions. The temperature dependence of soft mode frequency, dielectric permittivity and loss tangent are obtained for PbHPO4, PbHAsO4, BaHPO4 and CaHPO4 crystals. Present results are in good agreement with experimental data for dielectric permittivity reported by Arend et al. The modified model Hamiltonian is suitable to explain transitions in PbHPO4-type crystals.
- Published
- 2021
22. An analysis of the ferroelastic transition in Pb(Zr0.53Ti0.47)O3:Gd through the elastic stiffness constant
- Author
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H'Linh Hmŏk, Jesús M. Siqueiros, J. Portelles, Y. de Armas Figueroa, R. López-Noda, and J. Fuentes
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Doping ,Stiffness constant ,02 engineering and technology ,Soft modes ,Anomalous behavior ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,Condensed Matter::Materials Science ,0103 physical sciences ,General Materials Science ,0210 nano-technology ,Instrumentation - Abstract
The c66E values of PZT53/47 doped with 0.6% Gd2O3 show an anomalous behavior near 132°C as a consequence of a ferroelastic transition. A non-linear fit to the experimental data of the elastic stiff...
- Published
- 2021
23. Phase Transition Study of Thermal Dependence of Soft Mode Frequency, Dielectric Constant and Dielectric Tangent Loss Properties in CsH2PO4 (CDP) and CsD2PO4 (DCDP) Crystals
- Author
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Muzaffar Iqbal Khan and Trilok Chandra Upadhyay
- Subjects
Phase transition ,Materials science ,Anharmonicity ,Lattice (group) ,Thermodynamics ,Dielectric ,Soft modes ,Condensed Matter Physics ,01 natural sciences ,Ferroelectricity ,Atomic and Molecular Physics, and Optics ,010305 fluids & plasmas ,0103 physical sciences ,Dissipation factor ,General Materials Science ,Dielectric loss ,010306 general physics - Abstract
Modified two-sublattice pseudospin lattice coupled-mode (PLCM) model Hamiltonian by adding third- and fourth-order anharmonic interactions, extra spin–lattice interactions, direct spin–spin interaction as well as external applied electric field has been considered for $$\mathrm{CsH}_{2}\mathrm{PO}_{4}$$ (abbreviated CDP) and $$\mathrm{CsD}_{2}\mathrm{PO}_{4}$$ (abbreviated DCDP) crystals. By using double-time temperature-dependent Green’s function method and Dyson’s equation, the expressions for the shift, width, soft mode frequency, dielectric constant and loss tangent have been evaluated. By fitting the model values of various physical parameters in the expressions, the thermal variations in soft mode frequency, dielectric constant and loss tangent have been calculated. Our theoretical results show good agreement with the experimental data of Levstik et al. CDP undergoes a ferroelectric phase transition at $$T_{c}=153$$ K, whereas the ferroelectric phase transition in isomorphous DCDP is $$T_{c}=267$$ K, showing a large isotope effect explains the importance of the O–H–O bonds in the phase transition mechanism.
- Published
- 2021
24. Temperature dependence of dielectric properties in Potassium dihydrogen arsenate crystal
- Author
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Trilok Chandra Upadhyay, Pawan Singh, and Muzaffar Iqbal Khan
- Subjects
Crystal ,Phase transition ,Materials science ,Condensed matter physics ,Phonon ,Anharmonicity ,Dissipation factor ,Soft modes ,Dielectric ,Ferroelectricity - Abstract
Potassium Dihydrogen Arsenate (KH2AsO4, KDA) is an inorganic arsenate ferroelectric crystal which is a KDP-family member and undergoes a ferroelectric phase transition at 96 K. A simple pseudospin lattice coupled mode model (PLCM) with some higher order terms like direct spin–spin interaction, third and fourth-order phonon anharmonic interaction terms and external electric field term, with two-time temperature dependent Green’s function technique has been employed for the evaluation of expression of response function. We can obtain and calculate soft mode frequency ( Ω ^ ), Dielectric constant (e), and loss tangent (tanδ) expressions from response function for KDA crystal. We have shown temperature dependence of soft mode frequency ( Ω ^ ), Dielectric constant (e), and loss tangent (tanδ) in Fig. 1 , Fig. 2 , Fig. 3 . We have compared our findings, which seemed to be in fair alignment with experimental evidence.
- Published
- 2021
25. Quenchable amorphous glass-like material from VF3
- Author
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Raimundas Sereika, Sooran Kim, Takeshi Nakagawa, Hirofumi Ishii, Yang Ding, and Ho-kwang Mao
- Subjects
Materials science ,Condensed matter physics ,Phonon ,02 engineering and technology ,Soft modes ,Crystal structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Instability ,Amorphous solid ,Inorganic Chemistry ,Sphere packing ,Octahedron ,0103 physical sciences ,Deformation (engineering) ,010306 general physics ,0210 nano-technology - Abstract
The quite simple but relatively stable VF3-type compounds are known to be of major interest due to their building blocks – octahedra that are extremely important in perovskites as well. Here, we show that the VF6 octahedron in VF3 varies over a fairly wide pressure range (0–50 GPa), maintaining undisturbed rhombohedral crystal symmetry. Half of this pressure, VF6 rotates easily while the other undergoes strong uniaxial deformation in a “super-dense” condition. The congested sphere packing ultimately does not endure and drives the material to amorphize. We observed that the amorphous state could be quenched and acquire a transparent glass-like appearance when unloaded to ambient conditions. Dramatic, pressure-induced changes are clarified by phonon dispersion curves with the imaginary phonon mode, the so-called phonon soft mode, which indicates the structural instability. The distortion of the VF6 octahedra is attributed to the distinctive amorphization that could be further searched for throughout the whole almost identical VF3-type series providing metal trifluorides of various amorphous species.
- Published
- 2021
26. Study of ferroelectric phase transition in H-bonded triglycine selenate (TGSe) crystal
- Author
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Trilok Chandra Upadhyay, Muzaffar Iqbal Khan, and Pawan Singh
- Subjects
010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,Phonon ,Anharmonicity ,02 engineering and technology ,Soft modes ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Condensed Matter::Materials Science ,symbols.namesake ,Electric field ,0103 physical sciences ,symbols ,0210 nano-technology ,Hamiltonian (quantum mechanics) - Abstract
The modified two sublattice pseudospin lattice coupled-mode model Hamiltonian by adding third- and fourth-order phonon anharmonic interactions, extra spin–lattice interactions, direct spin–spin coupling interaction and applied electric field used for the study of ferroelectric and dielectric properties of triglycine selenate (TGSe) crystal. With the help of retarded double time temperature-dependent Green’s function method, Dyson’s equation and symmetric decoupling scheme, the expressions of ferroelectric soft mode frequency, dielectric constant and dielectric tangent loss have been derived. By fitted the model values of various physical parameters in the obtained expressions, the thermal variations of soft mode frequency, dielectric constant and dielectric tangent loss have been calculated. Theoretical results were compared with experimental data reported by Bye et al.
- Published
- 2021
27. Super-high Curie temperature ferroelectrics and superior TC tunability: lattice instability and ferroelectric phase transitions
- Author
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Seiji Kojima
- Subjects
010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,02 engineering and technology ,Soft modes ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Ferroelectricity ,Instability ,Electronic, Optical and Magnetic Materials ,Lattice (order) ,0103 physical sciences ,Curie ,Curie temperature ,0210 nano-technology - Abstract
Ferroelectric materials with high Curie temperatures, TC, and tuning of the TC over a large temperature range are very important for the basic sciences and engineering. This paper reviews the vario...
- Published
- 2020
28. Soft modes behavior in bilayer (Ba,Sr)TiO3/(Ba,Sr)TiO3 heterostructures
- Author
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V. B. Shirokov and Anna G. Razumnaya
- Subjects
010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,Bilayer ,Heterojunction ,02 engineering and technology ,Soft modes ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,0103 physical sciences ,Thin film ,0210 nano-technology - Abstract
We studied the bilayer heterostructures with the different consequence of the Ba0.4Sr0.6TiO3 and Ba0.8Sr0.2TiO3 layers grown on the single-crystal MgO and Si substrates. The thermodynamic theory fo...
- Published
- 2020
29. Making EuO multiferroic by epitaxial strain engineering
- Author
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Nicola A. Spaldin, Rainer Held, Stanislav Kamba, Darrell G. Schlom, Venkatraman Gopalan, Eric Bousquet, Veronica Goian, Phillipe Ghosez, Alexander Melville, Yakun Yuan, and Hua Zhou
- Subjects
Phase transition ,Materials science ,Condensed matter physics ,02 engineering and technology ,Soft modes ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Hybrid functional ,Condensed Matter::Materials Science ,Strain engineering ,Ferromagnetism ,Mechanics of Materials ,0103 physical sciences ,lcsh:TA401-492 ,Antiferromagnetism ,General Materials Science ,Multiferroics ,Condensed Matter::Strongly Correlated Electrons ,lcsh:Materials of engineering and construction. Mechanics of materials ,010306 general physics ,0210 nano-technology - Abstract
Multiferroics are materials exhibiting the coexistence of ferroelectricity and ideally ferromagnetism. Unfortunately, most known magnetoelectric multiferroics combine ferroelectricity with antiferromagnetism or with weak ferromagnetism. Here, following previous theoretical predictions, we provide clear experimental indications that ferroelectricity can be induced by epitaxial tensile strain in the ferromagnetic simple binary oxide EuO. We investigate the ferroelectric phase transition using infrared reflectance spectroscopy, finding that the frequency of the soft optical phonon reduces with increasing tensile strain and decreasing temperature. We observe such a soft mode anomaly at 100 K in (EuO)2/(BaO)2 superlattices grown epitaxially on (LaAlO3)0.29-(SrAl1/2Ta1/2O3)0.71 substrates, which is a typical signature for a displacive ferroelectric phase transition. The EuO in this superlattice is nominally subjected to 6.4% biaxial tensile strain, i.e., 50% more than believed needed from previously published calculations. We interpret our results with new first-principles density functional calculations using a hybrid functional, which provides a better quantitative agreement with experiment than the previously used local-density approximation and generalized gradient approximation functionals., Communications Materials, 1 (1), ISSN:2662-4443
- Published
- 2020
30. Dynamic origin of segment magnetization reversal in thin-film Penrose tilings.
- Author
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Montoncello, F., Giovannini, L., Farmer, B., and De Long, L.
- Subjects
- *
MAGNETIZATION , *MAGNETIC properties of thin films , *TILING (Mathematics) , *SPIN waves , *TOPOLOGY - Abstract
We investigate the low-frequency spin wave dynamics involved in the magnetization reversal of a Penrose P2 tiling using the dynamical matrix method. This system consists of a two-dimensional, connected wire network of elongated thin-film segments, whose complete reversal occurs as a cascade of successive local segment reversals. Using soft mode theory, we interpret the reversal of an individual segment as a first order magnetic transition, in which magnetization curve of the system suffers a small discontinuity. Near this discontinuity a specific mode of the spin wave spectrum goes soft (i.e., its frequency goes to zero), triggering a local instability of the magnetization. We show that this mode is localized, and is at the origin of the local reversal. We discuss the correlation of the mode spatial profile with the “reversal mechanism”, which is the passage of a domain wall through the segment. This process differs from reversal in periodic square or honeycomb artificial spin ices, where a cascade of reversing segments (e.g., “Dirac string”) follows an extended (though irregular) path across the sample; here the spatial distribution of successive segment reversals is discontinuous, but strictly associated with the area where a soft mode is localized. The migration of the localization area across the P2 tiling (during reversal in decreasing applied fields) depends on changes in the internal effective field map. We discuss these results in the context of spin wave localization due to the unique topology of the P2 tiling. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
31. Temperature dependence of the damping constant and the relaxation time close to the tetragonal-cubic phase transition in SrZrO3.
- Author
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Yurtseven, H. and Kiraci, A.
- Subjects
- *
STRONTIUM compounds , *TEMPERATURE effect , *DAMPING (Mechanics) , *CHEMICAL relaxation , *PHASE transitions - Abstract
The damping constant Γ sp due to the pseudospin-phonon coupling is calculated as a function of temperature using the pseudospin-phonon coupled model and the energy fluctuation model close to the tetragonal-cubic transition ( T C = 1443 K) in SrZrO 3 . Using the observed Raman frequencies and the linewidth (FWHM) of the soft modes (E g and A 1g ) from the literature, predictions of both models studied, are examined for the tetragonal-cubic transition in this crystalline system. Values of the activation energy U are extracted and also the inverse relaxation time is predicted as a function of temperature close to the phase transition studied in SrZrO 3 . Divergence behaviour of the damping constant (FWHM) of the soft modes is predicted from both models as also observed experimentally when T C is approached from the tetragonal to the cubic phase in SrZrO 3 . The relaxation time also diverges close to the T C in this crystal. It is indicated that the tetragonal-cubic transition is of a second order as predicted from both models studied here, as also observed experimentally in SrZrO 3 . [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
32. Does non-hydrostatic stress influence the equilibrium of metamorphic reactions?
- Author
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Hobbs, Bruce E. and Ord, Alison
- Subjects
- *
HYDROSTATICS , *METAMORPHIC rocks , *THERMODYNAMIC equilibrium , *MICROSTRUCTURE , *CLAUSIUS-Clapeyron relation - Abstract
We address the questions: are the temperature and thermodynamic pressure significantly different for thermodynamic equilibrium under hydrostatic versus non-hydrostatic stresses ? Moreover, is the nature of the equilibrium state comprising the number of phases and their microstructure different ? Only closed thermodynamic systems are considered involving both fluid present and fluid absent mineral reactions. Distinctions are drawn between hydrostatic, fluid, mechanical and thermodynamic pressures. The thermodynamic pressure is always equal to the mechanical pressure (the mean stress) for a linear elastic material but differs from the mechanical pressure if processes involving dissipative volume changes operate. The fundamental principle governing equilibrium in a crystalline aggregate under a non-hydrostatic stress at a given temperature and mean stress is that the elastic energy be minimised. This can be attained in a vast number of ways that involve changes in chemical composition and crystalline structure, as in the growth of garnet on biotite, subtle changes in chemical composition, as in a solid solution series or an order–disorder transition, microstructural rearrangements, as in subgrain formation, and combinations of all of these as in myrmekite formation. All involve changes in the elastic energy of the system and force a new conceptual approach to the definition of a phase and a phase diagram . A microstructural phase rule needs to be considered in conjunction with a mineral phase diagram. For practical purposes the thermodynamic pressure generally is close to the mean stress. A chemical potential for a stressed solid can always be defined if diffusive processes operate. For solid/fluid systems the difference in conditions defining equilibrium for hydrostatic and non-hydrostatic conditions is a second order effect; multiple equilibrium states can exist. Departures from hydrostatic conditions are marked by the form of the phase rule (that is, the topology of the phase diagram) and hence there must be either changes in the Clapeyron slope or the position of the equilibrium phase boundary unless all the modifications to the phase rule are achieved by microstructural rearrangements and subtle changes in chemical composition. For solid/solid systems the shift in equilibrium conditions for non-hydrostatic stresses can, in principle, be very large but such effects can be mitigated by softening of the elastic moduli at phase transitions and are also limited by the difference between the mean stress and the equilibrium hydrostatic pressure. For natural situations the difference between the non-hydrostatic and hydrostatic equilibrium temperature is not likely to exceed 20 K. For non-hydrostatic conditions if soft mode nucleation and growth processes dominate, departures from hydrostatic conditions are again marked by changes in the form of the phase rule. Departures in the phase rule from hydrostatic conditions in both fluid present and fluid absent reactions are expressed as variations in chemical composition and differences in the number of phases and their microstructural arrangements at equilibrium under non-hydrostatic as opposed to hydrostatic conditions. The types of microstructures expected at equilibrium under non-hydrostatic conditions include those well documented as arising from internal “spontaneous” stresses in crystals as well as distinct new mineral phases. If the couplings between elastic lattice distortions and diffusive processes, or plastic deformation, are strong then softening modes are suppressed or enhanced and large departures from the hydrostatic Clapeyron slope are possible. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
33. Damping constant and the relaxation time calculated for the lowest-frequency soft mode in the ferroelectric phase of Cd2Nb2O7.
- Author
-
Kiraci, A. and Yurtseven, H.
- Subjects
- *
CADMIUM compounds , *DAMPING (Mechanics) , *FERROELECTRIC materials , *SPIN-phonon interactions , *TRANSITION temperature , *RAMAN spectroscopy - Abstract
The temperature dependence of the phonon frequency ω p h and of the damping constant Γ s p due to pseudospin-phonon coupling of the lowest-frequency soft mode is calculated in the ferroelectric phase near the transition temperature (T C = 196 K) in Cd 2 Nb 2 O 7 . Raman frequency of the soft mode is used as an order parameter which is calculated from the molecular field theory. On that basis, the damping constant is calculated by fitting the expressions from the pseudospin-phonon coupled model and the energy fluctuation model to the observed linewidth from the literature below T C in Cd 2 Nb 2 O 7 . From our analysis, we find that the molecular field theory is adequate for the soft mode behaviour and that both models are also satisfactory for the divergence behaviour of the damping constant as T C is approached from the ferroelectric phase in Cd 2 Nb 2 O 7 . Values of the activation energy U are extracted from the temperature dependence of the damping constant (HWHM) of the soft mode in the ferroelectric phase of this crystal. Also, the inverse relaxation time is predicted using the Raman frequency and damping constant close to the T C in the ferroelectric phase of Cd 2 Nb 2 O 7 , which increases considerably as T C is approached from the ferroelectric phase, as observed experimentally. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
34. High-Pressure Raman Study of Fe(IO3)3: Soft-Mode Behavior Driven by Coordination Changes of Iodine Atoms
- Author
-
Saqib Rahman, Plácida Rodríguez-Hernández, Daniel Errandonea, Akun Liang, Alfonso Muñoz, Francisco Javier Manjón, and Gwilherm Nenert
- Subjects
Phase transition ,Coordination sphere ,Materials science ,Phonon ,macromolecular substances ,02 engineering and technology ,Soft modes ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Brillouin zone ,symbols.namesake ,General Energy ,FISICA APLICADA ,symbols ,Physical and Theoretical Chemistry ,Isostructural ,0210 nano-technology ,Dispersion (chemistry) ,Raman spectroscopy - Abstract
[EN] We report high-pressure Raman spectroscopy studies of Fe(IO3)(3) up to nearly 21 GPa that have been interpreted with the help of density functional theory calculations, which include the calculation of phonon dispersion curves and elastic constants at different pressures. Zero-pressure Raman-active mode frequencies and their pressure dependences have been determined. Modes have been assigned and correlated to atomic movements with the help of calculations. Interestingly, in the high-frequency region, there are several modes that soften under compression. These modes have been identified as internal vibrations of the IO3 coordination polyhedron. Their unusual behavior is a consequence of the changes induced by pressure in the coordination sphere of iodine, which gradually change from a threefold coordination to an almost sixfold coordination under compression. The coordination change is favored by the decrease of the stereoactivity of the iodine lone electron pair so that likely a real sixfold coordination is attained after a first-order phase transition previously reported to occur above 21 GPa. The strong nonlinear behavior found in Raman-active modes as well as in theoretically calculated elastic constants has been discovered to be related to the occurrence of two previously unreported isostructural phase transitions at 1.5-2.0 and 5.7-6.0 GPa as shown by dynamic instabilities close to the Brillouin zone center., This work was supported by the Spanish Ministry of Science, Innovation and Universities, the Spanish Research Agency (AEI), the European Fund for Regional Development (ERDF, FEDER) under grants MAT2016-75586-C4-1/2/3-P, PID2019-106383GB-C41/42/43, and RED2018-102612-T (MALTA Consolider-Team Network), and the Generalitat Valenciana under grant Prometeo/2018/123 (EFIMAT). A.L. and D.E. would like to thank the Generalitat Valenciana for the Ph.D. fellowship GRISOLIAP/2019/025).
- Published
- 2020
35. Anomalous Increase in Spectral Intensity of Soft-Mode Raman Scattering near the Temperature of the Ferroelectric Phase Transition in Lithium Tantalate Crystals
- Author
-
Vladimir S. Gorelik and A. Yu. Pyatyshev
- Subjects
Phase transition ,Materials science ,Lattice (group) ,General Physics and Astronomy ,Soft modes ,01 natural sciences ,Omega ,Ferroelectricity ,010309 optics ,Crystal ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,0103 physical sciences ,Lithium tantalate ,symbols ,Atomic physics ,010306 general physics ,Raman scattering - Abstract
Reported are the results of studying the sharp increase in the spectral intensity at the lattice soft mode near the temperature of the phase transition in the lithium tantalate crystal. The Raman scattering spectra are recorded in the x(zz)y polarization geometry corresponding to manifestation of the soft mode responsible for the ferroelectric phase transition in lithium tantalate at 898 K. The recording is performed at fixed temperatures T ( $$I(\omega {\kern 1pt} ',T)$$ , T = const) and at fixed spectrometer frequencies ( $$I(\omega {\kern 1pt} ',T)$$ , $$\omega {\kern 1pt} ' = {{\omega }_{0}} - T = {\text{const}}$$ ) under slow (1 deg./min) crystal temperature variation. Strong increase (by three orders of magnitude) is observed in the peak of the reduced spectral intensity i0(Ω) of the isofrequency temperature dependence at the fixed spectrometer frequency shift relative to the exciting radiation $$\Omega = {{\omega }_{0}} - \omega {\kern 1pt} ' = 10$$ cm–1 similar to the one earlier observed in quartz crystals.
- Published
- 2020
36. Central Peak in the Raman Spectra of Quartz Crystals in a Wide Temperature Range
- Author
-
A. F. Konstantinova, T. G. Golovina, and Vladimir S. Gorelik
- Subjects
Phase transition ,Materials science ,General Chemistry ,Soft modes ,Atmospheric temperature range ,Condensed Matter Physics ,Molecular physics ,symbols.namesake ,symbols ,General Materials Science ,Raman spectroscopy ,Radiant intensity ,Quartz ,Intensity (heat transfer) ,Raman scattering - Abstract
The spectral intensity of Raman scattering in quartz crystals has been calculated in a wide temperature range including the point of the α–β phase transition. It is established that a central peak is present in the scattered radiation spectrum at different temperatures with allowance for the interaction between the fundamental soft mode and an additional low-frequency oscillator. The intensity and half-width of the central peak are calculateed in a wide temperature range.
- Published
- 2020
37. A Comparative Analysis of Asymmetric (BaTiO3) 1−xΛ/(BaZrO3)xΛ Superlattices via X-Ray Diffraction and Raman Spectroscopy
- Author
-
Yu. I. Yuzyuk, Svetlana A. Barannikova, and O. A. Maslova
- Subjects
010302 applied physics ,Materials science ,General Engineering ,Analytical chemistry ,02 engineering and technology ,Soft modes ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Pulsed laser deposition ,symbols.namesake ,Tetragonal crystal system ,Lattice constant ,0103 physical sciences ,X-ray crystallography ,symbols ,General Materials Science ,0210 nano-technology ,Raman spectroscopy ,Monoclinic crystal system - Abstract
This work is aimed at studying asymmetric BaTiO31 − xΛ/BaZrO3xΛ ((BT) 1−xΛ/(BZ)xΛ) superlattices, grown by pulsed laser deposition onto (001) MgO substrates. The thicknesses of BT (ferroelectric) and BZ (paraelectric) layers were varied so that х ranged from 0 to 1 at a modulation period Λ of about 80 Å. The films were 400 nm thick. The out-of-plane lattice parameters of constituents were assessed using X-ray diffraction. The lattice dynamic peculiarities of superlattices were probed via Raman spectroscopy; special attention is paid to the analysis of E(1TO) and A1(2TO) ferroelectric soft modes. A comparative analysis of data acquired via both experimental techniques reveals the enhancement of stress between BT and BZ layers with a decrease in symmetry from the tetragonal to a monoclinic phase due to strains induced by the lattice parameter mismatch between the constituents.
- Published
- 2020
38. The Important Role of N(2)(CH3)4 Ion in the Phase-Transition Mechanism of [N(CH3)4]2ZnBr4
- Author
-
Ali Kiraci
- Subjects
Phase transition ,Materials science ,Acoustics and Ultrasonics ,Phonon ,Soft modes ,Type (model theory) ,01 natural sciences ,Molecular physics ,Ion ,Laser linewidth ,0103 physical sciences ,Ising model ,Electrical and Electronic Engineering ,010301 acoustics ,Instrumentation ,Monoclinic crystal system - Abstract
The chemical shift of the N(2)(CH3)4 ion, which has been found to exhibit the similar anomalous behavior of the monoclinic angle $\Delta \beta $ , was related to the order parameter to evaluate the temperature dependence of the linewidth (damping constant) for 14N nuclear magnetic resonance spectrum of this crystal in terms of the dynamic Ising models, namely the pseudospin-phonon-coupled (PS) and the energy fluctuation (EF) models. The results from both PS and EF models were successful to explain the abnormal behavior of the linewidth in the vicinity of the phase-transition temperature of ${T}_{C}= {287.6}$ K, when compared with the observed linewidth of the transverse acoustic soft mode in this crystal. As an extension of this work, the 14N relaxation time and the values of the activation free energy were calculated as a function of temperature. The results indicate that the ferroelastic–paraelastic phase transition in this compound is of the order–disorder type.
- Published
- 2020
39. Jumplike Magnetic Disordering Processes Stimulated by a Magnetic Field in Systems with Structural Instability
- Author
-
V.I. Mitsiuk, V. V. Koledov, B. M. Todris, V. I. Val’kov, and A. V. Golovchan
- Subjects
010302 applied physics ,Materials science ,Field (physics) ,Condensed matter physics ,Heisenberg model ,Soft modes ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Condensed Matter::Materials Science ,Paramagnetism ,Magnetization ,0103 physical sciences ,Magnetic refrigeration ,Helimagnetism ,010306 general physics - Abstract
A theoretical analysis of the features of first-order structural and magnetostructural transitions in magnetocaloric helimagnetic alloys of the Mn1 – xCrxNiGe system is performed. The observed structural transitions of the displacement type hex(P63/mmc) ↔ orth(Pnma) are described using the local soft mode model in the approximation of a displaced harmonic oscillator. In the absence of a magnetic field, the emergence of a helimagnetic order as a structurally induced second-order transition is described within the Heisenberg model with allowance for the dependence of the exchange integrals on the structural order parameters and elastic strains. In the presence of a magnetic field, it was found that the mutual approach of the characteristic temperatures for the helimagnetic state (HM(Pnma)) and the lability temperatures of the hexagonal paramagnetic state (PM(P63/mmc)), due to the action of the magnetic field, leads to the appearance of previously unexplored peripheral first-order magnetostructural transitions with insignificant magnetization jumps, increasing with increasing magnetic induction field. In this case, as the pressure increases to 4 kbar with a constant magnetic induction field, the peripheral transitions are transformed into reversible first-order magnetostructural transitions and, at even higher pressures (10–14 kbar), into full-scale first-order magnetostructural transitions with magnetization jumps comparable with the maximum magnetization. Experimental baric studies of the temperature dependences of the magnetization in static magnetic fields with an induction up to 1 T and pressure up to 14 kbar confirm the theoretical results.
- Published
- 2020
40. Raman opalescence and central peak scattering near phase transition point in crystals
- Author
-
Vladimir S. Gorelik
- Subjects
010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,Scattering ,02 engineering and technology ,Soft modes ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Ferroelectricity ,Light scattering ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,symbols.namesake ,Phase (matter) ,0103 physical sciences ,Opalescence ,symbols ,0210 nano-technology ,Raman spectroscopy - Abstract
Comparison of isotemperature and isofrequency temperature dependences was used for revealing the soft mode behavior near phase transition points in ferroelectric and ferro-structural phase transiti...
- Published
- 2020
41. Phase Behavior of TmVO4 under Hydrostatic Compression: An Experimental and Theoretical Study
- Author
-
Enrico Bandiello, Daniel Errandonea, Marco Bettinelli, Javier González-Platas, Alfonso Muñoz, Plácida Rodríguez-Hernández, and Catalin Popescu
- Subjects
Phase transition ,Condensed matter physics ,010405 organic chemistry ,Phonon ,Band gap ,Chemistry ,Soft modes ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Phase (matter) ,Density of states ,Density functional theory ,Physical and Theoretical Chemistry ,Electronic band structure - Abstract
We present a structural and optical characterization of magnetoelastic zircon-type TmVO4 at ambient pressure and under high pressure. The properties under high pressure have been determined experimentally under hydrostatic conditions and theoretically using density functional theory. By powder X-ray diffraction we show that TmVO4 undergoes a first-order irreversible phase transition to a scheelite structure above 6 GPa. We have also determined (from powder and single-crystal X-ray diffraction) the bulk moduli of both phases and found that their compressibilities are anisotropic. The band gap of TmVO4 is found to be Eg = 3.7(2) eV. Under compression the band gap opens linearly, until it undergoes a huge collapse following the structural phase transition (ΔEg = 1.15 eV). Ab initio structural and free energy calculations support our findings. Moreover, calculations of the band structure and density of states reveal that for both zircon and scheelite TmVO4 the band gap is entirely determined by the V 3d and O 2p states of the VO43– ion. The behavior of the band gap can thus be understood entirely in terms of the structural modifications of the VO4 units under compression. Additionally, we have calculated the evolution of the infrared and Raman phonons of both phases upon compression. The presence of soft modes is related to the dynamic instability of the low-pressure phase and to the phase transition.
- Published
- 2020
42. Anharmonicity Explains Temperature Renormalization Effects of the Band Gap in SrTiO3
- Author
-
Wissam A. Saidi, Paul R. Ohodnicki, Yuhua Duan, Jeffrey Wuenschell, Terumasa Tadano, Benjamin Chorpening, and Yu-Ning Wu
- Subjects
Physics ,Coupling ,Condensed matter physics ,Band gap ,Phonon ,Anharmonicity ,Harmonic (mathematics) ,02 engineering and technology ,Soft modes ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Measure (mathematics) ,0104 chemical sciences ,Renormalization ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Soft phonon modes in strongly anharmonic crystals are often neglected in calculations of phonon-related properties. Herein, we experimentally measure the temperature effects on the band gap of cubic SrTiO3, and compare with first-principles calculations by accounting for electron–phonon coupling using harmonic and anharmonic phonon modes. The harmonic phonon modes show an increase in the band gap with temperature using either Allen–Heine–Cardona theory or finite-displacement approach, and with semilocal or hybrid exchange-correlation functionals. This finding is in contrast with experimental results that show a decrease in the band gap with temperature. We show that the disagreement can be rectified by using anharmonic phonon modes that modify the contributions not only from the significantly corrected soft modes, but also from the modes that show little correction in frequencies. Our results confirm the importance of soft-phonon modes that are often neglected in the computation of phonon-related properties and particularly in electron–phonon coupling.
- Published
- 2020
43. Soft modes in HoFe2.5Ga0.5(BO3)4 solid solution
- Author
-
Alexander Vtyurin, Alexander S. Krylov, I. A. Gudim, and S. N. Krylova
- Subjects
010302 applied physics ,Huntite ,Materials science ,Condensation ,Analytical chemistry ,02 engineering and technology ,Soft modes ,engineering.material ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,0103 physical sciences ,symbols ,engineering ,0210 nano-technology ,Raman spectroscopy ,Solid solution - Abstract
The condensation of two soft modes has been found when studying the Raman spectra of the solid solution HoFe2.5Ga0.5(BO3)4 in the temperature range from 7 to 350 K. The first high-temperature soft ...
- Published
- 2020
44. Raman scattering from the effective soft mode in lead germanate crystal
- Author
-
Vladimir S. Gorelik and A. Yu. Pyatyshev
- Subjects
Crystal ,symbols.namesake ,Phase transition ,Materials science ,symbols ,General Materials Science ,Germanate ,Soft modes ,Raman spectroscopy ,Molecular physics ,Spectroscopy ,Raman scattering - Published
- 2020
45. The Regular Ground States of the Linear Boson Field in Terms of Soft Modes
- Author
-
Alfred Rieckers
- Subjects
Field (physics) ,General Mathematics ,Quantum electrodynamics ,Soft modes ,Boson ,Mathematics - Published
- 2020
46. Theoretical investigation of temperature and frequency dependent ferroelectric properties in Rochelle salt (RS) crystal
- Author
-
Muzaffar Iqbal Khan and Trilok Chandra Upadhyay
- Subjects
010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,Phonon ,Anharmonicity ,02 engineering and technology ,Soft modes ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Electric field ,Lattice (order) ,0103 physical sciences ,0210 nano-technology - Abstract
By adding cubic-order and quartic-order phonon anharmonic interactions terms with spin-spin interactions terms, extra interaction term and external electric field has been considered in two-sublattice pseudospin lattice coupled mode (PLCM) model for phase transitions and dielectric properties of order-disorder Rochelle salt (RS) crystal. Using double-time temperature Green function method, we obtain the expression for Soft mode frequency, dielectric constant and tangent loss have been obtained for Rochelle salt crystal. Numerical calculations will be performed by fitting model values of various parameters in the above expressions for RS crystal. Present theoretical results agree well with experimental results of Sandy and Jones.
- Published
- 2020
47. Modeling of AMg6 aluminum alloy jump-like deformation properties by machine learning methods
- Author
-
Sergiy Fedak, Yuri Lapusta, O. Yasniy, and Iryna Didych
- Subjects
Artificial neural network ,Computer science ,business.industry ,Alloy ,Diagram ,chemistry.chemical_element ,02 engineering and technology ,Soft modes ,Deformation (meteorology) ,engineering.material ,021001 nanoscience & nanotechnology ,Machine learning ,computer.software_genre ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Aluminium ,engineering ,Jump ,Artificial intelligence ,0210 nano-technology ,business ,computer ,Earth-Surface Processes ,Tensile testing - Abstract
There was studied a jump-like deformation of AMg6 aluminum alloy at static tensile test in the soft mode of loading. The experimental methods of jump-like deformation study of this alloy are often complicated, expensive and time-consuming. Therefore, it is more effective to model the stress-strain diagram numerically. One of the promising ways to predict the stress-strain diagram of AMg6 material is based on the application of machine learning methods, in particular by neural networks, boosted trees, support-vector machines, and k - nearest neighbors. It was discovered that the method of neural networks gives the least prediction error equal to 6.9%. The errors of the methods of boosted trees, support-vector machines and k - nearest neighbours are 9.1, 7.7, and 9.4% in test sets, respectively.
- Published
- 2020
48. Dielectric and electro-optic properties of two biphenylyl benzoate-based ferroelectric mesogens with tilted hexagonal phases
- Author
-
Dorota Węgłowska, Debarghya Goswami, and Pradip Kumar Mandal
- Subjects
Materials science ,010405 organic chemistry ,Hexagonal crystal system ,02 engineering and technology ,General Chemistry ,Soft modes ,Dielectric ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Ferroelectricity ,0104 chemical sciences ,Dielectric spectroscopy ,Core (optical fiber) ,Crystallography ,Liquid crystal ,General Materials Science ,0210 nano-technology - Abstract
Two partially fluorinated ferroelectric liquid crystals (2F3R, 3F3R) with biphenylyl benzoate core have been investigated by frequency domain dielectric spectroscopy and electro-optic metho...
- Published
- 2019
49. Calculating the Lattice Dynamics in the RFe3(BO3)4 Crystals in the Quasi-Harmonic Approximation
- Author
-
N. D. Andryushin and M. S. Pavlovskii
- Subjects
010302 applied physics ,Phase transition ,Materials science ,Condensed matter physics ,Solid-state physics ,Quasi-harmonic approximation ,Soft modes ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Brillouin zone ,Vibration ,Ab initio quantum chemistry methods ,Phase (matter) ,0103 physical sciences ,010306 general physics - Abstract
The frequencies of lattice vibrations in the RFe3(BO3)4 (R = Pr, Nd, Tb, Dy, or Ho) crystals in the high-temperature R32 phase and their temperature dependence have been calculated using the quasi-harmonic approximation. It has been found that, at the boundary point Λ of the Brillouin zone, the frequency of the unstable vibration mode the structural phase transition R32 → P3121 is related to strong changes with temperature in the TbFe3(BO3)4, DyFe3(BO3)4, and HoFe3(BO3)4 crystals. With increasing temperature, the frequency of the soft mode stabilizes and takes a real value. No significant changes in the phonon spectra, including the boundary point Λ, with increasing temperature for the PrFe3(BO3)4 and NdFe3(BO3)4 crystals have been observed.
- Published
- 2019
50. Origin and evolution of ferroelectricity in the layered rare-earth-titanate,R2Ti2O7, Carpy-Galy phases
- Author
-
Maribel Núñez Valdez and Nicola A. Spaldin
- Subjects
Condensed matter physics ,010405 organic chemistry ,Chemistry ,Parent structure ,Soft modes ,010402 general chemistry ,Polarization (waves) ,01 natural sciences ,Ferroelectricity ,Titanate ,0104 chemical sciences ,Inorganic Chemistry ,Materials Chemistry ,Polar ,Density functional theory ,Physical and Theoretical Chemistry ,Ground state - Abstract
We report a systematic first-principles study based on density functional theory (DFT) of the structural and ferroelectric properties of the R 2 Ti2O7 perovskite-related oxides with R = La, Ce, Pr, and Nd. We show that, in all cases, the ferroelectric distortion to the ground-state polar P 2 1 structure from its parent centrosymmetric P 2 1 / m phase is driven by a single polar soft mode consisting of rotations and tilts of the TiO6 octahedra combined with displacements of the R ions. A secondary centrosymmetric distortion, which is stable in the parent structure, contributes substantially to the energy lowering of the ground state. We evaluate the trends in structure and polarization across the series as a function of R and reconcile discrepancies in reported values of polarization in the literature. Our results confirm that the family of R 2 Ti2O7 materials belong to the class of proper geometric ferroelectrics.
- Published
- 2019
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