scholarly journals Фазовая диаграмма и особенности поведения мягких мод в твердых растворах со структурой хантита TbFe-=SUB=-3-x-=/SUB=-Ga-=SUB=-x-=/SUB=-(BO_3)-=SUB=-4-=/SUB=-

2022 ◽  
Vol 130 (1) ◽  
pp. 84
Author(s):  
А.С. Крылов ◽  
А.Н. Втюрин ◽  
И.А. Гудим ◽  
И.В. Немцев ◽  
С.Н. Крылова
Keyword(s):  
Phase Transition ◽  
Phase Diagram ◽  
Phase Transitions ◽  
Raman Spectra ◽  
Solid Solutions ◽  
Structural Phase ◽  
Temperature Phase ◽  
Structural Phase Transitions ◽  
Soft Modes ◽  
Temperature Phase Diagram

The Raman spectra of four crystals of TbFe3-хGax (BO3) 4 solid solutions (x from 0 to 0.54) were studied in the temperature range from 8 to 350 K. The temperatures of structural phase transitions were determined. The observed spectral behavior is characteristic to condensation and restoration of soft modes. Soft modes are associated with a structural phase transition from the R32 phase to the P3121 phase. The Compositions-Temperature phase diagram was constructed

Phase and Structural Behaviour in the NdAlO3-EuAlO3 System

2013 ◽  
Vol 200 ◽  
pp. 93-99 ◽  
Author(s):  
Natalia Ohon ◽  
Leonid Vasylechko ◽  
Yurii Prots ◽  
Marcus Schmidt ◽  
Caroline Curfs
Keyword(s):  
Phase Diagram ◽  
Phase Transitions ◽  
Binary System ◽  
Solid Solutions ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Structural Behaviour ◽  
First Order

Phase and structural behaviour in the NdAlO3–EuAlO3 system has been studied in the whole concentration range. Depending on x two kinds of solid solutions Nd1‑xEuxAlO3 exist at room temperature: one with rhombohedral (x < 0.15) and one with orthorhombic (x≈ 0.15–0.20, where the co-existence of both phases was observed. First-order structural phase transitions Pbnm↔Rc has been detected in Nd1-xEuxAlO3 with x = 0.3, 0.4, 0.6 at 520 K, 627 K and 988 K, respectively. Based on the experimental and literature data, the phase diagram of the pseudo-binary system NdAlO3–EuAlO3 has been constructed.

scholarly journals The origin of the lattice thermal conductivity enhancement at the ferroelectric phase transition in GeTe

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Đorđe Dangić ◽  
Olle Hellman ◽  
Stephen Fahy ◽  
Ivana Savić
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Phase Transitions ◽  
Thermoelectric Materials ◽  
Ferroelectric Phase Transition ◽  
Lattice Thermal Conductivity ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
High Symmetry ◽  
Structural Phase Transitions

AbstractThe proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ. However, the κ of GeTe increases at the ferroelectric phase transition near 700 K. Using first-principles calculations with the temperature dependent effective potential method, we show that this rise in κ is the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase. Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra. To account for these effects, we implement a method of calculating κ based on the Green-Kubo approach and find that the Boltzmann transport equation underestimates κ near the phase transition. Our findings elucidate the influence of structural phase transitions on κ and provide guidance for design of better thermoelectric materials.

X-ray diffraction and Raman study of DL-alanine at high pressure: revision of phase transitions

2012 ◽  
Vol 68 (4) ◽  
pp. 412-423 ◽  
Author(s):  
Nikolay A. Tumanov ◽  
Elena V. Boldyreva
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Structural Phase ◽  
Group Symmetry ◽  
Second Phase ◽  
Structural Phase Transitions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
Raman Study

The effect of pressure on DL-alanine has been studied by X-ray powder diffraction (up to 8.3 GPa), single-crystal X-ray diffraction and Raman spectroscopy (up to ∼ 6 GPa). No structural phase transitions have been observed. At ∼ 1.5–2 GPa, cell parameters b and c become accidentally equal to each other, but the space-group symmetry does not change. There is no phase transition between 1.7 and 2.3 GPa, contrary to what has been reported earlier [Belo et al. (2010). Vibr. Spectrosc. 54, 107–111]. The presence of the second phase transition, which was claimed to appear within the pressure range from 6.0 to 7.3 GPa (Belo et al., 2010), is also argued. The changes in the Raman spectra have been shown to be continuous in all the pressure ranges studied.

scholarly journals Manifestation of magnetoelastic interactions in Raman spectra of HoxNd1−xFe3(BO3)4 crystals

2018 ◽  
Vol 08 (02) ◽  
pp. 1850011 ◽  
Author(s):  
A. S. Krylov ◽  
S. N. Sofronova ◽  
I. A. Gudim ◽  
S. N. Krylova ◽  
Rajesh Kumar ◽  
...  
Keyword(s):  
Phase Transition ◽  
Raman Spectra ◽  
Structural Phase Transition ◽  
Solid Solutions ◽  
Order Parameter ◽  
Soft Mode ◽  
Magnetic Phase ◽  
Structural Phase ◽  
Exchange Interactions ◽  
Magnetoelastic Interaction

Raman spectra of Ho[Formula: see text]NdxFe(BO3)4 ([Formula: see text], 0.75, 0.5, 0.25) have been studied in temperature range 10–400[Formula: see text]K. Two compositions ([Formula: see text], [Formula: see text]) demonstrate structural phase transition with soft mode restoration. The addition of Nd atoms increases interatomic spacing and decreases the temperature of structural phase transition. The solid solutions ([Formula: see text], 0.5, 0.25) demonstrate the emergence of the peaks corresponding to magnetoelastic interaction below Néel temperature. The order parameter of the magnetic phase transition has been determined. The equal concentrations of holmium and neodymium atoms prevent magnon soft modes condensation caused by exchange interactions in Fe–O–Fe chains are observed. Calculations confirm the data obtained in the experiment.

Phase transitions of (1−x) PbZrO3 + x (Na1/2Bi1/2)TiO3 (0.01 ≤ x ≤ 0.15) solid solutions

1999 ◽  
Vol 14 (1) ◽  
pp. 83-89 ◽  
Author(s):  
Jung-Kun Lee ◽  
Hyuk-Joon Youn ◽  
Kug Sun Hong
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Solid Solutions ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Two Phase ◽  
Phase Transition Temperatures ◽  
Temperature Phase Transition ◽  
Increasing Temperature

Morphotropic phase boundaries and temperature dependent phase transitions of (1 – x) PbZrO3 + x (Na1/2Bi1/2)TiO3 (0.01 ≤ x ≤ 0.15) solid solutions were investigated by x-ray diffraction, differential scanning calorimetry (DSC), and dielectric property analysis. Two morphotropic phase transitions at room temperature were found at x = 0.1 and 0.13, which were from antiferroelectric orthorhombic (with 4 × 4 × 2 superlattice [orthorhombic (I)]) to antiferroelectric orthorhombic (with 2 × 2 × 2 superlattice [orthorhombic (II)]) and from orthorhombic (II) to ferroelectric rhombohedral, respectively. With increasing temperature, the samples with 0.01 ≤ x < 0.1 showed two phase transitions, i.e., from orthorhombic (I) to orthorhombic (II) and from orthorhombic (II) to cubic. The other samples had only one phase transition with increasing temperature. Phase transition temperatures of all the samples were measured using DSC, and a phase diagram for the solid solutions was constructed. A model illustrating the antiparallel shift of Pb ions in the orthorhombic (II) phase was also proposed.

Femtosecond time-resolved spectroscopy of soft modes in structural phase transitions of perovskites

1994 ◽  
Vol 50 (13) ◽  
pp. 8996-9019 ◽  
Author(s):  
Thomas P. Dougherty ◽  
Gary P. Wiederrecht ◽  
Keith A. Nelson ◽  
Mark H. Garrett ◽  
Hans P. Jenssen ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Time Resolved ◽  
Time Resolved Spectroscopy ◽  
Soft Modes
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