Pressure-induced structural phase transitions in bismuth tungstate Bi2WO6

2021 ◽  
Vol 77 (4) ◽  
Author(s):  
Olga N. Lis ◽  
Sergey E. Kichanov ◽  
Denis P. Kozlenko ◽  
Nadezhda M. Belozerova ◽  
Evgeniy V. Lukin ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Pressures ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Structural Phase Transitions ◽  
Structural Polymorphism ◽  
Bismuth Tungstate ◽  
Cell Parameters ◽  
Mutual Rotation

The pressure-induced structural phase transitions in bismuth tungstate Bi2WO6 have been studied using neutron diffraction and Raman spectroscopy at high pressures up to 7 and 30 GPa, respectively. A rich structural polymorphism was revealed. At P ≃ 3.5 GPa a phase transition from the initial orthorhombic phase of P21 ab symmetry to an orthorhombic phase of B2cb symmetry was observed. This transition is caused by the complex spatial rotation of the WO6 octahedra. A subsequent isostructural phase transition to another orthorhombic phase of B2cb symmetry was detected at P ≃ 5.9 GPa, accompanied by changes in both the mutual rotation and tilting of the oxygen octahedra with respect to the crystal b axis. Two more pressure-induced phase transitions in Bi2WO6 at high pressures of 11.5 and 20 GPa were observed in the Raman spectra. These pressure-driven phase transitions in bismuth tungstate are accompanied by anomalies in the pressure dependences of the unit-cell parameters, bond lengths and angles, and in the vibrational modes.

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 Structures, Phase Transitions and Tricritical Behavior of the Hybrid Perovskite Methyl Ammonium Lead Iodide

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
P. S. Whitfield ◽  
N. Herron ◽  
W. E. Guise ◽  
K. Page ◽  
Y. Q. Cheng ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Structural Phase ◽  
Photovoltaic Performance ◽  
Orthorhombic Phase ◽  
Structural Phase Transitions ◽  
Lead Iodide ◽  
First Order ◽  
Hybrid Perovskite ◽  
The Impact

Abstract We have examined the crystal structures and structural phase transitions of the deuterated, partially deuterated and hydrogenous organic-inorganic hybrid perovskite methyl ammonium lead iodide (MAPbI3) using time-of-flight neutron and synchrotron X-ray powder diffraction. Near 330 K the high temperature cubic phases transformed to a body-centered tetragonal phase. The variation of the order parameter Q for this transition scaled with temperature T as Q ∼ (Tc−T)β, where Tc is the critical temperature and the exponent β was close to ¼, as predicted for a tricritical phase transition. However, we also observed coexistence of the cubic and tetragonal phases over a range of temperature in all cases, demonstrating that the phase transition was in fact first-order, although still very close to tricritical. Upon cooling further, all the tetragonal phases transformed into a low temperature orthorhombic phase around 160 K, again via a first-order phase transition. Based upon these results, we discuss the impact of the structural phase transitions upon photovoltaic performance of MAPbI3 based solar cells.

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.

scholarly journals Structural and optical study of the phase transitions in Lead Hafnate, PbHfO3

2014 ◽  
Vol 70 (a1) ◽  
pp. C58-C58
Author(s):  
Steven Huband ◽  
Anthony Glazer ◽  
Krystian Roleder ◽  
Andrzej Majchrowski ◽  
Pam Thomas
Keyword(s):  
Phase Transitions ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Temperature Hysteresis ◽  
Structural Phase Transitions ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Fundamental Understanding ◽  
Distinct Temperature

Lead Hafnate undergoes two structural phase transitions as a function of temperature. The first occurs at about 1630C, consisting of a transition from an antiferroelectric orthorhombic Pbam structure [1] to another antiferroelectric orthorhombic phase with an as-yet undetermined space group. The second is to a paraelectric cubic Pm3m structure at 2090C. Dielectric spectroscopy measurements on a single crystal have shown a distinct temperature hysteresis at the orthorhombic to orthorhombic transition [2]. Recently, dielectric measurements on a ceramic sample have shown a much larger temperature hysteresis and following x-ray diffraction measurements, it is suggested that the second orthorhombic phase is in space group A2mm and undergoes another transition to a tetragonal P4mm structure before the cubic transition [3]. We report on the results of an investigation of a PbHfO3crystal using a combination of high-resolution x-ray diffraction and birefringence imaging measurements with the Metripol system. These measurements have been performed as a function of temperature from the room-temperature orthorhombic structure to the high-temperature cubic structure. The results are discussed both in the context of the published work and fundamental understanding of the origin of antiferroelectricity.

scholarly journals Computer simulation of the structural phase transitions in thin ferroelectric films

2017 ◽  
Vol 07 (01) ◽  
pp. 1750004 ◽  
Author(s):  
O. G. Maksimova ◽  
A. V. Maksimov ◽  
O. S. Baruzdina
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Boundary Conditions ◽  
Order Parameter ◽  
Mixed Boundary ◽  
Structural Phase ◽  
Film Surface ◽  
Mixed Boundary Conditions ◽  
Structural Phase Transitions ◽  
Ferroelectric Films

The influence of free surface and depolarizing field on structural phase transitions in thin ferroelectric films from an ordered state to a disordered one is investigated. The dependences of the order parameter on the distance from the free film surface are calculated. It is shown that with the presence of the depolarizing field and in its absence, the effective thickness of the surface layer depends on the temperature. Nearby the phase transition point, the thickness increases indefinitely. Calculations considering depolarizing field showed that the phase transition points for the bulk ferroelectrics and the film under given boundary conditions coincide. Also shown that in the absence of depolarizing field with mixed boundary conditions, the film thickness does not affect the order parameter, and in presence of the field, this influence is observed.

scholarly journals Magnetic and structural phase transitions in erbium at low temperatures and high pressures

2011 ◽  
Vol 84 (14) ◽  
Author(s):  
Sarah A. Thomas ◽  
Georgiy M. Tsoi ◽  
Lowell E. Wenger ◽  
Yogesh K. Vohra ◽  
Samuel T. Weir
Keyword(s):  
Phase Transitions ◽  
Low Temperatures ◽  
High Pressures ◽  
Structural Phase ◽  
Structural Phase Transitions

scholarly journals NQR and DSC Studies on Structural Phase Transitions and Lattice Stability in Some Tetrabromozincate(II) Compounds A2ZnBr4

2002 ◽  
Vol 57 (6-7) ◽  
pp. 425-430 ◽  
Author(s):  
Keizo Horiuchi ◽  
Hideta Ishihara ◽  
Naoko Hatano ◽  
Syuntaroh Okamoto ◽  
Tohru Gushiken
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Temperature Dependence ◽  
Single Phase ◽  
Structural Phase ◽  
Lattice Stability ◽  
Structural Phase Transitions ◽  
Melting Points ◽  
Dsc Studies ◽  
Disorder Type

The temperature dependence of 81Br NQR frequencies in some tetrabromozincate(II) compounds, pyridinium tetrabromozincate(II) (pyH)2ZnBr4, 4-picolinium tetrabromozincate(II) (4- piH)2ZnBr4, 2,6-lutidinium tetrabromozincate(II) (2,6-luH)2ZnBr4 and guanidinium tetrabromozincate( II) (guH)2ZnBr4,weremeasured between 77Kand temperatureswhere signals faded out.All compounds exhibited four NQR signals over the whole temperature range investigated. Moreover, DSC was measured between about 130 K and melting points. (4-piH)2ZnBr4 and (guH)2ZnBr4 showed no structural phase transition, while (pyH)2ZnBr4 and (2,6-luH)2ZnBr4 showed a single phase transition. The values of transition entropies obtained suggest that these transitions are of the order-disorder type. The nature of these transitions and the lattice stability in the present compounds were discussed

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

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