High-pressure phase transitions in the rare-earth orthoferrite LaFeO3

2014 ◽  
Vol 70 (3) ◽  
pp. 452-458 ◽  
Author(s):  
Martin Etter ◽  
Melanie Müller ◽  
Michael Hanfland ◽  
Robert E. Dinnebier
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Equations Of State ◽  
Spin Transition ◽  
Structural Phase ◽  
Two Phase ◽  
Pressure Derivative ◽  
Temperature Isotherm ◽  
Hydrostatic Limit

Sequential Rietveld refinements were applied on high-pressure synchrotron powder X-ray diffraction measurements of lanthanum ferrite (LaFeO3) revealing two phase transitions on the room-temperature isotherm up to a pressure of 48 GPa. The first structural phase transition of second order occurs at a pressure of 21.1 GPa, changing the space group fromPbnmtoIbmm. The second transition, involving a isostructural first-order phase transition, occurs at approximately 38 GPa, indicating a high-spin to low-spin transition of the Fe3+ion. Following the behavior of the volume up to the hydrostatic limit of methanol–ethanol it was possible to use inverted equations of state (EoS) to determine a bulk modulus ofB0= 172 GPa and a corresponding pressure derivative ofB′0= 4.3. In addition, the linearized version of the inverted EoS were used to determine the corresponding moduli and pressure derivatives for each lattice direction.

Phase Transition Behavior of Solids under Shock Compression

2010 ◽  
Vol 638-642 ◽  
pp. 1053-1058 ◽  
Author(s):  
Tsutomu Mashimo
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Equations Of State ◽  
Relaxation Times ◽  
Inorganic Materials ◽  
High Pressure Phase ◽  
High Time Resolution ◽  
Compression Process ◽  
Pressure Phase

Through the measurement of Hugoniot parameters, we can get useful information about high-pressure phase transitions, equations of state (EOS), etc. of solids, without pressure calibration. And, we can discuss the transition dynamics, because the relaxation times of phase transition and compression process are of the same order. We have performed the Hugoniot-measurement experiments on various kinds of compound materials including oxides, nitrides, borides and chalcogenides by using a high time-resolution streak photographic system combined with the propellant guns. The structure-phase transitions have been observed for several kinds of inorganic materials, TiO2, ZrO2, Gd3Ga5O12, AlN, ZnS, ZnSe, etc. The phase transition pressures under shock and static compressions of metals, ionic materials, semiconductors and some ceramics are consistent with each other. Those are not consistent for strong covalent bonding materials such as C, BN and SiO2. Here, the Hugoniot compression data are reviewed, and the shock-induced phase transitions and the dynamics are discussed, as well as the EOS of the high-pressure phase up to evem 1 TPa.

The Theoretical Study of the Cinnabar-to-Rocksalt Phase Transitions of HgTe and CdTe under High Pressure

2014 ◽  
Vol 1004-1005 ◽  
pp. 1608-1614 ◽  
Author(s):  
Xi Duo Hu ◽  
De Hai Zhu ◽  
Zhi Feng Zeng ◽  
Shao Rui Sun
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Theoretical Study ◽  
Chain Structure ◽  
Two Phase ◽  
Principle Calculation ◽  
First Principle Calculation ◽  
First Order ◽  
Rocksalt Phase

We performed the first-principle calculation to study the structures of cinnabar phase and the Cinnabar-to-rocksalt Phase transitions of HgTe and CdTe under high pressure. The calculated results show that for HgTe, the zincblende-to-cinnabar phase transition is under 2.2GPa, and the cinnabar-to-rocksalt phase transition is under 5.5 GPa; For CdTe, the two phase transitions occur under 4.0 GPa and 4.9 GPa, respectively, which well agree with the experimental results. The cinnabar-to-rocksalt phase transitions of most compounds, including HgTe and CdTe, except HgS are of first-order, and it is due to that their cinnabar phases are not chain structure as HgS and there are no relaxation process before the phase transition.

Understanding the structural phase transitions in lithium vanadium phosphate cathodes for lithium-ion batteries

2020 ◽  
Vol 8 (20) ◽  
pp. 10331-10336 ◽  
Author(s):  
Woong Oh ◽  
Hyunyoung Park ◽  
Bong-Soo Jin ◽  
Ranjith Thangavel ◽  
Won-Sub Yoon
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Lithium Ion Batteries ◽  
Structural Phase ◽  
Lithium Ion ◽  
Lithium Vanadium Phosphate ◽  
Phase Reaction ◽  
Structural Phase Transitions ◽  
Vanadium Phosphate ◽  
Two Phase

Inconspicuous two-phase reaction during Li0V2(PO4)3–Li2V2(PO4)3 phase transition in Li3V2(PO4)3 cathode.

PHASE TRANSITION AND THERMODYNAMIC PROPERTIES OF MAGNESIUM FLUORIDE BY FIRST PRINCIPLES

2014 ◽  
Vol 28 (08) ◽  
pp. 1450026 ◽  
Author(s):  
TIAN ZHANG ◽  
YAN CHENG ◽  
ZHEN-LONG LV ◽  
GUANG-FU JI ◽  
MIN GONG
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Thermodynamic Properties ◽  
First Principles ◽  
Density Functional ◽  
Structural Phase ◽  
Harmonic Approximation ◽  
Electronic Density ◽  
Good Agreement

The structural stabilities, phase transitions and thermodynamic properties of MgF 2 under high pressure and temperature are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the local density approximation. The calculated lattice parameters of MgF 2 in all four phases under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical results. Our results demonstrate that MgF 2 undergoes a series of structural phase transitions from rutile (P42/mnm)→ CaCl 2-type (Pnnm)→ modified fluorite (Pa-3)→ cotunnite (Pnam) under high pressure and the obtained transition pressures are in fairly good agreement with the experimental results. The temperature-dependent volume and thermodynamic properties of MgF 2 in the rutile phase at 0 GPa are presented and the thermodynamic properties of MgF 2 in the rutile, CaCl 2-type, modified fluorite and cotunnite phases at 300 K are also predicted using the quasi-harmonic approximation model (QHA) and the quasi-harmonic Debye model (QHD), respectively. Moreover, the partial density of states and the electronic density of the four phases under the phase transition are also investigated.

First Principles Investigations on the Controversy of Structural Phase Transitions in Thorium Dialuminide under Pressure

2021 ◽  
Author(s):  
Ashok Kumar Verma ◽  
Paritosh Modak
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
First Principles ◽  
Structural Phase ◽  
First Principles Calculations ◽  
Structural Phase Transitions ◽  
Structural Aspects

We study the high pressure structural aspects of thorium dialuminide, ThAl2, by performing evolutionary crystal structure searches and first principles calculations. We predict a phase transition from the ambient AlB2-type...

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 Pressure-Induced Structural Phase Transition and Metallization in Ga2Se3 up to 40.2 GPa under Non-Hydrostatic and Hydrostatic Environments

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 746
Author(s):  
Meiling Hong ◽  
Lidong Dai ◽  
Haiying Hu ◽  
Xinyu Zhang
Keyword(s):  
Phase Transition ◽  
Electrical Conductivity ◽  
High Pressure ◽  
Phase Transformation ◽  
Transport Properties ◽  
Electrical Transport ◽  
Structural Phase ◽  
Structure Evolution ◽  
Systematic Research ◽  
Electrical Transport Properties

A series of investigations on the structural, vibrational, and electrical transport characterizations for Ga2Se3 were conducted up to 40.2 GPa under different hydrostatic environments by virtue of Raman scattering, electrical conductivity, high-resolution transmission electron microscopy, and atomic force microscopy. Upon compression, Ga2Se3 underwent a phase transformation from the zinc-blende to NaCl-type structure at 10.6 GPa under non-hydrostatic conditions, which was manifested by the disappearance of an A mode and the noticeable discontinuities in the pressure-dependent Raman full width at half maximum (FWHMs) and electrical conductivity. Further increasing the pressure to 18.8 GPa, the semiconductor-to-metal phase transition occurred in Ga2Se3, which was evidenced by the high-pressure variable-temperature electrical conductivity measurements. However, the higher structural transition pressure point of 13.2 GPa was detected for Ga2Se3 under hydrostatic conditions, which was possibly related to the protective influence of the pressure medium. Upon decompression, the phase transformation and metallization were found to be reversible but existed in the large pressure hysteresis effect under different hydrostatic environments. Systematic research on the high-pressure structural and electrical transport properties for Ga2Se3 would be helpful to further explore the crystal structure evolution and electrical transport properties for other A2B3-type compounds.

High-pressure structural phase transition and metallization in Ga2S3 under non-hydrostatic and hydrostatic conditions up to 36.4 GPa

2021 ◽  
Author(s):  
Linfei Yang ◽  
Jianjun Jiang ◽  
Lidong Dai ◽  
Haiying Hu ◽  
Meiling Hong ◽  
...  
Keyword(s):  
Phase Transition ◽  
Raman Spectroscopy ◽  
High Pressure ◽  
Structural Properties ◽  
Structural Phase Transition ◽  
First Principles ◽  
Theoretical Calculations ◽  
Structural Phase

The vibrational, electrical and structural properties of Ga2S3 were explored by Raman spectroscopy, EC measurements, HRTEM and First-principles theoretical calculations under different pressure environments up to 36.4 GPa.

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