scholarly journals Phase transitions and critical phenomena of ice under high pressure

2014 ◽  
Vol 70 (a1) ◽  
pp. C894-C894
Author(s):  
Masakazu Matsumoto ◽  
Kazuhiro Himoto ◽  
Kenji Mochizuki ◽  
Hideki Tanaka
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Phase Boundary ◽  
Liquid Water ◽  
Tricritical Point ◽  
Melting Curve ◽  
Md Simulations ◽  
Free Energy Calculations ◽  
Lattice Points

Water distributes ubiquitously among the solar system and outer space in a wide variety of solid forms, i.e. more than ten kinds of crystalline ice, two types of amorphous ice, and clathrate hydrates. These polymorphs often play crucial roles in the planetary geology. Diversity of the stable ices and hydrates also suggests the existence of the various kinds of stable and metastable phases yet to be discovered [1]. Computer simulations and the theoretical treatments are useful to explore them. In this talk, we introduce the phase transitions of ice VII, which is one of the highest-pressure ice phases. The melting curve of ice VII to high-pressure liquid water has not been settled by experiments. We have proposed the intervention of a plastic phase of ice (plastic ice) between ice VII and liquid water, based on molecular dynamics (MD) simulations and the free energy calculations [2], which enables to account for large gaps among the various experimental curves of ice VII. In plastic ice, the water molecules are fixed at the lattice points, while they rotate freely. Interestingly, our additional survey by large-scale MD simulations elucidates that the phase transition between ice VII and plastic ice is first-order at low pressure as it was already predicted, while it is found to be second-order at higher pressures, where a tricritical point joins these phase boundaries together [3]. The critical fluctuations may give a clue for determining the phase boundary experimentally. We also argue about the phase transition dynamics of liquid water to ice VII at their direct phase boundary where metastable plastic ice phase plays an important role.

scholarly journals Viscosity Measurement of Olive Oil under Pressure

2021 ◽  
Vol 6 (5) ◽  
Author(s):  
Pawlicki LT
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Liquid Phase ◽  
Olive Oil ◽  
Measurement Method ◽  
Viscosity Measurement ◽  
Food Preservation ◽  
Characteristic Frequencies ◽  
Viscosity Changes

This article presents changes in the viscosity of olive oil during compression. The test was carried out indirectly by measuring the dependence of the resonance frequency of the piezoelectric immersed in olive oil on pressure. For this purpose, for successive pressures, the resonance curves were read and the values of the characteristic frequencies were determined. Viscosity changes were analysed and related to the compression and crystallization taking place in the tested substance. During this research, a phase transition from the liquid phase to the alpha crystalline phase was detected, during which the resonant frequency of the tested piezoelectric reached a minimum and the viscosity related to this frequency reached a maximum. The measurement method developed in this paper can be used to detect the phase transitions of oils subjected to pressure. This may find application in the oil production and high-pressure food preservation industries for which this knowledge is essential for the safe and trouble-free use of their machines.

Phase transitions of BaCO3 at high pressures

2008 ◽  
Vol 72 (2) ◽  
pp. 659-665 ◽  
Author(s):  
S. Ono ◽  
J. P. Brodholt ◽  
G. D. Price
Keyword(s):  
Phase Transition ◽  
Experimental Study ◽  
High Pressure ◽  
Phase Transitions ◽  
Bulk Modulus ◽  
First Principles ◽  
High Pressures ◽  
Ambient Conditions ◽  
The Stability ◽  
Previous Experimental Study

AbstractFirst-principles simulations and high-pressure experiments were used to study the stability of BaCO3 carbonates at high pressures. Witherite, which is orthorhombic and isotypic with CaCO3 aragonite, is stable at ambient conditions. As pressure increases, BaCO3 transforms from witherite to an orthorhombic post-aragonite structure at 8 GPa. The calculated bulk modulus of the post-aragonite structure is 60.7 GPa, which is slightly less than that from experiments. This structure shows an axial anisotropicc ompressibility and the a axis intersects with the c axis at 70 GPa, which implies that the pressure-induced phase transition reported in previous experimental study is misidentified. Although a pyroxene-like structure is stable in Mg- and Ca-carbonates at pressures >100 GPa, our simulations showed that this structure does not appear in BaCO3.

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.

scholarly journals Pressure-induced phase transition of 1,5-diamino-1H-tetrazole (DAT) under high pressure

RSC Advances ◽  
2020 ◽  
Vol 10 (50) ◽  
pp. 30069-30076
Author(s):  
Cheng Jin ◽  
Ying Liu ◽  
Lijuan Wang ◽  
Weijing Zhang ◽  
Tonglai Zhang ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions

DAT experiences phase transitions under pressure related to rotation of NH2 and distortion of the heterocycle.

scholarly journals X-Ray Diffraction and Electron Microscopy Studies of the Size Effects on Pressure-Induced Phase Transitions in CdS Nanocrystals

MRS Advances ◽  
2020 ◽  
pp. 1-9
Author(s):  
Lingyao Meng ◽  
Hongyou Fan ◽  
J. Matthew Lane ◽  
Luke Baca ◽  
Jackie Tafoya ◽  
...  
Keyword(s):  
Phase Transition ◽  
Particle Size ◽  
High Pressure ◽  
Phase Transitions ◽  
Size Effects ◽  
High Pressures ◽  
Bulk Material ◽  
Cds Nanoparticles ◽  
X Ray ◽  
Potential Applications

Abstract In recent years, investigations of the phase transition behavior of semiconducting nanoparticles under high pressure has attracted increasing attention due to their potential applications in sensors, electronics, and optics. However, current understanding of how the size of nanoparticles influences this pressure-dependent property is somewhat lacking. In particular, phase behaviors of semiconducting CdS nanoparticles under high pressure have not been extensively reported. Therefore, in this work, CdS nanoparticles of different sizes are used as a model system to investigate particle size effects on high-pressure-induced phase transition behaviors. In particular, 7.5, 10.6, and 39.7 nm spherical CdS nanoparticles are synthesized and subjected to controlled high pressures up to 15 GPa in a diamond anvil cell. Analysis of all three nanoparticles using in-situ synchrotron wide-angle X-ray scattering (WAXS) data shows that phase transitions from wurtzite to rocksalt occur at higher pressures than for bulk material. Bulk modulus calculations not only show that the wurtzite CdS nanomaterial is more compressible than rocksalt, but also that the compressibility of CdS nanoparticles depends on their particle size. Furthermore, sintering of spherical nanoparticles into nanorods was observed for the 7.5 nm CdS nanoparticles. Our results provide new insights into the fundamental properties of nanoparticles under high pressure that will inform designs of new nanomaterial structures for emerging applications.

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.

The phase diagrams of beryllium and magnesium oxide at megabar pressures

2022 ◽  
Author(s):  
Jizhou Wu ◽  
Felipe J González-Cataldo ◽  
Francois Soubiran ◽  
Burkhard Militzer
Keyword(s):  
High Pressure ◽  
Phase Diagrams ◽  
Magnesium Oxide ◽  
Phonon Dispersion ◽  
Harmonic Approximation ◽  
Melting Curve ◽  
Detailed Comparison ◽  
Free Energy Calculations ◽  
Hugoniot Curve ◽  
Stability Range

Abstract We perform ab initio simulations of beryllium (Be) and magnesium oxide (MgO) at megabar pressures and compare their structural and thermodynamic properties. We make a detailed comparison of our two recently derived phase diagrams of Be [Wu et al., Phys. Rev. B 104, 014103 (2021)] and MgO [Soubiran and Militzer, Phys. Rev. Lett. 125, 175701 (2020)] using the thermodynamic integration technique, as they exhibit striking similarities regarding their shape. We explore whether the Lindemann criterion can explain the melting temperatures of these materials through the calculation of the Debye temperature at high pressure. From our free energy calculations, we obtained a melting curve for Be that is well represented by the fit Tm(P) = 1564K*[1 + P/(15.8037 GPa)]^0.414 , and a melting line of MgO, which can be well reproduced by the fit Tm(P) = 3010K*(1 + P/a)^(1/c) with a = 10.5797 GPa and c = 2.8683 for the B1 phase and a = 26.1163 GPa and c = 2.2426 for the B2 phase. Both materials exhibit negative Clapeyron slopes on the boundaries between the two solid phases that are strongly affected by anharmonic effects, which also influences the location of the solid-solid-liquid triple point. We find that the quasi-harmonic approximation underestimates the stability range of the low-pressure phases, namely hcp for Be and B1 for MgO. We also compute the phonon dispersion relations at low and high pressure for each of the phases of these materials, and also explore how the phonon density of states is modified by temperature. Finally, we derive secondary shock Hugoniot curves in addition to the principal Hugoniot curve for both materials, and study their offsets in pressure between solid and liquid branches.

TRICRITICAL POINT IN ORDER-DISORDER PHASE TRANSITIONS FOR NEMATICS

1992 ◽  
Vol 06 (14) ◽  
pp. 2521-2530 ◽  
Author(s):  
G. BARBERO ◽  
L. R. EVANGELISTA ◽  
A. P. KREKHOV
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Liquid Crystals ◽  
External Field ◽  
Tricritical Point ◽  
Nematic Liquid Crystals ◽  
Complete Analysis ◽  
Disorder Phase Transition ◽  
Anchoring Strength ◽  
Strong Anchoring

A complete analysis of the order-disorder phase transition in nematic liquid crystals induced by an external field is presented. The case of nearly compensated nematics in weak anchoring situation is discussed. The investigation shows that the parameter controlling the order of the phase transition is a decreasing function of the anchoring strength. The important limiting cases of very weak and very strong anchoring are considered too.

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