Ab initioinvestigation of phase stability ofY2Ti2O7andY2Zr2O7under high pressure

2009 ◽  
Vol 80 (21) ◽  
Author(s):  
H. Y. Xiao ◽  
Fei Gao ◽  
W. J. Weber
Keyword(s):  
High Pressure ◽  
Phase Stability

scholarly journals Phase Stability of Iron Nitride Fe4N at High Pressure—Pressure-Dependent Evolution of Phase Equilibria in the Fe–N System

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3963
Author(s):  
Marius Holger Wetzel ◽  
Tina Trixy Rabending ◽  
Martin Friák ◽  
Monika Všianská ◽  
Mojmír Šob ◽  
...  
Keyword(s):  
High Pressure ◽  
Phase Equilibria ◽  
Phase Stability ◽  
Polymorphic Transition ◽  
Ex Situ ◽  
Stable Phase ◽  
Iron Nitride ◽  
Phase System ◽  
Target Composition ◽  
Heat Treated

Although the general instability of the iron nitride γ′-Fe4N with respect to other phases at high pressure is well established, the actual type of phase transitions and equilibrium conditions of their occurrence are, as of yet, poorly investigated. In the present study, samples of γ′-Fe4N and mixtures of α Fe and γ′-Fe4N powders have been heat-treated at temperatures between 250 and 1000 °C and pressures between 2 and 8 GPa in a multi-anvil press, in order to investigate phase equilibria involving the γ′ phase. Samples heat-treated at high-pressure conditions, were quenched, subsequently decompressed, and then analysed ex situ. Microstructure analysis is used to derive implications on the phase transformations during the heat treatments. Further, it is confirmed that the Fe–N phases in the target composition range are quenchable. Thus, phase proportions and chemical composition of the phases, determined from ex situ X-ray diffraction data, allowed conclusions about the phase equilibria at high-pressure conditions. Further, evidence for the low-temperature eutectoid decomposition γ′→α+ε′ is presented for the first time. From the observed equilibria, a P–T projection of the univariant equilibria in the Fe-rich portion of the Fe–N system is derived, which features a quadruple point at 5 GPa and 375 °C, above which γ′-Fe4N is thermodynamically unstable. The experimental work is supplemented by ab initio calculations in order to discuss the relative phase stability and energy landscape in the Fe–N system, from the ground state to conditions accessible in the multi-anvil experiments. It is concluded that γ′-Fe4N, which is unstable with respect to other phases at 0 K (at any pressure), has to be entropically stabilised in order to occur as stable phase system. In view of the frequently reported metastable retention of the γ′ phase during room temperature compression experiments, energetic and kinetic aspects of the polymorphic transition γ′⇌ε′ are discussed.

High-Pressure Synthesis and Phase Stability of Nickel Pernitride

2019 ◽  
Vol 2019 (33) ◽  
pp. 3753-3757 ◽  
Author(s):  
Ken Niwa ◽  
Riku Fukui ◽  
Toshiki Terabe ◽  
Takuya Kawada ◽  
Daiki Kato ◽  
...  
Keyword(s):  
High Pressure ◽  
Phase Stability ◽  
High Pressure Synthesis ◽  
Pressure Synthesis

scholarly journals Phase Stability and Compressibility of 3R-MoN2 at High Pressure

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Xuefeng Zhou ◽  
Mingqi Yan ◽  
Mingdong Dong ◽  
Dejiang Ma ◽  
Xiaohui Yu ◽  
...  
Keyword(s):  
High Pressure ◽  
Phase Stability

In situ X-ray observation of 10 Å phase stability at high pressure

2016 ◽  
Vol 101 (11) ◽  
pp. 2564-2569 ◽  
Author(s):  
Sergey V. Rashchenko ◽  
Seiji Kamada ◽  
Naohisa Hirao ◽  
Konstantin D. Litasov ◽  
Eiji Ohtani
Keyword(s):  
High Pressure ◽  
Phase Stability ◽  
X Ray

Phase Stability and Elastic Properties of оne Dimensional Long Period Structures of Al3Ti under High Pressure

2016 ◽  
Vol 850 ◽  
pp. 354-361
Author(s):  
Ping Ying Tang ◽  
Guo Hua Huang ◽  
Qing Lian Xie ◽  
Jin Li Huang
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Elastic Properties ◽  
Phase Stability ◽  
Antiphase Boundary ◽  
First Principles Calculations ◽  
One Dimensional ◽  
Long Period ◽  
Phase Transition Pressure ◽  
Order Polynomial

Phase stability and elastic properties of seven one dimensional long period structures (1D-LPSs) of Al3Ti under high pressure have been systematically investigated by first-principles calculations. The enthalpy differences indicate that Al3Ti will undergo a phase transition from 1D-LPSs to L12 structure at high pressure. With increase of antiphase boundary period parameter M’, the enthalpy initially decreases and then increases, and the enthalpy for D023 is the smallest. Oppositely, the phase transition pressure firstly increases and then decreases, and the maximum is for D023. The elastic constants and elastic moduli B, G and E increase monotonically with increase of pressure, and the corresponding second-order polynomial fits are also obtained. Interestingly, the pressure dependence of Poisson’s ratio show similar tendency with that of B/G ratio. Both the B/G ratios and the Cauchy pressures reveal that these 1D-LPSs exhibit brittleness at high pressure.

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