scholarly journals New insights on the GeSe x Te1−x phase diagram from theory and experiment

2019 ◽  
Vol 75 (2) ◽  
pp. 246-256 ◽  
Author(s):  
Markus Guido Herrmann ◽  
Ralf Peter Stoffel ◽  
Michael Küpers ◽  
Mohammed Ait Haddouch ◽  
Andreas Eich ◽  
...  
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
Low Temperature ◽  
Hexagonal Phase ◽  
Structure Type ◽  
Stability Field ◽  
Temperature Behaviour ◽  
Formation Enthalpies ◽  
The Stability

The high-pressure and low-temperature behaviour of the GeSe x Te1−x system (x = 0, 0.2, 0.5, 0.75, 1) was studied using a combination of powder diffraction measurements and first-principles calculations. Compounds in the stability field of the GeTe structure type (x = 0, 0.2, 0.5) follow the high-pressure transition pathway: GeTe-I (R3m) → GeTe-II (f.c.c.) → GeTe-III (Pnma). The newly determined GeTe-III structure is isostructural to β-GeSe, a high-pressure and high-temperature polymorph of GeSe. Pressure-dependent formation enthalpies and stability regimes of the GeSe x Te1−x polymorphs were studied by DFT calculations. Hexagonal Ge4Se3Te is stable up to at least 25 GPa. Significant differences in the high-pressure and low-temperature behaviour of the GeTe-type structures and the hexagonal phase are highlighted. The role of Ge...Ge interactions is elucidated using the crystal orbital Hamilton population method. Finally, a sketch of the high-pressure phase diagram of the system is provided.

High pressure–low temperature phase diagram of barium: Simplicity versus complexity

2015 ◽  
Vol 107 (22) ◽  
pp. 221908 ◽  
Author(s):  
Serge Desgreniers ◽  
John S. Tse ◽  
Takahiro Matsuoka ◽  
Yasuo Ohishi ◽  
Quan Li ◽  
...  
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
Low Temperature ◽  
Temperature Phase ◽  
Low Temperature Phase ◽  
Temperature Phase Diagram

scholarly journals Development of a CALPHAD Thermodynamic Database for Pu-U-Fe-Ga Alloys

2019 ◽  
Vol 9 (23) ◽  
pp. 5040 ◽  
Author(s):  
Emily E. Moore ◽  
Patrice E.A. Turchi ◽  
Alexander Landa ◽  
Per Söderlind ◽  
Benoit Oudot ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Density Functional ◽  
Ternary Phase Diagram ◽  
Thermodynamic Database ◽  
Impurity Effects ◽  
Functional Theory ◽  
Formation Enthalpies ◽  
Temperature Ranges ◽  
The Stability ◽  
First Time

The interaction of actinides and actinide alloys such as the δ-stabilized Pu-Ga alloy with iron is of interest to understand the impurity effects on phase stability. A newly developed and self-consistent CALPHAD thermodynamic database is presented which covers the elements: Pu, U, Fe, Ga across their whole composition and temperature ranges. The phase diagram and thermodynamic properties of plutonium-iron (Pu-Fe) and uranium-iron (U-Fe) systems are successfully reassessed, with emphasis on the actinide rich side. Density functional theory (DFT) calculations are performed to validate the stability of the stoichiometric (Pu,U)6Fe and (Pu,U)Fe2 compounds by computing their formation enthalpies. These data are combined to construct the Pu-U-Fe ternary phase diagram. The thermodynamic assessment of Fe-Ga is presented for the first time and application to the quaternary Pu-U-Fe-Ga system is discussed.

Thermodynamical Behaviour of PdSe2 while Subjected Isothermally to High Pressure - Axial Level Analysis

2008 ◽  
Vol 273-276 ◽  
pp. 277-282
Author(s):  
Veneta Grigorova
Keyword(s):  
High Pressure ◽  
Transition Point ◽  
Structure Type ◽  
First Order ◽  
Higher Temperature ◽  
First Order Transition ◽  
The Stability ◽  
Spatial Axis ◽  
Level Analysis ◽  
Specific Length

We study thermodynamically the behaviour of PdSe2 while subjected to high pressure under isothermal conditions. The present paper continues the study started in [1]. Here we present the results of the axial calculations and analyses. Specific lengths, linear adjusted Gibbs free energy changes and linear adjusted entropy generations were studied along each spatial axis separately. We found that the first-order transition from PdS2 structure type to pyrite one at 20oC is accompanied by saltatory contraction of a and b specific lengths and respective saltatory expansion of c specific length. Under 300oC all specific lengths contract saltatory. In the transition point under 20oC PdSe2 gains saltatory stability along a and b axis and looses along c one, respectively. Besides, the loose along c axis is bigger than the gains along a and b ones. Under 300oC the transition is accompanied by slight gain of stability along all three spatial axes. Plateaux duration affects the stability of PdSe2 strongly under higher temperature.

LOW TEMPERATURE RESISTANCE BEHAVIOR AND SUPERCONDUCTIVITY OF La–Sr–Cu–O SYSTEM: ROLE OF ALTERED Cu–VALENCE AND O–CONTENT

1990 ◽  
Vol 04 (05) ◽  
pp. 357-362 ◽  
Author(s):  
C. V. NARASIMHA RAO ◽  
S. K. AGARWAL ◽  
A. V. NARLIKAR ◽  
M. P. DAS
Keyword(s):  
Phase Diagram ◽  
Low Temperature ◽  
Oxygen Content ◽  
Temperature Resistance ◽  
Copper Valence ◽  
Mechanism Of Superconductivity ◽  
Low Temperature Resistance ◽  
Observed Behavior

In this note we are communicating the results obtained on various samples of lanthanum-based cuprate in which Sr and Zn have been partially substituted for La and Cu, respectively over a range where the superconductivity is gradually destroyed. The decrease in T c is accompanied by a changeover from metallic to semiconducting-like resistance behavior occurring at lower temperatures. The observed behavior is related to the effective copper valence and the change in the oxygen content of the samples and the results are discussed in terms of a tentative phase diagram which would be necessary to examine the mechanism of superconductivity.

scholarly journals Study of silica-undersaturated magmas through the Kalsilite- Nepheline-Diopside-Silica system at 4.0 GPa and dry conditions

2018 ◽  
Vol 18 (2) ◽  
pp. 87-102
Author(s):  
Márcio Roberto Wilbert de Souza ◽  
Rommulo Vieira Conceição ◽  
Daniel Grings Cedeño ◽  
Roberto Vicente Schmitz Quinteiro
Keyword(s):  
High Pressure ◽  
Solid Solutions ◽  
Negative Correlation ◽  
Stability Field ◽  
Thermal Barrier ◽  
High Pressure And Temperature ◽  
Alkaline Magma ◽  
Magma Genesis ◽  
Dry Conditions ◽  
The Stability

This study experimentally investigates the Kalsilite-Nepheline-Diopside-Silica system at high pressure and temperature, with emphasis on silica-undersaturated volume (leucite-nepheline-diopside — Lct-Nph-Di; and kalsilite-nepheline-diopside — Kls + Nph + Di — planes), at 4.0 GPa (~120 km deep), temperatures up to 1,400ºC and dry conditions, to better understand the influence of K2O, Na2O, and CaO in alkali-rich silica-undersaturated magma genesis. In the Lct-Nph-Di plane, we determined the stability fields for kalsilite (Klsss), nepheline (Nphss) and clinopyroxene (Cpxss) solid solutions, wollastonite (Wo) and sanidine (Sa); and three piercing points: (i) pseudo-eutectic Kls + Nph + Di + liquid (Lct62Nph29Di9) at 1,000ºC; (ii) Kls + Sa + (Di + Wo) + liquid (Lct75Nph22Di2) at 1,200ºC; and (iii) pseudo-eutectic Kls + Di + Wo + liquid (Lct74Nph17Di9) at 1,000ºC. Kalsilite stability field represents a thermal barrier between ultrapotassic/potassic vs. sodic compositions. In the plane Kls-Nph-Di, we determined the stability fields for Klsss, Nphss and Cpxss and two aluminous phases in smaller proportions: spinel (Spl) and corundum (Crn). This plane has a piercing point in Kls + Nph + Di(± Spl) + liquid (Kls47Nph43Di10) at 1,100ºC. Our data showed that pressure extends K dissolution in Nph (up to 39 mol%) and Na in Kls (up to 27 mol%), and that these solid solutions, if present, determinate how much enriched in K and Na an alkaline magma will be in an alkaline-enriched metasomatic mantle. Additionally, we noted positive correlation between K2O and SiO2 concentration in experimental melts, negative correlation between CaO and SiO2, and no evident correlation between Na2O and SiO2. 

Phase diagram of ZrZn2 at high pressure: Low-temperature features and elusive superconductivity

2006 ◽  
Vol 378-380 ◽  
pp. 411-412 ◽  
Author(s):  
Sergei M. Stishov ◽  
Vladimir A. Sidorov ◽  
Anatoly V. Tsvyashchenko ◽  
Eric D. Bauer ◽  
Alla E. Petrova ◽  
...  
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
Low Temperature

Ti-Ni Phase Diagram with Applied Stress

1993 ◽  
Vol 311 ◽  
Author(s):  
A.Peter Jardine
Keyword(s):  
Thin Film ◽  
Phase Diagram ◽  
Single Phase ◽  
Phase Evolution ◽  
The Other ◽  
Β Phase ◽  
The Stability ◽  
Tini Phase ◽  
Rich Side

ABSTRACTThe role of stress on the phase evolution of thin-film TiNi has not been investigated and may play an important role in the phase evolution of thin film TiNi. In this paper, a preliminary set of phase diagrams for Ni-Ti at different pressures are presented relating the stability of the stoichiometric TiNi phase to the other well-documented intermetallics TiNi3 and NiTi2. It is found that for sufficient pressure of the order of a GPa, the region where NiTi (β) phase is single phase shifts towards the Ti-rich side of the diagram. The implications on the annealing of TiNi thin film is discussed.

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