Effect of Pressure on Order and Stability in Alloys: The Case of Al-Ge

1992 ◽  
Vol 291 ◽  
Author(s):  
P. E. A. Turchi ◽  
M. Sluiter ◽  
G. M. Stocks
Keyword(s):  
Phase Separation ◽  
Phase Stability ◽  
Structural Difference ◽  
Normal Pressure ◽  
Energy Difference ◽  
Potential Approximation ◽  
Pure Species ◽  
Theoretical Predictions ◽  
Substitutional Alloys ◽  
Ordered State

ABSTRACTA parameter-free approach to phase stability in substitutional alloys is applied to the influence of pressure on order-disorder phenomena in Al-Ge. The methodology is based upon an application of the Generalized Perturbation Method to the Korringa-Kohn-Rostoker scattering formulation of the Coherent Potential Approximation. For fcc-based Al-Ge alloys, it is shown that the tendency towards phase separation at normal pressure originates from a structural difference between the pure species. By applying pressure, the structural energy difference is reduced, and a significant increase in the tendency towards order, especially for Al-rich alloys, is theoretically observed, leading, as an example, to the possible observation of a DO22 ordered state around 25 at. pct. Ge. The electronic origin of the ordering tendencies induced by pressure is discussed and the theoretical predictions are related to experimental facts.

First-Principles Study of Phase Stability in Pd-Rh Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
D.D. Johnson ◽  
P.E.A. Turchi ◽  
Marcel Sluiter ◽  
D.M. Nicholson ◽  
F.J. Pinski ◽  
...  
Keyword(s):  
Phase Separation ◽  
Phase Stability ◽  
First Principles ◽  
Ternary Addition ◽  
Potential Approximation ◽  
Effective Interactions ◽  
Reference Medium ◽  
Random Alloy ◽  
Substitutional Alloys ◽  
Effective Cluster

We present a study of the mixing energies and the effective cluster interactions which form the configurational part of the internal energy of Pd-Rh substitutional alloys. We discuss the tendency towards phase-separation and more generally phase stability. The effects of a substitutional ternary addition on the tendencies toward order or phase-separation are also reported. The Korringa-Kohn-Rostoker Coherent-Potential Approximation (KKR-CPA) is used to investigate the electronic structure effects and energetics of the random alloy. Moreover, we use the Generalized Perturbation Method (GPM), using the KKR-CPA random alloy as a reference medium, to investigate the effective interactions which determine phase stability. We briefly comment on other factors which may give important contributions to the total free-energy of the alloy. We also contrast the GPM with the Connolly-Williams approach for calculating phase diagrams from first-principles. Finally, we explore the inadequacies of the frozen-potential and Harris approximations to the energetics of alloying.

A Comparative First Principles Study of Phase Stability in Ni-Ti and Ni-Al Alloys Around Equiatomic Composition

1990 ◽  
Vol 186 ◽  
Author(s):  
P.E.A. Turchi ◽  
M. Sluiter ◽  
F.J. Pinski ◽  
D.D. Johnson
Keyword(s):  
Electronic Structure ◽  
Internal Energy ◽  
Phase Stability ◽  
First Principles ◽  
Al Alloys ◽  
Equiatomic Composition ◽  
Potential Approximation ◽  
Dependent Part ◽  
Substitutional Alloys ◽  
Effective Cluster

AbstractElectronic structure and phase stability properties of Ni-Ti and Ni-Al around equiatomic composition are investigated with a first principles approach. The study is based upon the generalized purturbation method applied to the Korringa-Kohn-Rostoker multiple scattering formulation of the coherent potential approximation. Within this framework, effective cluster interactions which build up the configuration-dependent part of the internal energy are calculated. The strength of ordering tendencies in both bcc-based substitutional alloys is compared and contrasted in terms of hybridisation effects, in relation with experimental evidences.

Gravity Measurements of the Juno Spacecraft Matched with Jupiter Models that rely on a Dilute Core and Deep Winds

2021 ◽  
Author(s):  
Burkhard Militzer ◽  
Sean Wahl ◽  
William Hubbard
Keyword(s):  
Phase Separation ◽  
Inner Core ◽  
Interior Layer ◽  
Gravity Fields ◽  
Gravity Measurements ◽  
Theoretical Predictions

<div><span>Since its arrival at Jupiter in 2016, the Juno spacecraft has measured the planet’s gravity fields with unprecedented precision. The interpretation of these measurements has been challenging because the magnitudes of the gravity coefficients J</span><sub>4</sub><span> and J</span><sub>6</sub><span> were smaller than predicted by traditional interiors models that included a dense inner core composed of rock and ice. Here we instead present models with dilute cores [Geophys. Res. Lett. 44 (2017) 4649] and deep-winds that conform to theoretical predictions of hydrogen-helium phase separation in the interior layer from approximately 0.8 to 0.85 Jupiter radii. Such models match the entire set of zonal gravity measurements by the Juno spacecraft. Our work is based on the accelerated version of the Concentric Maclaurin Spheroid method [Astrophysical J. </span><strong>879</strong><span> (2019) 78]. We conclude by comparing with models for Saturn’s interior. </span></div>

Collapse of Thin Orthotropic Elliptical Cylindrical Shells Under Combined Bending and Pressure Loads

1979 ◽  
Vol 46 (2) ◽  
pp. 363-371 ◽  
Author(s):  
J. Spence ◽  
S. L. Toh
Keyword(s):  
Shell Theory ◽  
Nonlinear Boundary ◽  
Cylindrical Shells ◽  
Normal Pressure ◽  
Nonlinear Ordinary Differential Equations ◽  
Pure Bending ◽  
Finite Deflection ◽  
Shooting Technique ◽  
Theoretical Predictions ◽  
Thin Shell Theory

The elastic collapse of thin orthotropic elliptical cylindrical shells subject to pure bending alone or combined bending and uniform normal pressure loads has been studied. Nonlinear finite deflection thin shell theory is employed and this reduces the problem to a set of nonlinear ordinary differential equations. The resulting two-point nonlinear boundary-value problem is then linearized, using quasi-linearization, and solved numerically by the “shooting technique.” Some experimental work has been carried out and the results are compared with the theoretical predictions.

Phase Separation and Destabilization of the Charge-Ordered State in Cr-Doped Manganites

2001 ◽  
Vol 70 (1) ◽  
pp. 267-271 ◽  
Author(s):  
Ryuichi Shoji ◽  
Shigeo Mori ◽  
Naoki Yamamoto ◽  
Akihiko Machida ◽  
Yutaka Moritomo ◽  
...  
Keyword(s):  
Phase Separation ◽  
Doped Manganites ◽  
Ordered State

First-principles investigations on the phase stability, elastic and thermodynamic properties of Zr–Al alloys

2015 ◽  
Vol 26 (12) ◽  
pp. 1550143 ◽  
Author(s):  
Leini Wang ◽  
Songjun Hou ◽  
Dewei Liang
Keyword(s):  
Thermodynamic Properties ◽  
Debye Temperature ◽  
Phase Stability ◽  
First Principles ◽  
Density Functional ◽  
Elastic Wave Velocity ◽  
Electronic Density ◽  
Functional Theory ◽  
High Bulk ◽  
Substitutional Alloys

In this paper, we employ first-principles methods based on electronic density functional theory (DFT) to investigate the phase stability, elastic and thermodynamic properties of Zr – Al binary substitutional alloys which are Zr 3 Al , Zr 2 Al , ZrAl , ZrAl 2 and ZrAl 3. By analyzing the elastic constants and enthalpy of formation, those phases both satisfy the generalized stability criteria and the results show that ZrAl 2 is the most stable. Due to high bulk modulus B, shear modulus G and Youngs modulus Y, ZrAl 2 also possesses excellent mechanical properties. Moreover, it is expected that there will be covalent bonding between Zr and Al atom in ZrAl 2 compound, which is confirmed by the electronic structure and the differences of charge density discussions. In the end, based on the calculated elastic modulus, the elastic wave velocity, Debye temperature ΘD and specific heat CV are discussed. As a result, ZrAl 3 possesses the highest Debye temperature and sound velocity, meaning a larger associated thermal conductivity and higher melting temperature.

A First Principles Examination of Phase Stability in Fcc-Based Ni-V Substitutional Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
J. Mikalopas ◽  
P.E.A. Turchi ◽  
M. Sluiter ◽  
P.A. Sterne
Keyword(s):  
Phase Stability ◽  
Ground State ◽  
First Principles ◽  
Cluster Variation Method ◽  
Variation Method ◽  
Many Body ◽  
Cluster Variation ◽  
Many Body Interactions ◽  
Ground State Energies ◽  
Substitutional Alloys

AbstractThe phase stability of fcc-based Ni-V substitutional alloys is investigated using linear muffin-tin orbitals total energy (LMTO) calculations. The method of Connolly and Williams (CWM) is used to extract many body interactions from the ground state energies of selected ordered configurations. These interactions are used in conjunction with the cluster variation method (CVM) to calculate the alloy phase diagram. The dependence of the interactions on the choice of configurations used to calculate them is examined.

Study of Process-Induced Cell Membrane Stability in Cell Direct Writing

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Jun Yin ◽  
Yong Huang
Keyword(s):  
Cell Membrane ◽  
Normal Pressure ◽  
Energy Difference ◽  
Membrane Stability ◽  
Bilayer Structure ◽  
Rupture Force ◽  
Direct Writing ◽  
Free Energy Difference ◽  
Cell Membrane Stability ◽  
Before And After

Process-induced damage to cells is of significant importance and must be mitigated for safe and reproducible cell direct writing. The objective of this study is to investigate the cell membrane stability under the external normal pressure. This investigation is performed by studying the dipalmitoylphosphatidylcholine bilayer behavior under different normal pressures using molecular dynamics. As the normal pressure increases, the force necessary to rupture the bilayer structure decreases, which indicates cell membrane instability under high normal pressure. This phenomenon can also be explained by the change of free energy difference before and after rupture under different normal pressures. The effect of the pulling speed on the rupture force is also investigated, showing that the rupture force increases almost linearly with the pulling speed.

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