First Principles Calculations of Thermodynamic Quantities and Phase Diagrams of High Temperature BCC Ta-W and Mo-Ta Alloys

2007 ◽  
Vol 26-28 ◽  
pp. 205-208
Author(s):  
Kinichi Masuda-Jindo ◽  
Vu Van Hung ◽  
P.E.A. Turchi
Keyword(s):  
High Temperature ◽  
Phase Diagrams ◽  
First Principles ◽  
Equilibrium Phase ◽  
Tight Binding ◽  
Configurational Entropy ◽  
Variation Method ◽  
Orbital Method ◽  
Thermodynamic Quantities ◽  
Cluster Approximation

The thermodynamic properties of high temperature metals and alloys are studied using the statistical moment method, going beyond the quasi-harmonic approximations. Including the power moments of the atomic displacements up to the fourth order, the Helmholtz free energies and the related thermodynamic quantities are derived explicitly in closed analytic forms. The configurational entropy term is taken into account by using the tetrahedron cluster approximation of the cluster variation method (CVM). The energetics of the binary (Ta-W and Mo-Ta) alloys are treated within the framework of the first-principles TB-LMTO (tight-binding linear muffin tin orbital) method coupled to CPA (coherent potential approximation) and GPM (generalized perturbation method). The equilibrium phase diagrams are calculated for the refractory Ta-W and Mo-Ta bcc alloys.

Phase Stability and Diagrams from First Principles

1992 ◽  
Vol 291 ◽  
Author(s):  
J.M. Sanchez ◽  
J.D. Becker
Keyword(s):  
Phase Stability ◽  
Cluster Expansion ◽  
First Principles ◽  
Density Functional ◽  
Equilibrium Phase ◽  
Configurational Entropy ◽  
Variation Method ◽  
Orbital Method ◽  
Vibrational Modes ◽  
Many Body Interactions

ABSTRACTFirst principles theories of alloy phase equilibrium have been successfully used in recent years to compute temperature-composition phase diagrams for solid state phases. One particular approach, originating with the successful phenomenological Ising models to describe the alloy Hamiltonian, uses a cluster expansion of the configurational energy in terms of short-ranged pair and many-body interactions. The approach is deeply rooted in our ability to compute accurate total energies of relatively complex compounds, using density functional theory in the local approximation, from which effective interactions may be obtained. Fundamental aspects of the method which include convergence of the cluster expansion, treatment of the configurational entropy and description of vibrational modes are reviewed. Applications of the theory are given for binary alloys in the Ru-Zr-Nb system using the Linear Muffin Tin Orbital method for the total energy calculations, the Cluster Variation method for the description of the configurational entropy, and the Debye-Gruneisen approximation for the vibrational modes. The results are used to compute the equilibrium phase diagram for the Zr-Nb system and to assess current experimental data on phase stability in the Ru-Nb system. In the latter case, the calculations indicate that the DO19 structure is a likely candidate structure for the experimentally observed hexagonal-based compound Ru3Nb. Investigation of the energies and interactions of tetragonal structures as a function of the c/a ratio suggest the L10 structure as a likely candidate for the observed tetragonal phase near 1:1 stoichiometry.

First-Principles Theory of Alloy Phase Diagrams

1988 ◽  
Vol 141 ◽  
Author(s):  
Alex Zunger ◽  
L. G. Ferreira ◽  
S.-H. Wei
Keyword(s):  
Phase Diagrams ◽  
First Principles ◽  
Low Temperatures ◽  
Local Density ◽  
Cluster Variation Method ◽  
Variation Method ◽  
Interaction Energies ◽  
Ordered Structures ◽  
Cluster Variation ◽  
Dependent Interaction

AbstractTemperature-composition phase diagrams of alloys are calculated by a new method combining (i) first principles total energy calculations (at T=0) for ordered structures, using the local density formalism, with (ii) finite-temperature statistical-mechanics approach (the Cluster Variation Method) to the solution of the multi-spin Ising model, using volume-dependent interaction energies obtained from (i). Novel features, including the appearance of metastable long-range ordered compounds at low temperatures are discovered.

scholarly journals A First-Principles Study of the Phase Stability of FCC-Based Ti-Al Alloys

1992 ◽  
Vol 278 ◽  
Author(s):  
Mark Asta ◽  
Didier De Fontaine ◽  
Mark Van Schilfgaarde ◽  
Marcel Sluiter ◽  
Michael Methfessel
Keyword(s):  
Phase Stability ◽  
First Principles ◽  
Cluster Variation Method ◽  
Stability Study ◽  
Al Alloys ◽  
Variation Method ◽  
Orbital Method ◽  
Temperature Phase ◽  
Full Potential ◽  
Cluster Variation

AbstractIn this paper we present results of a first-principles phase stability study of fcc-based Ti-Al alloys. In particular, the full-potential linear muffin tin orbital method has been used to determine heats of formation and other zero-temperature properties of 9 fcc ordered superstructures as well as fcc and hcp Ti, and fcc Al. From these results a set of effective cluster interactions are determined which are used in a cluster variation method calculation of the thermodynamic properties and the composition-temperature phase diagram of fcc-based alloys.

First-principles study of phase stability of Ti–Al intermetallic compounds

1993 ◽  
Vol 8 (10) ◽  
pp. 2554-2568 ◽  
Author(s):  
Mark Asta ◽  
Didier de Fontaine ◽  
Mark van Schilfgaarde
Keyword(s):  
Intermetallic Compounds ◽  
Phase Stability ◽  
First Principles ◽  
Experimental Studies ◽  
Cluster Variation Method ◽  
Variation Method ◽  
Orbital Method ◽  
Temperature Phase ◽  
Full Potential ◽  
Cluster Variation

Thermodynamic and structural properties of fcc- and hcp-based Ti–Al alloys are calculated from first-principles and are used to perform an ab initio study of phase stability for the intermetallic compounds in this system. The full potential linear muffin tin orbital method is used to determine heats of formation and other zero-temperature properties of 9 fcc- and 7 hcp-based intermetallic compounds, as well as of elemental fcc and hcp Ti and Al. From the results of these calculations, sets of effective cluster interactions are derived and are used in a cluster variation method calculation of the solid-state portion of the composition-temperature phase diagram for fcc- and hcp-based alloy phases. The results of our calculations are compared with those of experimental studies of stable and metastable phases in the Ti–Al system.

scholarly journals Electronic Structure of Substitutionally Disordered Alloys: Direct Configurational Averaging

1992 ◽  
Vol 278 ◽  
Author(s):  
C. Wolverton ◽  
D. De Fontaine ◽  
H. Dreysse ◽  
G. Ceder
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Local Density ◽  
Tight Binding ◽  
Ternary Alloys ◽  
Orbital Method ◽  
Thermodynamic Quantities ◽  
Local Density Of States ◽  
Disordered Alloys ◽  
Effective Cluster

AbstractThe method of direct configurational averaging (DCA) has been proposed to study the electronic structure of disordered alloys. Local density of states and band structure energies are obtained by averaging over a small number of configrations within a tight-binding Hamiltonian. Effective cluster interactions, the driving quantities for ordering in solids, are computed for various alloys using a tight-binding form of the linearized muffin-tin orbital method (TB-LMTO). The DCA calculations are used to determine various energetic and thermodynamic quantities for binary and ternary alloys.

Tight-Binding Study of the Electronic Structure of the high Temperature Superconductor La2CuO4

1987 ◽  
Vol 99 ◽  
Author(s):  
D. A. Papaconstantopoulos ◽  
M. J. Deweert ◽  
W. E. Pickett
Keyword(s):  
Electronic Structure ◽  
High Temperature ◽  
Band Structure ◽  
Fermi Surface ◽  
First Principles ◽  
High Temperature Superconductor ◽  
Tight Binding ◽  
Binding Study ◽  
Three Components

ABSTRACTWe have fit our first principles LAPW band structure results for the high Tc superconductor La2CuO4 to a tight-binding Hamiltonian that contains s, p, and d interactions from the three components of these materials. Our fit reproduces very accurately the 17 lower bands of this material and especially the Fermi surface.

First-Principles Calculations of Phase Stability for High Temperature Intermetallics

1990 ◽  
Vol 213 ◽  
Author(s):  
J.D. Becker ◽  
J.M. Sanchez ◽  
J.K. Tien
Keyword(s):  
Total Energy ◽  
First Principles ◽  
Configurational Entropy ◽  
Cluster Variation Method ◽  
Binding Energies ◽  
Variation Method ◽  
First Principles Calculations ◽  
Chemical Interactions ◽  
Volume Relaxation ◽  
Dependent Pair

ABSTRACTTotal energy electronic structure calculations are performed for the elements and selected binary ordered compounds of the ternary system Nb-Ru-Zr. These calculations provide binding energies, atomic volumes, bulk moduli, Debye temperatures, and Grüneiesen constants for the selected structures and compounds. Volume dependent pair and many-body chemical interactions are also obtained from the total energy results which, in turn, are used to study partially ordered alloys at finite temperatures. The stability of all the binary intermetallic compounds experimentally observed at low temperatures is correctly predicted by the first-principles calculations. The solid state portion of the Nb-Ru binary phase diagram is calculated using the chemical interactions obtained from the total energy calculations, a Debye-Grüneisen model for the vibrational free energy and the cluster variation method (CVM) for the configurational entropy with a local volume relaxation scheme. The calculations reproduce the experimentally observed ordering temperature of the NbRu3 intermetallic to within 2%.

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