scholarly journals Theoretical Investigation of Phase Stability in Non-Magnetic Fe-V Substitutional Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
M. Sluiter ◽  
P.E.A. Turchi
Keyword(s):  
Phase Diagram ◽  
Solid Solution ◽  
Electronic Structure ◽  
Phase Stability ◽  
Tight Binding ◽  
Variation Method ◽  
Equiatomic Composition ◽  
Bcc Lattice ◽  
Slow Kinetics ◽  
Four Levels

The assessed phase diagram of Fe-V exhibits a continuous high temperature bcc solid solution intersected at lower temperatures by a complex sigma phase centered around equiatomic composition [1]. Slow kinetics of the bcc to sigma transformation make it possible to retain the bcc solid solution at low temperature. It has been observed that this metastable solid solution has a tendency to order with a CsCl type structure (B2) below 970 K [1,2]. As a first attempt to describe this behavior from an electronic structure approach, this paper will study the phase stability on the bcc lattice using a realistic tight-binding Hamiltonian. Details of the tight-binding description have been given elsewhere [3]. Main features are as follows: Element and structure specific Slater-Koster parameters are used [4] and lattice parameter effects are incorporated through scaling [5]. Charge transfer is set to zero by rigidly shifting the onsite energies of one constituent. The Coherent Potential Approximation (CPA) is invoked with four levels corresponding to states with s, p, t2g and eg like symmetry. Effects of off-diagonal disorder (ODD) have not been included, instead, an average alloy Hamiltonian was defined using the Slater-Koster parameters of the components weighted by concentration. At equiatomic composition the effect of this approximation has been evaluated by repeating the electronic structure calculation with inclusion of ODD effects (see also [6]). Effective pair interactions, as defined within the Generalized Perturbation Method (GPM) [7], have been computed and have been used to evaluate the ground states of configurational order on the bcc lattice in the Fe-V system. Furthermore, the theoretically derived energetic properties have been used to determine the phase diagram pertaining to the (metastable) bcc lattice with the Cluster Variation Method (CVM) [8] in the tetrahedron approximation

Hydrogen Ordering and Metal-Semiconductor Transitions in Rare-Earth Hydrides

2008 ◽  
Vol 1122 ◽  
Author(s):  
P. Vajda
Keyword(s):  
Phase Diagram ◽  
Solid Solution ◽  
Magnetic Properties ◽  
Electronic Structure ◽  
Rare Earth ◽  
Fluorite Type ◽  
The Rare Earth

AbstractAfter an introduction to the rare earth – hydrogen phase diagram, stressing the often broad existence range of the solid solution (α), dihydride (β) and trihydride (γ) phases, we are describing in detail the fluorite-type dihydride and its superstoichiometric composition, RH2+x, where the x atoms occupy the available octahedral interstitial sites. It is shown how these additional x atoms interact with each other to form ordered H superlattices (sometimes distorting the cubic CaF2 structure) and how the latter influences the electronic structure of the systems modifying the magnetic properties and/or leading to metal-semiconductor transitions.

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.

scholarly journals PHASE STABILITY AND ELECTRONIC STRUCTURE OF TRANSITION-METAL ALUMINIDES

1993 ◽  
Vol 07 (01n03) ◽  
pp. 293-298 ◽  
Author(s):  
A. E. CARLSSON
Keyword(s):  
Electronic Structure ◽  
Transition Metal ◽  
Ab Initio ◽  
Phase Stability ◽  
Tight Binding ◽  
Magnetic Behavior ◽  
Binding Model ◽  
Electronic Density ◽  
Model Calculations ◽  
Site Model

This paper will describe the interplay between the electronic structure and structural energetics in simple, complex, and quasicrystalline Al-transition metal (T) intermetallics. The first example is the L1 2− DO 22 competition in Al 3 T compounds. Ab-initio electronic total-energy calculations reveal surprisingly large structural-energy differences, and show that the phase stability of both stoichiometric and ternary-substituted compounds correlates closely with a quasigap in the electronic density of states (DOS). Secondly, ab-initio calculations for the structural stability of the icosahedrally based Al 12 W structure reveal similar quasigap effects, and provide a simple physical explanation for the stability of the complex aluminide structures. Finally, parametrized tight-binding model calculations for the Al–Mn quasicrystal reveal a large spread in the local Mn DOS behavior, and support a two-site model for the quasicrystal's magnetic behavior.

Theoretical Investigation of Phase Stability in Non-Magnetic Copper-Nickel Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
M. Sluiter ◽  
P.E.A. Turchi
Keyword(s):  
Experimental Data ◽  
Phase Diagram ◽  
Theoretical Investigation ◽  
Phase Stability ◽  
Nickel Alloys ◽  
Tight Binding ◽  
Enthalpies Of Mixing ◽  
Ni Alloys ◽  
Copper Nickel ◽  
Densities Of States

AbstractThe phase stability of non magnetic Cu-Ni alloys is studied within a tight binding framework. Densities of states, enthalpies of mixing and ultimately the phase diagram are computed and compared to experimental data.

Electronic Structure and Phase Stability Properties of Ai-Li Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
Antonios Gonis ◽  
Patrice E.A. Turchi ◽  
Marcel Sluiter ◽  
Frank J. Pinski ◽  
Duane D. Johnson
Keyword(s):  
Phase Diagram ◽  
Electronic Structure ◽  
Perturbation Method ◽  
Multiple Scattering ◽  
Phase Stability ◽  
First Principles ◽  
Potential Approximation ◽  
Effective Interactions ◽  
Lattice Constants ◽  
Effective Cluster

AbstractRecently, the phase diagram of AI-Li alloys was calculated with the use of the Connolly-Williams method. In an effort to test the validity and to supplement the results of that study, equilibrium lattice constants and effective cluster interactions have been obtained using the generalized perturbation method within the first-principles multiple-scattering formalism of the Korringa-Kohn-Rostoker coherent-potential approximation. The implication of these effective interactions to the phase stability of these alloys is discussed.

Effective Interactions Approach to Phase Stability in Alloys Under Irradiation

1998 ◽  
Vol 538 ◽  
Author(s):  
Raúl A. Enrique ◽  
Pascal Bellon
Keyword(s):  
Phase Diagram ◽  
Phase Stability ◽  
Kinetic Monte Carlo ◽  
Theoretical Frameworks ◽  
Effective Interactions ◽  
Dynamical Phase ◽  
Thermodynamic Potentials ◽  
Simple Kinetic Model ◽  
Kinetic Monte Carlo Simulations ◽  
Competing Dynamics

AbstractPhase stability in alloys under irradiation is studied considering effective thermodynamic potentials. A simple kinetic model of a binary alloy with phase separation is investigated. Time evolution in the alloy results from two competing dynamics: thermal diffusion, and irradiation induced ballistic exchanges. The dynamical (steady state) phase diagram is evaluated exactly performing Kinetic Monte Carlo simulations. The solution is then compared to two theoretical frameworks: the effective quasi-interactions model as proposed by Vaks and Kamishenko, and the effective free energy model as proposed by Martin. New developments of these models are proposed to allow for quantitative comparisons. Both theoretical frameworks yield fairly good approximations to the dynamical phase diagram.

Intermetallic Formation in the Aluminum–Copper System

2003 ◽  
Vol 10 (04) ◽  
pp. 677-683 ◽  
Author(s):  
E. B. Hannech ◽  
N. Lamoudi ◽  
N. Benslim ◽  
B. Makhloufi
Keyword(s):  
Electron Microscopy ◽  
Phase Diagram ◽  
Solid Solution ◽  
Intermetallic Layer ◽  
Equilibrium Phase ◽  
Equilibrium Phase Diagram ◽  
Diffusion Couples ◽  
Intermetallic Formation ◽  
Parabolic Law ◽  
Scanning Electron

Intermetallic formation at 425°C in the aluminum–copper system has been studied by scanning electron microscopy using welded diffusion couples. Several Al–Cu phases predicted by the equilibrium phase diagram of the elements and voids taking place in the diffusion zone have been detected in the couples. The predominant phases were found to be Al 2 Cu 3 and the solid solution of Al in Cu, α. The growth of the intermetallic layer obeyed the parabolic law.

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