First-Principles Calculation of Ternary Phase Diagrams

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A first-principles electronic theory of alloy phase stability is used to investigate the thermodynamic properties and the temperature-composition phase diagrams of binary and ternary systems. The emphasis of this study is on the development and testing of computational schemes - based on quantum mechanical calculations of binding energies, vibrational entropies and configurational entropies - in order to predict solid state phase stability. Electronic structure calculations of the total energy of ordered compounds are carried out using the Linear Muffin-Tin Orbital and the Local Density Approximations. The Liner Muffin-Tin Orbitals total energy calculations are used to obtain multiatom effective chemical interactions, equilibrium lattice constants, bulk moduli, Debye temperatures, Gruneisen Constants and expansion coefficients of configurationally ordered compounds. These calculations provide all information necessary for the computation of equilibrium phase diagrams. Ternary equilibrium and metastable phase diagrams will be calculated for a number of important alumindes to establish trends which may offer predictive results. %%% Calculations of accurate alloy phase diagrams have usually been based on experimental input and phenomenological models. The resulting phase diagrams were sometimes lacking in predictive capability. The research proposed here will calculate phase diagrams based on first-principles; essentially providing only the properties of the atoms making up the alloy. The calculation of first-principles phase diagrams is an important step in the design of new materials having desired properties. The present work will develop techniques to do these calculations for the more difficult case of ternary alloys.