Structural properties of ordered high-melting-temperature intermetallic alloys from first-principles total-energy calculations

Abstract

Intermetallic compounds which are ductile at high temperatures are of great technological interest; however, purely experimental searches for improved intermetallic materials are time consuming and expensive. Theoretical studies can shorten the experimental search by focusing on compounds with the desired properties. While current ab initio density-functional calculations cannot adequately determine material properties at high temperature, it is possible to compute the static-lattice equation of state and elastic moduli of ordered binary compounds. Known correlations between equilibrium properties and high-temperature properties such as the melting temperature can then be used to point the way for experiments. We demonstrate the power of this approach by applying the linear augmented-plane-wave method to the calculation of the equation of state and all of the zero-pressure elastic moduli for SbY in the B1 (NaCl) phase, CoAl and RuZr in the B2 (CsCl) phase, and NbIr in the L${1}_{0}$ (Au-Cu I) phase. The calculated equilibrium lattice constants are all within 2% of the experimentally determined values. The only experimentally known elastic moduli in these systems are the bulk and shear moduli for polycrystalline SbY, CoAl, and NbIr. The predicted bulk moduli are with 7% of experiment. Theory enables us to place limits on the experimental polycrystalline shear modulus. The experimental shear moduli of SbY and CoAl are within our theoretical bounds, but the experimental shear modulus of NbIr is 35% smaller than our lower bound. We stress that in the case of CoAl our calculations provided a prediction for the bulk and shear moduli that were subsequently confirmed by the experiments of Fleischer. We also discuss the band structures and electronic density of states for these materials.