Competing Mechanisms for Ordering Tendencies in BCC CuAuZn2 and FCC AuFe Alloys

Abstract

We have implemented a first-principles theory of short-range order in high-temperature, disordered, multicomponent alloys (and magnetic and paramagnetic binary alloys) which determines the atomic (and magnetic) pair-correlations from the underlying local-density-functional electronic structure of the chemically (homogeneously) random alloy. Features in diffuse scattering intensities may be directly related to their electronic origins, for microscopic, system-dependent understanding of the ordering tendencies, or atomic short-range order (ASRO). We discuss briefly the electronic origins, and the novel competitions they produce, for the ordering tendencies in two different alloy systems. First, we discuss the ASRO indicating a high-temperature B2-type state in BCC (Heusler) CuAuZn2; the ordering tendency is determined by a competition between the different types of order associated with each of the three independent pair-correlations, with the dominant ordering originating from band filling. Second, the controversial ASRO observed in FCC AuFe alloys (prepared at high-temperature and rapidly quenched) arises from a competition between ordering (from hybridization) and clustering (from band-filling) tendencies within the same pair-correlation.