First-principles study of multiple order-disorder transitions in Cd{sub 2}AgAu Heusler alloys
- Department of Materials Science, University of California, Berkeley, California 94720 (United States)
The bcc-based Heusler alloys exhibit a series of order-disorder phase transitions as a function of temperature. The high-temperature phase is a disordered bcc solid solution, and the low-temperature phase is the Heusler structure. An intermediate ordered phase is also typically observed in real systems. A prototype cluster variation method (CVM) analysis is presented that shows that the relative stabilities of the Heusler and intermediate phases can vary continuously, depending on a fine balance between ordering tendencies in the constituent binary systems. Given these basic conclusions, a first-principles analysis of order-disorder transitions in Cd{sub 2}AgAu was performed. A cluster expansion Hamiltonian was constructed based on a series of linearized muffin-tin orbital calculations in the atomic sphere approximation. CVM calculations were then performed in the ternary bcc tetrahedron approximation. In addition to the transition temperatures, long-range order parameters, and sublattice occupations for Cd{sub 2}AgAu, an isoplethal section of the ternary phase diagram was also calculated. In general, agreement with experiment is excellent, given the first-principles nature of the calculation. This study clearly demonstrates the ability of first-principles statistical-mechanical calculations to treat complex ordering phenomena in {ital ternary} systems. {copyright} {ital 1996 The American Physical Society.}
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- AC03-76SF00098; AC36-83CH10093
- OSTI ID:
- 390386
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 54, Issue 14; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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