Computer Simulation of the Thermodynamics of Coherent Interfaces

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The classification of impurity behavior at coherent interfaces based on the ternary phase diagram, was studied. Cluster variation method (CVM) calculations were applied to the fcc - L1ィイD22ィエD2 interphase boundary, and the interphase boundary (IPB) energy, concentration profile and segregation, site preference and fcc/ L1ィイD22ィエD2 partitioning were computed. A strong correlation between site preference and partitioning and its temperature dependence was discovered. Moreover, impurities which have repulsive interactions with both A and B segregate away from an IPB and increase its energy. Other types of impurities segregated towards the IPB but lowered its energy only slightly.The (111) and (100) antiphase boundary (APB) energies in NIィイD23ィエD2Al alloyed with Ti were calculated from first principles. Effective interatomic interactions were computed from electronic total energy calculations and very large scale CVM calculations (using 10s of thousands of correlation functions) were carried out. Ti strongly segregated away from the (111) and (100) APBs and raises the APB energy by as much as 50 mJ/mィイD12ィエD1 per a/o Ti. This result agrees with the (scarce) experimental data.Sofar the effect of the long-ranged elastic strain was neglected. Therefore, a new way to compute this contribution to the solution energy of impurities was derived and applied to Mg, Sr, Li and vacancies in an fcc Al matrix and applied to antisite defects in GaAs. Somewhat surprisingly, the accurate solution energies were shown to be useful for obtaining enthalpies of mixing as well.