First-principles Theory Of The Coherency Strain, Defect Energetics, And Solvus Boundariesin The Pbte-agsbte_2 System

摘要

Using first-principles data for the elastic properties of PbTe, AgSbTe_2, and related compounds, we extend our previous theoretical study of the thermodynamics of PbTe-AgSbTe_2 and present an in-depth analysis of the effects of elastic strain on the thermodynamics of ordering and coherent solvus boundaries. We find that the substitutional site preference for Pb in ordered AgSbTe_2 and the large asymmetry of the PbTe-AgSbTe_2 miscibility gap share a common physical origin in the peculiar defect energetics of AgSbTe_2. In particular, we find that Pb substitution on Ag sites has approximately the same energy cost as a complex defect consisting of Pb substitution on an Sb site combined with an Sb_(Ag) antisite defect. Configurational entropy contributions strongly favor the latter, explaining why Pb substitutes almost exclusively on the Sb sites in AgSbTe_2. Coherency strain is shown to increase the solubility limits by a factor of ～2 relative to the bulk values both for Ag,Sb in PbTe and for Pb in AgSbTe_2.