EXAFS studies of the local environment of lead and selenium atoms in PbTe1−x Sex solid solutions

Abstract

EXAFS spectroscopy is used to study the local environment of lead and selenium atoms in PbTe1−xSex solid solutions. In addition to a bimodal distribution of the bond lengths in the first-coordination sphere, an unusually large value of the Debye-Waller factors for the Pb-Pb interatomic distances (second-coordination sphere) and a substantial deviation of this value from Vegard’s law are observed. Monte Carlo calculations show that these observations are related to the complicated structure of the distribution function for Pb-Pb distances. It is found that the number of Se-Se pairs in the second-coordination sphere exceeds the statistical value, which indicates that chemical factors play an important role in the structure of the solid solutions. The contribution of chemical factors to the enthalpy of mixing of the solid solution is estimated (≈0.5 kcal/mole) and this value is shown to be comparable to the deformation contribution.