The p-d hybridization in the electronic structure of alpha-Ag2Te

The electronic structure of cr-Ag,Te is discussed, with special attention paid to possible roles of the p-d hybridization, on the basis of density functional calculations in the local-density approximation; alpha-Ag2Te is a typical superionic conductor, and also exhibits interesting electronic properties. Fully self-consistent calculations based on the energy variational principle are carried out for a hypothetical crystalline compound, Ag2Te with the antifluorite structure, making use of the linearized augmented-plane-wave method. The calculated equilibrium lattice constant agrees with a measured value within an accuracy of 5%. The self-consistent determination of the relative sizes of the augmented-plane-wave spheres leads to an energy band structure similar to that of a narrow-gap semiconductor, in accordance with experiments. Also, the magnitudes predicted for the effective masses of the electrons and holes are almost within the experimental uncertainties. Such quantitative agreement even with the static model arises from the following facts: (i) the Ag d states and the Te p states are not hybridized to such an extent as to have a significant influence on the band-structure characteristics near the energy gap; and (ii) the lowest conduction band consists mainly of Ag and Te s states with extended character. Thus the p-d hybridization can hardly be considered to be the mechanism that induces the superionic conductivity in alpha-Ag2Te.