Crystal lattice and band structure of the intermediate high-pressure phase ofPbSe

Abstract

In the present paper the results of fitting synchrotron diffraction data are obtained for theintermediate high-pressure phase (9.5 GPa) of the lead selenide based compoundPb1−xSnxSe (x = 0.125)—an optoelectronic as well as a thermoelectric material—for two types of latticesymmetries Pnma (space group #62) and Cmcm (space group #63). Both lattice parametersand positions of atoms for the above mentioned structures have been used incalculations of the electron structure of high-pressure phases. The main differencebetween the electronic properties for Cmcm and Pnma structures establishedin electronic structure calculations is that in the first one the PbSe compoundwas found to be a metal, while in the second a small semiconductor gap (EG = 0.12 eV) was obtained. Moreover, the forces in the Cmcm structure are an order of magnitudelarger than those calculated for the Pnma lattice. In the optimized, Pnma structurewithin a generalized gradient approximation (GGA), the band gap increases up toEG = 0.27 eV. The result coincides with the data on thermoelectric powerand electrical resistance data pointing to a semiconductor gap of∼0.2 eVat ∼9.5 GPa. Thus, the Pmna type of lattice seems to be a preferable version for the intermediatephase compared with the Cmcm one.