Phase transition in Ge1-xAgx/2Bix/2Te solid solutions and related transport phenomena

The experimentally observed anomalies in temperature dependences of the Hall coefficients and the electrical resistivities for hot-pressed samples of Ge1-xAgx/2Bix/2Te with 0.095<x<0.333, due to the ferroelectric lattice instabilities in the phase transition region, are discussed. The Landau-Lifschitz type criterion for these phenomena shows that the phase transition is of second order. According to the soft-mode conception the main part of the anomalous increase in the resistivity is due to the soft-TO phonon scattering and the curvature caused by the soft-TO phonon near zero wavevector is accelerated with increasing AgBiTe2 content. (author)