Effect of fluctuations on electron and phonon processes and thermodynamic parameters of Ag2Te and Ag2Se in the region of phase transition

Temperature dependences of electrical conductivity sigma, thermoelectric power alpha, results of differential thermal analysis Delta T-y , thermal conductivity chi, temperature conductivity kappa, and heat capacity C-p were studied in Ag2Te and Ag2Se semiconductors in the region of the phase transition. Two extrema are observed in the temperature dependence chi(T): a maximum in the region of the alpha'->beta' transition and a minimum in the region of the beta'->beta transition; these extrema are caused by the similar dependence C-p (T). It is shown that the alpha ->alpha' and beta'->beta transitions are displacement transitions, while the alpha'->beta' transition is of reconstruction type. It is established that the disorder parameter eta in silver chalcogenides is highly smeared in the region of the phase transition; therefore, disordering of phases at the point of the phase transition is incomplete: 73, 62, and 48% in Ag2Te, Ag2Se, and Ag2S, respectively. The minimum volumes V-ph for new phases are calculated; it is shown that the value of V-ph in displacement transitions is larger than in the reconstruction-type transitions.