The variation of the equilibrium of chemical reactions in the process of (Bi 2Te 3)(Sb 2Te 3)(Sb 2Se 3) crystal growth

Abstract

Methods of computation for thermodynamic and differential thermal analysis were used to study the effect of the variation of the chemical equilibrium in the synthesis of (Bi 2Te 3) x (Sb 2Te 3) y (Sb 2Se 3) z ( x+ y+ z=100%) in an ampoule on the characteristics of crystals grown by vertical zone-melting technique. Measurements of thermoelectric characteristics of reference samples were made. The case study of pseudo-binary systems (antimony telluride—antimony selenide, x=0; bismuth telluride—antimony selenide, y=0; bismuth telluride—antimony telluride, z=0) proves the following. As a result of some components turning into a gas–vapour phase, some unreacted original components may be found in a condensed phase. With a single-stage synthesis the products of side reactions of chemical interactions may be formed in the condensed phase. The case study of (Bi 2Te 3) 25(Sb 2Te 3) 72(Sb 2Se 3) 3; (Bi 2Te 3) 70(Sb 2Te 3) 25(Sb 2Se 3) 5; (Bi 2Te 3) 90(Sb 2Te 3) 5(Sb 2Se 3) 5 shows that both the synthesis temperature and the dopants greatly affect the thermodynamic equilibrium between the condensed and gas–vapour phases through the variation of the content of basic components in a condensed phase. On the basis of the performed research, recommendations on the synthesis conditions and crystal growth by zone-melting technique are given.