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 (Bi2Te3)(x)(Sb2Te3)(y)(Sb2Se3)(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 (Bi2Te3)(25)(Sb2Te3)(72)(Sb2Se3)(3); (Bi2Te3)(70) (Sb2Te3)(25)(Sb2Se3)(5); (Bi2Te3)(90)(Sb2Te3)(5)(Sb2Se3)(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. (C) 2002 Elsevier Science B.V. All rights reserved.