Component distribution during the melting of solid solution (Bi,Sb)/sub 2/Te/sub 3/ grown from the excessive tellurium melt

Abstract

Based on general assumptions about the phase equilibrium diagram in the system Bi-Sb-Te near solid solutions (Bi,Sb)/sub 2/Te/sub 3/, the component distribution under various methods of melting has been studied. By the method of successive approximation we calculated the tellurium distribution along the ingots of solid solutions (Bi,Sb)/sub 2/Te/sub 3/ grown from the melt with excessive tellurium. Analytic expressions of the changes of tellurium concentration in the melt while growing (Bi,Sb)/sub 2/Te/sub 3/ by normal crystallisation, zone melting, by a method with floating crucible, and by zone levelling are obtained. With all methods of crystallisation, except for zone levelling, continuous changes of tellurium concentration in the melt are present. This predefines the non-uniform distribution of dissolved tellurium concentration in the solid phase and as a result non-uniform distribution of properties along the obtained ingots of solid solutions. The only one and simple to implement method in order to ensure approximately uniform properties distribution along the ingots could be zone levelling. Nevertheless approximate integrated equation of zone melting considering the dependence of solid phase antimony distribution coefficient on tellurium concentration in the melt shows that under zone levelling a slight non-uniformity of tellurium distribution in the solid phase is also observed.