Effusion reactions in the ZnSe–ZnIn 2Se 4 system

Abstract

Chemical changes during effusion of substances in the binary ZnSe–ZnIn 2Se 4 system were observed during 21 studies by the simultaneous Knudsen- and torsion-effusion method. Principal vapor species were taken to be Zn(g), In 2Se(g), and Se 2(g). Two intermediate solid phases were found in the temperature range 1100–1200 K, ZnIn 2Se 4(s) and (ZnSe) 5In 2Se 3(s). The latter phase vaporized congruently throughout the temperature range, but it effused congruently only above 1150 K; it was not observed at room temperature. ZnIn 2Se 4(s) effused incongruently to a vapor rich in zinc sulfide and a condensed phase rich in indium selenide. Here, proposed binary pressure-composition phase diagrams of this system at approximately 1120 and 1190 K are given, and equations for all effusion reactions in the system are presented. Stability of the two intermediate condensed phases relative to the chemically binary constituents are small, Δ H°(298 K) = –12.5 ± 3.5 kJ/mol for ZnIn 2Se 4(s), and for the other phase it was less than the experimental error.