A study on the vaporization of copper(II) selenide

Abstract

As reported by Esirkegenov and Valiev [1] the vapour phase above CuSe is practically constituted only of selenium gaseous species, with Se2 (g) the more abundant species. Therefore, according to the phase diagram [2], during the vaporization process of this compound in the temperature range 450-650 K, the consecutive solid phase transitions are: 7CuSe ~/3Cuz_xSe ~/3Cu2Se, where #Cu2_xSe isa defect compound at the selenium-rich side of a broad homogeneity field [2] in which the x vNue depends slightly on the temperature. These phase transitions were confirmed by an electron diffraction study [3]. The temperature dependence equation of the total vapour pressure over CuSe, in the temperature range 530-645 K, has been reported by Mills [4] from Rau's private communication. Apparently, this equation and a draft relationship derived from only four points measured at higher temperatures (673-973 K) by the dew point method [1], are the only vapour pressure data available for CuSe(s). Unfortunately these relationships are decidedly in disagreement (see Fig. 1). No vapour pressure data of the intermediate compound was found in the literature. Therefore as a part of our ongoing programme on the vaporization behaviour of the chalcogenides [5], we deemed it useful to investigate the vaporization of the CuSe by measuring its vapour pressure by the torsion method. The torsion assembly used in this work was described previously [6]. The sample used, 99.999% pure, was supplied by Strem Chemicals Inc. A preliminary run showed that the vaporization occurs in two steps: the first one starts at about 540 K and, considering Se2 the only gaseous species, it corresponds to the process