The investigation of the solid‐gas phase equilibrium of revealed that at about 400° sublimes initially by losing selenium to form nonstoichiometric , where ; the resulting compound sublimes congruently. Since existing thermodynamic data for are either incomplete or show significant differences, the high‐temperature thermodynamic properties of were reinvestigated using the Knudsen effusion technique. With the heat capacity function for measured for the first time in this work and with tabulated thermochemical data, the vapor pressure measurements were evaluated in terms of the standard heat of formation [ (third‐law evaluation)] and the absolute entropy [ (second‐law evaluation)] of . Previous investigations are reviewed and compared with present results.
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Sigai et al. (1972) studied this question.