Das System P₄S₃–P₄Se₃ / The P₄S₃-P₄Se₃ System

Abstract

The system P 4 S 3 -P 4 Se 3 was investigated by room temperature and high temperature X-ray techniques, MS- and 31 P NMR spectroscopy and differential scanning calorimetry. At room temperature the phase diagram contains three regions of solid solubility, one from P 4 S 3 to ca. 45 mole% P 4 Se 3 with the a-P 4 S 3 structure, the second from ca. 48 to 60 mole% P 4 Se 3 of unknown structure, and the third from ca. 65 mole% P 4 Se 3 to P 4 Se 3 with the β-P 4 Se 3 structure. On heating all these phases transform into a plastic-crystalline modification (ß) with complete solid solubility between P 4 S 3 and P 4 Se 3 . For β-P4S3 d-values are determined with Cr-Kɑ 1 -radiation. At higher temperatures the ß-phase transforms into a γ-phase, which was characterized by high-temperature X-ray methods. Mass and 31 P NMR spectra reveal a multicomponent system consisting of all possible molecules of the type P 4 S χ Se 3-χ (χ = 0-3). All samples prepared from the melt are composed of a mixture of all these cage molecules. For P 4 S 3 a new modification is found by the DSC measurements. It can be shown that the enthalpy of melting consists of the ß-γ transition enthalpy and the real enthalpy of fusion. Metastable γ-P 4 S 3 can be obtained over a broad temperature region (ca. 440-405 K) on cooling of the melt; it is probably isostructural with γ-P 4 Se 3 . For the a-ß and ß-γ transitions several kinds of hysteresis effects are described