The Mn-Se (manganese-selenium) system

Abstract

The only attempt to determine Se solubilities in the terminal Mn-base solid solutions is that of [62Say], who reported negligible solubilities in (~1Mn) and (~Mn) and small but finite solubility in (alVin). No specific temperatures were reported, and comparison of other results from this work with existing Mn phase diagrams suggests a considerable level of uncertainty. No liquidus measurements have been made in the system; the miscibility gap postulated in [Massalski2] is the result of analogy with the Mn-Te system. Although four crystalline modifications of MnSe exist, only the B1 NaCl-type (aMnSe) is stable at normal atmospheric pressure above room temperature. The solubility range is negligible at room temperature [69Wie], but excess Se solubility is indicated at higher temperatures by the vaporization experiments of [78Smo]. The congruent melting point of 1460 ~ given in [Massalski2] is taken from the measurement of [68Coo]; other reported values include 1510 ~ [69Van], 1610 ~ [79Leu], and 1615 ~ [67Meh]. At temperatures below ambient, aMnSe undergoes a solid-state transformarion to what most observers have identified as a B81 NiAstype structure, here designated as the 8 modification [63Mak, 66Sir, 70Jac, 80Hei, 88Mat]; the reported transformation temperature is usually in the-35 to 0 ~ range. Only one crystalline structure for MnSe 2 has been reported, the C2 pyrite type. As with MnSe, the stoichiometry range for this phase appears to be minimal [69Wie]. [69Wie] reported that MnSe 2 decomposed in sealed tubes at temperatures above 590 ~ to liquid Se and ~xMnSe, but [83Gar] was able to determine the magnetic susceptibility of solid MnSe 2 at temperatures up to 965 ~ and to report the solubility limit in molten Se in the same temperature range. Given the slowness of the decomposition reported by [69Wie], it is likely that the results of [83Gar] represent a metastable equilibrium; however, the need for accurate determination of the liquidus compositions for the whole system is apparent. No measurements of Mn solubility in solid Se have been reported.