Systeme Ga2Se3FeSe. Etude cristallographique diagramme de phase

The system is studied by D.T.A. and X rays diffraction methods. Several intermediate phases are observed. First of all, a very extended solid solution, from Ga2Se3 to n = 0,36 n = Mn at ( Mn at + Ga at ) is only obtained by quenching the melt. It has a tetrahedral structure going from wurtzite to blende with increasing content of MnSe. It is a metastable phase, at all temperatures for which the solids exist. It does not belong to the phase diagram. In the phase diagram are only present the following phases : 1. 1o - from n = 0 to n = 0.15 : a solid solution with a disturbed blende structure (odd h k 1 reflections are diffuse and a no-coherent parameter is calculated). 2. 2o - for n = 0.33, the MnGa2Se4 compound, which is dimorphous ; it has a tetragonal structure at low temperature, of the CdGa2Se4 type (as the ϕ6 phase of the Ga2S3-MnS system, but exactly stoichiometric for the selenide). At high temperature it has an orthorhombic structure of the ZnAl2S4 type (as the high temperature form of MnGa2S4). The transition occurs at 924°C. The compound undergoes a peritectic decomposition at 955°C. The eutectic is at 943°C and about n = 0.40.