Phase equilibria in the La-Mo-Se system at 1200 deg. C in the vicinity of LaMo6Se6 and Mo3Se4

Phase relations prevalent in the La-Mo-Se system at 1200 deg. C in the vicinity of the ternary (Chevrel) phase LaMo6Se8 and of the binary Mo3Se4 phase, have been established. Characteristic features of this system are as follows: (i) Two isostructural, but mutually immiscible, solid solutions covering considerable compositional intervals exist. One of them, defined as La-intercalated Mo3Se4, spreads over a triangular surface, with its origin at the binary Mo3Se4 and developing into the ternary system, as far as approx. 1 at% La. One edge of this triangle points towards the isostructural ternary phase LaMo6Se8. The second three-component solid solution is based on the Chevrel-type phase LaMo6Se8 and takes the shape of a rectangular surface about 2 at% La wide, with 6.67 at% La as the mean value. The domain runs along the line LaMo6+xSe8-x, from x=0 (40 at% Mo), characteristic of the exact stoichiometry 1:6:8, to x=0.75 (45 at% Mo). (ii) The continuous solid solution of the LaxMo6Se8 type(0≤x≤1), expected to occur between the binary Mo3Se4 and the ternary LaMo6Se8, is absent. The domains of both solid solutions have been established using x-ray powder diffractometry and the evolution of the critical temperatures (Tc) characteristic for each of the phases. (author)