PHASE-EQUILIBRIA IN THE IN-RH-AS SYSTEM AT 600-DEGREES-C

Phase equilibria were established in the In-Rh-As system at 600 degree s C, using X-ray diffraction, electron probe microanalysis, scanning e lectron microscopy and differential thermal analysis. InAs was demonst rated to be in thermodynamic equilibrium with RhIn3, Rh3In5As2, RhAs2, and RhAs3. The phase Rh3In5As2, which has not been reported previousl y in the literature, was found to possess the cubic Ir3Ge7 (cI40, D8(f )) structure, with the lattice parameter a=0.9165(3+/-6) nm. A combina tion of X-ray diffraction and differential thermal analysis experiment s indicated that Rh3In5As2 forms peritectically at 829+/-5 degrees C, according to the reaction: RhIn+L --> Rh3In5As2. A schematic 50 at.% i ndium In-Rh-As phase diagram isopleth was proposed to illustrate this reaction. RhAs was found to dissolve 8 at.% indium. Rh9+xAs7, RhIn3 an d RhIn also showed some ternary solubility. RhIn exhibited an apprecia ble range of binary homogeneity, extending from at least 44-49 at.% rh odium at 600 degrees C. The results of the present investigation sugge st that RhIn3 would be most suitable as a thermodynamically stable, rh odium-based contact to InAs.