Phase equilibria in the InRhAs system at 600 °C

Phase equilibria were established in the InRhAs system at 600 °C, using X-ray diffraction, electron probe microanalysis, scanning electron microscopy and differential thermal analysis. InAs was demonstrated to be in thermodynamic equilibrium with RhIn₃, Rh₃In₅As₂, RhAs₂ and RhAs₃. The phase Rh₃In₅As₂, which has not been reported previously in the literature, was found to possess the cubic Ir₃Ge₇ (cI40, D8_f) structure, with the lattice parameter α=0.9165_3±6 nm. A combination of X-ray diffraction and differential thermal analysis experiments indicated that Rh₃In₅As₂ forms peritectically at 829±5 °C, according to the reaction: RhIn+L→Rh₃In₅As₂. A schematic 50 at.% indium InRhAs phase diagram isopleth was proposed to illustrate this reaction. RhAs was found to dissolve 8 at.% indium. Rh_9+xAs₇ RhIn₃ and RhIn also showed some ternary solubility. RhIn exhibited an appreciable range of binary homogeneity, extending from at least 44-49 at.% rhodium at 600 °C. The results of the present investigation suggest that RhIn₃ would be most suitable as a thermodynamically stable, rhodium-based contact to InAs.