Phase equilibria studies of Cr3O-type structures in the vanadium- rhodium-silicon and niobium-rhodium-silicon ternary systems

Abstract

Phase equilibria studies of two ternary systems, the vanadium rhodium-silicon system and the niobium-rhodium-silicon system, were made to obtain information about the formation of the Cr₃O-type structure in these systems. All samples had compositions in the . vicinity of the stoichiometric Cr₃O composition line and were prepared by powder metallurgy techniques. The compacts were then arc-melted, given a homogenization anneal, and examined by x-ray diffraction. Complete solid solubility of silicon for rhodium was found across the V-Rh-Si system in the Cr₃O-type structure. A large range of vanadium compositions for the formation of the Cr₃O-type structure in the V-Rh-Si system was also found. A minimum lattice parameter was found for samples closely approximating the stoichiometric Cr₃O composition in the V-Rh-si system. Either an increase or a decrease in vanadium composition from stoichiometry caused an increase in the lattice parameter of the Cr₃O-type structure formed. No solid solubility of silicon for rhodium was found in the niobium-rhodium-silicon system. Apparently the only Cr₃O-type structure which forms in the Nb-Rh-Si system is of' the stoichiometric composition Nb₃Rh.