PHASE-DIAGRAM AND ELECTRICAL BEHAVIOR OF SILICON-RICH IRIDIUM SILICIDE COMPOUNDS

The iridium-silicon phase diagram on the silicon-rich side was investigated by means of X-ray powder diffraction, density, differential thermal analysis (DTA), metallography, microprobe analysis, and electrical resistivity. Attempts were made to prepare eight previously reported silicon-rich iridium silicide compounds by arc melting and Bridgman-like growth. However, microprobe analysis identified only five distinct compositions: IrSi, Ir4Si5, Ir3Si4, Ir3Si5 and IrSi(almost-equal-to 3). The existence of Ir2Si3, IrSi7, and IrSi2 could not be confirmed in this study. DTA in conjunction with X-ray powder diffraction confirm polymorphism in IrSi(almost-equal-to 3), determined to have orthorhombic and monoclinic unit cells in the high and low temperature forms. A eutectic composition alloy of 80.5 +/- 1 at.% Si was observed between IrSi(almost-equal-to 3) and silicon. Both IrSi5 and Ir3Si4 exhibit distinct metallic behavior while Ir3Si5 is semiconducting. IrSi and IrSi(almost-equal-to 3) exhibit nearly temperature-independent electrical resistivities on the order of (5-10) X 10(-6) OMEGA m.