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, metalography, 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 four distinct compositions: IrSi, Ir₃Si₄, Ir₃Si₅ and IrSi_∼3. The existence of Ir₄Si₅ could not be confirmed in this study, even though the crystal structure has been previously reported. Differential thermal analysis (DTA) in conjunction with X-ray powder diffraction confirm polymorphism in IrSi_∼3, determined to have orthorhombic and monoclinic unit cells in the high and low temperature forms. A eutectic composition alloy of 83±1 atomic % silicon was observed between IrSi_∼3 and silicon. Ir₃Si₄ exhibits distinct metallic behavior while Ir₃Si₅ is semiconducting. Both and IrSi and IrSi_∼3 exhibit nearly temperature independent electrical resistivities on the order of 5-10 × 10^-6 Ω-m.