Studies of the (Sc, Zr, Hf)-(Rh, Ir)-b systems

The (Zr, Hf)-(Rh, Ir)-B systems were investigated by X-ray analysis and phase equilibria were established at 1100 °C within the region below 40 at.% IVa metal. Three ternary compounds were found within the Zr-Ir-B system: ZrIr3B4, ZrIr≈3B≈4 and ZrIr≈3B≈2. The corresponding hafnium compounds are isotypic. Hf3Ir5B2 is isostructural with Ti3Co5B3. ScIr3B4 was found to crystallize with a ZrIr3B4-type structure. At 1100 °C rhodium does not form ternary borides with zirconium or hafnium. A remarkably high solubility of boron was found for the (Zr, Hf)(Rh, Ir)3 compounds (perovskite borides). Because of the high stability of the perovskite borides, ZrB2 and HfB2 cannot coexist in thermodynamic equilibrium with rhodium or iridium metal respectively.