High-Pressure Synthesis of Metallic Perovskite Ruthenate CaCu3Ga2Ru2O12

A new perovskite ruthenate, CaCu3Ga2Ru2O12, has been synthesized at 12.5 GPa and 1200 C and recovered to room pressure and temperature conditions. This oxide is Aisostructural with CaCu3Ti4O12 and CaCu3Ru4O12, crystallizing in space group Im(theta) with Ga and Ru cations disordered over the octahedral sites. CaCu3Ga2Ru2O12 exhibits a temperature-independent Pauli-paramagnetic and metallic character, indicating delocalized electrons for both Cu and Ru. Bond valence calculations based on the refined structure give oxidation states of 2.31 and 4.53 for copper and ruthenium cations, respectively. The itinerant electron behavior is thought to originate from a significant oxidation of Cu(II) by Ru(V). Such a situation corresponds to Cu(II)-O-Ru(V) Cu(III)-O-Ru (IV) valence degeneracy. This places CaCu3Ga2Ru2O12 among an unusual and interesting group of perovskites that show heteronuclear valence degeneracy