High-Pressure Synthesis of a Novel Quadruple Perovskite Oxide AgCu₃Cr₄O₁₂

A novel complex transition metal oxide AgCu3Cr4O12 has been obtained using high-pressure and high-temperature conditions of 12 GPa and 1223 K. The crystal structure is refined to be a cubic AA′3B4O12-type quadruple perovskite structure based on the Rietveld refinement of the synchrotron X-ray powder diffraction data. The density-functional theory calculation obtains a metallic band structure. The valence state is estimated to be Ag∼1.3+Cu∼2.2+3Cr4+4O12 by bond valence sum and X-ray absorption spectroscopy analyses. The valence state on ACu3Cr4O12 series (A = Ag, Ca, La, Ce) sequentially transforms from Ag∼1.3+Cu∼2.2+3Cr4+4O12, Ca2+Cu2+3Cr4+4O12, La3+Cu(2+δ)+3Cr(3.75−0.75δ)+4O12, to Ce4+Cu2+3Cr3.5+4O12, where the electrons are doped into the A′-site (Cu∼2.2+ → Cu2+), followed by predominant doping into the B-site (Cr4+ → Cr(3.75−0.75δ)+ → Cr3.5+). Their electron doping sequence is distinguished from those reported in other quadruple perovskite oxides, proposing characteristic features of the ACu3Cr4O12 family.