High-Pressure Synthesis of a Novel Quadruple Perovskite Oxide AgCu₃Cr₄O₁₂

Abstract

A novel complex transition metal oxide AgCu 3 Cr 4 O 12 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 AAA 3 B 4 O 12 -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 ³1.3+ Cu ³2.2+ 3 Cr 4+ 4 O 12 by bond valence sum and X-ray absorption spectroscopy analyses. The valence state on ACu 3 Cr 4 O 12 series (A = Ag, Ca, La, Ce) sequentially transforms from Ag ³1.3+ Cu ³2.2+ 3 Cr 4+ 4 O 12 , Ca 2+ Cu 2+ 3 Cr 4+ 4 O 12 , La 3+ Cu (2+¤)+ 3 Cr (3.75¹0.75¤)+ 4 O 12 , to Ce 4+ Cu 2+ 3 Cr 3.5+ 4 O 12, where the electrons are doped into the AA-site (Cu ³2.2+ ¼ Cu 2+ ), followed by predominant doping into the B-site (Cr 4+ ¼ Cr (3.75¹0.75¤)+ ¼ Cr 3.5+ ). Their electron doping sequence is distinguished from those reported in other quadruple perovskite oxides, proposing characteristic features of the ACu 3 Cr 4 O 12 family.