<i>A</i>‑Site-Ordered Perovskite MnCu₃V₄O₁₂ with a 12-Coordinated Manganese(II)

Abstract

A novel cubic perovskite MnCu₃V₄O₁₂ has been synthesized at a high pressure and high temperature of 12 GPa and 1373 K. This compound crystallizes in the <i>A</i>-site-ordered perovskite structure (space group <i>Im</i>3̅) with lattice constant <i>a</i> = 7.26684(10) Å at room temperature. The most notable feature of this compound lies in the fact that the Mn²⁺ ion is surrounded by 12 equidistant oxide ions to form a regular icosahedron; the situation of Mn²⁺ is unprecedented for the crystal chemistry of an oxide. An anomalously large atomic displacement parameter <i>U</i>_iso= 0.0222(8) Ų is found for Mn²⁺ at room temperature, indicating that the thermal oscillation of the small Mn²⁺ ion in a large icosahedron is fairly active. Magnetic susceptibility and electric resistivity measurements reveal that 3d electrons of Mn²⁺ ions are mainly localized, while 3d electrons in Cu²⁺ and V⁴⁺ ions are delocalized and contribute to the metallic conduction