CuCu₃Fe₂Os₂O₁₂: A Room-Temperature Ferrimagnet with Reduced Thermal Conductivity

The transition-metal-only A- and B-site-ordered perovskite oxide CuCu₃Fe₂Os₂O₁₂ was successfully synthesized under high-pressure (18 GPa) and high-temperature (1475 K) conditions. The compound adopts a cubic lattice with the charge configuration Cu⁺Cu₃²⁺Fe₂³⁺Os₂^5.5+O₁₂, in which Cu(1)⁺ and Cu(2)²⁺ exhibit a 1:3 ordering at the A-site and Fe³⁺ and Os^5.5+ arrange in a rock-salt-type ordered pattern at the B-site. A ferrimagnetic transition is found to occur at 290 K due to magnetic interactions among the corner-shared Cu(2)O₄ planar squares, FeO₆ octahedra, and OsO₆ octahedra. Low-temperature specific heat data suggest the presence of itinerant electronic behavior, in agreement with the half-metallic electronic band structure calculated in theory. Different from most itinerant electronic systems, the current CuCu₃Fe₂Os₂O₁₂ shows unusually low thermal conductivity (1.4 W K^-1 m^-1 at 300 K) since the small-size A-site Cu(1)⁺ ions "rattle" within large cuboctahedron units along the [111] direction. This study opens up a new way to design metallic conductive materials with unusually low thermal conductivity in perovskite oxides.