Thermoelectric properties of the AA′3B4O12-type ordered perovskite oxides

The perovskite transition-metal oxide ABO3 has been extensively studied in various areas in solids. While the B ion determines the electronic properties, e.g., ferroelectricity, ferromagnetism, and superconductivity, the A site has been regarded as a “back-seat player” to change the doping level or the bandwidth. However, in the ordered perovskite oxide AA′3B4O12, the A site order is closely related to the peculiar electronic states. In CaMn3Mn4O12, the unusually small bandwidth justifies to extrapolate the transport data to the high-temperature limit, and in CaCu3Ru4O12, a novel heavy-fermion state is realized through the Cu–O–Ru interaction.