Structure and transport properties in Ca3Co4−xMxO9 (M=Re and Pt) ceramics

The effect of Re and Pt doping on the structural, electrical and thermal transport properties of Ca3Co4−xMxO9 (0≤x≤0.2, M=Re and Pt) samples have been investigated systematically. As Re7+ or Pt4+ ions are doped into Ca3Co4O9 lattice, the resistivity and the metal–insulator-transition temperature increase monotonously with increasing x, indicating that both Re- and Pt-substitution can result in more stable spin-density-wave state. For Re-doped samples, the thermopower increases with increasing x, while the thermopower of Pt-doped samples decreases monotonously. Although the decreased thermal conductivity of both Re- and Pt-doped samples is beneficial to the thermoelectric performance, their ZT value decreases with increasing x. The result shows that both Re and Pt doping may indeed exert a significant influence in the structural and transport properties of Ca3Co4O9 system, which are suggested to originate from the variations of carrier concentration and electronic correlation induced by Re or Pt doping.