Objective: To discover thermoelectric materials that are environmentally friendly and exhibit high value for ZT, the standard figure of merit used for thermoelectrics. Oxide materials are considered ideal for such applications.

Approach: Our approach is based on the fact that Tb (terbium) doping causes a reduction in the relative concentration of Co4+ (cobalt) ions, which leads to a decrease in the concentration of holes in the material. A reduction in the hole concentration gives rise to a larger Seebeck coefficient (the thermoelectric sensitivity of the material) and a lower thermal conductivity, corresponding to a higher ZT value.

Results and Significance: We have achieved the enhanced thermoelectric response in polycrystalline Ca3Co4O9 on doping Tb ions in the material. Specifically, a high figure of merit (ZT) of 0.74 at 800 K was observed for Ca2.5Tb0.5Co4O9.