Abnormal Grain Growth as a Method To Enhance the Thermoelectric Performance of Nb-Doped Strontium Titanate Ceramics

Driven by the need for high-temperature n-type thermoelectrics for energy-harvesting sectors, SrTi0.8Nb0.2O3 +/-delta ceramics are prepared here from powders with average particle sizes of 270 and 800 nm by the conventional sintering in air at 1450 degrees C and further in H-2/N-2 at 1400 degrees C. In contrast to coarse particle powders, the use of fine particle powders under these conditions leads to abnormal grain growth and thereby bimodal grain size distribution in SrTi0.8Nb0.2O3 +/- ceramics. As a result, a 3-fold increase in the thermoelectric figure of merit to 0.36 at 970 K is achieved, thus establishing the record value for bulk Nb-doped strontium titanate up to this temperature.