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

Abstract : Driven by the need for high-temperature n-type thermoelectrics for energy-harvesting sectors, SrTi0.8Nb0.2O3±δ ceramics are prepared here from powders with average particle sizes of 270 and 800 nm by the conventional sintering in air at 1450 °C and further in H2/N2 at 1400 °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±δ 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.