Enhanced Densification and Thermoelectric Performance of In4Sn3O12 by Reactive Sintering in the In-Sn-Ga-O System

The thermoelectric properties of the fluorite‐related oxide, In4Sn3O12, have been investigated by studying the system In4−xGaxSn3O12, with 0 ≤ x ≤ 0.15. It has been shown that Ga does not enter the In4Sn3O12 matrix, and two secondary phases form via the Ga introduction: SnO2 and Ga2In6Sn2O16. By reactive sintering between In2O3, SnO2, and Ga2O3 precursors, the density of the samples is considerably increased from 66% (actual density/theoretical density) for x = 0 up to 90% for x = 0.15, which significantly decreases the electrical resistivity. This is attributed to the large number of grain boundaries localized among the secondary phases, which inhibit the grain growth and hence favor the densification. The phase In4Sn3O12 is for the first time reported to exhibit a semi‐metallic behavior. The Seebeck coefficient does not change significantly with respect to the pristine matrix in accordance with the fact that Ga does not play any role as a doping agent. The thermal conductivity increases with the Ga content. The maximum figure of merit, ZT = 0.23, at 1000 K obtained at a very low Ga content (x = 0.05), is comparable to the value obtained for Ge doped In2O3 (ZT ~ 0.3). This study suggests that In4Sn3O12 can be a potential material for thermoelectric applications.