Electronic Structure and Thermoelectric Properties of Highly Oriented Ba₂NaNb₅O₁₅ Reduced Ceramics

Often, thermoelectric (TE) materials cannot realize energy harvesting at ∼200 °C. If a fine structure arranged oxide TE material could convert electricity from waste heat, its TE application potential is increased. We report a dimensionless figure of merit (ZT) with low thermal conductivity (κ) ≈ 200 °C of highly oriented n-type Ba2NaNb5O15 (BNN) reduced ceramics, prepared to investigate orientation on transport and thermal dynamics. ZT and κmin for BNN were evaluated to be 0.1 and a surprisingly small 0.2 W/mK, respectively, at ∼200 °C using the Harman method. TE properties of BNN were discussed in terms of transport and thermal dynamics considering electronic structure, small polaron, and anomalies with calculations.