Thermoelectric power factor enhancement of textured ferroelectric Sr _xBa_1-x Nb₂O_6-δ ceramics

A promising n-type thermoelectric oxide, based on the tungsten bronze-structured ferroelectric Sr_xBa_1-xNb ₂O_6-δ (SBN, x̃0.61), was investigated to enhance the thermoelectric power factor through templated grain growth (textured polycrystalline). In the reduced SBN textured, both the electrical conductivity (σ) and the magnitude of thermopower (S) are increased in the c axis: σ33 > σ11 and |S₃₃| > |S₁₁|, and consequently, the thermoelectric power factor (PF) increased significantly due to crystal anisotropy and grain boundary density reduction. It was found in randomly oriented polycrystalline ceramics that the thermoelectric properties are dominated by a-axis properties. A ferroelectric-thermoelectric anomaly is observed at 4mm-4/mmm phase transition temperature (T_C) and depends on temperature and reduction degree, consistent with our earlier observations in single crystal SBN. Above T_C, the carrier transport mechanism is controlled by polaron hopping conduction, and below T_C the behavior depends on the degree of reduction. However, the magnitude of the Seebeck coefficient is dependent on the crystal anisotropy.