High-Figure-of-Merit Thermoelectric La-Doped A-Site-Deficient SrTiO3 Ceramics

ABSTRACT: The structure and thermoelectric (TE) properties of La-doped, A-site-deficient SrTiO3 (Sr1−3x/2LaxTiO3) ceramics sintered in air and N2/5% H2 have been investigated. Airsintered ceramics with 0.10 ≤ x < 0.30 appear cubic by X-ray diffraction (XRD) but exhibit superstructure consistent with a tetragonal cell (a0 a0 c −), according to electron diffraction (ED) studies. 0.30 ≤ x < 0.50 have additional short-range A-site vacancy (VA) ordering, and x ≥ 0.50 are orthorhombic with an a−a−c + tilt system and long-range VA ordering. 0.10 ≤ x ≤ 0.50 reduced in N2/5% H2 are oxygen-deficient and appear cubic in XRD patterns but exhibit superstructure compliant with an a0 a0 c − tilt system by ED. For x = 0.50, additional short-range VA order is observed, and x > 0.50 are orthorhombic with an a−a−c + tilt system and long-range VA ordering. x = 0.15 sintered in N2/5% H2 shows the largest dimensionless TE figure-of-merit ZT = 0.41 at 973 K reported for n-type SrTiO3-based ceramics, suggesting that the accommodation of La through formation of (VSr) coupled with reduction in N2/5% H2 represents a new protocol for the development of oxide-based thermoelectrics.