Perovskite-type SrTiO3−δ ceramics are multifunctional materials with significant potential as n-type thermoelectric (TE) materials. The electronic and thermal transport properties of spark plasma sintered polycrystalline Sr1−xYxTiO3−δ (x = 0.05, 0.075, 0.1) ceramics are systematically investigated from (15–800) K. The Sr0.9Y0.1TiO3−δ simultaneously exhibits a large Seebeck coefficient, α > −80 μV/K and moderately high electrical resistivity, ρ ∼ 0.8 mΩ-cm at a carrier concentration of ∼1021 cm−3 at 300 K resulting in a high TE power factor defined herein as (α2σT) ∼ 0.84 W/m-K at 760 K. Despite the similar atomic masses of Sr (87.6 g/mol) and Y (88.9 g/mol), the lattice thermal conductivity (κL) of Sr1−xYxTiO3−δ is significantly reduced with increased Y-doping, owing to the smaller ionic radii of Y3+ (∼1.23 Å, coordination number 12) compared to Sr2+ (∼1.44 Å, coordination number 12) ions. In order to understand the thermal conductivity reduction mechanism, the κL in the Sr1−xYxTiO3−δ series are phenomenologically modeled with a modified Callaway's equation from 30–600 K. Phonon scattering by elastic strain field due to ionic radii mismatch is found to be the prominent scattering mechanism in reducing κL of these materials. In addition, the effect of Y-doping on the elastic moduli of Sr1−xYxTiO3−δ (x = 0, 0.1) is investigated using resonant ultrasound spectroscopy, which exhibits an anomaly in x = 0.1 in the temperature range 300–600 K. As a result, the phonon mean free path is found to be further reduced in the Sr0.9Y0.1TiO3−δ compared to that of SrTiO3−δ, resulting in a considerably low thermal conductivity κ ∼ 2.7 W/m-K at 760 K. Finally, we report a thermoelectric figure of merit (ZT) ∼ 0.3 at 760 K in the Sr0.9Y0.1TiO3−δ, the highest ZT value reported in the Y-doped SrTiO3 ceramics thus far.

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