PUB-2014-ROP

Role of phonon scattering by elastic strain field in thermoelectric Sr1− xYxTiO3− δ

S Bhattacharya, A M. Dehkordi, S Tennakoon, R Adebisi, JR Gladden, H.N. Alshareef, TM Tritt, “Role of phonon scattering by elastic strain field in thermoelectric Sr1− xYxTiO3− δ”
J. Appl. Phys. 115, 223712 (2014);
S Bhattacharya, A M. Dehkordi, S Tennakoon, R Adebisi, JR Gladden, H.N. Alshareef, TM Tritt
Phonon, Thermal conductivity, Ceramics
2014
Perovskite-type SrTiO ceramics are multifunctional materials with significant potential as n-type thermoelectric (TE) materials. The electronic and thermal transport properties of spark plasma sintered polycrystalline SrYTiO (x = 0.05, 0.075, 0.1) ceramics are systematically investigated from (15–800) K. The SrYTiO simultaneously exhibits a large Seebeck coefficient, α > −80 V/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 () of SrYTiO 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 in the SrYTiO 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 of these materials. In addition, the effect of Y-doping on the elastic moduli of SrYTiO (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 SrYTiO compared to that of SrTiO, resulting in a considerably lowthermal conductivity  ∼ 2.7 W/m-K at 760 K. Finally, we report a thermoelectric figure of merit (ZT) ∼ 0.3 at 760 K in the SrYTiO, the highest ZT value reported in the Y-doped SrTiOceramics thus far.