Optimization of Dimensionless Figure of Merit in Oxide Thin Film Thermoelectrics

The ability of uniquely functional thermoelectric materials to convert waste heat directly into electricity is critical considering the global energy economy. Profitable, energy-efficient thermoelectrics possess thermoelectric figures of merit ZT $\ge $ 1. We examined the effect of metal nanoparticle -- oxide film interfaces on the thermal conductivity $\kappa $ and Seebeck coefficient S in bilayer and multilayer thin film oxide thermoelectrics in an effort to improve the dimensionless figure of merit ZT. Since a thermoelectric's figure of merit ZT is directly proportional to S/$\kappa $, reducing $\kappa $ and increasing S are key strategies to optimize ZT. We reduced $\kappa $ by phonon scattering due to the inclusion of metal nanoparticles in the bulk of the thermoelectric thin film, and increased S due to energy-dependent electron scattering at the metal - oxide interfaces. Doped strontium titanate (STO) thin film/Au nanoparticle composites were synthesized by alternate ablation of Au and Nb-doped STO targets during pulsed laser deposition. Characterization of the thermoelectric films involve XRD, XPS, and TEM analyses, Seebeck coefficient measurements, and also measurements of the thermal conductivity via time-domain thermoreflectance. The measured thermal conductivities and Seebeck coefficients of the thin films shows a strong dependence on the nanoscale interfaces of the films.