Strain-enhanced thermoelectric properties of Nb-doped SrTiO₃ thin films

Abstract

The development of high-performance thermoelectric materials can help solve the energy crisis in the future. Thin-film thermoelectric materials can meet the requirement for flexibility of wearable devices while supplying electrical power to them. In this study, high-quality Nb-doped SrTiO₃ films (Nb:STO) with different thickness are prepared on SrTiO₃ (STO) and La_0.3Sr_0.7Al_0.65Ta_0.35O₃ (LSAT) substrates by pulsed laser deposition. The surface morphologies, crystal structures, and thermoelectric performances of the films are characterized. The results show that the thermoelectric performance of the strain-free film increase with thickness increasing. The power factor at room temperature increases by 187%. The Seebeck coefficient of the 144 nm-thick Nb:STO/LSAT sample with strain is greatly improved to <inline-formula><tex-math id="M2">\begin{document}$265.95\;{\text{μ}}{\rm{V}}/{\rm{K}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222301_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222301_M2.png"/></alternatives></inline-formula> at room temperature, which is likely to be due to the strain induced changes in the energy band of the thin film. The improvement of the thermoelectric performances of Nb:STO thin films by strain engineering provides a new approach to improving the thermoelectric properties of oxide thin films.