Thermoelectric performance of oriented SrTiO3 nanofilms containing Σ3{111} grain boundary interfaces

• Nanostructured SrTiO 3 has great promise in heat-recovery technologies. • Nanostructuring can reduce lattice thermal conductivity. • Interfaces lead to undesirable reductions electronic properties. • The effect of interfaces on the power factor is detrimental. Heat-recovery technologies such as thermoelectric power are key to achieving Net Zero. Oxide perovskites are abundant, cost effective and stable thermoelectric materials, but their performance is limited by high lattice thermal conductivity, κ l a t t . While nanostructuring is often used to control the κ l a t t , its impact on the electrical transport is less well understood. In this work, we report a first principles modelling study of nanofilms of SrTiO 3 containing Σ3{1 1 1} grain boundaries, providing detailed microscopic insight into how different stacking sequences affect the electrical and thermal transport and the thermoelectric figure of merit, zT . We find that structurally complex interfaces can reduce the κ l a t t by > 80 % compared to the bulk, but lead to undesirable reductions in the Seebeck coefficient, electrical conductivity and thermoelectric power factor. Our results highlight the importance of nanostructuring to length scales above the electron mean-free path, and show that the κ l a t t can be optimised by engineering the grain-boundary structure.