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

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 SrTiO₃ containing Σ3{111} grain boundaries, providing detailed microscopic insights into how different stacking sequences affect the electrical and thermal transports, 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 bulk SrTiO₃, but lead to undesirable reductions in the Seebeck coefficient, electrical conductivity and thermoelectric power factor. This implies the need for concurrent doping strategies alongside nanostructuring. 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.