By controlling the crystallinity and average grain size of thermoelectric NaxCoO2 thin films, a doubling of the thermoelectric power factor is achieved in combination with a strong suppression of the thermal conductivity. These structurally engineered NaxCoO2 thin films outperform single crystalline and polycrystalline samples at room temperature and demonstrate the potential of thermoelectric oxide thin films. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thickness-driven electronic phase transitions are broadly observed in different types of functional perovskite heterostructures. However, uncertainty remains whether these effects are solely due to spatial confinement, broken symmetry, or rather to a change of structure with varying film thickness. Here, this study presents direct evidence for the relaxation of oxygen-2p and Mn-3d orbital (p–d) hybridization coupled to the layer-dependent octahedral tilts within a La2/3Sr1/3MnO3 film driven by interfacial octahedral coupling. An enhanced Curie temperature is achieved by reducing the octahedral tilting via interface structure engineering. Atomically resolved lattice, electronic, and magnetic structures together with X-ray absorption spectroscopy demonstrate the central role of thickness-dependent p–d hybridization in the widely observed dimensionality effects present in correlated oxide heterostructures.