The interface formation of Nb-doped SrTiO 3 single crystals and ͑Ba, Sr͒TiO 3 thin films with Pt has been studied by using photoelectron spectroscopy with in situ sample preparation. For the single crystal sample, a Schottky barrier height for electrons of 0.5-0.6 eV is determined after deposition of Pt in vacuum environment. After annealing in 0.05 Pa oxygen pressure, a strong increase in the barrier height to Ն1.2 eV is observed. X-ray induced photovoltages of up to 0.7 eV are observed in this case and have to be taken into account for a proper determination of the barrier height. A subsequent annealing in vacuum reduces the barrier again. Hence, the barrier height can be reversibly switched between an oxidized state with a large barrier height and a reduced state with a low barrier height. Quantitative analysis of the barrier heights indicates that the changes are related to the changes of interfacial defect concentration. Due to the occurrence of a Ti 3+ related signal, the defects are identified as oxygen vacancies. The same effects are observed at interfaces between Pt and ͑Ba, Sr͒TiO 3 thin films with a smaller absolute value of the barrier height in the oxidized state of ϳ1 eV. Deposition of ͑Ba, Sr͒TiO 3 onto a metallic Pt substrate also results in a barrier height of 1.0 eV.

The energy band alignment at interfaces between different materials is a key factor, which determines the function of electronic devices. While the energy band alignment of conventional semiconductors is quite well understood, systematic experimental studies on oxides are still missing. This work presents an extensive study on the intrinsic energy band alignment of a wide range of functional oxides using photoelectron spectroscopy with in‐situ sample preparation. The studied materials have particular technological importance in diverse fields as solar cells, piezotronics, multiferroics, photo‐electrochemistry and oxide electronics. Particular efforts have been made to verify the validity of transitivity, in order to confirm the intrinsic nature of the obtained band alignment and to understand the underlying principles. Valence band offsets up to 1.6 eV are observed. The large variation of valence band maximum energy can be explained by the different orbital contributions to the density of states in the valence band. The framework provided by this work enables the general understanding and prediction of energy band alignment at oxide interfaces, and furthermore the tailoring of energy level matching for charge transfer in functional oxides. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Accurate control of residual defect density is required for reliable investigation and use of ferroelectric materials. After reviewing the long term endeavor to decrease defect contributions in bulk materials, which reached mass production decades ago, recent challenges are underlined. These mostly result from the continuous trend towards integration which has reached the nanometre range. The contribution of solid state chemistry is of key relevance for improving the present processing routes and suggesting alternative ones, for example by controlling a large density of charged defects to reach unprecedented functionalities. Some of these breakthroughs are reviewed.