Shallow donor level associated with hydrogen impurities in undoped BaTiO3

The influence of hydrogen impurities on the electronic properties of undoped BaTiO3 was studied from a microscopic point of view using the muon spin rotation and relaxation technique. Electron localization around an implanted positive muon, by analogy a hydrogen impurity, was observed below ∼80 K. The effective electron binding energy was estimated to be ∼10−2 eV, indicating that the hydrogen-induced defect forms a shallow donor level. At room temperature, the weakly bound electron is excited into the conduction band and behaves as a free carrier, which causes insulation degradation undesirable for capacitor applications.