Hydrogen trapping in oxygen-deficient hafnium silicates

Isotopic substitution, nuclear reaction analysis, and x-ray photoelectron spectroscopy were employed to show that oxygen-deficient hafnium (Hf) silicates trap hydrogen atoms. Based on this experimental observation, we used first-principles calculations to investigate the structure, energetics, and electronic properties of H interacting with O vacancies in a hafnium silicate model. We found that O vacancies close to a Si atom are energetically favored when compared to vacancies in HfO2-like regions, implying that close-to-Si O vacancies are more likely to occur. Trapping of two H atoms at a close-to-Si O vacancy passivates the vacancy-induced gap states. The first H interacts with neighboring Hf atoms, whereas the second H binds to the Si atom.