On the quantification of hydrogen in lithium metal oxides

Abstract

Hydrogen incorporation during crystal growth or other treatment has attracted research interest for a long time, but inconsistent literature data exist about the bulk hydrogen concentration in the lithium metal oxides LiMO₃ with M = Nb and Ta. Hydrogen binds to oxygen and forms hydroxyl groups (OH⁻), which can be easily detected optically by FT-IR spectroscopy. However, this method cannot determine an absolute hydrogen concentration. With a reliably characterised concentration reference, a calibration for the fast and non-destructive FT-IR spectroscopy could be obtained. In this study, the hydrogen contents of as-grown and hydrogen-doped congruent and near-stoichiometric LiMO₃ crystals were investigated by elastic recoil detection analysis (ERDA), carrier gas hot extraction (CGHE), ¹H magic angle spinning nuclear magnetic resonance (¹H MAS NMR) and hydrogen microscopy via proton–proton (p–p) scattering. However, not every method is suitable for the investigation of hydrogen in the LiMO₃ host lattices. Based on p–p scattering, the A/c_H calibration factors for FT-IR spectroscopy can be specified with (4.52 ± 0.58) × 10⁻¹⁷ cm and (6.46 ± 0.96) × 10⁻¹⁷ cm for LiNbO₃ and LiTaO₃, respectively.