Chemical environment and occupation sites of hydrogen in LiMO₃

Abstract

A description of the hydrogen occupation site in LiNbO3 and LiTaO3 is made based on theoretical structural models and validated by measured OH− stretching vibrational modes.

On the quantification of hydrogen in lithium metal oxides

“…It can be seen from Table 1 that no difference between the as-grown and protonated states of C-LiTaO 3 and C-LiNbO 3 can be found within the measurement uncertainty (see ESI S1† for more information on error estimation). However, from the known infrared absorption data 16,17,52–54,88 and also from the data presented in this study (see Section 7), a significant difference is expected between the as-grown and the protonated states, but also between the hydrogen concentration of congruent and near-stoichiometric crystals. In particular, the near-stoichiometric crystals show a very weak OH − absorption band, indicating a significantly lower H concentration than in the congruent material.…”

“…The presence of defect clusters and the preferential decoration of lithium vacancies with hydrogen is considered as the reason for the strong inhomogeneous line broadening. 52 In contrast to the congruent crystals, the concentration of intrinsic defects should be signicantly lower in the near-stoichiometric materials. The spectra show a dominant narrow component at ∼3460 cm −1 (see inset (1) for NST-LiTaO 3 in Fig.…”

“…16,17,53,54,88,[157][158][159] Beginning from a high quality nearstoichiometric crystal towards congruent composition, strong inhomogeneous broadening mechanisms are observed due to the intrinsic defects. 15,52 Thus, discrepancies can easily arise when comparing two different crystal stoichiometries. In this work, the A/c H parameter is used as a more suitable calibration factor due to the proportionality between the total OH − absorption band area and the hydrogen concentration.…”

“…The OH − absorption band shape in LiMO 3 crystals is composed of several sub-bands, which arise from the hydrogen decoration of defects and thus the shape changes depending on the crystal stoichiometry. 17,52,53,146 For this reason, we use the total integrated area of the vibrational bands to provide the calibration factor for LiMO 3 using the concentration measurements described above. For the specied error bars of the integral band areas in this study, the relative error of ∼2% from a reference measurement series of 15 single measurements is used.…”

“…15,43,[46][47][48][49][50][51] Recently, experimental and theoretical approaches have been used to show that hydrogen preferentially decorates other material defects. 52 For congruent material the hydrogen preferentially occupies the oxygen in the vicinity of a lithium vacancy V 0 Li . In the near-stoichiometric material hydrogen decorates extrinsic defects on regular Li lattice sites.…”