Revisiting the configurations of hydrogen impurities in SrTiO3: Insights from first-principles local vibration mode calculations

TL;DR

This study uses first-principles calculations to clarify hydrogen impurity configurations in SrTiO3, revealing which complexes match experimental vibrational spectra and emphasizing the importance of accurate functionals.

Contribution

It systematically investigates hydrogen impurity configurations in SrTiO3 using hybrid functionals, providing new insights into their vibrational properties and experimental relevance.

Findings

Interstitial hydrogen is unlikely to account for dominant IR bands.

Strontium vacancy complexes with hydrogen match main absorption bands.

Titanium vacancy complexes with two hydrogen relate to additional IR features.

Abstract

The specific configurations of hydrogen impurities in SrTiO3 (STO) are still ambiguous. In this study, we systematically investigate the configurations and vibrational properties of hy-drogen impurities in cubic STO using first-principles local vibration mode calculations. Em-ploying the appropriate hybrid exchange correlation functional with the fraction of exact ex-change setting to 0.2, we revisit the interstitial hydrogen (Hi), Hi complexes (2Hi), and various intrinsic cation vacancy complexes with Hi, including VSr-Hi, VSr-2Hi, VTi-Hi, and VTi-2Hi. Comparison of the computed vibrational frequencies with experimental infrared absorption bands reveals that Hi, with a frequency of 3277 cm-1, is unlikely to account for the dominant absorption bands near 3500 cm-1. Instead, strontium vacancy complexes with interstitial hydro-gen (VSr-Hi and VSr-2Hi) exhibit vibrational frequencies that align with the main absorption bands, whereas titanium vacancy complex with two interstitial hydrogen (VTi-2Hi) corresponds to additional absorption bands around 3300 cm-1. These findings provide insights into the im-portance of hydrogen-related complexes in governing the electronic properties of STO, and meanwhile underscore the necessity of employing accurate exchange correlation functionals for reliable theoretical predictions of vibrational properties.