Hydrogen Donors in Anatase TiO2

Abstract

Two hydrogen‐related donors in anatase —interstitial hydrogen () and hydrogen substituting for oxygen ()—are addressed by means of ab initio density functional theory and vibrational mode spectroscopy. First‐principles calculations and infrared (IR) absorption measurements reveal that forms an OH bond lying in the basal plane of the crystal characterized by a stretch local vibrational mode (LVM) with a frequency of 3412 . According to the calculations, the vibrational spectrum of the threefold‐coordinated hydrogen in includes two stretch LVMs with the frequencies of 1014 and 1294 . The theoretically predicted modes occur within the strong two‐phonon absorption band of , so the conclusions of theory cannot be verified by conventional IR absorption spectroscopy. In accordance with experimental findings, is shown to be unstable at room temperature, whereby formation of interstitial should be a preferential sink for hydrogen in defect‐free anatase. It is also found that of , , and , the latter is the most energetically favorable defect, which may account for the “hidden” hydrogen unavailable for the standard spectroscopic techniques.