High-resolution infrared spectroscopy of hydrogen impurities in strontium titanate

A high-resolution infrared spectroscopic investigation of structure related to the O-H dipole stretching mode (around 3500 ${\mathrm{cm}}^{\mathrm{-}1}$) was carried out in ${\mathrm{SrTiO}}_3$. We discuss various models for the position of the hydrogen impurity in the matrix and justify the position that we have suggested in a previous paper. With this new assignment, we discuss the 16 highest intensity peaks observed at low temperature. The high-energy satellites are interpreted as arising from the absorption of hydrogen impurities located on inequivalent sites. These sites are made inequivalent by a combination of the antiferrodistortive transition at 105 K and the ferroelectric fluctuations that become important when the temperature decreases.