Mid-infrared and near-infrared properties of SrTiO3 from transmission and reflection measurements

We measured transmittance and reflectance spectra of commercial SrTiO3 crystals in the infrared region (25-12 000 cm(-1)). The reflectance R(v) spectra confirm recent results. The transmittance T(v) spectra show that SrTiO, is transparent above 1000 cm(-1), while the model usually employed to describe the complex dielectric function of SrTiO3 predicts a negligible transmittance in all the infrared region. By combining T(v) and R(v) spectra, we directly determine the frequency dependence of the refractive indices n and k which accounts for the spectra measured in the mid-infrared and near-infrared range. This result will be important for a correct analysis of the infrared spectra of films deposited on SrTiO3.