Strontium Titanate (SrTiO3)

Abstract

Strontium Titanate (SrTiO 3 ) crystallizes in the cubic perovskite structure. Therefore, the optical properties of this material are isotropic. SrTiO 3 behaves like a ferroelectric material in the paraelectric phase. This property is referred to as incipient ferroelectric. The hypothetical Curie temperature takes place just below the absolute-zero temperature. As a result, the dielectric constant is strongly dependent on temperature and increases by a factor as large as 10 when the sample is cooled from room temperature to liquid-helium temperature. As the dielectric constant is the extrapolation down to zero frequency of the dielectric response optical constants also vary with temperature but mainly in the far infrared. This chapter provides an overview of the optical properties of SrTiO 3 and reviews the data related to optical constants of this material. Doping with Nb 5+ or reduction of strontium titanate confers semiconducting properties to the material. Then the absorption related to free carriers drastically modifies the optical constants in the infrared depending on the doping level. In the infrared range, the reflectivity measurements performed on a sintered and polished strontium–titanate ceramic sample are practically indistinguishable from those performed on a single crystal. The chapter presents the data that are obtained from the studies on single crystals, which are also valid for ceramics.