High-frequency dielectric response of SrTiO3 crystals, ceramics and thin films

Far infrared (FIR) soft-mode dielectric responses of bulk SrTiO3 single cry stal, flux-grown plate-like crystal, bulk ceramics and several thin films i n the 10-300 K range are measured and compared. Huge differences among the samples are observed, particularly below the antiferrodistortive transition , where the soft mode frequency in films and ceramics levels off near simil ar to 60 cm(-1). The reason for it is connected mainly with internal stress es induced by the transition, however quantitative estimates are missing. S oft mode spectroscopy is shown to be extremely sensitive to the quality of the film.