High-frequency dielectric response of SrTiO sub(3) crystals, ceramics and thin films

Far infrared (FIR) soft-mode dielectric responses of bulk SrTiO sub(3) single crystal, flux-grown plate-like crystal, bulk ceramics and several thin films in 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 approx. 60 cm super(-1). The reason for it is connected mainly with internal stresses induced by the transition, however quantitative estimates are missing. Soft mode spectroscopy is shown to be extremely sensitive to the quality of the film.