FAR-INFRARED SPECTROSCOPY OF A SRTIO3 THIN-FILM

Far-infrared transmittance of a SrTiO3 thin film deposited on a sapphi re substrate by laser ablation was measured in the frequency range 25- 200 cm(-1) at temperatures from 5K up to 300 K. An interesting differe nce between the temperature behaviour of the polar soft mode in the th in him and the one in bulk material was observed. Below the structural transition near 105 K the mode stops softening and its damping increa ses on further cooling. The values of the total low-frequency permitti vity in the film are substantially lower than those in bulk SrTiO3. Th e suggested explanation is based on the fact that the film contains re levant internal stress.