RAMAN-SCATTERING STUDY OF SRTIO3 AT HIGH-PRESSURE

The pressure dependence of the Raman spectra of SrTiO3 was investigate d up to 15.5 GPa. The anti-ferrodistortive cubic-tetragonal phase tran sition (phonon condensation at the R point of the Brillouin zone) occu rs at about 6 GPa. The strong, broad bands, present under ambient cond itions, sharpen and change their profile with increasing pressure. The y diminish rapidly in their intensity above 13 GPa and disappear by 15 .5 GPa. These pressure-induced changes can be due to increasing harmon icity of the stretching and bending Ti-O vibrations, leading to reduce d intensity of the second-order Raman scattering, and/or due to the in hibition of the off-center dynamic distortions at the Ti4+ cation site s, and thus due to the decrease in intensity of the 'disorder-induced' first-order Raman scattering. The spectrum at 15.5 GPa shows weak ban d splittings, which might indicate a further transformation to an orth orhombic phase of SrTiO3. (C) 1997 John Wiley & Sons, Ltd.