LOCAL DISORDER STUDIED IN SRTIO3 AT LOW-TEMPERATURE BY EXAFS SPECTROSCOPY

The temperature dependence of the local distortions in SrTiO3 has been studied by EXAFS spectroscopy at the titanium K edge (4982 eV). The o xygen-ion Debye-Waller factor al has been determined from 4.5 to 240 K . The antiferrodistortive transition at 105 K is evidenced by a step i n this Debye-Waller factor. At about 31 K, a maximum of sigma0(2) is d etected and the EXAFS oscillations due to the first oxygen shell incre ase. This is the signature of a maximum disorder in the lattice vibrat ions in this temperature range. A quasiharmonic model with a sinusoida l modulation of the Ti-O distance cannot account for these observation s. The lattice and electronic excitations which could support our data are qualitatively described.