Structural fluctuations of SrTiO3 in the cubic phase

We studied thermal vibrations of SrTiO 3 by means of X-ray structure analysis at many temperatures in the cubic phase. In contrast to the cubic BaTiO 3 , no structural disordering is found at all. Thermal vibrations of the O atom in the face centered plane become large when approaching a structural phase transition temperature T t = 105 K, indicating a twisting motion of the TiO 6 octahedron due to the R 2 5 mode. The twisting angle at T t is estimated at about 0. 9°. An anharmonic atom-potential analysis reveals that, in addition to the softening of the R 2 5 mode, the thermal vibrations perpendicular to the face centered plane become soft for the O and Ti atoms. This thermal motion is explained by the ferroelectric soft mode which remains stabilized down to O K by a quantum paraelectric effect.