We measured phonon dispersion in single crystal EuTiO3 using inelastic x-ray scattering. A structural transition to an antiferrodistortive phase was found at a critical temperature T0=287±1 K using powder and single-crystal x-ray diffraction. Clear softening of the zone boundary \emph{R}-point \textbf{q}=(0.5 0.5 0.5) acoustic phonon shows this to be a displacive transition. The mode energy plotted against reduced temperature could be seen to nearly overlap that of SrTiO3, suggesting a universal scaling relation. Phonon dispersion was measured along Γ-X (0 0 0)→(0.5 0 0). Mode eigenvectors were obtained from a shell model consistent with the \textbf{q}-dependence of intensity and energy, which also showed that the dispersion is nominally the same as in SrTiO3 at room temperature, but corrected for mass. The lowest energy optical mode, determined to be of Slater character, softens approximately linearly with temperature until the 70-100 K range where the softening stops, and at low temperature, the mode disperses linearly near the zone center.
@article{arxiv.1210.2014,
title = {Phonon Softening and Dispersion in EuTiO3},
author = {David S. Ellis and Hiroshi Uchiyama and Satoshi Tsutsui and Kunihisa Sugimoto and Kenichi Kato and Daisuke Ishikawa and Alfred Q. R. Baron},
journal= {arXiv preprint arXiv:1210.2014},
year = {2015}
}