David S. Ellis, Hiroshi Uchiyama, Satoshi Tsutsui, Kunihisa Sugimoto, Kenichi Kato, Daisuke Ishikawa, Alfred Q. R. Baron
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 R (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 Gamma-X (0 0 0)->(0.5 0 0) and a shell model showed that the dispersion is nominally the same as in SrTiO3 at room temperature, but corrected for mass. As the temperature is brought lower into the tetragonal phase, the spectral weight of the lowest energy mode is down-shifted, and at low temperature, the lowest energy optic mode disperses linearly, characteristic of a soft mode. However, from fine structure in the spectra, there may be more than one mode responsible for the observed spectral weight shift.
View original:
http://arxiv.org/abs/1210.2014
No comments:
Post a Comment