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arXiv · 1210.2014

Phonon Softening and Dispersion in EuTiO3

David S. Ellis·Hiroshi Uchiyama·Satoshi Tsutsui·Kunihisa Sugimoto·Kenichi Kato·Daisuke Ishikawa·Alfred Q. R. Baron
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Abstract

We measured phonon dispersion in single crystal EuTiO$_3$ using inelastic x-ray scattering. A structural transition to an antiferrodistortive phase was found at a critical temperature $T_0$=287$\pm$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 $\rm SrTiO_3$, suggesting a universal scaling relation. Phonon dispersion was measured along $Γ$-$X$ (0 0 0)$\rightarrow$(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 $\rm SrTiO_3$ 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.

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David S. Ellis, Hiroshi Uchiyama, Satoshi Tsutsui, Kunihisa Sugimoto, Kenichi Kato, Daisuke Ishikawa, Alfred Q. R. Baron. 2012-11-13. Phonon Softening and Dispersion in EuTiO3. https://doi.org/10.1103/physrevb.86.220301

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