separated from other contributions, e.g. incoherent scattering. Fig. \[fig:energies\] summarises the results of all phonon measurements that were conducted at various temperatures in the range $10$ K $\le T \le 200$ K. A transverse optic phonon branch is visible at $E \approx 20\,\mathrm{meV}$ near the zone boundary. Attempts using both triple-axis and time of flight measurements failed to track this mode closer to the zone centre.

![\[fig:scans\] Typical data for transverse phonons TA1 and TA2 are shown for $T = 10$ K and $T = 80$ K. There is a clear softening of the TA2 mode in the cubic phase when compared with the low temperature tetragonal phase. ](samplescans){width="1\columnwidth"}

The dispersion of the LA and TA1 phonon branches do not show appreciable changes between the cubic and the tetragonal phases. In contrast, the TA2 branch exhibits an observable $T$-dependence. At intermediate $q$-values, the dispersion shows a “spoon-like” anomalous behaviour, i.e. the phonons soften in energy when entering the cubic phase for $T > T_{OO}$. While the data is suggestive of a softening in energy of the TA2 phonon near the zone centre, the effect is not as large as at intermediate wavevectors. The effect at small $q$ close to the 