zone centre $\Gamma$ is also less pronounced than the $q \rightarrow 0$ behaviour reported by Watanabe *et al.* [@Watanabe14] using ultrasound sensitive to acoustic fluctuations on the MHz timescale.

![image](gx_gk){width="100.00000%"}

The detailed temperature dependence of two TA2 phonons at $q = \left(\overline{0.075}\ 0.075\ 0\right)$, $q = \left(\overline{0.3}\ 0.3\ 0\right)$, and $q=\left( \overline{\frac{1}{2}} \frac{1}{2} 0 \right)$ are shown in Fig. \[fig:detailscan\]. Both the modes at small and large $q$ soften by ca. 0.1 meV and 0.4 meV, respectively, when entering the cubic phase. For $T_{OO} < T < 200 $ K, the low-$q$ phonons harden by ca 0.2 meV, while the large-$q$ modes further soften by ca. 0.2 meV.

![\[fig:detailscan\] The dispersion of the TA2 phonons softens and hardens at $q = (\overline{0.075}\ 0.075\ 0)$ (top) and $q = (\overline{0.5}\ 0.5\ 0)$ (bottom), respectively, when approaching the cubic-tetragonal phase transition near $T_{OO} = 63$ K from high temperatures. For $q = (\overline{0.3}\ 0.3\ 0)$ (middle) there is no change in phonon energies in the $T > T_{OO}$ region. Please note that at MIRA we measured using neutron energy gain ($-E$) for reasons of analyser efficiency and angular constraints at the instrument. The physics of the system is unaffected by this choice. 