Synchrotron X-ray Study of Lattice Vibrations in CdCr2O4

Using inelastic x-ray scattering we have investigated lattice vibrations in a geometric frustrated system CdCr 2 O 4 that upon cooling undergoes a spin-Peierls phase transition at $T_{\text{N}} = 7.8$ K from a cubic and paramagnetic to a tetragonal and Neél state. Phonon modes measured around Brillouin zone boundaries show energy shifts when the transition occurs. Our analysis shows that the shifting can be understood as the ordinary effects of the lowering of the crystal symmetry.