Lattice dynamics and high-pressure Raman scattering studies of CoTeMoO6 crystal

We have performed lattice dynamics calculations for CoTeMoO6 telluromolybdate and proposed assignment of modes to respective vibrations of atoms in the unit cell. We have also performed pressure-dependent Raman scattering studies that revealed unusual negative pressure dependence of the highest wavenumber modes. We provide explanation of this behavior based on strongly layered nature of CoTeMoO6 crystal. High-pressure data also indicate weak compressibility of the TeO4 groups associated with large changes in the MoOTe bridges. The spectra remain qualitatively the same up to 6.3 GPa but some very subtle changes in the spectra have been observed near 2.6-3.0 GPa that might indicate onset of a very subtle structural transformation in the studied crystal.