The pressure response of Raman active phonon modes of Tm3Al5O12

We present the Raman spectrum of Tm3Al5O12 single crystal and its pressure dependence for hydrostatic pressure up to 11 GPa and room temperature. Tm3A l5O12 belongs to the crystal family of rare earth garnets (Re3Al2(AlO4)(3), Re: Gd, Tb, Dy, Er,...), which crystallize in the body-centered cubic latt ice and contains eight molecular units in the conventional unit cell. Group theory predicts 25 Raman active modes for these compounds, while experimen tally are observed 15 modes. As crystal volume decreases all Raman peaks ex hibit pressure coefficients varying from 0.7 to 5.6 cm(-1)/GPa. A large par t of the vibrational spectra of these compounds could be explained taking i nto account the vibrational properties of molecular subunits, namely AlO4.