The IR and Raman spectra of tellurates Ln3Te,Li30,, (Ln-Pr..
.Lu, Y), Ca3TelZn,0,, and Na3TezM:+0,, (M" = Al, Ga, Fe) with the garnet structure are presented and discussed on the basis of a group theoretical analysis, and of 6Li-7Li isotopic frequency shifts. The assignment of the high-frequency bands to stretching vibrations of the TeO, octahedra is only an approximation whose validity depends on the nature of the tetrahedral cation (Li, Zn or M3+) and of the symmetry properties of the vibrations: cationic mass effects play an important role in the antisymmetric, IR-active vibrations, whereas the bonding forces are the determining factor in the totally symmetric, Raman active vibrations. For the Na3Te2M~Ou garnets, the (TeO,) internal modes approximation is unacceptable since the stretching frequencies of the TeOd and M3+04 groups are of the same order of magnitude. No detailed assignments are available for the medium-frequency bands: they are due in part to the bending vibrations of the TeO, octahedra, but the contribution of the tetrahedral cation Zn2+ or M"+ to this region of the spectrum remains largely unknown. The translational frequencies of the dodecahedral Ln3+ cations have been identified in the low frequency region (below 250 cm-') by comparison of the frequencies of the Ln and Y garnets.