Infrared and Raman measurements are reported for the lattice vibration modes of the fast ion conductors M gallate and M gallate where M is Na, K, Rb, Ag, or Tl, and are compared with similar measurements for -aluminate. The transverse- and longitudinal-optic modes are obtained from the infrared reflectivity. The exclusion principle states that for crystals with a center of inversion the infrared and Raman modes transform as different irreducible representations and hence have different frequencies. By comparing the experimental results for a given M, it can be seen that the exclusion principle is obeyed for the high-frequency modes for both the gallates and the aluminates. However, for the lowest-frequency modes the gallates still appear to obey the exclusion principle, but the aluminates do not. The corresponding frequencies in the gallates and aluminates are compared with comments on the lowest-frequency modes. The complete polarized Raman spectra for one K -gallate crystal was measured. The results compare favorably with the published results for Na -aluminate. © 1980 The American Physical Society.