The infrared lattice spectra from 700 to 50 cm-1 of eight cubic rare earth oxides are reported. It is evident from these data that the crystal structure determines the frequency position, and clearly shows the effect of the lanthanide contraction in this series of compounds.
NEIL T. McDEVITT and A. D. DAVIDSON, "Infrared Lattice Spectra of Cubic Rare Earth Oxides in the Region 700 to 50 cm-1," J. Opt. Soc. Am. 56, 636-638 (1966)