LATTICE PERTURBATIONS IN CAWO4 AND CAMOO4

Frequency assignments for the vibrational modes of species Bu in CaWO4 and CaMoO4 are made. Bu modes are both infrared inactive and Raman inactive in unstrained material, but become infrared active and exhibit Eu characteristics under xz or yz shear strain and Au characteristics under xy shear strain. In the present paper previously published infrared data are interpreted in terms of strain-induced mode mixing, and the nature of the crystalline strain is discussed. The assignment of the three Bu modes in CaWO4 completes the task of identifying the 18 internal modes of the WO4- ions.