The vibrational spectra and structures of rare earth oxides in the A modification

Crystallographic studies of La 2 O 3 and the oxides isostructural with it have failed to decide between noncentrosymmetric space group D 3 2 (P321) and the centrosymmetric space group D 3d 3 (P3m1) for their structure. The infrared and Raman spectra of La 2 O 3 and Nd 2 O 3 have been obtained and the absence of coincidences between the spectra unequivocally favours the centrosymmetric space group. The vibrational spectra have been analysed using the Wilson FG matrix method and force constants for metal-oxygen and oxygen-oxygen interactions derived, assuming a quadratic central force field.