Vibrational spectra and force field studies of Ki,i25Rbi,875La(VO4)2 vanadate

This work is focused on the vibrational study of K1125Rb1 875La(VO4)2 vanadate (space group P2i/m). The infrared and Raman spectra have been interpreted in molecular group (Td) according to previous works. A previously X-rays diffraction study shows that this compound presents two non homologous VO4 in the unit cell. The vibrationnal spectra can not permit to distinguish between the vibrations of each kind of vanadate. So a force-field calculation has been made in order to make a separation between the vibrations of the two different VO4 and to complete the interpretation in the factor group (C2h).