Vibrational spectra and factor group analysis of lanthanide and zirconium phosphates MIII0.33Zr2(PO4)3, where MIII = Y, La–Lu

Double anhydrous orthophosphates of zirconium and rare earth elements with general formula MIII0.33Zr2(PO4)3, where MIII = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, belonging to the structure type of NaZr2(PO4)3 (NZP), have been synthesized by precipitation method and characterized by Raman and infrared spectroscopy in a crystalline state. Factor group analysis has been carried out for space groups P3¯, P3¯c1. On the basis of the analysis of possible PO4 unit vibrations and considering symmetry interrelations among trigonal NZP phases it was shown that due to ordered (Y, Ce–Lu) or quasiordered (La) distribution of lanthanide atoms in the structure type of NaZr2(PO4)3, sp. gr. R3¯c, leads to the reduction of the symmetry to the space groups P3¯c1 or P3¯ correspondingly. The assignments of the internal and external modes of PO43− ions have been made.