Vibrational spectrum of nasicon-like, rhombohedral orthophosphates MIMIV2(PO4)3

The Raman and i.r. spectra of nasicon-type MIMIV2(PO4)3 rhombohedral phosphates (MI = Li, Na, K, Rb, Cs, Tl; MIV = Ge, Sn, Ti, Zr, Hf) exhibit intricate relationships between the spectra and the chemical composition. The pattern of the PO4 stretching frequencies is more or less strongly modified by the nature of both MIV and MI cations. Still greater variations are observed in the medium and low frequency region, although some external modes have been identified by the study of mass effects (6Li7Li, 70Ge76Ge, ZrHf etc.). The origin of this complex behaviour is discussed in relation to the structure. © 1986.