SHORT-RANGE ORDER AND F- ION DIFFUSION INSIDE THE PB1-XALXF2-SOLUTION.1. F-19-NMR INVESTIGATION(X SOLID)

A F-19-NMR investigation of the Pb1-xAlxF2+x (0 less than or equal to x less than or equal to 0.12) solid solution and of the ordered Pb9Al2 F24 phase is undertaken as a function of temperature. Several F-ion gr oups become progressively mobile at the NMR time scale at increasing t emperature, the first, (F-i)(Pb) and (F-n)(Pb), are located in the sur roundings of Pb2+ cations, the second ones, (F-rd)(Al) and (F-ra)(Al), in that of Al3+ cations. Four types of fluoride ions are distinguishe d in the F-19-NMR spectra of rigid lattice at low temperature (T = 175 K) and the distribution of fluoride ions among the four sites is dete rmined by deconvolution of the spectra registered. The sites occupied by the (F-n)(Pb) anions an identified with the normal anionic sites of the fluorite network, the others with different interstitial sites.