Ionic conductivity and 19F NMR investigations of some series of ZrF 4-based fluoride glasses containing LaF 3 or YF 3

Abstract

A comparative study of transport properties of two series of fluoride glasses ZrF 4(0.55)AlF 3(0.04) BaF 2(0.385 − x)LaF 3(0.025 + x) (0.00 ≲ x ≲ 0.07) and ZrF 4(0.55)AlF 3(0.04)BaF 2(0.37 − x)YF 3(0.04 + x) (0.00 ≲ x ≲ 0.05) has been carried out as a function of x. The ac conductivity data have been analyzed by the complex modulus formalism. An Arrhenius behavior is shown for dc conductivity and modulus relaxation time with very close activation energies, and a hopping mechanism for transport in these materials is suggested. A 19F NMR investigation showed that the NMR line is due to the existence of differing fluoride ion sublattices and that a partial exchange occurs between with increasing temperature. The deconvolution of spectra measured at low temperature is composed of two peaks which have been interpreted in terms of non-bridging and bridging fluoride ions. Composition dependence of dc conductivity, conductivity relaxation time and 19F NMR lines indicate an enhancement of electrical performance with an increase of BaF 2.