Zr-EXAFS study of fluoride ion-conducting ZrF 4-BaF 2-CsF glasses

Abstract

Fluorine coordination environment around zirconium in fluoride ion-conducting 55ZrF 4·(45- x)BaF 2· xCsF glasses was investigated by means of Zr-EXAFS spectroscopy using SOR. EXAFS experiments were carried out on glasses of x=0, 7, 14, 20, 27, 34 and 40, and crystalline Li 2 ZrF 6. The Zr-F peaks in the Fourier transform magnitude curves of glasses shifted to shorter distances with the substitution of CsF for BaF 2. In the Zr-F peaks of the x=27, 34 and 40 glasses, at the same time, small but discernible shoulders emerged at the right sides of the peaks, growing more prominently in this order. The Fourier backfiltering and curve fitting treatments of these Zr-F peaks revealed that, although the F coordination numbers of Zr hardly vary with the substitution of CsF for BaF 2, the Zr-F interatomic distances split into two largely different ones with the substitution of CsF more than about 20 mol%. For instance, the Zr-F interatomic distances and the F numbers at the distances were 2.07 Å/6.5 in the 55ZrF 4·45BaF 2 glass, 2.06 Å/6.4 and 2.27 Å/0.6 in the 55ZrF 4·18BaF 2·27CsF glass, and 2.05 Å/5.1 and 2.23 Å/1.9 in the 55ZrF 4·5BaF 2·40CsF glass. The present Zr-EXAFS result may give an interpretation for the anomalous compositional dependence of the activation energy for conduction in electrical conductivity that was previously observed for ZrF 4-BaF 2-CsF glasses.