Fluorine mobility in an aluminum-doped CeF3 crystal:: NMR and conductivity studies

Electrical conductivity and NMR measurements were carried out for an aluminum-doped CeF3 crystal to study the influence of substitutional impurities on the superionic fluorine mobility. Activation enthalpy was found to remain constant from low temperatures to about 325 K and to increase as compared to that of a pure CeF3 crystal. Above about 325 K, a trend towards gradual conductivity saturation was observed. This change was ascribed to a superionic phase transition not accompanied by structural transformations. NMR also revealed some alterations in the local fluorine dynamics as compared to that reported for a pure CeF3 crystal. According to NMR measurements, the superionic phase transition near 325 K results in acceleration of the exchange between rigid or slow fluorine in the F-1, F-2, and F-3 sublattices, while highly mobile F-1 fluorine ions move independently at least until 400 K. (C) 2004 MAIK Nauka/Interperiodica.