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 F1, F2, and F3 sublattices, while highly mobile F1 fluorine ions move independently at least until 400 K.

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