A strong and thermally stable ionic thermo-current band, which peaked at 316K, was observed in Eu-free crystals. It was found that the resultant ionic thermo-current spectrum could be described by an Arrhenius relationship; with an attempt frequency of 1.90 x 10-13 s and an activation energy of 0.93eV. The new band was very sensitive to Eu doping, and the ionic thermo-current peak intensity was markedly reduced by the addition of only 0.002mol%Eu. At the same time, a high-temperature ionic thermo-current band which was due to mobile interstitial F ions appeared at 416K. A fading of the new band at 316K was explained by assuming that mobile F vacancies were compensated by F ions which were introduced as charge compensators for the trivalent Eu ions.

K.Tanaka, Q.Zhuang, K.Tanaka, K.Kawano, R.Nakata: Journal of the Physics and Chemistry of Solids, 1996, 57[3], 307-14