Electrical properties of annealed, fully metamict REE2Fe2+Be2Si2O10

Highlights: → Alpha-decays occurring in the gadolinite structure made it more open in comparison to other non-metamict silicates due to significant fractality of the structure. → Results presented in our work suggest that electric current relaxation in the higher temperature range is a consequence of the hydroxyl group dynamics. → For the lower temperature range, we propose VRH of small polarons as the mechanism. - Abstract: The electrical properties of annealed, fully metamict gadolinite REEFe2+Be2Si2O10 are studied as a function of annealing temperature. Changes due to annealing are also probed by 57Fe Moessbauer spectroscopy and X-ray diffraction. The electrical conductivity measured at f = 100 Hz between 110 and 750 K varies markedly, ranging from 10-10 to 10-6 S m-1 for untreated samples and 10-9 to 10-3 S m-1 for sample annealed in argon at 1373 K. Average measured activation energies for electrical conduction are 0.47 and 0.63 eV for ranges of 400-450 K and 500-600 K, respectively. The dielectric permittivity shows strong dispersion effects above 235 K. After high temperature annealing, the electrical conductivity shows a marked dispersion below 604 K. The combination of polaron hopping and hydroxyl anion migration is proposed for the electrical conduction mechanism.