Electrical properties of annealed, fully metamict REE2Fe2+Be2Si2O10

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 Mössbauer 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.