Effect of fluoride doping on impedance spectra of barium strontium titanate glass ceramics

A system of barium strontium titanate glass ceramics with different fluoride concentrations were prepared by melt-annealing technique. The effect of fluoride doping on impedance spectra of the barium strontium titanate glass ceramics were investigated. According to the impedance spectroscopy studies, three (low, middle, and high frequency) electrical responses, which corresponds to glass phase, crystal–glass interface and crystal interior were identified. It is shown that with the increase of fluoride concentration, the resistivity of the glass phase passed through a minimum and then increased. In addition, the capacitance of the crystal–glass interface increased and the capacitance of the crystal phase decreased with the increase of the fluoride concentration. Moreover, as a result of ac conductivity calculation and analysis, it is believed that the dc conduction was affected by the glass and crystal–glass interface regions and ac regime was attributed to the crystal phase. Based on the results, a change of the compensation mechanism from electronic to ionic one with variation in fluoride concentration was proposed.