Crystallization process and dielectric property of amorphous (Li1−xNax)2B4O7

We prepared amorphous (Li1−xNax)2B4O7 and measured thermal and dielectric properties to investigate the mixed alkali effects. Differential scanning calorimetry in the temperature range from 303 to 873 K and impedance/gain-phase analysis in the frequency range from 100 Hz to 15 MHz was used for the measurements of structural and dielectric changes. We have observed a mixed alkali effect from the anomalous change of the glass transition and crystallization temperatures. Dielectric properties in frequency and temperature domains have been analyzed by using the power law. We have found that there is a strong non-linearity of the electrical conduction with the Na concentration. The Na concentration dependence of the activation energy of the dc conductivity also shows a mixed alkali effect and the effect is understood with the structural random ion distribution model.