DIELECTRIC-DISPERSION AND IMPEDANCE RELAXATION IN LI2B4O7 SINGLE-CRYSTALS

The complex dielectric constant and impedance in Li2B4O7 single crysta ls were measured over the temperature range 30-degrees-C approximately 700-degrees-C at several frequencies. Anomalous behaviors of the real part of the dielectric constant epsilon' were observed in the tempera ture range from 100-degrees-C to 500-degrees-C. Analyzing the impedanc e Cole-Cole plot, we have found two different conduction mechanisms, w hich have different activation energies DELTA1=0.36 eV and DELTA2=0.97 eV. The equivalent circuit and dc bias effect were adopted to explain the impedance relaxational behavior. We suggest that the impedance re laxation in the high-frequency region is due to hopping of Li+ ions an d that in the low-frequency region it is due to space-charge relaxatio n. Also, it seems that the origin of dielectric dispersions is due to the two different conduction mechanisms.