ELECTRIC CONDUCTION OF SINGLE-CRYSTAL AND GLASS OF LI2B4O7

The dc and ac conductivity of single crystal and glass of Li2B4O7 have been measured at various temperatures. It has been shown that these materials are mixed conductors in which electronic and ionic conduction coexist. In the single crystals, both the electronic conduction and ionic conduction along the c axis are much smaller than that perpendicular to the c axis. The anisotropy in the electronic conduction is considered to be due to the conduction by the pi electron of the BO3 layer located on the (001) crystallographic plane. The anisotropy in the ionic conduction is also considered to be due to the diffusion of Li ions and/or protons between the BO3 layers. The thermal activation energies of the electronic conduction were 0.65 eV for glass, 1.61 eV for the crystal parallel to the c axis, and 0.78 eV for the crystal perpendicular to the c axis. The activation energy of the ionic conduction was 0.46 eV for the crystal perpendicular to the c axis.