Calculation of the ionic conductivity of h-BN and its effect on the dielectric loss

By using an ab initio local-density approach and considering the defect locations of substitutional sites and midplane sites in hexagonal boron nitride (h-BN) graphite structure, the defect formation energies of N, O, C ions in h-BN ceramic and then the ionic conductivities are calculated. On comparing with the experimental results, it is indicated that the main contribution of ionic conductivity is due to the oxygen ionic defects. At high temperatures, no loss peak is observed in the measured dielectric loss spectrum, because the large conduction loss may obscure the loss peaks, which reflect the intrinsic dielectric relaxation. By eliminating the conduction loss in the measured dielectric loss, the loss peaks can be recovered. This research is helpful for the application of h-BN at high temperatures by understanding the ionic conduction and high temperature relaxation processes.