Dielectric high-temperature behaviour of undoped and MgO-doped LiNbO3single crystals

Dielectric measurements of Czochralski grown LiNbO3 single crystals with different Li/Nb ratio and with MgO concentrations up to 8 mole-% were performed in a temperature range from 500°C to 1200°C at 100Hz to 100kHz. The results of undoped LiNbO3 confirm the well known rise of the Curie point with increasing Li content. It is found that the Curie temperature increases with MgO doping which may be due to a decrease of Nb5+ vacancies at the B-sites of LiNbO3 lattice. Based on Jonscher's ‘universal law’ of the dielectric response the complete dielectric behaviour can be interpreted as the result of a hopping conductivity by electrons or ions. The density of these charge carriers is lowered by MgO doping. The mobility of the charge carriers seems to be reduced in LiNbO3 containing less vacancies by a stronger localization.