The frequency dependence of the dielectric loss factor in undoped and La-doped crystals was investigated, using frequencies ranging from 10Hz to 10MHz, at temperatures ranging from 40 to 370C. Typical dielectric relaxation was observed in the case of La-doped samples. The results suggested that intrinsic mobile defects existed in the pure crystals and that Pb vacancies were the predominant mobile defects. In the case of La-doped crystals, La3+ ions were thought to be located at Pb2+ sites and to combine with Pb vacancies so as to form dipole complexes: [2(LaPb3+)•-VPb"]. These were suggested to be the cause of the dielectric relaxation in La-doped crystals.

B.Han, X.Feng, G.Hu, P.Wang, Z.Yin: Journal of Applied Physics, 1998, 84[5], 2831-4