OBSERVATION OF DIPOLE COMPLEXES IN PBWO4-LA3-CRYSTALS( SINGLE)

The frequency dependence of dielectric loss factor (tan delta) in undo ped and La-doped PbWO4 crystals has been investigated over a frequency range from 10 Hz to 10 MHz and a temperature range from 40 to 370 deg rees C. A typical dielectric relaxation phenomenon in PbWO4:La3+ has b een observed. Experimental results indicate that there exist intrinsic mobile defects in pure PbWO4 crystals and lead vacancies are the pred ominant mobile defects. In La-doped PbWO4 crystals, La3+ ions may be l ocated at the Pb2+ sites and combine with lead vacancies to form the d ipole complexes [2(La-Pb(3+))(.-) V''(Pb)] which may be the origin of the dielectric relaxation phenomenon in PbWO4:La3+ crystals. (C) 1998 American Institute of Physics. [S0021-8979(98)08317-0].