EFFECTS OF NIOBIUM SUBSTITUTION FOR TITANIUM ON ELECTRICAL-PROPERTIESIN SINGLE-CRYSTALS OF LEAD BISMUTH TITANATE

Single crystals of Nb-doped lead bismuth titanate; PbBi4(Ti0.99Nb0.01) (4)O-15, were synthesized by the vertical gradient freeze method, and electrical properties of the crystals were investigated by measuring D C conductivity, dielectric permittivity, and the D-E hysteresis loop. The p-type conductivity decreased upon Nb doping by as much as one to two orders of magnitude in the direction parallel to the bismuth layer . The dielectric permittivities decreased at Curie temperature (T-c) b ut increased about threefold at room temperature upon Nb doping. From the D-E hysteresis curves, the absence of spontaneous polarization in the direction perpendicular to the bismuth layer was confirmed in undo ped and Nb-doped single crystals. The coercive field decreased in the direction parallel to the bismuth layer upon Nb doping at room tempera ture. It was found that Nb doping has effects to give a lower conducti vity, favorable to high-temperature poling for polycrystals, and to im prove ferroelectricity and dielectric permittivity at room temperature .