Electrical anisotropies in layer-structured lead bismuth titanate single crystals

Single crystals of lead bismuth titanate (PbBi4Ti4O15) were grown by the vertical gradient freeze method. Electrical anisotropy of the crystals was investigated by measuring dielectric permittivity, DC conductivity, and complex impedance. The dielectric permittivity measured at 1 MHz was 18300 in the direction parallel to the bismuth layer (crystallographic a(b) axis) at the Curie temperature of 570 °C. This value was about 43 times higher than that in the perpendicular direction (c axis). The DC conductivity at 700 °C was about one order of magnitude higher in the direction parallel to the bismuth layer than in the perpendicular direction. Results of complex impedance measurements suggest that the bismuth layer has a lower capacitance and a higher resistivity than those of the pseudo-perovskite blocks and shows paraelectric character from a low temperature below Tc.