Electrical anisotropy of dielectric and DC/AC conducting properties of single crystals of barium bismuth titanate (BaBi4Ti4O15), which is a member of bismuth layer-structured ferroelectrics, has been studied and compared with those of polycrystalline samples. It was found that BaBi4Ti4O15, when measured at 1MHz, showed about 6 times and 58 times higher dielectric permittivity in the direction parallel to bismuth layer (crystallographic a (b)-axis) than those in the perpendicular direction (c-axis) at room temperature and the Curie temperature, respectively. DC/AC conductivity showed a higher value in the direction parallel to the bismuth layer than those in the perpendicular direction. On the other hand, the activation energy for electric conduction in the direction parallel to the bismuth layer showed a lower value. Polycrystalline samples had intermediate properties of those of the two directions in single crystals. Complex impedance measurements also showed anisotropy in the dielectric and the DC conducting properties even for paraelectric phase. Thus, the bismuth layer was thought to act as an insulating and paraelectric layer in BaBi4Ti4O15.
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Kim et al. (1994) studied this question.