Electrical anisotropy in single crystals of Bi-layer structured ferroelectrics

Abstract Single crystals of PbBi 2 Nb 2 O 9 (PBN), PbBi 4 Ti 4 O 15 (PBT) and Pb 2 Bi 4 Ti 5 O 18 (P 2 BT), belonging to the bismuth layer-structured ferroelectric compound, were grown and dielectric, conducting and ferroelectic properties were evaluated separately in directions of a ( b )-axis and c -axis. The relationship between crystal structure (the number of oxygen octahedra in the perovskite block m ) and electrical properties was discussed comprehensively. The dielectric permittivity at T c in the a ( b )-axis direction was more than 20 times larger than for the c -axis direction. The anisotropy depended on m and was larger in the compound with even-number m than that with odd-number m . The DC conductivity increased with increasing m in both a ( b )-axis and c -axis directions. The spontaneous polarization in the c -axis direction was not recognized for PBN and PBT with even-number m but observed for P 2 BT with odd-number m , although the value of remanent polarization was much smaller than for the a ( b )-axis direction.