INCOMMENSURATION AND THE DISTORTED OXYGEN OCTAHEDRON OF ANTIFERROELECTRIC TIN-MODIFIED LEAD-ZIRCONATE-TITANATE

A study of the thermal-mechanical properties of incommensurate antifer roelectric tin-modified lead zirconate titanate has been performed as functions of Sn and Ti contents. Deviation from a linear temperature d ependence in the thermal-expansion strain (epsilon) was observed below similar to 400 degrees C. The deviation resulted from a contraction o f the lattice relative to an extrapolation of a high-temperature linea r behavior. Dielectric property measurements were also performed. Stro ng deviations from Curie-Weiss behavior were found to high temperature s, however with increasing Ti content, the degree of deviation from li nearity in epsilon decreased, whereas that in the reciprocal dielectri c constant increased. This indicates that the nonlinearity in epsilon does not arise due to an electrostrictive coupling of polarization flu ctuations to the lattice. Rather,an oxygen octahedra tilt mechanism is proposed. The existence of 1/2 [111] superlattice reflections (F spot s) to temperatures close to that of the onset of nonlinearity in epsil on gives support to this possibility.