The correlation between electrical and mechanical losses in ferroelectric ceramics has been investigated theoretically and experimentally. The theoretical derivation is based on the assumption that both loss types are induced by 90° domain walls moving under the influence of electrical or mechanical fields. A proportionality between both loss types is found. The factor of proportionality includes material constants such as spontaneous polarization and striction, permittivity, and elastic compliance, but is independent of the specific energy dissipation mechanism of a moving domain wall. In a compositional series of differently doped PLZT ceramics with a broad range of losses the theoretically derived relations have been checked experimentally. Good agreement between the experimental and theoretical results was found.
To cite this article: N. A. Schmidt (1981) Coercive force and 90° domain wall motion in ferroelectric PLZT ceramics with square hysteresis loops, Ferroelectrics, 31:1, 105-111,The polarization reversal of some tetragonal-phase PLZT ceramics is studied. The results are explained in terms of 90" domain wall motions. A reported theory originally derived for rhombohedral-phase PLZT 6/65/35 ceramics is shown to be applicable to tetragonal-phase PLZT ceramics also by introducing the remanent degree of 90" domain alignment yq0. As a result, the calculation of coercive force is possible for various PLZT compositions considering the interaction of90" domain wall motions and reacting forces established by the internal stress state of ferroelectric ceramics. The frequency dependence of coercive force and measurements of switching strain, including depolarization data obtained from either mechanically or electrically produced external forces, confirm the interpretatlon of predominantly occuring 90" reorientations and are consistent with the extended theory.
The oscillation of domain walls caused by alternating fields is often thought to be the origin of dielectric losses. In this paper the physical nature of losses is explained by the damping of moving 90° domain walls. For frequencies up to 108 Hz the origin of damping of the wall motion is ascribed to point defects within the 90° domain wall. At high frequencies damping results from the reflection of thermal-lattice waves impinging on a moving 90° domain wall.
Rhombohedral PLZT ceramics of the composition 6/65/35 exhibit a continuous increase of the permittivity subjected tc uniaxial pressure. Together with strain measurements detsted informations about 71°/109° processes (simplifying denoted as 90° processes) are obtainable. With these experimental results and an appropriate averaging procedure the dielectric single crystal anisotropy can be determined.
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