A theory is developed based on the model of random interactions between a large number of lattice defects and domain walls in ferroelectric materials. The theory gives the characteristic parameters of the hysteresis loop such as initial dielectric constant εi, Rayleigh constant ν, and coercive field Ec in terms of the microstructure of the domain walls and the number and interaction strength of the lattice defects. Results from large amplitude measurements on BaTiO3 doped with Fe show that a linear relationship exists between the dielectric constant and the ac field as required by Rayleigh’s law. In addition, the Rayleigh constant itself is inversely proportional to the Fe concentration as predicted by the model. Therefore, it is concluded that Fe as a dopant in BaTiO3 can act as obstacles to domain wall motion and control the characteristics of the hysteresis loop.
Kobalteinkristalle wurden bei mehreren Temperaturen im Zngversuch plastisch verformt. Auch bei tiefen Temperaturen war die Verformbarkeit der Einkristalle sehr gut. Verfestigungskurve und elektronenmikroskopisches Gleitlinienbild gleichen qualitativ denjenigen anderer hexagonaler Metalle und konnen in gleicher Weise gedeutet werden. Neben der Abgleitung auf der Basisebene werden bei den untersuchten Kristallorientierungen 11 122)und {11~4}-Zwillingsebenen beobachtet. Die geometrischen Verhaltiiisse bei dieser sogenannten anomalen Zwillingsbildung werden diskutiert.Kobalt single crystals were plastically deformed in tension at various temperatures. The ductility of the crystals remained good even at lorn temperatures. The work-hardening curves and the elektron microscopy slip line patterns are qualitatively similar to those of other hexagonal metals and may be similarly interpreted. Besides plastic shear on the basal plane, {11%?} and (1134) twin planes are observed for the investigated crystal orientations. The geometry of this so-called anomalous twin formation is discussed.
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