Properties of Tetragonal PLZT with Reference to its Diffuse Phase Transition

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Abstract
Measurements were made of the dielectric, elastic, electrostrictive, piezoelectric and linear thermal expansion constants together with an X-ray analysis of the hot-pressed ceramics of PLZT X/55/45, X being varied from 0 to 15. Here, a new model is introduced regarding the structure of the intermediate state between the paraelectric and the ferroelectric states, the so-called “slim-loop ferroelectric state.” It is assumed that this state is composed of polar microdomains embedded within a non-polar paraelectric matrix and whose orientations change with time. On the basis of this model, the temperature dependence of the dielectric constant and the free energy are calculated with appropriate approximations. It is also shown that this model can explain the so-called “glassy polarization” which extends far above the Curie temperature.