Macroscopic Characteristics of Relaxor Ferroelectrics

The relationship between frequency and is often expressed in terms of the empirical Vogel-Fulcher-Tammaim law (often just called the Vogel-Fulcher law, usually encountered in discussion of the viscous flow of amorphous liquids and glasses) and expressed for relaxors as 

There is no Curie-Weiss behaviour immediately above but only at a much higher temperature, the Bums temperature, T. Between and the relationship between the relative permittivity and the temperature is usually better described by a quadratic law  

Moreover, the crystal stmcture does not change significantly at T, while in a normal ferroelectric there is a noticeable change of symmetry, easily revealed by X-ray diffraction. 

In the second group, the diffuse peak in relative permittivity is steeper on the low-temperature side compared to the canonical relaxors, and at a temperature below which is generally similar to the value of for a canonical relaxor, the material 

The relative permittivity and other dielectric behaviour of a relaxor ferroelectric as a function of temperature is often different depending upon whether the sample is cooled from higher temperatures in an electric field (FC) or in no electric field (ZFC). For example, the non-ferroelectric low-tenperature state of a canonical relaxor can be transformed irreversibly into a ferroelectric state by the application of a sufficiently high electric field or if the material is cooled in the presence of an electric field. As with non-canonical relaxors, this state transforms to the ergodic state above 

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