DOMAIN CONTRIBUTION TO THE DIELECTRIC PROPERTIES OF THE CRYSTALS OF TRIGLYCINE SULPHATE GROUP AND ROCHELLE SALT

Abstract

The dielectric properties of the crystals of nominally pure triglycine sulphate (TGS), deuterated TGS, TGS doped with L,α – alanine, TGS with impurity of phosphorus Р⁵⁺ ions, TGS subjected to X-ray radiation as well as of Rochelle salt crystal were investigated. Temperature dependences of domain components of the real and imaginary parts of the dielectric permittivity measured in a weak ac electric field were obtained.  The existence of a moveable domain structure in defect-free TGS crystals does not lead to a deviation from the thermodynamic Curie – Weiss law in the ferroelectric phase, but causes a violation of the "law of two". In TGS crystals with impurity or radiation defects, pinning the domain structure, the both laws work well. For the studied crystals of the TGS group near the phase transition, there is no quantitative correlation between temperature behavior of static geometric parameters of the domain structure (density N and total length L of the domain boundaries), and the measured dielectric characteristics. The number of thermal cycles of heating and cooling with a transition through the Curie point practically does not affect the value of the domain component of the dielectric constant in TGS crystals, while an increase of the rate of passage of the phase transition leads to its significant decrease. In Rochelle salt crystals the domain part of the dielectric permittivity near the lower phase transition is considerably less than near the upper one, but it occupies a wider temperature range.