Critical Behaviour of Dielectric Permittivity and Spontaneous Polarization of Triglycine Sulphate Single Crystals Doped with Organic Molecules

Abstract

Dielectric permittivity, ε₂₂, spontaneous polarization, P_s, and coercive field, E_c, of triglycine sulphate (TGS) crystals doped with d-l alanine, orthonitroaniline, paranitroaniline or aniline molecules have been measured from room temperature up to the transition point. A remarkable displacement of the hysteresis loops of polarization along the direction of the field axis and a broadened transition from the polar to the non-polar phase are detected. An increase in the value of P_s and a decrease of both ε₂₂ and E_c are also observed. The changes in both ε₂₂ and P_s attributed to the creation by the dopants of an internal electric field, E_b. The internal bias affects the Curie constant and ε_max in a way similar to that introduced by an external bias. The value of E_b in the vicinity of the phase transition and the parameters of the statistical dipolar theory of ferroelectricity have been calculated.