Effect of Uniaxial Pressure on the Ferroelectric Phase Transition of Tri-Glycine Sulfate

Abstract

The behavior of the dielectric constant ε_b of TGS as a function of temperature for different values of the uniaxial pressures applied to x-, y- and z-axis was investigated up to 600 bar. The Curie-Weiss law, ε_b≅C⁄(T−T₀), was almost unaffected by uniaxial pressures along the three axes except for the vicinity of shifted transition temperature. The paraelectric Curie temperature T₀ was linearly shifted with a rate of ∂T₀⁄∂X₁=−6.7±0.5 and ∂T₀⁄∂X₂=−9.1±0.7 for x-and y-axis, respectively, and ∂T₀⁄∂X₃=19.0±1.5 for z-axis for pressures up to about 300 bar, all in unit of °C/kbar. The values of the three rates can reproduce fairly well the values given by previous experiments of hydrostatic and two dimensional pressures, and agree with those predicted by the Ehrenfest relation, the phenomenological theory and the Janovec’s theory. It was shown that there is no thermodynamic contradiction between the Ehrenfest relation and the phenomenological theory.