Effect of Hydrostatic Pressure on the Ferroelectric Properties of Tri-Glycine Sulfate and Selenate

Abstract

The transition temperatures ${T}_{c}$ of tri-glycine sulfate and isomorphous tri-glycine selenate are raised by the application of hydrostatic pressure. Up to 2700 atmos, the dependence of ${T}_{c}$ on pressure is linear with a slope of 2.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ degrees/atmos for the sulfate and 3.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ degrees/atmos for the selenate. The Curie-Weiss law, ${\ensuremath{\epsilon}}_{b}\ensuremath{\cong}\frac{C}{(T\ensuremath{-}{T}_{c})}$, is unaffected by pressure except for the shift in transition temperature. The curve of the spontaneous polarization is shifted accordingly along the temperature axis; in the vicinity of the transition point, the square of the spontaneous polarization depends linearly on temperature and pressure. The results are discussed in terms of the thermodynamic theory of ferroelectrics.