Organic salt of hydrogen l-tartaric acid: a novel wide-temperature-range ferroelectrics with a reversible phase transition

Abstract

4-Ethylanilinium hydrogen (2R,3R)-tartrate, a novel wide-temperature-range ferroelectric was synthesized. DSC measurement discloses that the homochiral organic salt undergoes an isosymmetric reversible phase transition at about 186 K with a sharply narrow heat hysteresis of 0.7 K. The heat capacity C_p obtained from the calorimetric measurement exhibits a sharp peak at 185.8 K, characteristic of a first-order phase transition. However temperature-dependence dielectric constant measurements reveal no dielectric anomaly near the phase transition point. The measurement of the unit cell parameters except for c axis versus temperature suggests that the values change abruptly and remarkably between 180 and 190 K with the cell volume doubled. The crystal structures determined at 123(2) K (a = 7.461 Å, b = 11.930 Å, c = 14.873 Å, α = 95.34°, β = 91.95°, γ = 107.92°) and 298(2) K (a = 6.078 Å, b = 7.478 Å, c = 14.951 Å, α = 87.66°, β = 82.69°, γ = 71.80°) also show that the phase transition could be a type of isosymmetric change with the same triclinic space group P1 (No. 1). Structural analysis shows that the different modes of hydrogen bonds probably affect the configurations of the phenyl rings from the cations, consequently leading to a reversible structural phase transition.