We have investigated effects of random substitution of proton sites with deuterons on the temperature- and pressure-induced phase transitions in squaric acid crystal, which consists of ferroelectrically ordered molecular sheets of [C4O4]2- (SQ2-) skeletons and intervening protons or deuterons. In the isotopically mixed crystals (H 1-xDx)2SQ, the critical temperature T c for the dielectric phase transition was found to increase linearly with the deuterium concentration x, while the critical pressure Pc increases nonlinearly with x at 300 K. Around the pressure ∼20 kbar above Pc, the constituent SQ2- skeletons in the paraelectric phase show a symmetry change from the asymmetric (C1h) to centrosymmetric (C4h) form, which is likely caused by the deformation of the correlated proton (deuteron) potential.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry