Ferroelectric Transition of a Chiral Molecular Crystal BINOL∙2DMSO

We report dielectric, thermodynamical, acoustic, and optical properties of a chiral molecular crystal, 1,1′-bi-2-naphthol 2-dimethylsulfoxide (BINOL∙2DMSO). We find two successive phase transitions at Tc1 = 190 K and Tc2 = 125 K. The first transition at Tc1 is characterized by an order–disorder transition of the guest molecules DMSO along with ferroelectricity. At the second transition of Tc2, the crystal structure deforms from tetragonal to monoclinic, leading to domain formation. Low-temperature x-ray diffraction suggests that the space group changes from P41212 (P43212) to P41 (P43) at Tc1, and down to P1121 at Tc2.