Neutron Structure Analysis of Paraelectric and Ferroelectric Phases of (CH₃)₂NH₂H₂PO₄

Abstract

Crystal structure of dimethylammonium dihydrogen phosphate has been determined in the paraelectric phase at 298 K and in the ferroelectric phase at 223 K by a single crystal neutron diffraction method. Two inequivalent protons in the hydrogen bonds forming the H 2 PO 4 − chains are disordered over two-equilibrium positions each other with separations 0.47 and 0.49 Å in the paraelectric phase. In the ferroelectric phase, they order at a position nearly equal to one of two positions related to the proton disorder. Accompanying the proton order, the PO 4 tetrahedra deform the structure in the paraelectric phase.