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.

Keywords:

• (CH₃)₂NH₂H₂PO₄
• hydrogen bond
• phase transition
• neutron structure analysis

Acknowledgments

Neutron diffraction was carried out under the Visiting Researcher's Program of the Research Reactor Institute, Kyoto University. This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (No. 20540317).