Neutron Diffraction Study of Crystal Structures of Glycinium Phosphite H_3NCH_2COOH・H_2PO_3 in Paraelectric and Ferroelectric Phases (Condensed Matter: Structure, Mechanical and Thermal Properties)

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Crystal structure of H_3NCH_2COOH・H_2PO_3 was studied in the paraelectric phase (P phase) at 298 K and in the ferroelectric phase (F phase) at 170 K by means of the single crystal neutron diffraction. Two independent protons in the hydrogen bonds forming the H(HPO_3)^- chains are disordered over two sites with the separations of 0.486(3) and 0.474(5)Å in the P phase. In the F phase, they are ordered at a position nearly equal to one of two sites related by the disorder. With the proton order, lengths of the P-O bonds with the oxygens involved in the hydrogen bonds forming the chain deviate from their values determined in the P phase. A possible mechanism for the appearance of the spontaneous polarization is discussed in connection with the deformation of the HPO^<2->_3 anions in the F phase.
社団法人日本物理学会の論文
2003-05-15