Hydrogen-Bond Network and Ferroelectric Transition in Sodium Trihydrogen Selenite, NaD_3(SeO_3)_2 by Nuclear Magnetic Resonance Study

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Deuteron and ^<23>Na magnetic resonances are measured of single crystals of NaD_3(SeO_3)_2 between 134°K and 298°K to reveal the nature of the ferroelectric transition (T_c∼267°K). Deuteron resonance lines D_a and D_b (relative intensity 1:2) above T_c split into two and into four, respectively. The ^<23>Na resonance line above T_c also splits into two below T_c. Following conclusions are derived from measurements of temperature and angular dependences of the quadrupole splittings for these deuteron and ^<23>Na resonance lines. All the hydrogen atoms are linked with moderately strong hydrogen bonds, and are jumping back and forth in the double well potential above T_c. The phase transition is accompanied not only by order-disordering of hydrogen atoms in hydrogen bonds, but also by slight rotations of SeO_3-- ions and by a slight distortion of lattice in the neighborhood of Na^+ ions. The crystalline symmetry below T_c is monoclinic, and the cell-doubling occurs along the b axis. Hydrogen-bond network below T_c is estimaeted from the present study. This structrue has permanent polarization in the ac plane.
社団法人日本物理学会の論文
1969-03-05