Proton Spin-Lattice Relaxation in Stress Induced Ferroelectric Phasa of NaNH_4-Tartrate and Na(NH_4)_xK_<1-x>-Tartrate

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The proton spin-lattice relaxarion time (T_1) has been measured in the stress induced ferroelectric Phase of NaNH_4-tartrate, NaK-tartrate and in the solid solution of Na(NH_4)_xK_<1-x>-tartrate between 300K and 4.2K. Four minima were found in the temperature dependence of T_1 in NaNH_4-tartrate; the first minimum is attributed to the flip-flop motion of H_2O molecules, the second to the reorientation of the NH_4-ions about the threefold axis, and the third and fourth due to the reorientation about the twofold axis. The temperature dependence of T_1 in Na(NH_4)_xK_<1-x>-tartrate, including x=1, between 100K and 4.2K is defferent from that at high temperatures and the correlation time of the reorientation of the NH_4-ion obtained by using B. B. P. theory does not follow the relation τ=τ_0exp (E_a/RT), which is attributed to the fact the dominant relaxation is due to the tunneling motion.
社団法人日本物理学会の論文
1974-12-15