Proton Spin-Lattice Relaxation in Stress Induced Ferroelectric Phase of NaNH4-Tartrate and Na(NH4)xK1-x-Tartrate

The proton spin-lattice relaxation 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 ) x K 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 2 O 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 ) x K 1- x -tartrate, including x =1, between 100K and 4.2K is different 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 0 exp ( E a / R T ), which is attributed to the fact the dominant relaxation is due to the tunneling motion.