1H NMR study on the motion of NH4+ in ferroelectric NH4H(ClH2CCOO)2 and mixed (NH4)1-xRbxH(ClH2CCOO)2 (x=0.15)

Temperature-dependent proton NMR relaxation time measurements have been performed at 60 MHz in order to study the NH4+ dynamics in ferroelectric NH4H(ClH2CCOO)(2) and mixed Rb-x(NH4)(1-x)(ClH2CCOO)(2), where x = 0.15. The data indicate that the dominant relaxation mechanism for the NMR spin-lattice relaxation time T-1 in both crystals involves simultaneous NH4 group reorientation about their C-2 and C-3 symmetry axis in the paraelectric phase. Details of the NH4+ reorientation have been inferred from analysis of temperature dependence of T-1 assuming the Watton model. The activation parameters of the motionshave been determined. It has been found that the substitution of Rb does not change the activation parameters of the NH4 group dynamics.