85,87Rb, 14N NMR studies of successive phase transitions and incommensurate phase in R2Pb[Cu(NO2)6] (R = NH4, Rb)

Rb-88,Rb-87 and N-14 NMR spectra and spin-lattice relaxation time (T-1) were measured for R2Pb[Cu(NO2)(6)] (R = Rb, NH4). The quadrupole coupling constant (e(2)Qq/h), asymmetry parameter (eta), and the effective transverce relaxation time (T-2(*)) were estimated from the simulation of NMR spectra. The NMR spectra in commensurate phase III can be explained by the superposition of two components corresponding to two inequivalent sites of the R+ ion. In the incommensurate phase II, e(2)Qq/h and T-2(*) decreased with increasing temperature, while eta was almost temperature independent. T-1 in phase II is found to be determined by the contribution of acoustic phason with multi-soliton limits.