NQR AND NMR-STUDIES OF PHASE-TRANSITIONS IN R(2)PB[CU(NO2)(6)] (R=K, RB, TL, CS, AND NH4)

K-39, Rb-87,Rb-85, Cs-133, Tl-205, and H-1,H-2 NMR spin-lattice relaxa tion times T-1 and N-14 NQR spin-lattice times T-1Q were determined fo r R(2)Pb[Cu(NO2)(6)](R = K, Rb, Tl, Cs, and NH4). T-1 of K-39 and Rb-8 7 showed very short values in the incommensurate phase as compared wit h those in the other phases. When the commensurate-incommensurate phas e transition point is approached from below N-14 T-1Q of the R = K, Rb , Tl, and NH4 compounds showed rapid decrease. On the other hand, that of the R = Cs compound began to decrease first after passing beyond t he corresponding transition point. The difference of the T-1Q behavior may be ascribed to the difference of the condensed phonon mode in the incommensurate phase.