The impurity-concentration dependence of the ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ NMR line shapes and phason-induced spin-lattice relaxation rates has been studied over a wide temperature range in substitutionally disordered incommensurate (${\mathrm{Rb}}_{1\mathrm{-}\mathit{x}}$${\mathrm{K}}_{\mathit{x}}$${)}_2$${\mathrm{ZnCl}}_4$ for x=0.00, 0.02, and 0.06. The results yield information on the impurity-concentration dependence of the phason gap and phase fluctuations of the modulation wave as well as on the nature of the coupling of the impurities to the incommensurate modulation wave.

• Received 7 March 1994

DOI:https://doi.org/10.1103/PhysRevB.50.2827