Solid-state nuclear magnetic resonance (NMR) of the ${}^{87}\mathrm{Rb}$ has been employed to investigate the phase transitions in polycrystalline ${\mathrm{LiRbSO}}_4.$ The spin-lattice relaxation time $T_1$ and the NMR line shape were measured using magic angle spinning (MAS) and multiple quantum magic angle spinning (MQMAS) methods between 373 and 488 K. The quadrupole coupling constant, $Q_{\mathrm{cc}},$ the asymmetry parameter, ${\eta }_Q,$ and the isotropic chemical shift, ${\delta }_{\mathrm{CS}},$ were determined from the analysis of MAS and MQMAS spectra. The anomalies of $Q_{\mathrm{cc}}$ near the IV-III phase transition were associated with the deformation of the local environment of the Rb ions in the crystal lattice. The measurements of the spin-lattice relaxation rate as a function of temperature and Larmor frequency showed the existence of a damped soft mode near the V-IV and IV-III phase transitions.

• Received 26 June 2000

DOI:https://doi.org/10.1103/PhysRevB.63.064107