Study of the phase transitions by observation of the A and 1H nuclear magnetic resonance in ANH4SO4 (A = 7Li, 39K and 87Rb) single crystals with excellent optical quality

ANH4SO4 (A = Li, K and Rb) single crystals were grown using the slow evaporation method. We studied the spectra, spin-lattice relaxation times, T1, and spin-spin relaxation times, T2, of the 1H, 7Li, 39K and 87Rb nuclei in these three types of single crystals. The nuclear magnetic resonance observations provided a consistent description of the dynamics of the studied nuclei in these materials. The T1 values for the 1H nuclei are similar in all three crystals and the 1H spin-lattice relaxation times increase with increasing temperature. However, as the radii of the metal ions increase, a corresponding decrease in the spin-lattice relaxation times of the A nuclei is observed. The differences observed in the spin-lattice relaxation times of the A nuclei upon changing the alkali-metal ion may be related to the ionic radius and the lengths of the A-O bonds. Therefore, the occurrence of phase transitions in these materials seems to be essentially dependent on the presence of the metal ions