Study of the phase transitions by observation of the A and¹H nuclear magnetic resonance in ANH₄SO₄(A =⁷Li,³⁹K and⁸⁷Rb) single crystals with excellent optical quality

Abstract

ANH 4 SO 4 (A = Li, K and Rb) single crystals were grown using the slow evaporation method. We studied the spectra, spin-lattice relaxation times, T 1 , and spin-spin relaxation times, T 2 , of the 1 H, 7 Li, 39 K and 87 Rb 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 T 1 values for the 1 H nuclei are similar in all three crystals and the 1 H 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.