Nuclear spin phonon relaxation by Raman process in Na3H(SO4)2 single crystals with the electric–quadrupole-type interaction using 1H and 23Na NMR

Abstract

Abstract Successive phase transitions in a Na3H(SO4)2 single crystal were found at 296, 513, and 533 K. To investigate the mechanism of the phase transition at 296 K, the 1H and 23Na spin–lattice relaxation time and the spin–spin relaxation time of Na3H(SO4)2 were measured near the phase transition temperature using a FT NMR spectrometer. The spin–lattice relaxation time, T1, for 1H in Na3H(SO4)2 crystals exhibits a minimum below TC1 (=296 K) indicating the presence of distinct molecular motion governed by the Bloembergen–Purcell–Pound (BPP) theory. Although the results for the 1H and 23Na relaxation times provide no evidence of the phase transition at TC1, the separation of the 23Na resonance lines changes abruptly at TC1. The phase transition at 296 K produces a change in the separation of the Na resonance line that is associated with a change in the atomic positions in the vicinity of the Na ions. Also, the nuclear spin–lattice relaxation process in Na3H(SO4)2 crystals with the electric–quadrupole-type interaction proceed via Raman process. These results are compared with those obtained for other M3H(SO4)2 (M=K, Rb, and Cs) crystals, which have similar hydrogen-bonded structures.