A nuclear magnetic resonance study of the phase transitions and electric quadrupole Raman processes of M5H3(SO4)4·H2O (M=Na, K, Rb, and Cs) single crystals

The spin-lattice relaxation times and spin-spin relaxation times for 1H and M in M5H3(SO4)4·H2O (M=Na, K, Rb, and Cs) single crystals grown using the slow-evaporation method were measured as functions of temperature. Two kinds of protons were identified in the M5H3(SO4)4·H2O structure: acid protons and water protons. Our experimental results show that the acid and water protons in Cs5H3(SO4)4·H2O are involved in phase transitions of this crystal, whereas neither type of proton is involved in the phase transitions of the other three crystal type (M5H3(SO4)4·H2O; M=Na, K, and Rb). Moreover, the relaxation times for the M (=Na, K, and Rb) nuclei in these crystals were found to decrease with increasing temperature and can be described with T1-1∝Tk (k=2). The T1 results for M (=Na, K, and Rb) in M5H3(SO4)4·H2O crystals can be explained in terms of a relaxation mechanism in which the lattice vibrations are coupled to the nuclear electric quadrupole moments.