Relaxation mechanisms of Rb2Co(SO4)2 ⋅ 6H2O single crystals studied by 1H and 87Rb nuclear magnetic resonance

The spin-lattice relaxation time, T1T1, and the spin–spin relaxation time, T2T2, for 1H and 87Rb nuclei in Rb2Co(SO4)2⋅6H2O crystals were investigated. The phase transitions occur near 370K(=TC1), 402K(=TC2), 413K(=TC3), and 458K(=TC4). The 87Rb spectrum changes near TC1TC1 from Rb(1) and Rb(2) central resonance lines to one Rb central resonance line, and this change is due to the structural phase transition. The change in the 1H T1T1 near TC1TC1 and the changes in T1T1 and T2T2 for Rb(1) and Rb(2) near TC1TC1 and TC2TC2 are also due to the phase transitions, and are related to changes in the symmetry of the octahedra of water molecules and slight rotations of the SO4 tetrahedra surrounding Rb+. Further, below TC1TC1 the spin-lattice relaxation rates, T1−1, for Rb(1) and Rb(2) are proportional to T−2T−2, which implies that these relaxations occur mainly via Raman processes.