NMR relaxation study of the phase transitions and relaxation mechanisms of the alums MCr(SO4)2·12H2O (M=Rb and Cs) single crystals

► The physical properties and phase transition mechanisms of MCr(SO4)2·12H2O (M=Rb and Cs) crystals ► The NMR spectra and the spin-lattice relaxation times T1 of the 87Rb and 133Cs nuclei in the two crystals ► The variations in the symmetry of the octahedra of water molecules surrounding Rb+ and Cs+.