Study on structural phase transitions and relaxation processes of Cs2Co(SO4)2·6H2O and Cs2Zn(SO4)2·6H2O crystals

The structural phase transitions and relaxation processes of Cs2Co(SO4)2·6H2O and Cs2Zn(SO4)2·6H2O single crystals were investigated, with the phase transitions of both crystals being determined from NMR data. The spin–lattice relaxation time, T1, of the 133Cs nucleus in two crystals undergoes a significant change near the phase transition temperature, TC, and these changes coincide with the changes in the splitting of the 133Cs resonance lines. The variations in the temperature dependence for the splitting of the 133Cs resonance lines and T1 near TC are related to changes in the symmetry of surrounding Cs+. In addition, the 133Cs T1 of Cs2Co(SO4)2·6H2O, which contains paramagnetic ions, was found to be shorter than that of Cs2Zn(SO4)2·6H2O. This relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ions. The differences between the 133Cs T1 of these compounds are probably due to the differences between the electronic structures of their metal ions.