The
87Rb and
133Cs spin-lattice relaxation rates of RbCdCl
3 and C
sCdCl
3 single crystals grown using the slow evaporation method were measured over the temperature range 160–400 K. The changes in the
87Rb spin-lattice relaxation rate near 340, 363, and 395 K correspond to phase transitions of the RbCdCl
3 crystal. The jump in
T1−1 at 395 K is due to a shortening in the
c-direction as a result of a phase transition from a cubic to a tetragonal structure. We suggest that the cubic Rb environment is favored above 395 K due to the fast motions and soft modes, which cause relaxation and average out the quadrupolar splittings. The temperature dependence of the relaxation rate below 340 K in RbCdCl
3 can be represented by
![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WM2-4GY8B2J-3-21/0?wchp=dGLbVtb-zSkWb)
and is thus in accordance with a Raman process. The
133Cs nuclei in the CsCdCl
3 crystal produce only one resonance line, which indicates that the local structure around the Cs atoms is cubic. The temperature dependence of the relaxation rate of the Cs nuclei can also be described with the quadratic equation
![Click to view the MathML source](http://www.sciencedirect.com/cache/MiamiImageURL/B6WM2-4GY8B2J-3-K/0?wchp=dGLbVtb-zSkWb)
. In the case of the RbCdCl
3 and CsCdCl
3 crystals, which are of electric quadrupolar type, their relaxations proceed via Raman processes, whereas in RbMnCl
3 and CsMnCl
3 crystals, which are of magnetic relaxation type, the relaxations proceed via single phonon processes. Therefore, the relaxation mechanisms of these different types of
ABCl
3 crystals (quadrupolar and magnetic) are completely different NMR behavior.