(207)Pb Spin-Lattice Relaxation in Solid PbMoO(4) and PbCl(2)

We have measured the (207)Pb nuclear spin-lattice relaxation rate R as a function of temperature T at two nuclear magnetic resonance frequencies omega(0) in the ionic solids lead molybdate (PbMoO(4)) and lead chloride (PbCl(2)). R is unexpectedly large, proportional to T(2), and independent of omega(0). Taken together with previous work in lead nitrate [Pb(NO(3))(2)], these results show that the relaxation does not depend on the nature or rotational motion of the counterion, particularly since the counterion in lead chloride is a single chlorine atom. The theory that explains the observed relaxation rate is reviewed. A second-order Raman process dominates the observed relaxation process. It involves the modulation of the spin-rotation interaction by the lattice vibrations