Sc-45 and Nb-93 NMR in relaxors

The narrow components in the Nb-93(I = 9/2) and (SC)-S-45(I = 7/2) NMR spec tra, of single crystalline PMN and disordered single crystalline PST are du e to the 1/2 --> -1/2 NMR transition whereas the broad background component s are due to satellite transitions. The macroscopic cubic symmetry is locally broken on the NMR time scale. Fro m the NMR point of view, the structure is homogeneous and there is no need to invoke the existence of "pinned" chemical clusters. The observed NMR spe ctra in PMN and PST can be described in terms of reorientable dynamic polar nanoclusters-mainly due to Pb2+ site disorder-as invoked by the spherical random bond-random field model.