A quadrupole coupling induced 47Ti and 49Ti satellite background which transforms into well-defined satellite lines below T(c) in the ferroelectric phase has been observed in the cubic phase of an ultrapure BaTiO3 single crystal. The results demonstrate the coexistence of a displacive and order-disorder component in the phase transition mechanism and tetragonal breaking of the cubic symmetry due to biased Ti motion between off-center sites in the paraelectric phase above T(c).

The temperature dependence of the Edwards-Anderson order parameter q EA and the local polarization distribution function W ͑ p͒ have been determined in a PMN single crystal via 2D 93 Nb NMR. A glasslike freezing of reorientable polar clusters occurs in the temperature range of the diffuse relaxor transition, whereas the NMR spectra corresponding to pinned nanodomains do not change with temperature. The obtained form of W ͑ p͒ as well as the temperature dependence of q EA and the nonlinear dielectric susceptibility can be well described by a newly proposed spherical random bondrandom field model of relaxor ferroelectrics.

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