93Nb NMR of the random-field-dominated relaxor transition in pure and doped SBN -: art. no. 134109

The ferroelectric relaxor transitions in Sr0.61Ba0.39Nb2O6 (SBN61) and Sr0.61-yCeyBa0.39Nb2O6 (SBN61:Ce y=0.0066) have been studied by quadrupole perturbed Nb-93 NMR. The spectra are inhomogeneous frequency distributions ft (nu) consisting of a central component due to the 1/2 <----> - 1/2 transition and a broad background due to the satellite transitions. From the temperature dependence of the width and position of the central component spectrum and from the T dependence of T-2 we determined the T dependence of the Edwards-Anderson order parameter and of the normalized spontaneous polarization P. The random bond-random field Ising model parameters are J0=485 K, J=388 K, and Delta /J(2) =0.14. The random-field contribution <(<Delta>)over tilde> = Delta /J(2) is here by two orders of magnitude larger than in the perovskite relaxor PbMg1/3Nb2/3O3 (PMN).