${}^{93}\mathrm{Nb}$ NMR has been used to investigate the local structure and cation order/disorder in solid solutions of $\left(1\mathrm{}-x\right)\mathrm{Pb}\left({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}\right){\mathrm{O}}_3-x\mathrm{Pb}\left({\mathrm{Sc}}_{1/2}{\mathrm{Nb}}_{1/2}\right){\mathrm{O}}_3,$ as a function of concentration x. These relaxor ferroelectric solid solutions have been well characterized by x-ray diffraction, transmission electron microscopy, and dielectric response measurements. NMR magic angle spinning (MAS) spectra are presented for ${}^{93}\mathrm{Nb}$ at 14.0 and 19.6 T. Seven narrow peaks and two broad components are observed. Narrow peaks are assigned to configurations of ${}^{93}\mathrm{Nb}$ nuclei with only ${\mathrm{Mg}}^{2+}$ and/or ${\mathrm{Sc}}^{3+}$ (no ${\mathrm{Nb}}^{5+})$ cations occupying the six nearest B neighbor sites $\mathrm{}\left(\mathrm{nBn}\right);$ and are designated 0–6 according to the number of ${\mathrm{Mg}}^{2+}$ cations in the $\mathrm{nBn}$ configuration. The two broad components are assigned to configurations with more than one ${\mathrm{Nb}}^{5+}$ cation in the nearest B sites. In order to fit the MAS line shapes it is necessary to include distributions of the electric-field gradient parameters and dispersions in isotropic chemical shifts; these have been obtained from the data. The relative intensities of each spectral component are analyzed and the data strongly support a modified random site model of B-site order. Monte Carlo simulations of B cation ordering are presented to explain the observed NMR intensities and to validate the model.

• Received 9 August 2002

DOI:https://doi.org/10.1103/PhysRevB.66.224103