Solid State 93Nb NMR and 93Nb Nutation Studies of Polycrystalline Pb(Mg1/3Nb2/3)O3 and (1-x)Pb(Mg1/3Nb2/3)O3/xPbTiO3 Solid-Solution Relaxor Ferroelectrics

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Solid-state 93Nb static and MAS NMR and 93Nb nutation studies of polycrystalline Pb(Mg1/3Nb2/3)O3, (PMN) and (1 − x)Pb(Mg1/3Nb2/3)O3/xPbTiO3 (x = 0.05 to 0.50) solid-solutions are reported. The 93Nb static and MAS NMR spectra of PMN measured at 14.1 T have two major resonances due to the central transition (1/2 ↔ −1/2), a sharp peak at −902 ppm (1950 Hz fwhh) and a broad resonance (12 800 Hz fwhh) centered at −980 ppm. Two-dimensional 93Nb nutation spectra measured at 9.4 T, by contrast, have three different resonances, a sharp peak due to niobiums with a CQ < 0.8 MHz that is correlated with the sharp 93Nb signal at −902 ppm, and two resonances due to niobiums with a CQ of ≈ 17 MHz and a CQ > 62 MHz, respectively, that are associated with the broad 93Nb peak centered at −980 ppm. The sharp 93Nb peak for PMN is assigned to Nb(V) B-sites of cubic or high local symmetry in Mg(II)-rich regions with Nb(OMg)6 configurations. The broad 93Nb resonance at −980 ppm is assigned to a range of Nb(ONb)6-x(OMg)x site configurations, where x = 0 to 5, contained in the Nb(V)-rich regions in PMN. The lower symmetry of these Nb(V) B-sites is likely due to neighboring Mg/Nb B-site distributions, that alter the Nb−O bond lengths and O−Nb−O bond angles. Substantially different 93Nb NMR and nutation behavior is observed for (1 − x)PMN/xPT powders (x = 0.05 to 0.50). Decreased intensity of the sharp −902 ppm peak is due to increasing incorporation of Ti4+ ion from PT into the B-sites of Nb(OMg)6 configurations in 5 to 50 mol % PMN/PT solid-solutions. Increasing substitution of Ti4+ ions into the Nb(V) B-sites of Nb(ONb)6-x(OMg)x configurations at higher mol % PT (∼34 to 50 mol % PT) is also correlated with line shape changes of the broad 93Nb NMR peak at −980 ppm and changes in the shape of the contour plots of the nutation spectra. In addition, chemical shift and quadrupolar dispersion effects likely contribute to the observed line shape of the −980 ppm peak for the 0.50PMN/0.50PT sample as a result of B-site occupation by three different cations (Mg2+, Ti4+, and Nb5+) in the different Mg(II)- and Nb(V)-rich substructural regions in PMN/PT materials.

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Journal of the American Chemical Society





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