Abstract

Solid solutions of (1− x)Pb(Mg 1/3Nb 2/3)O 3 xPb(Sc 1/2Nb 1/2)O 3 (PMN/PSN) have been investigated using high-resolution 93Nb 3-quantum magic-angle spinning nuclear magnetic resonance experiments (3QMAS NMR). In previous MAS NMR investigations, the local B-cation ordering in these relaxor ferroelectric solid solutions was quantitatively determined. However, in conventional one-dimensional MAS spectra the effects of chemical shifts and quadrupole interaction are convoluted; this, in addition to the insufficient resolution, precludes reliable extraction of the values of isotropic chemical shift and quadrupole coupling product. In the current 3QMAS investigation, 93Nb spectra are presented for concentrations x=0, 0.1, 0.2, 0.6, 0.7, and 0.9 at high magnetic field (19.6 T) and fast sample spinning speed (35.7 kHz). Seven narrow peaks and two broad components are observed. The unique high-resolution of the two-dimensional 3QMAS spectra enables unambiguous and consistent assignments of spectral intensities to the specific 28 nearest B-site neighbor (nBn) configurations, ( N Mg, N Sc, N Nb) where each number ranges from 0 to 6 and their sum is 6. It is now possible to isolate the isotropic chemical shift and quadrupole coupling product and separately determine their values for most of the 28 nBn configurations. The isotropic chemical shift depends linearly on the number of Mg 2+ cations in the configuration; δ iso CS=(13.7±0.1) N Mg−970±0.4 ppm, regardless of the ratio N Sc/ N Nb. For the seven Nb 5+-deficient configurations ( N Mg, 6- N Mg, 0) and the pure niobium configuration (0, 0, 6), the quadrupole coupling products (and hence the electric field gradients) are small ( P Q∼6–12 MHz) and for the remaining configurations containing small, ferroelectric active Nb 5+ ions, the quadrupole coupling products are significantly larger ( P Q∼40 MHz), indicating larger electric field gradients.

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