John J. Fitzgerald

Pure-phase two-dimensional niobium-93 nutation spectroscopic study of lead metaniobate and the piezoelectric lead magnesium niobate

An NMR technique to measure pure-phase two-dimensional nutation NMR spectra, that yields higher resolution than traditional nutation experiments is reported. Using this technique 93Nb nutation NMR spectra of PbNb2O6 and the technologically important Pb(Mg1/3Nb2/3)O3 (PMN) have been measured and the quadrupolar coupling constant of the niobium site in PbNb2O6 (C(Q) = 19 +/- 2 MHz) determined. Estimates of the quadrupolar coupling constants for three different resonances associated with different niobium(V) sites in PMN (C(Q) < 1.2 MHz, approximately 17 MHz, and > 62 MHz) are also reported.

Solid-state 93Nb MAS NMR studies of single crystal Pb(Mg1/3Nb2/3)O3, (PMN) and Pb(Zn1/3Nb2/3)O3, (PZN) and related lead titanate solid-solution relaxor ferroelectrics

Solid-state 93Nb MAS NMR spectra measured at 14.1 Tesla of single crystal Pb(Mg1/3Nb2/3 (PMN), Pb(Zn1/3Nb2/3)O3 (PZN), 0.93 PMN/0.07 PT, and 0.92 PZN/0.08 PT, and polycrystalline PMN and 0.90 PMN/0.10 PT materials have two major resonances due to the central transition (+l/2↔-l/2), a sharp peak at ≈-900 ppm, and a broad resonance centered near -980 ppm. The sharp 93Nb signal has a small CQ (≤1 MHz) consistent with high symmetry Nb(V) ion B-sites as a consequence of local Mg/Nb (and Zn/Nb) ordering, and is tentatively assigned to near-cubic Nb(V) B-sites of Nb(OMg)6 (and Nb(OZn)6) configurations. The broad Nb signal near -980 ppm consists of two or more overlapping powder patterns with large CQ values, and are tentatively assigned to lower symmetry Nb(ONb)6-x(OMg)x and Nb(ONb)6-x(OZn)x configurations (where x=0 to 5).The 93Nb NMR spectra of single crystal 0.93 PMN/0.07 PT, 0.65 PMN/0.35 PT, and 0.92 PZN/0.08 PT, and polycrystalline 0.90 PMN/0.10 PT and 0.66 PMN/0.34 PT compared to PMN and PZN are correlate...

Solid-State 25Mg, 45Sc and 93Nb MAS NMR Studies: Local B-Site Chemical Environments and Ordering in PB(MG1/3NB2/3)O3 (PMN) and Related Relaxor Ferroelectrics

Solid-state 25Mg, 45Sc and 93Nb NMR spectroscopic studies of the local chemical environments and relative degree of B-site ordering in lead-based perovskite relaxor ferroelectrics are reported. 93Nb MAS NMR spectra of PMN and PZN provide conclusive evidence for significant B-site disorder, while 93Nb and 45Sc MAS NMR indicate B-site ordering in PSN. 93Nb MAS NMR spectra of PMN show resonances with different CQ values assigned to different types of Nb(V) B-sites of pseudo-cubic, axial and rhombic symmetry. For PSN, 93Nb and 45Sc MAS NMR spectra support the presence of predominantly a single Nb(V) and Sc(III) site with intermediate CQ values assigned to axially distorted B-sites. 25Mg MAS NMR of PMN also show evidence for at least two different Mg(II) sites of local cubic and axial symmetry due to partial B-site disorder in PMN. 25Mg and 93Nb NMR spectra of La3+-substituted PMN (at 25 mol%) show that A-site substitution by La(III) leads to increased B-site ordering in the Mg-rich and Nb-rich nanodomains of PMN. By contrast, the 25Mg and 93Nb NMR spectra of BMN, a Ba2+ A-site analog of PMN, demonstrate that BMN has a more highly ordered Mg/Nb B-site distribution than PMN. These multinuclear NMR approaches demonstrate the enormous potential of solid-state NMR spectroscopy to provide both qualitative and quantitative information about the chemical environments, cation ordering and motional behavior of the B-site cations in a diverse range of perovskite relaxor ferroelectrics.