Peidong Zhao

Document Type

Thesis - University Access Only

Award Date

1998

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

Abstract

Solid-state 207Pb and 93Nb NMR spectroscopy were used to study Pb(Mg1/3Nb2/3)O3 (PMN). (l-x)Pb(Mg 1/3Nb2/3)O3-xPbTiO3 (PMN/PT), Pb(ZrxTi 1-x)O3 (PZT) and a series of model compounds because niobium and lead contained in these materials play a crucial role in their behavior. Static and MAS 207Pb NMR spectra of PMN, PMN/PT, PZT and a series of related compounds have been measured. The principle components of the CSA tensor and the spin-lattice relaxation time have been determined for most of these compounds. The symmetry of the lead environment and the covalency of the Pb-0 bonds are determined to be the best indicator of the 207Pb isotropic and anisotropic chemical shifts. PMN, PMN/PT, and PZT have single 207Pb NMR resonance, with shifts and linewidths consistent with the Pb-0 bonds being less covalent than those in PbO and more covalent than the Pb-0 bonds in PbTiO3, and PbZrO3 In addition, a novel NMR technique was used to measure 207Pb NMR powder patterns as broad as 330 kHz, efficiently and quantitatively. One-dimensional spectra of central transition of 93Nb (spin= 9/2) has been measured also in a series of model compounds at different fields. NMR parameters for both the chemical shift interaction and quadrupolar interaction and were determined for some of the materials. The longitudinal and transverse relaxation times of 93Nb were measured. Study shows that the quadrupolar interaction is more sensitive to the variations of local electric charge distribution than the chemical shift interaction. The distortion of octahedral environment of niobium due to the variation of bonding conditions is the major cause for the variation of coupling constants. The second nearest neighbor atoms may account for some of this effect also. The covalency or ionicity of the Nb-O bonds is an indicator of the symmetry environment and thus the quadrupolar interaction. Multidimensional 93Nb NMR experiments such as DAS, multiple quantum coherence and pure phase nutation were presented. Their theoretical backgrounds, application to piezoelectric materials and limitation of these techniques are also fully discussed. In addition, the theoretical background of general solid state NMR is provided in first part of this thesis.

Library of Congress Subject Headings

Piezoelectric materials
Nuclear magnetic resonance spectroscopy

Format

application/pdf

Number of Pages

216

Publisher

South Dakota State University

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