Document Type

Dissertation - University Access Only

Award Date

2003

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Jay Shore

Abstract

Lead magnesium niobate (PMN, Pb(Mg113Nb213)03) and (l-x)Pb(Mg113Nb213)03- xPbTi03 (PMN/PT) ferroelectric materials have been extensively studied due to their high dielectric constants, high electrostrictive strain coefficients and broad diffuse phase transition. Recently sol-gel processing has been used to prepare thin-layer and film PMN/PT materials for multilayer capacitors and various actuators. The composition of the mixed-metal alkoxide precursors plays an important role in the metal ion distributions of the hydrolysis intermediates and the final products. But, the solution chemistry of these sol-gel precursors is not fully understood. The sol-gel alkoxide precursors in both ethanol and 2-methoxyethanol systems to PMN/PT materials were synthesized. GPC and 13 C, 47, 49 Ti and 93Nb NMR measurements were used to examine the solution species and their structures. This is the first time GPC has been used to study the extremely moisture-sensitive metal alkoxides. GPC was used to separate the precursors into their components and characterize their homogeneity on the molecular level. Both a UV detector and a differential refractometer in-line were vi effective in detecting solution species present in the precursors, and they are complementary to each other. NMR spectroscopy was used to obtain structural information. Elemental analysis techniques for Pb, Mg, Nb and Ti present in the PMN/PT alkoxide precursors were developed. Concentrations of the metals in the collected fractions were determined to obtain information about the formation of heterometallic complexes in the mixed-metal alkoxide precursors. GPC analysis showed that the oligomeric heterometallic complexes were formed and present as the major components in the PMN mixed-metal alkoxide precursors. The existence of several species indicates that the PMN precursors were not homogeneous on the molecular level. The 2-methoxyethanol system was indicated to be better for sol-gel synthesis of PMN thin film compared to the ethanol system. Uniform magnesium niobium alkoxide complex (Mg(Nb(OR)6h) precursors were produced. The formation mechanism of magnesium niobium ethoxide from niobium pentaethoxide was proposed. A modified synthesis of the PT alkoxide precursor produced more homogeneous products than the PT alkoxide precursors currently used.

Library of Congress Subject Headings

Ferroelectric thin films.
Alkoxides.
Gel permeation chromatography.
Nuclear magnetic resonance spectroscopy.

Publisher

South Dakota State University

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Rights Statement

In Copyright