Date of Degree

5-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Stephen O'Brien

Committee Members

Jackie Li

Jonathan Owen

Maria Tamargo

Andrei Jitianu

Subject Categories

Ceramic Materials | Inorganic Chemistry | Materials Chemistry

Keywords

barium titanate, composite, energy storage, capacitor, multiferroic, magnet

Abstract

Nanocrystalline transition metal oxides with unique chemical, physical, magnetic and dielectric properties have very broad applications, ranging from photocatalysis, capacitor energy storage and 4-state memory. Frequency stable, high permittivity nanocomposite capacitors produced under mild processing conditions offer an attractive replacement to MLCCs derived from conventional ceramic firing. In one project reported herein, 0-3 nanocomposites were prepared using BaTiO3 (barium titanate, BTO) nanocrystals, suspended in a poly(furfuryl alcohol) matrix, resulting in a stable, high effective permittivity, low and stable loss dielectric. Effective medium approximations were used to compare this with similar nanocomposite systems. The use of synthesized BTO nanocrystal photocatalysts on mustard-gas surrogate compound degradation is briefly described. The investigation of a multiferroic crystal system is also reported; materials which are intrinsically ferroelectric and ferromagnetic are known as single-phase multiferroics, and offer opportunities for sensors, 4-state memory and spintronic devices. BaMn3Ti4O14.25 (BMT-134) is a recently discovered single-phase multiferroic complex oxide exhibiting antiferromagnetic and ferroelectric behavior. To modulate magnetic properties, ultimately towards a room temperature ferroic order response, BMT-134 was doped with Fe in varying ratios. The parent compound and four distinct variations of nanocrystals were synthesized; BaMn3Ti4O14.25 (BMT) and BaMn3-xFexTi4O14.25 (BMFT) with x = 1, x = 1.5, x = 2, and x = 2.25. High product precursor fidelity was observed. Using a chemical solution approach colloquially referred to as the ‘gel-collection method’, BTO and BMFT nanocrystal systems were synthesized as a part of each of the aforementioned projects. Structural, elemental, magnetic, chemical and dielectric characterization of the nanocrystals was performed. Characterization techniques include transmission and scanning electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, FTIR, energy dispersive X-ray spectroscopy, magnetic property measurement system M-H hysteresis curves, M-T Curie-Weiss fitting, Mossbauer spectroscopy, LCR impedance analysis and effective medium approximations.

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