Date of Degree

9-2021

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor

Stephen O'Brien

Committee Members

Maria Tamargo

Ilona Kretzschmar

Simon Billinge

Matthew Sfeir

Subject Categories

Chemistry | Materials Chemistry

Abstract

The synthesis and characterization of nanocrystalline transition and rare-earth metal oxides have been studied widely over the past years. These materials possess unique physical, chemical, magnetic and dielectric properties which make them potential candidates for a wide range of applications such as electronics, energy storage and photocatalysis. There are a number of synthesis methods for preparing these materials, where most of them require stringent conditions such as high pressure and high temperature. However, in this study, a modified sol-gel synthesis has been used with a lower calcination temperature to make uniform nanocrystals of the transition/rare-earth metal oxide family. The focus of this project is the synthesis and characterization of europium doped into barium titanate crystal structure. Recently, EuTiO3 and certain substituted such as Eu0.5Ba0.5TiO3 have come into attention due to their potential magnetoelectric applications. In order to prepare europium titanate compounds, two different crystal structures were synthesized based on different processing conditions: one in the form of perovskite (ABO3) and the other as a pyrochlore structure (A2B2O7). After successful synthesis of Eu-Ti-O systems, the project moved further to the preparation of Eu-Ba-Ti-O system to get advantages of both magnetic properties of Eu ions, and Barium titanate (BaTiO3) as a prototypical ferroelectric material. The perovskite Eu-Ba-Ti-O system having 50%-50% of europium and barium atoms, displays large dielectric polarization, alongside ferroelectricity and ferromagnetism in low temperature. Most approaches to synthesize the EBTO systems lies in the solid-state reaction methods. However, here we used a chemical solution approach (referred to gel-collection method), which produces nanoscale particles of europium barium titanate at lower temperatures. Moreover, other ratios of Eu/Ba atoms including 0.25/0.75 and 0.75/0.25 was investigated. In order to figure out the properties of synthesized nanocrystals, a series of characterization including structural, elemental, magnetic and dielectric properties were performed on the EBTO nanoparticles, followed by two potential applications in nanocomposite fabrication and photocatalytic activity. The characterization techniques include X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), LCR impedance analysis, ferroelectricity measurements and magnetic property measurement system (MPMS) in the form of M-H hysteresis curve and M-T curie-Weiss fitting.

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