Date of Award

8-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemistry

Advisor

Hwu, Shiou-Jyh

Committee Member

Daw , Murray

Committee Member

Kolis , Joe

Committee Member

Pennington , Bill

Abstract

The ultimate goal of the research presented in this dissertation was to explore new systems containing low–dimensional magnetic nanostructures in hopes of finding new extended solids exhibiting novel magnetic properties due to the confined magnetic lattices. The scope of this research is threefold: 1) to explore new solids containing low–dimensional magnetic nanostructures in the A–M–X–O system, where A is an alkali or alkalinendash;earth metal cation, M is a first–row transition metal cation, and X is P, As, or V, 2) to characterize these new materials and, through chemical substitution, fine tune (and optimize) magnetic and electronic properties of solids that exhibit confined magnetic nanostructures, and 3) to perform structure/property correlation studies to seek the origins of any unusual physical phenomena associated with the size, shape, and geometry of the magnetic nanostructures.
Throughout this study, diamagnetic oxyanions XOmn− were utilized to structurally insulate and electronically confine the transition metal oxide lattices. Typical reactions included various transition metal oxides, main group oxides such as P4O10 or As2O5, and alkali/alkaline–earth metal oxides. Most of these starting materials have high melting points and low solubility. As a result, highndash;temperature solid state methods are utilized. In the solid state, single crystal growth sometimes suffers because of slow diffusion across the crystalline interface. In order to alleviate this problem, alkali and alkaline–earth metal halides are employed as a high–temperature flux. These salts have much lower melting points than covalent metal oxides and can aid in the synthesis and crystal growth of materials that cannot be achieved in other solvent media.
There are additional advantages to using molten halide fluxes, for they can also act as reactants in the synthetic systems. First, it was considered that, like the aforementioned diamagnetic oxyanions, ionic salt could also be utilized to reduce the
dimensionality of the TM–oxide magnetic lattices. The difference between these two diamagnetic insulators is found in their bonding interactions with respect to the transition metal oxide nanostructures. The oxyanions are covalent in nature, while the salt is more ionic in nature and therefore is less likely to function as a pathway for superexchange. As a result, it was thought that this salt could further aid in the confinement of the magnetic TM–oxide lattices, hence, many of the reactions were carried out in a huge
excess of salt. This was done not only to increase the reaction kinetics, but also in hopes of obtaining interesting phase formations such as metal oxide nanostructures engulfed in a sea of salt.
In this study, diamagnetic oxyanions XOmn− and/or salt, utilized to terminate the
propagation of the transition metal oxide lattices, allowed the formation of structures
with 2–D sheets, 1–D chains, and 0–D clusters. Exploratory synthesis in this mixed
polyhedral system consisting of the tetrahedral oxyanions and the transition metal oxide
with varying coordination environments, has proven to be extremely rich and has
rendered many new compounds of magnetic and catalytic interest. The new discoveries
are grouped into chapters according to their lattice types, where Chapter 3 and Chapter 5
present two extensive compound families that contain two dimensional metal oxide
sheets, Chapter 6 presents a lattice with 1–D [MO4Cl] chains, and Chapters 4, 7, and 8 all present materials containing 0–D magnetic metal oxide clusters.

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