Date of Award

2018

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

College of Arts and Sciences

First Advisor

Hans-Conrad zur Loye

Abstract

The primary objective of this dissertation is to inform about the single crystal growth of complex first and third row transition metal oxides via molten flux methods. Particular focus is given to complex oxides that contain transition metals with unpaired electrons. This fundamental research is motivated by a singular question: What can a critical analysis of chemical structure elucidate about magnetic order in oxide materials? Throughout the eight chapters of this dissertation, including an introductory chapter, this structure-property relationship will be investigated. These seven chapters will be organized into three parts, each corresponding to the general structure type of the family of oxides being studied.

Part one is dedicated to the discussion of structural and magnetic studies of complex platinum group metal (PGM) containing perovskites, encompassing chapters 2- 5. Chapter 2 focuses on the design, crystal growth, and magnetic investigation of a series of monoclinically distorted double perovskite iridates. In this study, double perovskites serve as ideal host structures to study how changes in monoclinic distortion affect magnetic order. Chapter 3 discusses a follow-up study of the iridates studied in chapter 2 using powder neutron diffraction, synchrotron X-ray diffraction, and Density Functional Theory (DFT) calculations to determine the magnetic structure of these iridates. Specifically, this study seeks to explain the determined magnetic structure through a critical analysis of the crystal structure.

Chapters 4 and 5 investigate the synthesis, characterization, and magnetic property measurements of triple and quadruple perovskites, focusing on how perturbations in the local symmetry environment of magnetic cations affect the electronic structure. More specifically, chapter 4 outlines the role of site-disorder in a polar, noncentrosymmetric triple perovskite with semiconducting properties and near room temperature magnetic ordering. Chapter 5 focuses on a quadruple perovskite that possesses the coexistence of Ni(II) and Ni(IV) with direct metal-metal bonding between Ni(IV) and Ir(V). Analysis of the resulting electronic structure from direct metal-metal bonding is discussed to understand the observed magnetic properties.

Part two will center on structural and magnetic studies of complex PGM containing perovskite-related oxides, encompassing chapters 6 and 7. Chapter 6 discusses a series of 2H-hexagonal perovskite-related oxides. This study elucidates the chemical structure of a family of incommensurate oxides using magnetic property measurements. Chapter 7 focuses on a series of layered perovskite-related oxides that provide insight into Ir(IV)-Ir(IV) super-superexchange, in addition to being a versatile host structure to test how changes in magnetic lanthanide ions affect magnetic order.

Part three will include chapter 8, the final chapter of this dissertation. This work examines two diferrite structures of the family BaO-nFe2O3, to which the multiferroic hexaferrites belong. Both materials crystallize in a novel structure type, magnetically order higher (870 K) than even the commercially used hexaferrites, and were studied via neutron diffraction to discern their magnetic structure.

Rights

© 2018, Timothy Ferreira

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