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Investigations Into the Structure and Properties of Ordered Perovskites, Layered Perovskites, and Defect Pyrochlores

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Investigations Into the Structure and Properties of Ordered Perovskites, Layered Perovskites, and Defect Pyrochlores INVESTIGATIONS INTO THE STRUCTURE AND PROPERTIES OF ORDERED PEROVSKITES, LAYERED PEROVSKITES, AND DEFECT PYROCHLORES. DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Meghan C. Knapp ***** The Ohio State University 2006 Dissertation Committee: Approved by Professor Patrick M. Woodward, Advisor Professor Claudia Turro _________________________________ Professor Terry Gustafson Advisor Graduate Program in Chemistry Professor Mohit Randeria ABSTRACT The work described in this thesis explores the effects of chemical substitution on the structures and properties of perovskites, layered perovskites, and defect pyrochlores. Layered perovskites, particularly of the variety K2NiF4, the n = 1 Ruddlesden-Popper structure, were studied to determine the factors that drive octahedral tilting distortions. It was determined that these structures, which are more inherently strained than perovskites, are influenced by the bonding environment around the anions and the A-cation as well as the electrostatic interactions between layers. The effects of cation ordering on the symmetry of Ruddlesden-Popper structures are also presented. Dion-Jacobson structures were also analyzed, and it was found that the trends that govern the behavior of Ruddlesden-Popper structures were not applicable. When n = 1 for Dion-Jacobson structures, the weak inter-layer interactions make the parent structure prone to tilting and plane slippage. This stoichiometry has several competing structures, many of which are observed for AMO4 compounds with highly covalent M-O interactions. Stoichiometric perovskites with multiple A-cations rarely exhibit layered ordering of the A-cations. Double perovskites having two A-cations and two M-cations with the formula AA'MM'O6 (A= Na, K, Li, A' = La, M = Mg, Sc M' = W, Nb, Sb, Te, or when M = M', M = Ti, Zr) were studied to determine the driving force for layered ordering of A-site cations. ii It was determined that such ordering is cooperative with the displacement of d0 transition metals from the M-cation site, which allows for relief of the bonding strain on the intra- layer oxygen ions. This represents a novel way to propagate cation displacements, i.e. via the ordering of the A-cation which works synergistically with the M-site cation displacements. Such displacements can produce desirable dielectric properties, and these properties can be further enhanced by the use of an A-cation with a stereo-chemically active lone pair. As such, analogous compounds were prepared where A' = Bi3+. It was found that when perovskites were formed, no layered ordering of the A-cations was produced. When M' was a main group element, namely Sb5+, the perovskite phase and the defect pyrochlore phase were observed to be competitive. The dielectric properties of these materials were tested and it was found that the bismuth structure containing Nb5+ had the highest dielectric constant. iii DEDICATION For Samantha and Charlotte You Can iv ACKNOWLEDGMENTS My time at Ohio State has been a fascinating period of intellectual development and personal growth. This work would not have been possible without the help and support of many people. I would like to acknowledge the people who helped me with the acquisition and treatment of my data: Dr. Gordan Renkes for his assistance with X-ray powder diffraction; Dr. Judith Stalick for use of the BT-1 line at NIST, Dr. Cameron Begg for SEM elemental analysis, Dr. Harold Stokes for help with ISOTROPY, and Dr. Suzanna Garcia-Martin for SAED analysis of NaLaMgWO6. I would also like to acknowledge Dr. Bruce Bursten for his mentorship in my career development, both as a teacher and a scientist. I had the opportunity to TA for honors chemistry under Bruce and to discuss teaching methodology. He has provided both guidance and encouragement in exploring my options for teaching at the collegiate level. I have benefited from his contagious enthusiasm for Group Theory and his dedication to his craft. I would like to thank the members of the Woodward group, both past and present for their help with my academic career. Paris Barnes, Hank Eng, and Mike Lufaso, taught me all about solid state synthesis and X-ray powder diffraction. Young-il Kim taught me about the measurement and treatment of impedance data. Fus, Matt, Rebecca, v and Harry helped me to learn our craft the best way there is: by teaching it. Fus also taught me to use CASTEP… three times! All the Woodward group members provided feedback and support for my preparations for presentations, candidacy, and graduation. Of course, it is important for me to acknowledge my advisor, Dr. Pat Woodward. As with all good advisors, he supported me in my research by constructively critiquing my analysis and forcing me to think more critically about my work. He has always been available for discussion, but has given me a great deal of freedom in the conduction of my research. Additionally, Pat has served as a role model of a parent-scientist, being able to advance in his career while staying actively involved in his kids’ lives. Without his support, completion of my degree would not have been possible while still being the kind of mother I want to be to my girls. Special thanks go to my family for their support of my decision to return to school. In particular my parents, Penny and Jerry, seemed to know more than I did how much I needed this. My husband Peter has gone above and beyond what most women expect of their spouses in support of me. He has listened to and read countless presentations of my research, and advised me on mathematical calculations. He has taken over almost all aspects of maintaining our home. He has been a stellar parent at all times, and has managed on his own on the numerous occasions that I have traveled to conferences. Peter has managed my stress far better than I have, and been the primary witness to my tears in the past few months, even as he has had his own stresses. Without his love and support, I would never have considered returning to school, let alone had the confidence to complete my degree. vi VITA 28 October 1975. Born – Indianapolis, Indiana 8 May 1998. Bachelor’s of Science Peabody College at Vanderbilt University. 1998 – 2001. Science Teacher. The Columbus City Schools. 2001 – 2002. University Distinguished Fellow. The Ohio State University. 2002 – 2005. Teaching/Research Asst. The Ohio State University. 2003 – 2004. NSF GK-12 Fellow. The Ohio State University. 2005 – 2006. University Distinguished Fellow. The Ohio State University. PUBLICATIONS Research Publications 1. Knapp, Meghan C.; Woodward, Patrick M. A-site cation ordering in AA'BB'O6 perovskites. Journal of Solid State Chemistry (2006), 179(4), 1076-1085. FIELDS OF STUDY Major Field: Chemistry vii TABLE OF CONTENTS P a g e Abstract. ii Dedication. .iv Acknowledgments . .v Vita . .vii List of Tables. .xii List of Figures . xiv Abbreviations. xvi Chapters: 1. INTRODUCTION. .1 1.1. Background, properties and applications of perovskites and related structures. .1 1.1.1. Historical Background 1.1.2. Properties of Ordered Perovskites 1.1.3. Properties of Layered Perovskites 1.1.4. Properties of Pyrochlores 1.2. Introduction to the Perovskite Structure. .5 1.2.1. General Description of the Perovskite Structure 1.2.2. Octahedral Tiliting Distortions and Notations 1.3. Layered Perovskites. 6 1.3.1. The Ruddlesden-Popper and Dion-Jacobson Structures 1.3.2. Notations for Tilting Distortions 1.4. Perovskites with A- and B-site Cation Ordering. .11 viii 1.5. Pyrochlores . .15 1.5.1. General Description of the Pyrochlore Structure 1.5.2. Defect Pyrochlore Structure 1.6. References. .18 2. GROUP THEORETICAL ANALYSIS OF LAYERED PEROVSKITES . 20 2.1. Introduction. .20 2.2. Distortions in Ruddlesden-Popper Structures . 20 2.2.1. Symmetry Allowed Distortions 2.2.2. Octahedral Tilting Distortion 2.3. Distortions in n = 1 Dion-Jacobson Structures. 37 2.3.1. Symmetry Allowed Distortions 2.3.2. Octahedral Tilting Distortions 2.4. Conclusions. .48 2.5. References. .48 3. EVALUATION OF OCTAHEDRAL TILTING DISTORTION TRENDS IN RUDDLESDEN-POPPER AND DION-JACOBSON STRUCTURES. 50 3.1. Introduction. .50 3.2. Ruddlesden-Popper Structures. 50 3.2.1. Lattice Strain and Bond Valence Sums 3.2.2. Measures of Strain 3.2.3. Known n=1 Ruddlesden Popper Structures 3.2.4. Modeling of RP n = 1 Structures Using Lattice Eneries 3.3. Dion-Jacobson Structures . 71 3.3.1. Lattice Strain 3.3.2. Known n = 1 Dion Jacobson Structures 3.3.3. Structures with n > 1 3.4. Conclusions. .71 3.5. Referencecs. .73 4. STRUCTURAL STUDIES OF NaLaMM'O6 PEROVSKITES AND THE INFLUENCE OF CATION SUBSTITUTION ON THE LAYERED ORDERING OF SODIUM AND LANTHANUM . 85 ix 4.1. Introduction . 85 4.2. Effects of distortions cation ordering on X-ray powder diffraction. 86 4.2.1. M-site Cation Ordering 4.2.2. A-site Cation Ordering 4.2.3. Distortions and Group Theoretical Analysis 4.3. Experimental . 93 4.3.1. Synthesis 4.3.2. Structural Characterization (XRD, NPD, SAED) 4.3.3. Data Analysis 4.4. Results. 97 4.4.1. NaLaMgWO6 4.4.2. NaLaMgTeO6 4.4.3. NaLaScNbO6 4.4.4. NaLaScSbO6 4.4.5. NaLaTi2O6 and NaLaZr2O6 4.4.6. KLaMgWO6 and LiLaMgWO6 4.5. Discussion. .113 4.6. Conclusion. .115 4.7. References. .115 5. STRUCTURAL STUDIES OF NaBiMM'O6 STRUCTURES AND THE INFLUENCE OF THE STEREO-ACTIVE LONE PAIR ON ORDERING AND THE STABILITY OF THE PEROVSKITE structure. 118 5.1. Introduction. .118 5.2. Introduction to Dielectrics. .119 5.3. Experimental. .120 5.3.1. Synthesis 5.3.2. Structural Characterization 5.3.3. Dielectric Measurements 5.4.
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