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Structure-Property Relationships of Layered Oxypnictides

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AN ABSTRACT OF THE DISSERTATION OF Sean W. Muir for the degree of Doctor of Philosophy in Chemistry presented on April 17, 2012. Title: Structure-property Relationships of Layered Oxypnictides Abstract approved:______________________________________________________ M. A. Subramanian Investigating the structure-property relationships of solid state materials can help improve many of the materials we use each day in life. It can also lead to the discovery of materials with interesting and unforeseen properties. In this work the structure property relationships of newly discovered layered oxypnictide phases are presented and discussed. There has generally been worldwide interest in layered oxypnictide materials following the discovery of superconductivity up to 55 K for iron arsenides such as LnFeAsO1-xFx (where Ln = Lanthanoid). This work presents efforts to understand the structure and physical property changes which occur to LnFeAsO materials when Fe is replaced with Rh or Ir and when As is replaced with Sb. As part of this work the solid solution between LaFeAsO and LaRhAsO was examined and superconductivity is observed for low Rh content with a maximum critical temperature of 16 K. LnRhAsO and LnIrAsO compositions are found to be metallic; however Ce based compositions display a resistivity temperature dependence which is typical of Kondo lattice materials. At low temperatures a sudden drop in resistivity occurs for both CeRhAsO and CeIrAsO compositions and this drop coincides with an antiferromagnetic transition. The Kondo scattering temperatures and magnetic transition temperatures observed for these materials can be rationalized by considering the expected difference in N(EF)J parameters between them, where N(EF) is the density of states at the Fermi level and J represents the exchange interaction between the Ce 4f1 electrons and the conduction electrons. In addition to studying these 4d and 5d substituted systems the LaFeSbO compositional system was investigated. While LaFeSbO has not been successfully synthesized the transition metal free layered oxypnictide composition La2SbO2 was discovered and its structural and physical properties have been examined along with the properties of La2BiO2. Density functional theory was used to calculate the heats of formation for competing phases within the LaFeSbO system, in order to better understand the stability of LaFeSbO and why it has not yet been observed. The materials La2SbO2 and La2BiO2 were investigated for the presence of oxygen vacancies using powder neutron diffraction. Structure refinement reveals that there is significant disorder within the a-b plane for Sb compositions. ©Copyright by Sean W. Muir April 17, 2012 All Rights Reserved Structure-property Relationships of Layered Oxypnictides by Sean W. Muir A DISSERTATION submitted to Oregon State University In partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented April 17, 2012 Commencement June 2012 Doctor of Philosophy dissertation of Sean W. Muir presented on April 17, 2012. APPROVED: Major Professor, representing Chemistry Chair of the Department of Chemistry Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. Sean W. Muir, Author ACKNOWLEDGMENTS There is no way I can possibly list everyone that has helped me along the way with research advice, words of encouragement, and general kindness. Thus I apologize to all those I will miss in my attempt. First off I need to thank my thesis advisor Mas Subramanian for giving me all the freedom, encouragement, and resources needed grow into the best possible scientist and chemist I can be. By providing such a great laboratory to work in I was allowed to truly work at the limits of my own ability. Thanks to my three awesome office mates who helped to transform it from just an office into a tropical jungle and who tolerated the curious system of organization used on my desk; Geneva Laurita-Plankis, Rosa Grajczyk, and Whitney Schmidt. Thanks to James Eilertsen, Romain Berthelot, and Alvin Gatimu for many a great discussion. Double thanks to these guys and thanks to Peng Jiang, Theeranun Siritanon, and Krishnendu Biswas for help in the lab and for never telling me to turn down my music while working in the glove box right outside their offices. Thanks to Jun Li for helpful conversations about x-ray diffraction. Thanks to Andy Smith for showing me around the lab when I first arrived at OSU. Special thanks to Arthur Sleight, Michael Lerner, Brady Gibbons, and Guenter Schneider for serving as my thesis committee and critically reviewing this work, with a double thanks to Guenter Schneider and to Jason Vielma as well for insightful discussions about band structure computations and for happily collaborating on the investigation of LaFeSbO. I have also been blessed to encounter a number of amazing science educators along my path going all the way back way to my undergraduate days. Richard Nafshun and Christine Pastorek have been a huge influence on me since arriving at OSU. Their advice both as professional mentors and just genuinely nice people has been quite helpful. Extra thanks to Rick for guidance and encouragement during my time teaching one of the general chemistry courses and to Chris for letting me be a teaching assistant as part of the integrated chemistry series, both experiences helped immensely to solidify my love for teaching. Going back to my days before OSU at Evergreen State College, where my passion for science was first realized, I need to thank Rebecca Sunderman, Dharshi Bopegedera, Judy Cushing, and Robert Knapp as each of them took part in steering me to the course I am now on. A huge shout out needs to go out to Chris Knutson and Bill Cowell for many exciting and enlightening discussions about all topics under the sun. Also to all members past, present, and future of the SSA, a forum that has provided me with as many personal friends as it has connections to stellar scientists and academics. Last and most importantly, I must thank my family. Thanks to my pops, for always being there. Each day as I grow older I understand more fully what it took for you to be the amazing person you are and to have made the sacrifices you did. Thanks to my mom, for nurturing my body and mind as a child and for showing me the depth of human nature. Thanks for my brothers and sister for providing all the stories and memories that only growing up together can give. Finally I get to thank the most wonderful people I have in my life, my beautiful wife and children. It is for you that I try to succeed and it is you all that want to continue journeying through life with. Thanks for filling my dining room table office with enough music, art, tasty food, and love to see me through this scientific voyage. CONTRIBUTION OF AUTHORS Chapter 2: Dr. Mas Subramanian and Dr. Arthur Sleight contributed in the preparation and review of the manuscript on which this chapter is primarily based, Muir, S., Sleight, A.W., Subramanian, M.A., 2010. Mat. Res. Bull. 45, 392–395. Chapter 3: Dr. Mas Subramanian and Dr. Arthur Sleight contributed in the preparation and review of the manuscript on which this chapter is primarily based, Muir, S., Sleight, A.W., Subramanian, M.A., 2011. J. Solid State Chem. 184, 1972– 1976. Chapter 4: Dr. Mas Subramanian and Dr. Arthur Sleight contributed in the preparation of the manuscript on which this chapter is primarily based. Dr. Guenter Schneider and Jason Vielma performed the density functional theory calculations which provided the heats of formation and the phonon dispersion plot for LaFeSbO and related phases. They each also contributed to the writing and review of the resulting manuscript, Muir, S., Vielma, J., Schneider, G., Sleight, A.W., Subramanian, M.A., 2012. J. Solid State Chem. 185, 156–159. Dr. Maxim Avdeev collected the neutron powder diffraction data for La2SbO1.5 and La2BiO1.5 samples on the Australian Nuclear Science and Technology Organization - Bragg Institute’s Echidna diffractometer. Appendix A: Mas Subramanian and Omar Rachdi contributed to the preparation and review of the manuscript on which this chapter is based, Muir, S., Rachdi, O.D., Subramanian, M.A., 2012. Mat. Res. Bull. 47, 798–800. Omar Rachdi also contributed to the synthesis of these compositions as an undergraduate researcher under the guidance of S. Muir Appendix B: Mas Subramanian, Chris Knutson, and Richard Nafshun contributed to the review of the manuscript on which this chapter is based. Additionally Chris Knutson helped with the classroom outreach component of this project. TABLE OF CONTENTS Page 1 General Overview and Introduction to Layered Oxypnictides................................... 1 1.1 Introduction ......................................................................................................... 1 1.2 Introduction to LnMAsO materials (where Ln = Lanthanoid, M = late transition metal) ......................................................................................................................... 4 1.3 References .......................................................................................................... 27 2 Superconductivity within the LaFe1-xRhxAsO system ............................................... 32 2.1 Abstract .............................................................................................................
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