SYNTHESIS AND STRUCTURE-PROPERTY RELATIONSHIPS OF A FEW FLUORIDE COMPOUNDS: (I) MIXED-METAL FLUOROCARBONATES AND (II) A REDUCED NIOBIUM OXYFLUORIDE ------------------------------------------------------ A Dissertation Presented to the Faculty of the Department of Chemistry University of Houston ------------------------------------------------------ In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy ------------------------------------------------------ By Thanh Thao Tran May 2015 SYNTHESIS AND STRUCTURE-PROPERTY RELATIONSHIPS OF A FEW FLUORIDE COMPOUNDS: (I) MIXED-METAL FLUOROCARBONATES AND (II) A REDUCED NIOBIUM OXYFLUORIDE _________________________________________ Thanh Thao Tran APPROVED: ________________________________________ Dr. P. Shiv Halasyamani, Chair ________________________________________ Dr. Arnold M. Guloy ________________________________________ Dr. Bernd Lorenz ________________________________________ Dr. Eric Bittner ________________________________________ Dr. Jakoah Brgoch ________________________________________ Dean, College of Natural Sciences and Mathematics ii Dedicated to my family: my Mother, Father and Sister Truc for their never ending love, encouragement and support iii ACKNOWLEDGEMENTS Firstly, I would like to thank my advisors, Dr. P. Shiv Halasyamani and Dr. Arnold M. Guloy. I have no doubt in my mind that having two of them as my advisors was a great gift. To Dr. P. Shiv Halasyamani, words cannot express how grateful I am to him. When I started out my journey at the University of Houston, I had no clues in the field I was entering. I was totally blank and he spent his time out of his tight schedule teaching me. Always, he offered me countless opportunities, not only in our work but also in our collaborations with other research groups internationally, to learn and experience a great deal of valuable lessons. His encouragement, enthusiasm and dedication to science have influenced my thoughts. It is my understanding that I am, at some points, ‘abnormal’. Patiently and nicely, he has drawn me to the way I should be simply by what he did and how he did that. All he has taught me, in and out chemistry, I shall carry along with me for years to come. Also, I would like to thank his entire beautiful family – Shiv, Angela, gorgeous Oliver and Ingrid – for the warm conversations we engaged in every time I had a chance meeting with them. To Dr. Arnold M. Guloy, I would like to thank you very much for opening up a new direction for my research. His lightheartedness and enthusiasm about our research made me easy to ask questions. He created a relaxed and yet motivating atmosphere to work in. From him, I learned how to approach things systematically. Also I learned how to be iv open to new ideas and critical of them at the same time. It is my intention to implement many of these lessons to my independent career. I would also like to thank the members of my committee, Dr. Bernd Lorenz, Dr. Eric Bittner and Dr. Jakoah Brgoch for their mindful suggestions to my research as well as my dissertation. I am especially thankful to Dr. Bernd Lorenz for his assistance and stimulating discussions in magnetism and transport property. Whenever I got lost, he was the person who was always there to help me out. From him, my background on physics of condensed matters was improved. In addition, I would like to express my deep gratitude to Dr. Jakoah Brgoch and Dr. James M. Rondinelli, Dr. Jiangang He (Northwestern University) for the theoretical calculations, Dr. Kenneth R. Poeppelmeier, Dr. Shichao Wang, Dr. Martin Donakowski (Northwestern University) for assistance in FTIR measurements, Dr. Alexander P. Litvinchuk (Raman scattering), Dr. Melissa Gooch (magnetic and transport measurements). I would also like to thank Dr. James D. Korp and Dr. Xiqu Wang for their assistance and helpful discussions in crystallography. I am grateful to Dr. James Meen and Dr. Karoline Mueller for their training and assistance in SEM/EDS analysis. A university is not a school at all without students and post-docs, and the University of Houston is one of sharing. Several good friends shared my life of a graduate student in the Halasyamani group: Dr. Weiguo Zhang, Dr. Jeongho Yeon, Dr. Sang-Hwan Kim, Dr. Hongwei Yu, Dr. Sau Nguyen, Dr. Sunwoo Kim, Ilyana Derkach and Philip Ayazi; and the Guloy group: Dr. Zhongjia Tang, Dr. Phuong Doan, Maurice Sorolla, Sean See, John Manongdo and Xin Zhong. I also cannot forget a great time hanging out with Thien Si v Nguyen (and his family), Ha Le, Thien Trong Nguyen, Phong Le, Ha Do, Hung Tran, Yi- ting Chen, Nui and the other friends I made. A number of my other colleagues and friends back in Vietnam and all around the world made my stay here more pleasant through their letters, emails and phone calls. They are Dat Dang, Thanh Bui, Nguyen H. Nguyen, Phuc Nguyen, Minh Tran, Nhan Nguyen, Tanh Nguyen and Phuoc Dinh. I would not be a person who I am now if I did not meet my professor, Ngoc Minh Huynh, back in Ho Chi Minh, Vietnam, more than 12 years ago. He changed my mind to follow inorganic chemistry instead of information technology, which was a ‘hot’ college major back in 2003. This diversion helped me find the person within me. A mentor, he is more than a mentor. A great friend, he is more than a great friend. If someone truly understands me, at both my bad (definitely) and ‘acceptable’ (probably) corners, it is him. The influence he had on me was, and still is, tremendous. There were times where I did not think I could complete my studies, he always stood by my side and walked me through all that. “Follow your heart, everything else is just secondary,” he said to me. Yet, I cannot thank him enough for his belief in me, his constant support in everything I set my heart to and his relentless patience even at the time where I became impossible of being put up with. I understand I could certainly not have gone this far without him. At last, but definitely not least, my deepest gratitude goes to my parents and my ‘little’ sister Truc for their support, love and encouragement. Without them, I would vi probably not have written this dissertation, and even if I had this dissertation done, it would have had no meaning. This work was supported by the United State Department of Energy – Basis Energy Sciences (DE-SC0005032) and the Welch Foundation (Grant E-1457). Also, it was in part supported by the Welch Foundation (E-1297), the State of Texas through the Texas Center for Superconductivity and the US AFOSR. vii SYNTHESIS AND STRUCTURE-PROPERTY RELATIONSHIPS OF A FEW FLUORIDE COMPOUNDS: (I) MIXED-METAL FLUOROCARBONATES AND (II) A REDUCED NIOBIUM OXYFLUORIDE ------------------------------------------------------ An Abstract of a Dissertation Presented to the Faculty of the Department of Chemistry University of Houston ------------------------------------------------------ In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy ------------------------------------------------------ By Thanh Thao Tran May 2015 viii ABSTRACT This dissertation focuses on the synthesis and structure-property relationships of new complex metal fluorides of (i) alkaline-metal lead fluorocarbonates, alkaline-metal magnesium fluorocarbontes and (ii) a reduced niobium oxyfluoride. We have designed new structure building units, PbO6F and PbO6F2, in layered compounds of KPb2(CO3)2F and K2.70Pb5.15(CO3)5F3, that were then developed to three-dimensional noncentrosymmetric RbPbCO3F and CsPbCO3F. Powder second-harmonic generation (SHG) measurements on K2.70Pb5.15(CO3)5F3, RbPbCO3F and CsPbCO3F using 1064 nm radiation revealed SHG efficiencies of approximately 40, 250 and 300 -SiO2, 2+ 2+ respectively. The Mg substitution of the Pb cation in APbCO3F (A = alkaline-metal) resulted in KMgCO3F and RbMgCO3F with unique coordination environments of magnesium, i.e., pentagonal arrangements in the ab-plane. These compounds are second- harmonic generation (SHG) phase-matching at both 1064 nm (120 and 160 -SiO2) and 532 nm (0.33 and 0.6 -BaB2O4) with short UV cut-off edges, below 200 and 190 nm for KMgCO3F and RbMgCO3F, respectively. These mixed-metal fluorocarbonates were also characterized by infrared spectroscopy, thermogravimetric and differential thermal analysis. In addition, we report a new highly correlated electron system, Nb2O2F3. It is a new low-valent niobium (III/IV) oxyfluoride that features [Nb2X10] units (X = O, F) with short (2.5739(1) Å) Nb-Nb metal-metal bonds. The [Nb2X10] units are connected through shared O/F vertices to form a 3D structure. Nb2O2F3 undergoes a structural transition (below 90 K), from a monoclinic to a triclinic structure, which can be described as a ix 7+ charge ordering or disproportionnation of [Nb2] dimers. That resulted in a doubly (2.5000(9) Å) and a singly bonded (2.6560(9) Å) Nb2 dimers. The structural change is associated with unusual field-independent ‘spin-gap-like’ magnetic and electronic phase transition. x TABLE OF CONTENTS Chapter 1 General Introduction .......................................................................................1 1.1 Related Literature and Scope of the Study ....................................................................1 1.2 Summary of Chapters ....................................................................................................3 1.3 References ......................................................................................................................5 Chapter 2 Theoretical Background ..................................................................................7