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Thermoelectric Property Studies on Lead Chalcogenides, Double-Filled Cobalt Tri-Antimonide and Rare Earth

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Thermoelectric Property Studies on Lead Chalcogenides, Double-Filled Cobalt Tri-Antimonide and Rare Earth Thermoelectric Property Studies on Lead Chalcogenides, Double-filled Cobalt Tri-Antimonide and Rare Earth- Ruthenium-Germanium by Huijun Kong A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Physics) in The University of Michigan 2008 Doctoral Committee: Professor Ctirad Uher, Chair Professor Massoud Kaviany Professor Bradford G . Orr Professor Leonard M. Sander Associate Professor Cagliyan Kurdak © Huijun Kong All Rights Reserved 2008 Dedicated to my parents ii Acknowledgments I first wish to thank Professor Ctirad Uher, my committee chair and research advisor. Throughout the past four years, Professor Uher has supported me in completing this dissertation. He has taught me the work ethics as an experimental physicist by example. I am very grateful for his kindness, patience and encouragements, and for allowing me the freedom to work at my own pace. My committee members deserve thanks for serving on my doctoral committee and for their insightful comments. Special thanks are due to my collaborators, Professor Donald Morelli, Dr. Xun Shi, Professor Mercouri G. Kanatzidis, Dr. Pierre F. P. Poudeu, Dr. John Androulakis, Dr. Chia-Her Lin and Joseph Sootsman. The research presented in this dissertation would not have been possible without their contributions. My current labmates, Dr. Yi-Jiunn Chien, Dr. Changpeng Li, my junior Lynn Endicott also merit special acknowledgement for helping and assisting me in the lab on a daily basis. I would like to thank Dr. Carl Henderson at EMAL for helping me with EPMA measurement. I greatly appreciate his assistance. My parents have always been supporting me wholeheartedly. They provide me many opportunities in life. I am eternally grateful for their unconditional love and support. Financial support for this thesis work was provided by the Office of Naval Research under MURI program, titled New Thermoelectric Materials for Direct Energy Conversion. iii Table of Contents Dedication .......................................................................................................................... ii Acknowledgments ............................................................................................................ iii List of Figures .................................................................................................................. vii List of Tables .......................................................................................................................x Abstract ............................................................................................................................. xi Chapter I Introduction to Thermoelectrics ..........................................................................1 1.1 Thermoelectric Phenomena .....................................................................................2 1.1.1 Seebeck Effect .........................................................................................................2 1.1.2 Peltier Effect ............................................................................................................3 1.1.3 Thomson Effect ........................................................................................................4 1.1.4 Thomson Relationships ............................................................................................5 1.2 Thermoelectric Figure-of-merit ...............................................................................5 1.3 Optimization of Thermoelectric Performance .........................................................6 1.4 Thermoelectric Applications ....................................................................................7 1.4.1 Power generation .....................................................................................................7 1.4.2 Thermoelectric Refrigeration .................................................................................10 1.5 State-of-the-art Thermoelectric Materials ..............................................................12 References to Chapter I .....................................................................................................16 Chapter II Transport Theory in Solids ..............................................................................17 2.1 Transport Equation .................................................................................................17 2.2 Electrical Conductivity and Seebeck Coefficient ..................................................19 2.3 Thermal Conductivity ............................................................................................22 2.3.1 Electronic Thermal Conductivity ...........................................................................23 2.3.2 Lattice Thermal Conductivity ................................................................................25 References to Chapter II ....................................................................................................29 Chapter III Experimental Techniques ...............................................................................30 3.1 Material Synthesies ................................................................................................30 3.2 Chemical and Structural Analysis ..........................................................................31 3.2.1 X-ray Powder Diffraction (XRD) ...............................................................................31 3.2.2 Electron Microprobe Analysis ...................................................................................31 iv 3.3 Low Temperature Property Measurements ............................................................31 3.4 High Temperatuare Property Measurements ..........................................................33 3.4.1 Seebeck Coefficient ...............................................................................................33 3.4.2 Electrical Conductivity ..........................................................................................35 3.4.3 Thermal Conductivity ............................................................................................36 3.5 Magnetic Property Measurements .........................................................................37 3.6 Automation of High Temperature Apparatus .........................................................40 3.6.1 Electrical Conductivity ..........................................................................................40 3.6.2 Seebeck Coefficient ...............................................................................................41 References to Chapter III ...................................................................................................42 Chapter IV Lead Chalcogenides .......................................................................................43 4.1 Crystalline Structure ..............................................................................................44 4.2 Carrier Scattering Mechanism ...............................................................................44 4.3 Phonon Scattering Mechanisms ............................................................................45 4.4 Transport and Magnetic Characterization ..............................................................46 4.5 Established Nano-structured Bulk Lead Chalcogenides ........................................47 4.6 Results and Discussions .........................................................................................50 4.6.1 Sb-doped Lead Telluride/Lead Selenide ................................................................50 4.6.2 Bi/Sb/InSb-doped Lead Telluride ..........................................................................53 4.6.3 Nanostructured Lead Tin Telluride – Lead Sulfide ................................................56 4.6.4 Europium-doped Lead Telluride ............................................................................61 4.7 Conclusions ............................................................................................................67 References to Chapter IV ...................................................................................................68 Chapter V Double-filled Cobalt Tri-Antimonide ..............................................................69 5.1 Skutterudite Structure ............................................................................................70 5.2 Resonant Phonon Scattering ..................................................................................73 5.3 Results and Discussions .........................................................................................73 5.4 Conclusions and Future Work ................................................................................85 References to Chapter V ....................................................................................................86 Chapter VI Rare-Earth Ruthenium Germanium Compounds ...........................................87 6.1 Crystal Structure ....................................................................................................87 6.2 Experimental Methods ...........................................................................................88 6.3 Results and Discussions of R3Ru4Ge13 Samples ....................................................89 6.3.1 Structural Characterization ....................................................................................89
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