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Investigations on the Parent Compounds of Fe-Chalcogenide Superconductors

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Investigations on the Parent Compounds of Fe-Chalcogenide Superconductors Investigations on the parent compounds of Fe-chalcogenide superconductors DISSERTATION zur Erlangung des akademischen Grades Doctor rerum naturalium (Dr. rer. nat.) vorgelegt der Fakultät Mathematik und Naturwissenschaften der Technischen Universität Dresden von Cevriye Koz geboren am 29.06.1983 in Karaman, Türkei Eingereicht am:…………. Die Dissertation wurde in der Zeit von Januar/2010 bis Juni/2014 im Max- Planck Institut für Chemische Physik fester Stoffe angefertigt. Tag der Verteidigung: Gutachter: PD. Dr. Ulrich Schwarz Prof. Dr. Michael Ruck Dedicated to my parents Acknowledgements First and foremost, I am deeply indebted to Prof. Juri Grin and Prof. Dr. Liu Hao Tjeng for giving me an opportunity to work in Max Planck Institute for Chemical Physics of Solids as a doctoral student. I owe my deepest gratitude to my supervisor PD Dr. Ulrich Schwarz for his unlimited and constructive guidance, advice, suggestions and comments during my thesis. I would like to express my sincere gratitude to Dr. Sahana Rößler who has supported and encouraged me throughout my study with her patience and knowledge. Also I would like to thank PD Dr. Steffen Wirth for his support and guidance. I am grateful to Dr. Alexander A. Tsirlin for his guidance and patience during the synchrotron X-ray diffraction measurements at ESRF. I want to express my gratitude to Dr. Walter Schnelle, Mr. Ralf Koban for the physical property measurements and valuable discussions on measurements and data analysis. I would like to thank Dr. Marcus Schmidt and Ms. Anne Henschel for sharing their knowledge and experience on chemical vapor transport reactions. Also, I would like to express my gratitude to Dr. Horst Borrmann, Dr. Yurii Prots, and Mr. Steffan Hückman for performing X-ray diffraction measurements, Dr. Ulrich Burkhardt, Ms. Petra Scheppan, Ms. Monika Eckert, and Ms. Sylvia Kostmann for the metallographic preparations as well as EDXS and WDXS measurements. I gratefully acknowledge Dr. Steffan Hoffman and Ms. Susan Scharsach for thermal analysis, Dr. Wilder Carillo-Cabrera for SAED and TEM measurements, Dr. Michael Nicklas and Dr. Kamal Mydeen for the physical property measurements under high-pressure, Dr. Gudrun Auffermann, Ms. Ulrike Schmidt, and Ms. Anja Völzke for chemical analysis measurements. I would like to thank Ms. Dona Cherian for her cooperation and fruitful discussions, Ms. Ceren Zor and Mr. Gercek Armagan for sample preparation during their summer internship. I gratefully acknowledge Dr. Zhiwei Hu, Dr. Nils Hollmann, and Dr. Kyung-Tae Ko for XMCD measurements and their guidance during the beam-time. Also I would like to thank Dr. Carina Börrnert and Dr. Deepa Kashinathan for their contributions on high-pressure X-ray diffraction measurements. I am thankful to many of my colleagues to support me in numerous ways, especially Dr. Umut Aydemir, Dr. Burgehan Terlan, Dr. Alim Ormeci, Dr. Katrin Meier-Kirchner. I also would like to thank Prof. Mehmet Somer to introduce me into a nice working environment in Max Planck Institute for Chemical Physics of Solids. I am indebted for stimulating discussions with Prof. John Mydosh and Prof. Paul Canfield. I also thank for the financial support of the Deutsche Forschungsgemeinschaft (SPP 1458) and the Max Planck Society. i Table of Contents Chapter 1: Introduction .............................................................................................. 4 Chapter 2: Literature Overview ................................................................................. 7 2.1 History of superconductivity ................................................................................ 7 2.2 Iron-based superconductors ................................................................................. 9 2.3 The effects of chemical substitution and pressure on iron-based super- conductors ................................................................................................................ 10 Chapter 3: Preparation Methods and Experimental Techniques ......................... 14 3.1 Synthesis ............................................................................................................ 14 3.1.1 Materials and chemicals used for synthesis ................................................ 14 3.1.2 Polycrystalline synthesis by solid state reaction ......................................... 14 3.1.3 Single crystal growth by chemical vapor transport ..................................... 15 3.2 Characterization ................................................................................................. 16 3.2.1 X-ray diffraction ......................................................................................... 16 3.2.2 Metallographic investigations ..................................................................... 18 3.2.3 Electron microscopy ................................................................................... 18 3.2.4 ICP-OES, carbon and oxygen detection technique ..................................... 19 3.2.5 Thermal analysis ......................................................................................... 19 3.3 Physical property measurements ........................................................................ 19 3.3.1 Magnetic properties .................................................................................... 19 3.3.2 Resistivity ................................................................................................... 20 3.3.3 Specific heat ................................................................................................ 20 Chapter 4: Iron Selenide: β-FexSe ............................................................................ 21 4.1 Reinvestigation of the homogeneity range of β-FexSe ....................................... 21 4.2 Physical properties of polycrystalline β-FexSe .................................................. 29 4.3 Single crystal growth of β-FexSe by chemical vapor transport reaction ............ 31 4.4 Physical properties of β-FexSe single crystals grown by CVT .......................... 37 4.5. Conclusions ....................................................................................................... 46 Chapter 5: Iron Telluride: Fe1+yTe ........................................................................... 48 5.1 Preparation and characterization of Fe1+yTe poly- and single crystalline samples ..................................................................................................................... 48 5.2 Specific heat, magnetization, and resistivity of Fe1+yTe .................................... 58 5.3 Low-temperature structural transitions and phase diagram of Fe1+yTe ............. 64 5.4 Conclusions ........................................................................................................ 82 Chapter 6: Pressure Effects on Fe1+yTe ................................................................... 83 6.1 Pressure-induced structural transitions of Fe1.08Te at low temperature ............. 83 6.2 Electrical resistivity of Fe1.08Te under pressure ................................................. 96 6.3 Pressure-induced structural transitions of Fe1.12Te and Fe1.14Te at low temperature .............................................................................................................. 98 6.5 Conclusions ...................................................................................................... 107 ii Chapter 7: Substitution Studies on Fe1+yTe ........................................................... 108 7.1 Anionic substitutions in Fe1+yTe ...................................................................... 108 7.1.1. Selenium substitution in Fe1+yTe ............................................................. 108 7.2 Cationic substitutions in Fe1+yTe ..................................................................... 119 7.2.1. Nickel substitution in Fe1+yTe .................................................................. 119 7.2.2. Cobalt substitution in Fe1+yTe .................................................................. 128 7.3 Conclusions ...................................................................................................... 132 Chapter 8: Summary and Outlook ......................................................................... 134 Chapter 9: Appendix ............................................................................................... 138 References ................................................................................................................. 147 List of Symbols and Abbreviations ........................................................................ 159 Curriculum Vitae ..................................................................................................... 161 Publications .............................................................................................................. 162 iii Chapter 1: Introduction _____________________________________________________________________ Chapter 1 Introduction Since the discovery of superconductivity in the compound LaO1-xFxFeAs with a critical temperature of Tc = 26 K [1], a vast number of studies has been reported for similar iron-based materials with layered crystal structures. These superconductors can be categorized into six different major classes according to their structural organization (see Chapter 2). Among these families, tetragonal β-FexSe (P4/nmm) with Tc = 8 K can be considered as the binary
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