Thermoelectric Properties of Alkaline Earth Metal Substituted Europium Titanates Xingxing Xiao Dissertation submitted as a requirement for the degree of Doctor of Natural Science August 2019 – Technical University of Darmstadt (TUD)- D17 This page intentionally left blank Thermoelectric Properties of Alkaline Earth Metal Substituted Europium Titanates Dissertation submitted to the Department of Materials and Earth Sciences at Technische Universität Darmstadt in Fulfillment of the Requirements for the Degree of Doctor of Natural Science (Dr. rer. nat.) by Xingxing Xiao Technische Universität Darmstadt, Hochschulkennziffer D17 Date of Submission: 20.01.2020 Date of Oral Examination: 12.03.2020 Referee: Prof. Dr. Anke Weidenkaff Co-referee: Prof. Dr. Rainer Niewa Darmstadt 2020 Xiao, Xingxing: Thermoelectric Properties of Alkaline Earth Metal Substituted Europium Titanates Darmstadt, Technische Universität Darmstadt Publication Year of Dissertation at TUprints: 2021 URN: urn:nbn:de:tuda-tuprints-145931 Date of Oral Examination: 12.03.2020 Published under CC BY-SA 4.0 International https://creativecommons.org/licenses/ THESIS SUPERVISORS Prof. Dr. Anke Weidenkaff Materials Science / Department of Materials and Earth Sciences / Technische Universität Darmstadt Materials Recycling and Resource Strategies / Fraunhofer IWKS Prof. Dr. Rainer Niewa Institute of Inorganic Chemistry / University of Stuttgart THESIS COMMITTEE Referee: Prof. Dr. Anke Weidenkaff Materials Science / Department of Materials and Earth Sciences / Technische Universität Darmstadt Materials Recycling and Resource Strategies / Fraunhofer IWKS Co-referee: Prof. Dr. Rainer Niewa Institute of Inorganic Chemistry / University of Stuttgart Examiner: Prof. Dr. Lambert Alff Materials Science / Department of Materials and Earth Sciences / Technische Universität Darmstadt Examiner: Jun. Prof. Dr. Hongbin Zhang Materials Science / Department of Materials and Earth Sciences / Technische Universität Darmstadt i This page intentionally left blank ii Acknowledgments This dissertation would not have been possible without the help, support, and encouragement of supervisors, colleagues, friends, and family. First of all, I would like to express my sincere gratitude to my supervisor, Prof. Dr. Anke Weidenkaff, for giving me the opportunity to complete my Ph.D. study in her group. She constantly provided me with valuable support since 2012 when I was an internship in her group. She is my good mentor in my career and a great friend in my life. I deeply thank my secondary supervisor, Prof. Dr. Rainer Niewa, for his unconditional support on my work, and I do appreciate his trust towards me. Special thanks go to Prof. Dr. Lambert Alff and Prof. Dr. Hongbin Zhang for being my thesis examiners. I especially thank my daily supervisor Dr. Marc Widenmeyer. He is always very patient in providing guidance and assistance whenever I need his help in my work. His careful and serious scientific attitude has affected me a lot, which will definitely benefit my whole life. I am also grateful to my officemate Dr. Songhak Yoon. He always tried his best to help me to solve problems as soon as possible and gave me encouraging support. I truly cherish the moments when we had lots of unfettered discussion on scientific work. Very special gratitude has to be extended to my collaborators. I am grateful to Prof. Dr. Marco Scavini for his help on high-resolution XRD Rietveld refinements. He is an approachable and friendly person and opened a window for me to see the world of crystallography. Thanks to his introduction and recommendation, Prof. Dr. Carlo Castellano did the EXAFS analysis and Dr. Stefano Checchia performed the PDF analysis for me. Although we communicated via email and never had face-to-face conversations, they trusted me and provided me with constructive suggestions and valuable contributions to my research. I am also grateful to the European Synchrotron Radiation Facility for the provision of beam time and sincerely indebted to Dr. Mauro Coduri for his assistance in using the ID22 beam-line. Many thanks must also go to Dr. Kathrin Müller and Prof. Dr. Ulrich Starke for the XPS measurements. Kathrin took lots of time to carry out the experiments and analyse the results for me. I would also like to thank one of my office-mates, Dr. Stefan Kilper. He is always very friendly and helpful during the work. I would also like to express my gratitude to Dr. Dongxia Ma, Dr. Zhicheng Zhong, and Dr. Philipp Hansmann for the DFT calculations. Dongxia helped me a lot to understand some fundamental knowledge of theoretical calculations. I admire her very much for her kindness, optimism, enthusiasm and wisdom. I am also grateful to Dr. Andrei Kovalevsky and his Ph.D. student Kiryl Zakharchuk. In addition to helping me fabricate desired bulk samples in his laboratory, Andrei also gave me wise advice for the publications. I thank Dr. Kai Philippi from the group of Prof. Dr. Hidenori Takagi for his PPMS measurements and scientific discussions. I thank Dr. Konstantin Skokov who did the low-temperature specific heat measurements for me. Many thanks also go to Prof. Dr. Jian He from Clemson University. He guides me to feel the charm of solid-state physics. His willingness to answer all of my questions on physics encouraged me to be more confident and braver to continue studying. They all gave me great help and professional support, thus I could complete this work and broaden my knowledge. I would like to express my thanks to all colleagues of Chair 3 in the Institute for Materials Science at the University of Stuttgart for their professional support and enjoyable working iii atmosphere. I often discussed various topics with Cora Bubeck, including work, study, and personal life. My thanks also go to our kind and helpful secretary, Mrs. Juliane Kränzl. She helped me a lot to do the countless administrative paperwork. I want to thank our technicians, Mr. Traugott Worner, Mr. Martin Schweizer, and Mr. Frank Hack for their professional and efficient assistance. I would like to thank my Chinese colleagues Ruijuan Yan, Tianhua Zou, Guoxing Chen, Wenmei Liu, Pingjun Ying, Bingjie Tang, Jingjing Jiang. We always had our lunch with fun chatting at canteen, which was the most relaxing time during the working days. It was a great pleasure to work together with all of you. Last but not least, the deepest gratitude belongs to my family. I would like to thank my husband and my lovely son for accompanying me to walk along the path of life. I would like to thank my parents, sisters, and brother for giving me unconditional love always. With you, my life is much more meaningful! Xingxing Xiao Darmstadt. August. 2019 iv Biographical note EDUCATION Ph.D. Materials Science Supervised by Prof. Dr. Anke Weidenkaff & Prof. Dr. Rainer Niewa 04 / 2019 ~ Technische Universität Darmstadt Department of Materials and Earth Sciences 12 / 2013 ~ 04 / 2014 University of Stuttgart 06 / 2015 ~ 03 / 2019 Institut für Materialwissenschaft 05 / 2014 ~ 05 / 2015 maternity leave M.Sc. Materials Science Supervised by Prof. Dr. Xinfeng Tang & Prof. Dr. Qingjie Zhang 09 / 2008 ~ 06 / 2011 Wuhan University of Technology (WUT) State Key Laboratory of Advanced Technology for Materials Synthesis and Processing B.Eng. Materials Science and Supervised by Engineering Prof. Dr. Xiaohong Xu 09 / 2004 ~ 06 / 2008 Wuhan University of Technology WORK EXPERIENCE 12 / 2013 ~ 04 / 2014 Research Assistant University of Stuttgart, Germany 06 / 2015 ~ 03 / 2019 Swiss Federal Laboratories for Materials Science 09 / 2012 ~ 12 / 2013 Internship and Technology (Empa), Switzerland 03 / 2011 ~ 02 / 2012 Teaching Assistant Wuhan Huaxia University of Technology, China 09 / 2008 ~ 06 / 2011 Laboratory Assistant Wuhan University of Technology, China 09 / 2006 ~ 06 / 2008 Student Assistant Wuhan University of Technology, China PUBLICATIONS 1. X. Xiao, M. Widenmeyer, K. Mueller, M. Scavini, S. Checchia, C. Castellano, D. Ma, S. Yoon, W. Xie, U. Starke, K. Zakharchuk, A. Kovalevsky, A. Weidenkaff, “A squeeze on the perovskite structure improves the thermoelectric performance of Europium Calcium Titanates”, Materials Today Physics, 2018, 7: 96-105. 2. X. Xiao, M. Widenmeyer, W. Xie, T. Zou, S. Yoon, M. Scavini, S. Checchia, Z. Zhong, P. Hansmann, S. Kilper, A. Kovalevsky, A. Weidenkaff, “Tailoring the structure and thermoelectric 2+ properties of BaTiO3 via Eu substitution”, Physical Chemistry Chemical Physics, 2017, 19(21): 13469-13480. v 3. K. V. Zakharchuk, D. M. Tobaldi, X. Xiao, W. Xie, S. M. Mikhalev, J. F. Martins, J. R. Frade, A. Weidenkaff, A. V. Kovalevsky, “Synergistic effects of zirconium- and aluminum co-doping on the thermoelectric performance of zinc oxide”, Journal of the European Ceramic Society, 2019, 39(4): 1222-1229. 4. T. Zou, W. Xie, M. Widenmeyer, X. Xiao, A. Weidenkaff, “Enhancing point defect scattering in copper antimony selenides via Sm and S Co-doping”, Rare Metals, 2018, 37(4): 290-299. 5. T. Zou, T. Jia, W. Xie, Y. Zhang, M. Widenmeyer, X. Xiao, A. Weidenkaff, “Band structure modification in thermoelectric Heusler-phase TiFe2Sn via Mn substitution”, Physical Chemistry Chemical Physics, 2017, 19(28): 18273-18278. 6. W. Xie, S. Populoh, K. Galazka, X. Xiao, L. Sagarna, Y. Liu, M. Trottmann, J. He, A. Weidenkaff, “Thermoelectric Study of Crossroads Material MnTe via Sulfur Doping”, Journal of Applied Physics, 2014, 115(10): 103707. 7. X. Xiao, W. Xie, X. Tang, Q. Zhang, “Phase Transition and High Temperature Thermoelectric Transport Properties of Copper Selenide