Electron microscopical investigation of interdiffusion and phase formation at Gd 2 O 3-CeO 2- and Sm 2 O 3-CeO 2-Interfaces

Christian Rockenhäuser adresses phase formation and cation interdiffusion of the GdxCe1-xO2-x/2-and SmxCe1-xO2-x/2-material systems at temperatures ranging from 970 to 1270°C. Diffusion couples with CeO2/Sm2O3 and CeO2/Gd2O3 interfaces were fabricated for the investigations. The resulting reaction phases were investigated utilizing transmission electron microscopy (TEM) and allow conclusions regarding the phase diagrams in the examined temperature range. A miscibility gap can be ruled out for GdxCe1-xO2-x/2 across the whole composition range. Cation interdiffusion coefficients were determined for both material systems by measuring and evaluating concentration profiles at the material interfaces. The activation enthalpies for interdiffusion were calculated using the temperature dependence of the interdiffusion coefficients. The study for the first time compiles comprehensively the previous results regarding the phase diagrams of the two material systems since 1923. Foreword 8 Acknowledgement 10 Contents 11 List of Figures 14 List of Tables 15 Acronyms 16 Symbols 18 Introduction 22 1 Fundamentals 24 1.1 Application of Gd2O3-doped CeO2 (GDC) and Sm2O3-doped CeO2 (SDC) in Electrochemical Devices 26 1.2 Phases in Doped CeO2 Systems 27 1.2.1 Pure CeO2 28 1.2.2 The GdxCe1-xO2-x/2 System 30 1.2.3 The SmxCe1-xO2-x/2 System 33 1.3 Binary Diffusion Couples 38 1.3.1 Solution of the Diffusion Equation 38 1.3.2 Binary Diffusion Couples in Multiphase Binary Systems 41 1.4 Temperature Dependence of Diffusion 45 1.4.1 The Arrhenius Relation 45 1.4.2 Grain Growth Experiments 45 2 Experimental Techniques and Instrumentation 49 2.1 Electron Microscopical Instrumentation 49 2.2 Transmission Electron Microscopy (TEM) 50 2.2.1 Bright-Field Transmission Electron Microscopy (BFTEM) 51 2.2.2 High-Resolution Transmission Electron Microscopy (HRTEM) 51 2.2.3 Selected Area Electron Diffraction (SAED) 52 2.3 Scanning Transmission Electron Microscopy (STEM) and Beam Broadening 53 2.4 Quantitative Energy-Dispersive X-ray Spectroscopy (EDXS) 55 2.5 Electron Energy Loss Spectroscopy (EELS) 58 2.5.1 Thickness Determination 59 2.5.2 EELS Composition Analysis 61 3 The GdxCe1-xO2-x/2 System:Phase Formation and Cation Interdiffusion 66 3.1 Specimen Fabrication 66 3.1.1 Substrate Preparation 66 3.1.2 Thin Film Deposition 68 3.1.3 Thermal Treatments 68 3.1.4 Sample Preparation for Transmission Electron Microscopy 69 3.2 Microstructure Characterization 69 3.3 Cation Interdiffusion 73 3.4 Discussion 75 3.4.1 Phase Formation in the GdxCe System 76 3.4.2 Interdiffusion at the Gd 2O3/CeO2 Interface 78 4 The SmxCe1-xO2-x/2 System: Phase Formation and Cation Interdiffusion 81 4.1 Specimen Fabrication 81 4.1.1 Substrate Preparation 81 4.1.2 Thin Film Deposition 81 4.1.3 Thermal Treatments 82 4.1.4 Sample Preparation for Transmission Electron Microscopy 82 4.2 Microstructural Characterization 82 4.3 Cation Interdiffusion 90 4.4 Discussion 91 4.4.1 Phase Formation in the SmxCe 1-xO2-x/2 System 92 4.4.2 Cation Interdiffusion 95 4.5 Comparison of the Phase Evolution of the SDC and GDC systems 96 5 Summary 98 Bibliography 101 Own Publications and Contributions to Conferences 116 Reviewed Publications 116 Contributions to Conferences 116 Oral Presentations 116 Poster Presentations 117 Front Matter....Pages 1-22 Fundamentals....Pages 3-27 Experimental Techniques and Instrumentation....Pages 29-45 The Gd x Ce 1-x O 2-x/2 System: Phase Formation and Cation Interdiffusion....Pages 47-61 The Sm x Ce 1-x O 2-x/2 System: Phase Formation and Cation Interdiffusion....Pages 63-79 Summary....Pages 81-83 Back Matter....Pages 85-102 Christian Rockenhauser adresses phase formation and cation interdiffusion of the GdxCe1-xO2-x/2-and SmxCe1-xO2-x/2-material systems at temperatures ranging from 970 to 1270 DegreesC.