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Understanding the conductivity degradation mechanism and enhancing the kinetic stability of Er2O3-stabilized Bi2O3 at 600℃

Title
Understanding the conductivity degradation mechanism and enhancing the kinetic stability of Er2O3-stabilized Bi2O3 at 600℃
Translated Title
비스무스기반 이온전도체의 600℃ 에서의 이온전도도 저하 원인 규명 및 이온전도도 저하 개선
Authors
Yun, Byung Hyun
DGIST Authors
Yun, Byung Hyun; Lee, Kang Tak
Advisor(s)
Lee, Kang Tak
Co-Advisor(s)
Lee, Chan Woo
Issue Date
2016
Available Date
2016-02-12
Degree Date
2016. 2
Type
Thesis
Keywords
stabilized Bi2O3ionic conductivityphase transformation안정화 비스무스이온전도도상변이
Abstract
Erbia-stabilized Bi2O3 (ESB) possesses higher ionic conductivity compared to conventional ionic conductors such as doped CeO2 and stabilized ZrO2. However, the stabilized Bi2O3 experiences conductivity degradation on extended annealing at 600°C. In order to examine this phenomenon, X-ray diffraction was carried out on ESB for over 400h, and it was found that ESB transforms from cubic to rhombohedral phase. X-ray diffraction analysis revealed that ESB transformed from cubic to rhombohedral phase during first 100h. However, discrepancy in time constant between the evolution of rhombohedral phase (65h) and conductivity degradation(52h) was observed. In order to investigate this discrepancy, the activation energy of low temperature domain after annealing was measured. The activation energy of as-sintered sample was 1.2eV, while that of annealed sample was 1.01eV. Such a drop of the activation energy is partially attributed to the order-disorder transition of the anion sublattice. Thus, it could be concluded that the conductivity degradation of ESB at 600°C resulted from the combined effect of the phase transformation and the order-disorder transition of the anion sublattice. In order to suppress such a decay of ionic conductivity in ESB, aliovalent dopants with higher oxidation state were added into ESB. On this regards, ZrO2 was added to ESB and the stability was evaluated as a function of ZrO2 contents. The solubility limit was 5% and higher concentration led to unwanted secondary phase. The stability was the highest for ESB with 5% ZrO2 and it was found that the lattice constant and bond length of Bi-O was the shortest for this composition. The reason ESB with 5% ZrO2 is the most stable might be attributed to the fact that bonding gets stronger as bond length gets short. Thus, atomic diffusion, involved in the phase transition, becomes hard. Lastly, in order to observe the effect of ionic radii on the long-term stability, the same contents of TiO2, ZrO2 and CeO2 was added to ESB. As a result, the one with the highest stability was ESB with ZrO2, and the one with the poorest stability was ESB with CeO2. ⓒ 2016 DGIST
Table Of Contents
1. INTRODUCTION -- 2. BACKGROUND INFORMATION -- 2.1. PRINCIPLES OF THE SOLID OXIDE FUEL CELL -- 2.2. STRUCTURAL AND ELECTRICAL PROPERTIES OF Bi2O3 -- 2.2.1. POLYMORPHISM AND CONDUCTIVITY OF PURE Bi2O3 -- 2.2.2. STRUCTURE OF δ-Bi2O3 -- 2.2.3. STABILIZATION OF δ-Bi2O3 -- 2.2.4. CONDUCTIVITY DECAY OF STABILIZED BISMUTH OXIDES -- 2.3. IMPEDANCE SPECTROSCOPY -- 2.4 REITVELD REFINEMENT -- 3. MECHANISM OF THE CONDUCTIVITY DEGRADATION OF ERBIA-STABILIZED Bi2O3 AT 600℃ -- 3.1 INTRODUCTION -- 3.2 EXPERIMENTAL PROCEDURE -- 3.3 RESULTS AND DISCUSSION -- 3.4 CONCLUSION -- 4. ENHANCED LONG-TERM STABILITY OF Bi2O3-BASED OXYGEN ION CONDUCTOR -- 4.1 INTRODUCTION -- 4.2 EXPERIMENTAL PROCEDURE -- 4.3 RESULTS AND DISCUSSION -- 4.4 CONCLUSION -- 5. CONCLUSION -- 6. 요약문 -- 7. APPENDIX-GUIDE TO CARRYING OUT GSAS SOFTWARE -- 8. REFERENCES
URI
http://dgist.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000002226144
http://hdl.handle.net/20.500.11750/1450
DOI
10.22677/thesis.2226144
Degree
Master
Department
Energy Systems Engineering
University
DGIST
Files:
Collection:
Energy Science and EngineeringThesesMaster


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