固態氧化物燃料電池之LaGaO3基電解質的結構模擬及探討

The structural simulation and study of LaGaO3-based electrolyte in the solid oxide fuel cell

張承龍(Cheng-Long Chang)

指導教授 ： 吳玉娟

國立臺北科技大學/工程學院/材料科學與工程研究所/碩士(2013年)

https://doi.org/10.6841/NTUT.2013.00682

摘要

固態氧化物燃料電池(SOFC)主要是由陽極、陰極和電解質所組成，反應操作溫度約600∼1000℃，中溫型固態氧化物燃料電池(IT-SOFC)約400∼800℃，大部分以氧化釔安定化氧化鋯(8 mole% YSZ)螢石立方晶結構為電解質材料，其離子導電率為0.036 S/cm、操作溫度為1000℃。在LaGaO3基電解質材料中摻雜Sr2+和Mg2+後的La1-xSrxGa1-yMgyO3-δ(LSGM)能提高離子導電率到0.1 S/cm和減少操作溫度至800℃。
然而大部份的研究都利用實驗合成方式多過模擬軟體方式分析材料，所以本研究將使用模擬軟體方式來進行，主要是透過原子投影圖、立體投影圖、電子繞射圖和多面體圖形的相轉換去探討，從文獻中得知LaGaO3基的相轉換會隨著摻雜含量和溫度不同而改變，晶體結構將從：斜方Pnma(62)=>偽-斜方Imma(74)[像單斜I2/a(15)]=>偽-菱方
R-3c(167)=>[像單斜I2/a(15)]菱方R-3c(167)=>立方Pm-3m(221)。
從文獻中知道室溫的LaGaO3因其GaO6八面體結構扭曲，所以對稱中心降低，從模擬軟體的原子投影圖中可比較不同晶體結構扭曲的程度，再看到各結構彼此重疊的立體投影圖可得知許多重疊的方向點及其晶相關係，而文獻中LSGM結構大部份都是靠XRD、中子繞射和Rietveld refinement method分析，但因XRD不易去分辨細微的晶體結構變化，所以較常使用中子繞射和Rietveld refinement分析。本研究模擬軟體(CaRIne Crystallography 3.1)分析重點是用電子繞射圖去探討4種不同的晶體結構和5種空間群，得到的結果是有繞射方向[210]//[210]//[0-2-1]//[00-1][000-1]//[1-1-1]和[11-1]//[11-1]//[-1-1-2]//[-2-1-1][-101-1]//[1-10]相互平行的關係，繞射圖形除了斜方Pnma(62)和其它較不相同外，斜方Imma(74)和單斜I2/a(15)和菱方R-3c(167)的繞射圖很相似，難以區分。最後可能只能進一步使用CBED或LACBED來加以分析。

關鍵字

SOFC ； 晶體結構 ； 電子繞射 ； LSGM

並列摘要

A Solid Oxide Fuel Cell(SOFC) is composed of anode, cathode and electrolyte. The operating temperature of SOFC is between 600 to 1000℃, and it is between 400 to 800℃ for Intermediate Temperature Solid Oxide Fuel Cell(IT-SOFC). Most of the electrolyte materials are Yttrium stabilized Zircomic(8mole％YSZ) CaF2 cubic crystal. The ion conductivity of CaF2 cubic crystal is 0.036 S/cm, and its operating temperature is 1000℃. After doping Sr2+ and Mg2+-substituted La1-xSrxGa1-yMgyO3-δ(LSGM) in the LaGaO3-based electrolyte material, the ion conductivity is increased to 0.1 S/cm and the operating temperature is decreased to 800℃.
Most research used synthesis method to analyze the material rather than used simulation software. In this study, simulation software is used and the phase transition is discussed based on the adopt atom projection pattern, stereographic projection pattern, electron diffraction, and polyhedron. According to the reference, phase transition of LaGaO3-based changes with the dopant content and the temperature. The following is the transformation of the crystal structure: orthorhombic Pnma(62) => pseudo-orthorhombic Imma(74)[like monoclinic I2/a(15)] => pseudo-rhombohedral R-3c(167)[ like monoclinic I2/a(15)] =>? rhombohedral R3c(167) => cubic Pm-m(221)。
According to references, GaO6 octahedral crystal structure of LaGaO3 distorted at the room temperature, and that lowered the symmetry. The atom projection pattern created by simulation software showed the degree of distortion of different crystal structures, and Watching overlapped stereographic projection pattern of every structure knows overlapping relation for direction and mirror. The LSGM structure is mostly analyzed by XRD, neutron diffraction, Rietveld refinement method analysis, but XRD could not observe the subtle changes in crystal structure. Hence, neutron diffraction and Rietveld refinement analysis are used more often. The study, which used the simulation software (CaRIne Crystallography 3.1), mainly used electron diffraction to analyze the four different crystal structures and the five space groups. It is concluded that the diffraction direction [210]//[210]//[0-2-1]//[00-1]
[000-1]//[1-1-1] and [11-1]//[11-1]//[-1-1-2]//[-2-1-1][-101-1]//[1-10] relation for parallel each other. The diffraction pattern of orthorhombic Pnma(62) is different from other space groups. The diffraction patterns of orthorhombic Imma(74) and monoclinic I2/a(15) and rhombohedral
R c(167) are very similar to distinguish. CBED or LACBED may have to be used for further analysis.

並列關鍵字

SOFC ； Crystal structure ； Electron diffraction ； LSGM

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