Spectroscopic insight into the structural and microstructural properties of La2Ce2O7 ceramics

IF 2.7 4区 材料科学 Q1 MATERIALS SCIENCE, CERAMICS Boletin de la Sociedad Espanola de Ceramica y Vidrio Pub Date : 2024-09-01 DOI:10.1016/j.bsecv.2024.07.002
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Abstract

Ceria-based compounds with trivalent dopant ions are currently being investigated as electrolytes for solid oxide fuel cells operating at low to intermediate temperatures. In these materials, the dependence of the ionic conductivity on the dopant content, the relative cation size and the dopant/vacancy or vacancy/vacancy interactions are the subject of intense research, but there is scarce information about a possible correlation between these properties and microstructural ones, such as texture. Here, we address this question in the heavily doped fluorite-like La2Ce2O7 oxide, using a combination of X-ray diffraction, electron microscopy, optical absorption, Raman scattering and impedance spectroscopy. In all cases, materials with varying degree of 〈1 1 1〉 texture are compared with untextured samples. In this context, the most relevant Raman signatures are the fluorite-like mode at ∼448 cm−1 and a vacancy-related band at ∼578 cm−1. Although remarkable changes were observed upon varying the sintering temperature or the excitation wavelength, both textured and untextured materials displayed similar evolution. A selective enhancement of the vacancy-related band was observed upon decreasing the excitation wavelength from 647 to 488 nm, which is attributed to a resonance phenomenon involving vacancy-related electronic transitions. An indication of incipient vacancy ordering was given by the observation of an intense band at ∼346 cm−1, denoting C-R2O3-like short-range order; its enhancement with the annealing temperature is attributed to the growth of the C-like regions. Conductivity was measured in textured and untextured, fully dense pellets, in the former along and across the texture direction. Impedance plots suggest that the conductivity is dominated by oxide ions and do not allow to separate a grain boundary contribution in these materials with grain size around 1–2 μm. The conductivity amounts to around 10−5 S/cm at 650 K, with activation energy of 1.08–1.16 eV in the temperature range from around 470 to 870 K. Results were similar in textured and untextured materials. We conclude that there is no significant correlation between texture and vacancy concentration or vacancy ordering. A similar conclusion – no influence of texture – is reached concerning the electrical properties.
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通过光谱深入了解 La2Ce2O7 陶瓷的结构和微观结构特性
目前正在研究将含有三价掺杂离子的铈基化合物作为在中低温下工作的固体氧化物燃料电池的电解质。在这些材料中,离子电导率与掺杂剂含量、相对阳离子尺寸和掺杂剂/空位或空位/空位相互作用的关系是研究的热点,但有关这些特性与微观结构特性(如质地)之间可能存在的相关性的信息却很少。在此,我们结合使用 X 射线衍射、电子显微镜、光学吸收、拉曼散射和阻抗光谱,在重掺杂萤石类 La2Ce2O7 氧化物中解决了这一问题。在所有情况下,具有不同程度〈1 1 1〉纹理的材料都与无纹理样品进行了比较。在这种情况下,最相关的拉曼特征是 ∼448 cm-1 处的萤石样模式和 ∼578 cm-1 处的空位相关带。尽管在改变烧结温度或激发波长时观察到了明显的变化,但有纹理和无纹理材料都显示出类似的演变。当激发波长从 647 纳米降低到 488 纳米时,观察到空位相关带有选择性地增强,这归因于涉及空位相关电子跃迁的共振现象。在 ∼346 cm-1 处观察到一个强烈的条带,表示类似 C-R2O3 的短程有序,这表明了空位有序化的萌芽;它随退火温度的升高而增强,这归因于类似 C 区域的增长。在有纹理和无纹理、完全致密的颗粒中测量了前者沿纹理方向和跨纹理方向的电导率。阻抗图显示,导电性主要由氧化物离子主导,无法从这些晶粒尺寸约为 1-2 μm 的材料中分离出晶界的贡献。在 650 K 时,电导率约为 10-5 S/cm,在约 470 至 870 K 的温度范围内,活化能为 1.08-1.16 eV。我们得出结论:质地与空位浓度或空位排序之间没有明显的相关性。在电学特性方面,我们也得出了类似的结论--质地没有影响。
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来源期刊
Boletin de la Sociedad Espanola de Ceramica y Vidrio
Boletin de la Sociedad Espanola de Ceramica y Vidrio 工程技术-材料科学:硅酸盐
CiteScore
5.50
自引率
2.90%
发文量
72
审稿时长
103 days
期刊介绍: The Journal of the Spanish Ceramic and Glass Society publishes scientific articles and communications describing original research and reviews relating to ceramic materials and glasses. The main interests are on novel generic science and technology establishing the relationships between synthesis, processing microstructure and properties of materials. Papers may deal with ceramics and glasses included in any of the conventional categories: structural, functional, traditional, composites and cultural heritage. The main objective of the Journal of the Spanish Ceramic and Glass Society is to sustain a high standard research quality by means of appropriate reviewing procedures.
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