Quantitative evaluation of biaxial compressive strain and its impact on proton conduction and diffusion in yttrium-doped barium zirconate epitaxial thin films
Quantitative evaluation of biaxial compressive strain and its impact on proton conduction and diffusion in yttrium-doped barium zirconate epitaxial thin films
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DOI：
10.1088/2515-7655/ac889e
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发表时间：
2022-08
期刊：
影响因子：
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通讯作者：
J. Hyodo;Y. Yamazaki
中科院分区：
文献类型：
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作者：
J. Hyodo;Y. Yamazaki
质子传导氧化物，包括 20 mol% 钇掺杂 BaZrO3 (BZY20)，作为质子陶瓷燃料电池 (PCFC) 和质子传导固体氧化物电池等环保电化学电池的电解质，引起了广泛关注。由于水合、化学晶格膨胀、质子迁移、质子捕获和局部变形等复杂的物理化学现象，这些氧化物表现出快速的质子传导。在电化学装置中使用质子传导氧化物作为电解质膜会引入界面，该界面会通过热和化学方式产生机械应变。在这里，我们简要回顾了电化学器件中使用的散装样品和薄膜中质子传导氧化物的研究现状。我们使用脉冲激光沉积在 (001) Nb 掺杂 SrTiO3 单晶基底上制备了 18 和 500 nm 厚的 20 mol% BZY20 外延薄膜，以形成质子导电和非质子导电材料之间的模型界面，并使用薄膜 X 射线衍射、热重分析、二次离子质量量化了机械应变、质子浓度、质子电导率和扩散率谱分析和交流阻抗谱分析。对于 18 和 500 nm 厚的薄膜，分别测量到 -2.1% 和 -0.85% 的压缩应变，这些应变在 375 °C 下分别使质子传导和扩散降低了 5 个和 1 个数量级。基于简单捕获模型的分析表明，质子传导的减少是由于移动质子扩散速度减慢造成的，而质子捕获贡献的变化可以忽略不计。该模型表明，在 600 °C 时功率密度为 740 mW cm−2 的高性能 PCFC 所报告的高欧姆电阻只能通过电池中估计的压缩应变来解释。这项研究表明，通过适当选择电解质-电极组合和制造工艺来最小化双轴压缩应变对于最大化电化学电池的性能非常重要。
Proton-conducting oxides, including 20 mol% yttrium-doped BaZrO3 (BZY20), have attracted considerable attention as electrolytes for environmentally friendly electrochemical cells, such as proton ceramic fuel cells (PCFCs) and proton-conducting solid oxide cells. These oxides exhibit fast proton conduction due to the complex physicochemical phenomena of hydration, chemical lattice expansion, proton migration, proton trapping, and local distortion. Using a proton-conducting oxide as an electrolyte film in electrochemical devices introduces an interface, which thermally and chemically generates mechanical strain. Here, we briefly review the current state of research into proton-conducting oxides in bulk samples and films used in electrochemical devices. We fabricated 18 and 500 nm thick 20 mol% BZY20 epitaxial films on (001) Nb-doped SrTiO3 single-crystal substrates to form a model interface between proton-conductive and non-proton-conductive materials, using pulsed laser deposition, and quantified the mechanical strain, proton concentration, proton conductivity, and diffusivity using thin-film x-ray diffractometry, thermogravimetry, secondary ion mass spectrometry, and AC impedance spectroscopy. Compressive strains of −2.1% and −0.85% were measured for the 18 and 500 nm thick films, respectively, and these strains reduced both the proton conduction and diffusion by five and one orders of magnitude, respectively, at 375 °C. Analysis based on a simple trapping model revealed that the decrease in proton conduction results from the slower diffusion of mobile protons with a negligible change in the proton trapping contribution. The model shows that the high ohmic resistance reported for a high-performance PCFC with a power density of 740 mW cm−2 at 600 °C can be solely explained by the estimated compressive strain in the cells. This study shows that minimizing biaxial compressive strain by appropriate choices of the electrolyte–electrode combination and fabrication process is important for maximizing the performance of electrochemical cells.