Ueno Katsuhiro, Hashimoto Atsunori, Toyoura Kazuaki, Hatada Naoyuki, Sato Shigeo, Uda Tetsuya
Department of Materials Science and Engineering, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto, 606-8501, Japan.
Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki, 316-8511, Japan.
Dalton Trans. 2024 Mar 26;53(13):6070-6086. doi: 10.1039/d3dt03544a.
We previously reported that Zr substitution improves the chemical stability of BaYO and nominally 20 mol% Zr-substituted BaYO is an oxide-ion conductor at intermediate temperatures (500-700 °C). However, the influence of Zr substitution on the structural properties of BaYO was poorly understood. This paper aims to comprehensively understand the crystal structure of BaYO with Zr substitution by powder X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements, and first-principles calculations. From the results, firstly we found that the hexagonal unit cell of BaYO reported in the database should be revised as doubled along the -axis in terms of the periodicity of oxide-ion positions. The revised unit cell of BaYO consists of 18 layers of BaO and 24 layers of Y which periodically stack along the -axis. In this work, we focused on the cationic lattice and noticed that the periodical stacking of Ba and Y layers comprises a similar sequence to that in the body-centered cubic (BCC) structure. There are two regions in the BaYO structure: one is a hetero-stacking region of Ba and Y layers (Ba-Y-Ba-Y-Ba) and the other is a homo-stacking region (Ba-Y-Y-Ba). It is noteworthy that the former region is similar to a cubic perovskite. In Zr-substituted BaYO, Zr ions preferentially substitute for Y ions in the hetero-stacking region, and therefore the local environment of Zr ions in BaYO is quite similar to that in BaZrO. Besides, the Zr substitution for Y in BaYO increases the fraction of the cubic-perovskite-like region in the stacking sequences. The structural change in the long-range order strongly affects the other material properties such as chemical stability and the ionic-conduction mechanism. Our adopted description of perovskite-related compounds based on the stacking sequence of the BCC structure should help in understanding the complex structure and developing new perovskite-related materials.
我们之前报道过，Zr取代提高了BaYO的化学稳定性，名义上20 mol% Zr取代的BaYO在中温（500 - 700 °C）下是一种氧离子导体。然而，Zr取代对BaYO结构性质的影响却知之甚少。本文旨在通过粉末X射线衍射（XRD）、扩展X射线吸收精细结构（EXAFS）测量和第一性原理计算，全面了解Zr取代的BaYO的晶体结构。从结果来看，首先我们发现数据库中报道的BaYO的六方晶胞应沿c轴加倍，这是基于氧离子位置的周期性。修正后的BaYO晶胞由18层BaO和24层Y组成，它们沿c轴周期性堆叠。在这项工作中，我们关注阳离子晶格，并注意到Ba和Y层的周期性堆叠包含与体心立方（BCC）结构中相似的序列。BaYO结构中有两个区域：一个是Ba和Y层的异质堆叠区域（Ba - Y - Ba - Y - Ba），另一个是同质堆叠区域（Ba - Y - Y - Ba）。值得注意的是，前一个区域类似于立方钙钛矿。在Zr取代的BaYO中，Zr离子优先取代异质堆叠区域中的Y离子，因此BaYO中Zr离子的局部环境与BaZrO中的非常相似。此外，BaYO中Zr取代Y增加了堆叠序列中类立方钙钛矿区域的比例。长程有序的结构变化强烈影响其他材料性质，如化学稳定性和离子传导机制。我们基于BCC结构的堆叠序列对钙钛矿相关化合物的描述应有助于理解复杂结构并开发新的钙钛矿相关材料。
