Growth of Ba1－xSrxZrO3 nanoparticles in supercritical water
Growth of Ba1－xSrxZrO3 nanoparticles in supercritical water
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Ba1－xSrxZrO3纳米颗粒在超临界水中的生长
DOI：
10.1039/c6ra12288d
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发表时间：
2016
期刊：
影响因子：
3.9
通讯作者：
Yoshito Oshima
中科院分区：
文献类型：
--
作者：
Akira Yoko;Makoto Akizuki;Naoto Umezawa;Takahisa Ohno;Yoshito Oshima
我们利用超临界水研究了Ba1−xSrxZrO3（0≤x≤1）纳米粒子在高过饱和条件下的形成。已知钙钛矿结构中的b位Zr在成核阶段起主导作用，在超临界条件下具有较高的成核速率；这是由于与a位离子相比，Zr的溶解度明显较低（即Zr沉淀更快，在Zr成核后，a位离子被吸收到粒子中）。然而，在本研究中，我们发现a位Ba和Sr对纳米颗粒的粒径、a位缺位率和表面oh密度有显著影响。颗粒大小的差异表明，即使在超临界水热合成等高度过饱和条件下，成核阶段后发生的成熟或聚并也是决定颗粒大小的主要因素。详细分析了超临界水中形成的纳米结构特征；研究了a位缺乏率和表面oh密度等变量。利用x射线吸收精细结构证实了a位空位的存在，得到了高度缺陷的结构，特别是当Ba含量高时。利用x射线光电子能谱和第一性原理计算研究了纳米颗粒的表面状态，目的是了解粒径的差异，以及a位缺乏的影响；表面oh的量与a位缺乏率成反比，与粒径成反比。
We studied the formation of Ba1−xSrxZrO3 (0 ≤ x ≤ 1) nanoparticles under highly super-saturated conditions, using supercritical water. It is known that B-site Zr in the perovskite structure plays a dominant role at the nucleation stage, with high nucleation rates under supercritical conditions; this is due to the significantly lower solubility of Zr, compared with A-site ions (i.e., Zr precipitates faster, and A-site ions are taken up into particle after the Zr nucleation). However, in this study, it was found that A-site Ba and Sr significantly influenced the particle size, the A-site deficiency rate, and the surface-OH density of the nanoparticles. The differences in particle size suggested that the ripening or coalescence that occurred after the nucleation stage was dominant in determining the particle size, even under highly super-saturated conditions such as those realized in the supercritical hydrothermal synthesis. The characteristic nanostructure formed in the supercritical water was analyzed in detail; variables such as the A-site deficiency rate and the surface-OH density were investigated. The existence of vacancies at the A-site was confirmed using X-ray absorption fine structure, and a highly defective structure was obtained, particularly when the Ba content was high. The surface state of the nanoparticles was also studied using X-ray photoelectron spectroscopy and first-principles calculations, with the aim of understanding the differences in particle size, and the effects of the A-site deficiencies; the amount of surface-OH corresponded to the A-site deficiency rate, and had an inverse relationship with the particle size.