Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.
Dalton Trans. 2013 May 21;42(19):7167-76. doi: 10.1039/c3dt32828g.
In this study, we report a rapid and simple technique for obtaining cobalt aluminate having a spinel structure. The products were prepared from a hydroxide precursor synthesized by coprecipitation of cobalt (Co(2+)) and aluminum (Al(3+)) nitrates with an alkaline solution. The chosen precursor enabled low temperature fabrication of cobalt aluminate with a spinel structure by sintering it for 2 hours at low temperatures (>400 °C). Crystallographic and thermal analyses suggest that the low-temperature-sintered products contain Co(3+) ions stabilized by chemisorbed water and/or hydroxide groups, which was not observed for products sintered at temperatures higher than 1000 °C. The color of the products turned from clear blue (Thenard's blue) to dark green when sintering temperatures were below 1000 °C. Magnetic quantities, Curie constants, and Weiss temperatures show a strong dependence on the sintering temperature. These findings suggest that there are mixed valent states, i.e. Co(2+) and Co(3+), and unique cation distributions at the different crystallographic sites in the spinel structure, especially in the products sintered at lower temperatures.
在这项研究中，我们报告了一种快速而简单的方法，用于获得具有尖晶石结构的铝酸钴。该产品是通过共沉淀钴（Co（2+））和铝（Al（3+））硝酸盐与碱性溶液合成的氢氧化物前体制备的。所选择的前体通过在低温下烧结 2 小时（>400°C）即可实现具有尖晶石结构的铝酸钴的低温制造。晶体学和热分析表明，低温烧结产物中含有通过化学吸附水和/或氢氧化物稳定的 Co（3+）离子，而在高于 1000°C 的温度下烧结的产物中则没有观察到这种情况。当烧结温度低于 1000°C 时，产物的颜色从清澈的蓝色（纳塔尔蓝）变为深绿色。磁性量、居里常数和魏斯温度显示出对烧结温度的强烈依赖性。这些发现表明，在尖晶石结构中存在混合价态，即 Co（2+）和 Co（3+），以及独特的阳离子分布在不同的晶体学位置，特别是在较低温度下烧结的产物中。
