Bridging hcp-Ni and Ni3C via a Ni3C1-x Solid Solution: Tunable Composition and Magnetism in Colloidal Nickel Carbide Nanoparticles
Bridging hcp-Ni and Ni3C via a Ni3C1-x Solid Solution: Tunable Composition and Magnetism in Colloidal Nickel Carbide Nanoparticles
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DOI：
10.1021/cm200410s
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发表时间：
2011-05-10
影响因子：
8.6
通讯作者：
Schaak, Raymond E.
中科院分区：
文献类型：
--
作者：
Schaefer, Zachary L.;Weeber, Kaitlyn M.;Schaak, Raymond E.
元素镍的纳米颗粒支撑着大量的磁性和催化应用，通过形成不同的同素异形体来调节这些特性的可能性非常有趣。虽然块状元素镍采用面心立方（fcc）结构，但越来越多的报告表明，胶体镍纳米粒子可以以亚稳态六方密堆积（hcp）结构结晶。然而，文献中关于 hcp-Ni 的形成存在一些分歧，特别是在晶体学相关的 Ni3C 相方面。最值得注意的是 hcp-Ni 的一系列晶格常数和磁性。在这里，我们证明反应时间可用于调节 Ni3C1-x 固溶体的碳含量。重要的是，Ni3C1-x 胶体纳米粒子可以帮助通过实验合理化 hcp-Ni 和 Ni3C 的晶格常数和磁性能范围，有效地桥接这两个端元系统。所有样品（包括 Ni2+ 还原为 Ni-0 后立即分离的样品）都含有一些碳，如 XRD、XPS、TGA、DSC、TEM 和 SQUID 磁力测定法所证明。随着反应时间的增加，平均碳含量增加，这与晶胞体积的系统增加和饱和磁化强度的系统减少相关。这些结果还为调节同晶镍纳米颗粒的磁性能提供了一条简单的途径。
Nanoparticles of elemental nickel underpin a large number of magnetic and catalytic applications, and the possibility of tuning these properties via the formation of different allotropes is intriguing. While bulk elemental nickel adopts a face centered cubic (fcc) structure, a growing number of reports suggest that colloidal nickel nanoparticles can crystallize in the metastable hexagonal close packed (hcp) structure. However, there is some disagreement in the literature concerning the formation of hcp-Ni, particularly with respect to the crystallographically-related Ni3C phase. Most notable is a range of lattice constants and magnetic properties that have been attributed to hcp-Ni. Here, we show that reaction time can be used to tune the carbon content of a Ni3C1-x solid solution. Importantly, colloidal nanoparticles of Ni3C1-x can help to experimentally rationalize the range of lattice constants and magnetic properties reported for hcp-Ni and Ni3C, effectively bridging these two end-member systems. All samples, including those isolated immediately upon reduction of Ni2+ to Ni-0, contained some carbon, as evidenced by XRD, XPS, TGA, DSC, TEM, and SQUID magnetometry. As reaction time increases, the average carbon content increases, and this correlates with a systematic increase in unit cell volume and a systematic decrease in saturation magnetization. These results also provide a straightforward pathway for tuning the magnetic properties of isomorphous Ni nanoparticles.