Zhang Hui, Hu Tao, Wang Xiaohui, Li Zhaojin, Hu Minmin, Wu Erdong, Zhou Yanchun
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Sci Rep. 2015 Sep 21;5:14192. doi: 10.1038/srep14192.
The conventional wisdom to tailor the properties of binary transition metal carbides by order-disorder phase transformation has been inapplicable for the machinable ternary carbides (MTCs) due to the absence of ordered phase in bulk sample. Here, the presence of an ordered phase with structural carbon vacancies in Nb4AlC3-x (x ≈ 0.3) ternary carbide is predicted by first-principles calculations, and experimentally identified for the first time by transmission electron microscopy and micro-Raman spectroscopy. Consistent with the first-principles prediction, the ordered phase, o-Nb4AlC3, crystalizes in P63/mcm with a = 5.423 Å, c = 24.146 Å. Coexistence of ordered (o-Nb4AlC3) and disordered (Nb4AlC3-x) phase brings about abundant domains with irregular shape in the bulk sample. Both heating and electron irradiation can induce the transformation from o-Nb4AlC3 to Nb4AlC3-x. Our findings may offer substantial insights into the roles of carbon vacancies in the structure stability and order-disorder phase transformation in MTCs.
通过有序-无序相变来调整二元过渡金属碳化物性能的传统方法，由于块状样品中不存在有序相，因此不适用于可加工的三元碳化物（MTCs）。在此，通过第一性原理计算预测了Nb4AlC3-x（x≈0.3）三元碳化物中存在具有结构碳空位的有序相，并首次通过透射电子显微镜和显微拉曼光谱进行了实验鉴定。与第一性原理预测一致，有序相o-Nb4AlC3以P63/mcm空间群结晶，a = 5.423 Å，c = 24.146 Å。有序（o-Nb4AlC3）相和无序（Nb4AlC3-x）相的共存导致块状样品中出现大量形状不规则的畴。加热和电子辐照均可诱导o-Nb4AlC3向Nb4AlC3-x转变。我们的发现可能为碳空位在MTCs结构稳定性和有序-无序相变中的作用提供重要见解。
