Concurrent ordering and phase transformation in SmCo7 nanograins
Concurrent ordering and phase transformation in SmCo7 nanograins
复制标题
SmCo7 纳米颗粒的并行有序化和相变
DOI：
10.1039/c5nr02592c
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发表时间：
2015-01-01
期刊：
影响因子：
6.7
通讯作者：
Rettenmayr, Markus
中科院分区：
文献类型：
--
作者：
Seyring, Martin;Song, Xiaoyan;Rettenmayr, Markus
具有稳定的SmCo 7相的Sm-Co合金是高级高温永磁体的最突出的候选者，其中SmCo 7相的稳定化可以通过纳米结构化来实现。在SmCo 7纳米颗粒的复杂的并发过程的有序和相变的特点是在原子尺度上。对于第一次的相变的早期阶段是可见的，通过突出显示特定的超级结构在单个纳米颗粒使用傅立叶重建的高分辨率透射电子显微镜图像。超结构只能被检测到，并且只能在特定的晶体学方向上区分。原子排列在晶体结构中的演变被证明为同时有序化过程和相变。在亚稳SmCo 7相的分解过程中，六方Sm 2Co 17超结构（2：17 H）首先形成为菱方Sm 2Co 17超结构（2：17 R）的前体-这只能通过分析单个晶粒来检测，迄今为止还没有描述。通过对单个纳米晶粒的广泛的晶体学分析，发现超结构相的分数与晶粒尺寸之间存在明显的相关性，直接且明确地显示了纳米晶合金中相变的晶粒尺寸依赖性，这种现象到目前为止仅使用体积平均法间接显示。
Sm-Co alloys with the stabilized SmCo7 phase are most prominent candidates for advanced high temperature permanent magnets, where the stabilization of the SmCo7 phase can be effectuated by nanostructuring. The complex concurrent processes of ordering and phase transformation in a SmCo7 nanograin are characterized on the atomic scale. For the first time early stages of the phase transformation are made visible by highlighting specific superstructures in single nanograins using Fourier reconstruction of high-resolution transmission electron microscopy images. The superstructures are only detectable and can only be distinguished in specific crystallographic orientations. The evolution of the atom arrangement in the crystal structures is demonstrated for the concurrent ordering process and phase transformation. During decomposition of the metastable SmCo7 phase, the hexagonal Sm2Co17 superstructure (2:17H) forms at first as a precursor of the rhombohedral Sm2Co17 superstructure (2:17R) - this can only be detected by analysis of individual grains and has not been described so far. By extensive crystallographic analysis of individual nanograins, a distinct correlation between the fraction of the superstructure phases and the grain size is found, showing directly and unambiguously the grain size dependence of the phase transformation in the nanocrystalline alloy, a phenomenon that so far has only been shown indirectly using volume averaging methods.