Anisotropic thermal expansions of select layered ternary transition metal borides: MoAlB, Cr2AlB2, Mn2AlB2, and Fe2AlB2
Anisotropic thermal expansions of select layered ternary transition metal borides: MoAlB, Cr2AlB2, Mn2AlB2, and Fe2AlB2
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DOI：
10.1063/1.5054379
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发表时间：
2018-11-28
影响因子：
3.2
通讯作者：
Barsoum, M. W.
中科院分区：
文献类型：
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作者：
Verger, L.;Kota, S.;Barsoum, M. W.
用原位高温粉末X射线衍射法计算了三元硼化物MoAlB、Cr2AlB2、Mn2AlB2和Fe2AlB2以及二元硼化物CrB的热膨胀系数(CTE)。平均线膨胀系数从低到高依次为MoAlB(7.3×10(-6)K-1)、CrB(8.6×10(-6)K-1)、Fe2AlB2(10.3×10(-6)K-1)、Cr2AlB2(10.5×10(-6)K-1)、Mn2AlB2(14.0×10(-6)K-1)。尽管它们的结构和化学结构相似，但它们的CTE各向异性是不同的，可以分为两组。在第一组MoAlB和Fe2AlB2中，CTE值最高的是沿堆积方向，最低的是平行于B-B链。在第二组Cr2AlB2、Mn2AlB2和CrB中，CTE最低的是沿堆积方向，最高的是垂直于链的方向。除MoAlB外，所有三元系中平行于B-B链的热膨胀系数(32%~103%)均显著低于垂直于B-B链的热膨胀系数。总的来说，在M2AlB2三元和相应的二元单硼化物中，平行于B-B链的相对CTE表明，B-B键的强烈共价性至少是观察到的大的热膨胀各向异性的部分原因。由AIP出版公司出版。
The coefficients of thermal expansion (CTE) of the ternary borides, MoAlB, Cr2AlB2, Mn2AlB2, and Fe2AlB2, and the binary boride, CrB, were calculated from in situ high-temperature powder X-ray diffraction patterns. The order-from low to high-of the average linear thermal expansions was MoAlB (7.3 x 10(-6) K-1), CrB (8.6 x 10(-6) K-1), Fe2AlB2 (10.3 x 10(-6) K-1), Cr2AlB2 (10.5 x 10(-6) K-1), and Mn2AlB2 (14.0 x 10(-6) K-1). Despite their structural and chemical similarities, the CTE anisotropies of these phases were different and could be grouped into two groups. In the first group, MoAlB and Fe2AlB2, the highest CTE values were along the stacking direction and the lowest were parallel to the B-B chains. In the second group, Cr2AlB2, Mn2AlB2, and CrB, the lowest CTE was along the stacking direction and the highest was normal to the chains. The thermal expansions parallel to the B-B chains were significantly lower (32% to 103%) than those perpendicular to the chains in all the ternaries except for MoAlB. In general, the relative CTEs parallel to the B-B chains in both the M2AlB2 ternaries and corresponding binary monoborides suggest that strong covalent character of the B-B bonds are at least partially responsible for the large thermal expansion anisotropies observed. Published by AIP Publishing.