Structural variations, relationships and properties of M2B metal borides
Structural variations, relationships and properties of M2B metal borides
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DOI：
10.1016/j.jssc.2018.12.014
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发表时间：
2019-02-01
影响因子：
3.3
通讯作者：
Fokwa, Boniface P. T.
中科院分区：
文献类型：
--
作者：
Iyer, Abishek K.;Zhang, Yuemei;Fokwa, Boniface P. T.
金属硼化物代表了一类具有多种晶体结构的材料，但它们的物理和催化性能绝大多数未被充分研究。在这篇综述中，我们介绍了金属硼比 (M:B) 为 2:1 的金属硼化物的结构变化、关系和性质，这些硼化物具有 130 多种已知相（从二元到四元），可结晶出 21 种结构类型。虽然大多数这些结构类型仅包含孤立的硼原子，但在其中 9 个（不到一半）中观察到 B-B 键 (d(B-B) < 2.0 埃）。尽管发现了硼原子的几种配位环境，但三角棱柱配位（CN = 6(+3)，存在于十七种结构类型）是迄今为止最常见的，其次是正方反棱柱配位（CN = 8）。这些三棱柱可以像 CeCo3B2 类型那样不扭曲，因此硼位于精确的中心，但在 Co2Si 类型中也发现扭曲的棱柱。像 ZrCo3B2 型那样更强的扭曲会导致形成短 B-B 键（d(B-B) < 2.0 埃）。当以 B 为中心的三棱柱共用矩形面时，相邻硼之间会发生键合。 Ni3ZnB2 和 Ti1+xRh2-x+yIr3-yB3 是锯齿形 B-4 片段的例子，在 Ti1+xOs2-xRuB2 中发现了三角形平面 B-4 片段。在MoAlB型的情况下，矩形面是共享的，导致锯齿形B链。除了反MoS2型（Pt2B，存在性仍有争议）之外，这些结构中短轴的晶胞长度总是接近3.0埃，这对应于典型B[M-6]棱镜的高度。在 URu3B2 和 ZrCo3B2 的情况下，与相关的 CeCo3B2 型相比，由于其超结构，短轴分别增加了一倍和三倍。尽管在许多相（特别是在 CeCo3B2 型中）以及一些令人着迷的催化行为（例如在 CuAl2 型相中）已经报道了有趣的磁性和超导特性，但还必须进一步研究。 未来将利用这个 2:1 硼化物成分空间的结构多样性。
Metal borides represent a class of materials with a large variety of crystal structures, yet their physical and catalytic properties are overwhelmingly understudied. In this review, we present the structural variations, relationships and properties of metal borides with a metal-to-boron ratio (M:B) of 2:1, which have over 130 known phases (from binaries to quaternaries) that crystallize with 21 structure types. While most of these structure types contain isolated boron atoms only, B-B-bonds (d(B-B) < 2.0 angstrom) are observed in nine of them (less than half). Even though several coordination environments for boron atoms are found, the trigonal prismatic coordination (CN = 6(+3), present in seventeen structure types) is by far the most common followed by the square anti-prismatic coordination (CN = 8). These trigonal prisms can be undistorted like in the CeCo3B2-type, where boron consequently resides in the exact center, but also distorted prisms are found for example in the Co2Si-type. Stronger distortions like in the ZrCo3B2-type can lead to the formation of short B-B-bonds (d(B-B) < 2.0 angstrom). When B-centered trigonal prisms share common rectangular faces, bonding between neighboring boron occurs. Ni3ZnB2 and Ti1+xRh2-x+yIr3-yB3 are examples with zigzag B-4 fragments and in Ti1+xOs2-xRuB2 trigonal planar B-4 fragments are found. In the case of the MoAlB-type the rectangular faces are shared leading to a zigzag B-chain.Except for the anti-MoS2-type (Pt2B, existence is still debated), the unit cell length of the short axis in these structures is always close to 3.0 angstrom, which corresponds to the height of a typical B[M-6] prism. In the case of URu3B2 and ZrCo3B2 the short axis is doubled respectively tripled due to their superstructure in comparison to the related CeCo3B2-type.Even though interesting magnetic and superconducting properties have been reported in many phases (especially in the CeCo3B2-type) as well as some fascinating catalytic behaviors (such as in CuAl2-type phases), more must be done in the future to capitalize on the structural diversity from this 2:1 borides composition space.