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Evolution of boron clusters in iron tetraborides under high pressure: semiconducting and ferromagnetic superhard materials

机译：高压下铁四硼化物中硼簇的演变：半导体和铁磁超硬材料

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We investigated the high-pressure structures and properties of iron tetraborides (FeB4) using a combination of an ab initio high-throughput search and a particle-swarm optimization algorithm for crystal structure prediction. We found that, under compression, the boron sublattice in FeB4 from the buckled boron layer first polymerizes into B-4 tetrahedral clusters and then forms cubo-octahedral B-12 clusters. At 55 GPa, the orthorhombic crystal structure with a Pnnm space group (58-FeB4) transforms into a tetragonal I4(1)/acd structure (142-FeB4), which is stable within a wide pressure range up to 695 GPa. Then, a cubic Im (3) over barm phase (229-FeB4) emerges at higher pressures up to at least 1 TPa. The computed Vicker's hardnesses of 58-, 142-, and 229-FeB4 are 61.58, 47.44, and 50.87 GPa, respectively. All of them can be considered as superhard materials. Compared to the previously reported 58-FeB4 as a superhard superconductor, the B-4 tetrahedral cluster-based 142-FeB4 is a superhard semiconductor with an indirect band gap of 1.34 eV. The pressure-induced metal-to-semiconductor transition can be related to a unique Fe-B-B three-center covalent bond. Moreover, 229-FeB4, which is composed of cubooctahedral B-12 clusters, is ferromagnetic with a magnetic moment of 0.929 mu(B) per Fe atom at ambient pressure. The magnetic moment will decrease rapidly with increasing pressure and be completely quenched as pressure exceeds 40 GPa. The pressure-induced evolution of boron cluster units not only adds new features to boron chemistry, but also gives rise to novel superhard semiconductors or ferromagnetic materials. Moreover, our results may inspire further experimental and theoretical interest in designing new materials using clusters as pseudo-atoms with expected properties.
机译：我们使用AB Initio高通量搜索的组合和用于晶体结构预测的粒子 - 群优化算法的组合来研究铁四硼化物（FEB4）的高压结构和性质。我们发现，在压缩下，从屈曲硼层的22B4中的硼子分子首先聚合成B-4四面体簇，然后形成浴八面体B-12簇。在55GPa，具有PNNM空间组（58-FEB4）的正交晶体结构转化为四方I4（1）/ ACD结构（142-FEB4），其在宽的压力范围内稳定，高达695GPa。然后，在BARM阶段（229-FEB4）上的立方IM（3）在高达至少1吨TPA的较高压力下出现。计算的维肯的硬度为58-，142-和229-FeB4分别为61.58,47.44和50.87GPa。所有这些都可以被视为超硬材料。与先前报道的58-FEB4相比，作为超硬超导体，基于B-4四束聚类的142-FEB4是具有1.34eV的间接带隙的超空地半导体。压力诱导的金属至半导体转变可以与独特的Fe-B-B三中心共价键有关。此外，由CubooctaheDral B-12簇组成的229-FeB4是在环境压力下每Fe原子0.929μ（b）的铁磁。磁矩将随着压力的增加而迅速降低，随着压力超过40GPa，完全淬火。硼簇单元的压力诱导的演化不仅为硼化学增加了新的特征，而且还引发了新型超硬半导体或铁磁性材料。此外，我们的结果可能会激发使用簇作为具有预期特性的伪原子的簇设计新材料的进一步的实验和理论兴趣。

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  • 来源
    《RSC Advances》 |2015年第59期|共12页
  • 作者

    Jiang Xue; Zhao Jijun;

  • 作者单位

    Dalian Univ Technol Key Lab Mat Modificat Laser Ion &

    Electron Beams Minist Educ Dalian 116024 Peoples R China;

    Dalian Univ Technol Key Lab Mat Modificat Laser Ion &

    Electron Beams Minist Educ Dalian 116024 Peoples R China;

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  • 正文语种 eng
  • 中图分类 化学;
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