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Pressure-induced polymorphism in SrB_6 and deformation mechanisms of covalent networks

机译：压力诱导的SRB_6多态性和共价网络的变形机制

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摘要

We study the high-pressure structures of SrB6 up to 200 GPa using first-principles structure prediction calculations and high-pressure x-ray diffraction experiments. The computations show that the ambient-pressure cubic phase transforms to an orthorhombic structure (Cmmm) at 48 GPa, and then to a tetragonal structure (14/mmm) at 60 GPa. The high-pressure experiments are consistent with the theoretically predicted tetragonal structure, which was quenched successfully to ambient conditions. Pressure induces simple boron octahedra to form complex networks in which the electrons are delocalized, leading to metallic ground states with large density of states at the Fermi level. Calculated stress-strain relations for the 14/mmm structure of SrB6 demonstrate its intrinsic hard nature with an estimated Vickers hardness of 15 GPa, and reveal a novel deformation mechanism with transient multicenter bonding that results in the combination of high strength and high ductility. Our findings offer valuable insights for understanding the rich and complex crystal structures of SrB6, which have broad implications for further explorations of hexaboride materials.
机译：我们使用第一原理结构预测计算和高压X射线衍射实验研究了SRB6高达200GPa的高压结构。计算表明，环境压力立方相在48GPa的正交结构（CMMM）中变换，然后在60gPa下进行四边形结构（14 / mmm）。高压实验与理论上预测的四方结构一致，其成功地淬火到环境条件下。压力诱导简单的硼octahedra以形成复杂的网络，其中电子被划分的网络化，导致在费米水平处具有大状态密度的金属地面状态。计算出SRB6的14 / MMM结构的应力应变关系证明了其具有15GPa的估计维氏硬度的其内在难性，并揭示了一种具有瞬态多中心粘合的新型变形机制，导致高强度和高延展性的组合。我们的调查结果为了解SRB6的丰富和复杂的晶体结构提供了有价值的见解，这对六硼化物材料的进一步探索具有广泛的影响。

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  • 来源
    《Physical review》 |2019年第21期|214102.1-214102.7|共7页
  • 作者

    Zhu Li; Borstad Gustav M.; Cohen R. E.; Strobel Timothy A.;

  • 作者单位

    Carnegie Inst Sci Geophys Lab 5251 Broad Branch Rd NW Washington DC 20015 USA;

    Carnegie Inst Sci Geophys Lab 5251 Broad Branch Rd NW Washington DC 20015 USA;

    Carnegie Inst Sci Geophys Lab 5251 Broad Branch Rd NW Washington DC 20015 USA|Ludwig Maximilians Univ Munchen Dept Earth & Environm Sci D-80333 Munich Germany;

    Carnegie Inst Sci Geophys Lab 5251 Broad Branch Rd NW Washington DC 20015 USA;

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