Computational Search for Novel Hard Chromium-Based Materials,The Journal of Physical Chemistry Letters

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Computational Search for Novel Hard Chromium-Based Materials
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2017-01-31 00:00:00 , DOI: 10.1021/acs.jpclett.6b02821
Alexander G. Kvashnin _{1,

2} , Artem R. Oganov _{1,

2,

3,

4} , Artem I. Samtsevich ₁ , Zahed Allahyari _{1,

2}

Affiliation

Nitrides, carbides, and borides of transition metals are an attractive class of hard materials. Our recent preliminary explorations of the binary chemical compounds indicated that chromium-based materials are among the hardest transition metal compounds. Motivated by this, here we explore in detail the binary Cr–B, Cr–C, and Cr–N systems using global optimization techniques. Calculated enthalpy of formation and hardness of predicted materials were used for Pareto optimization to define the hardest materials with the lowest energy. Our calculations recover all numerous known stable compounds (except Cr₂₃C₆ with its large unit cell) and discover a novel stable phase Pmn2₁-Cr₂C. We resolve the structure of Cr₂N and find it to be of anti-CaCl₂ type (space group Pnnm). Many of these phases possess remarkable hardness, but only CrB₄ is superhard (Vickers hardness 48 GPa). Among chromium compounds, borides generally possess the highest hardnesses and greatest stability. Under pressure, we predict stabilization of a layered TMDC-like phase of Cr₂N, a WC-type phase of CrN, and a new compound CrN₄. Nitrogen-rich chromium nitride CrN₄ is a high-energy-density material featuring polymeric nitrogen chains. In the presence of metal atoms (e.g., Cr), polymerization of nitrogen takes place at much lower pressures; CrN₄ becomes stable at ∼15 GPa (cf. 110 GPa for synthesis of pure polymeric nitrogen).

中文翻译：

新型硬铬基材料的计算搜索

过渡金属的氮化物，碳化物和硼化物是一类有吸引力的硬质材料。我们最近对二元化合物的初步研究表明，铬基材料是最坚硬的过渡金属化合物之一。因此，在这里，我们使用全局优化技术来详细研究二元Cr-B，Cr-C和Cr-N系统。计算出的形成焓和预测材料的硬度用于Pareto优化，以定义具有最低能量的最坚硬材料。我们的计算恢复所有许多已知稳定的化合物（除铬₂₃ Ç ₆以其大单元电池），并发现了一种新的稳定相Pmn的2 ₁ -Cr ₂ C.我们解决Cr的结构₂ N并发现它是抗CaCl ₂型（空间群Pnnm）。这些相中有许多具有显着的硬度，但只有CrB ₄是超硬的（维氏硬度为48 GPa）。在铬化合物中，硼化物通常具有最高的硬度和最大的稳定性。在压力下，我们预测Cr ₂ N的层状TMDC相，CrN的WC型相和新的化合物CrN _4会稳定。富氮氮化铬CrN ₄是一种高能量密度材料，具有聚合物氮链。在金属原子（例如Cr）的存在下，氮气的聚合反应在低得多的压力下进行。CrN ₄ 在约15 GPa时变得稳定（参见110 GPa，用于合成纯聚合氮）。

更新日期：2017-01-31

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