Boron-Rich Molybdenum Boride with Unusual Short-Range Vacancy Ordering, Anisotropic Hardness, and Superconductivity,Chemistry of Materials

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Boron-Rich Molybdenum Boride with Unusual Short-Range Vacancy Ordering, Anisotropic Hardness, and Superconductivity
Chemistry of Materials ( IF 7.2 ) Pub Date : 2019-12-30 , DOI: 10.1021/acs.chemmater.9b04052
Hu Tang ₁ , Xiang Gao ₁ , Jian Zhang ₂ , Bo Gao ₁ , Wenju Zhou _{1,

2} , Bingmin Yan ₁ , Xue Li ₃ , Qinghua Zhang ₄ , Shang Peng ₅ , Dajian Huang ₁ , Lijun Zhang ₆ , Xiaohong Yuan ₁ , Biao Wan ₆ , Chong Peng ₆ , Lailei Wu ₆ , Dongzhou Zhang ₇ , Hanyu Liu ₃ , Lin Gu ₄ , Faming Gao ₈ , Tetsuo Irifune ₉ , Rajeev Ahuja ₁₀ , Ho-Kwang Mao ₁ , Huiyang Gou ₁

Affiliation

Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China
State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
State Key Laboratory of Superhard Materials & Innovation Center for Computational Physics Methods and Software, College of Physics, Jilin University, Changchun 130012, China
Beijing National Laboratory for Condensed Matter and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
School of Physics and Technology, Wuhan University, Wuhan 430072, China
Key Laboratory of Metastable Materials Science and Technology, College of Material Science and Engineering, Yanshan University, Qinhuangdao 066004, China
Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
Key Laboratory of Applied Chemistry, College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004, China
Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan
Condensed Matter Theory Group, Materials Theory Division, Department of Physics & Astronomy, Uppsala University, 75120 Uppsala, Sweden

Determination of the structures of materials involving more light elements such as boron-rich compounds is challenging and technically important in understanding their varied compositions and superior functionalities. Here we resolve the long-standing uncertainties in structure and composition about the highest boride (termed MoB₄, Mo_1–xB₃, or MoB₃) through the rapid formation of large-sized boron-rich molybdenum boride under pressure. Using high-quality single-crystal X-ray diffraction analysis and aberration-corrected scanning transmission electron microscopy, we reveal that boron-rich molybdenum boride with a composition of Mo_0.757B₃ exhibits P6₃/mmc symmetry with a partial occupancy of 0.514 in 2b Mo sites (Mo1), and direct observations reveal the short-range ordering of cation vacancies in (010) crystal planes. Large anisotropic Young’s moduli and Vickers hardness are seen for Mo_0.757B₃, which may be attributed by its two-dimensional boron distributions. Mo_0.757B₃ is also found to be superconducting with a transition temperature (T_c) of ∼2.4 K, which was confirmed by measurements of resistivity and magnetic susceptibility. Theoretical calculations suggest that the partial occupancy of Mo atoms plays a crucial role in the emergence of superconductivity.

中文翻译：

富硼硼化物，具有异常的短程空位有序，各向异性硬度和超导性

确定包含更多轻元素（例如富硼化合物）的材料的结构具有挑战性，并且在理解它们的各种组成和优异功能性方面在技术上很重要。在这里，我们通过在压力下快速形成大型富硼钼硼化物，来解决最高硼化物（称为MoB ₄，Mo _{1- x} B ₃或MoB ₃）的结构和组成方面的长期不确定性。使用高质量的单晶X射线衍射分析和像差校正的扫描透射电子显微镜，我们发现组成为_0.757 B ₃的富硼硼化钼表现出P6 ₃ / mmc的具有0.514在部分占用对称2B Mo位（MO1）和直接观察揭示在（010）晶面的阳离子空位的短程有序。Mo _0.757 B ₃具有较大的各向异性杨氏模量和维氏硬度，这可能归因于其二维硼分布。还发现Mo _0.757 B ₃具有约2.4 K的转变温度（T _c）超导，这可以通过测量电阻率和磁化率来证实。理论计算表明，Mo原子的部分占有在超导性的产生中起着至关重要的作用。

更新日期：2019-12-31

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