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

• Published in: Chemistry of materials Vol. 32; no. 1; pp. 459 - 467
• Main Authors: Tang, Hu, Gao, Xiang, Zhang, Jian, Gao, Bo, Zhou, Wenju, Yan, Bingmin, Li, Xue, Zhang, Qinghua, Peng, Shang, Huang, Dajian, Zhang, Lijun, Yuan, Xiaohong, Wan, Biao, Peng, Chong, Wu, Lailei, Zhang, Dongzhou, Liu, Hanyu, Gu, Lin, Gao, Faming, Irifune, Tetsuo, Ahuja, Rajeev, Mao, Ho-Kwang, Gou, Huiyang
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.01.2020
• ISSN: 0897-4756; 1520-5002; 1520-5002
• DOI: 10.1021/acs.chemmater.9b04052

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, Mo1–x B3, 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 Mo0.757B3 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 Mo0.757B3, which may be attributed by its two-dimensional boron distributions. Mo0.757B3 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.