Zhou Chao, Yu Hongyu, Zhang Zihan, Yu Zekun, Zhu Jinming, Bao Kuo, Cui Tian
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.
Institute of High Pressure Physics, School of Physical Science and Technology, Ningbo University, Ningbo 315211, China.
J Chem Phys. 2024 Aug 28;161(8). doi: 10.1063/5.0225610.
Recent experiments on α-MoB2 with MgB2-type structure achieved superconductivity at ∼32 K under 90 GPa, the highest among transition-metal diborides, rekindling interest in their superconducting properties. Our study systematically investigates the band structures of AlB2-type transition metal diborides. We found that the superior superconductivity of MoB2, WB2, and TcB2 correlates with their von Hove singularities near the Fermi level (EF), potentially linked to electron-phonon coupling. These three diborides exhibit similar critical temperature (Tc) trends under pressure: rising initially, peaking around 60 GPa, and then declining. While unstable at ambient pressure, their thermodynamic and dynamical stability limits vary significantly, possibly explaining experimental discrepancies. To stabilize MoB2 at ambient pressure, we designed MoXB4 compounds (X = other transition metals) by substituting every other Mo layer in MoB2 with an X layer. This modification aims to stabilize the structure and enhance superconductivity by reducing d-electron concentration at EF. This principle extends to other potential superconducting diborides, such as WB2 and TcB2. Using Nb as an example, we found that Nb atoms in AlB2-type MoNbB4 may exhibit random occupancy, potentially explaining disparities between theoretical predictions and experimental results. Our study offers valuable insights into superconductivity in transition metal diborides, paving the way for future research and applications.
最近对具有MgB₂型结构的α-MoB₂进行的实验在90吉帕斯卡的压力下于约32开尔文实现了超导性，这在过渡金属二硼化物中是最高的，重新引发了人们对其超导特性的兴趣。我们的研究系统地研究了AlB₂型过渡金属二硼化物的能带结构。我们发现，MoB₂、WB₂和TcB₂的优异超导性与其费米能级（EF）附近的范霍夫奇点相关，这可能与电子 - 声子耦合有关。这三种二硼化物在压力下呈现出相似的临界温度（Tc）趋势：最初上升，在约60吉帕斯卡时达到峰值，然后下降。虽然在常压下不稳定，但它们的热力学和动力学稳定性极限差异很大，这可能解释了实验上的差异。为了在常压下稳定MoB₂，我们通过用X层替代MoB₂中每隔一层的Mo层来设计MoXB₄化合物（X = 其他过渡金属）。这种改性旨在通过降低EF处的d电子浓度来稳定结构并增强超导性。这一原理也适用于其他潜在的超导二硼化物，如WB₂和TcB₂。以Nb为例，我们发现AlB₂型MoNbB₄中的Nb原子可能表现出随机占据，这可能解释了理论预测和实验结果之间的差异。我们的研究为过渡金属二硼化物的超导性提供了有价值的见解，为未来的研究和应用铺平了道路。
