Dahlqvist Martin, Jansson Ulf, Rosen Johanna
Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden.
J Phys Condens Matter. 2015 Nov 4;27(43):435702. doi: 10.1088/0953-8984/27/43/435702. Epub 2015 Oct 7.
Transition metal diborides in hexagonal AlB2 type structure typically form stable MB2 phases for group IV elements (M = Ti, Zr, Hf). For group V (M = V, Nb, Ta) and group VI (M = Cr, Mo, W) the stability is reduced and an alternative hexagonal rhombohedral MB2 structure becomes more stable. In this work we investigate the effect of vacancies on the B-site in hexagonal MB2 and its influence on the phase stability and the structure for TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, CrB2, MoB2, and WB2 using first-principles calculations. Selected phases are also analyzed with respect to electronic and bonding properties. We identify trends showing that MB2 with M from group V and IV are stabilized when introducing B-vacancies, consistent with a decrease in the number of states at the Fermi level and by strengthening of the B-M interaction. The stabilization upon vacancy formation also increases when going from M in period 4 to period 6. For TiB2, ZrB2, and HfB2, introduction of B-vacancies have a destabilizing effect due to occupation of B-B antibonding orbitals close to the Fermi level and an increase in states at the Fermi level.
具有六方AlB₂型结构的过渡金属二硼化物通常为IV族元素（M = Ti、Zr、Hf）形成稳定的MB₂相。对于V族（M = V、Nb、Ta）和VI族（M = Cr、Mo、W），稳定性降低，另一种六方菱面体MB₂结构变得更稳定。在这项工作中，我们使用第一性原理计算研究了六方MB₂中B位空位的影响及其对TiB₂、ZrB₂、HfB₂、VB₂、NbB₂、TaB₂、CrB₂、MoB₂和WB₂的相稳定性和结构的影响。还对选定的相进行了电子和键合性质分析。我们发现趋势表明，引入B空位时，V族和IV族的M的MB₂会得到稳定，这与费米能级处的态数减少以及B-M相互作用增强一致。从第4周期的M到第6周期的M，空位形成时的稳定性增强也会增加。对于TiB₂、ZrB₂和HfB₂，由于靠近费米能级的B-B反键轨道被占据以及费米能级处的态数增加，引入B空位会产生去稳定作用。
