posted on 2019-05-03, 00:00authored byChunmei Zhang, Tianwei He, Sri Kasi Matta, Ting Liao, Liangzhi Kou, Zhongfang Chen, Aijun Du
Three-dimensional
diborides MB2, featured in stacking
the M layer above the middle of the honeycomb boron layer, have been
extensively studied. However, little information on the two-dimensional
counterparts of MB2 is available. Here, by means of evolutionary
algorithm and first-principles calculations, we extensively studied
the monolayer MB2 crystal with M elements ranging from
group IIA to IVA covering 34 candidates. Our computations screened
out eight stable monolayers MB2 (M = Be, Mg, Fe, Ti, Hf,
V, Nb, Ta), and they exhibit Dirac-like band structures. Dramatically,
among them, groups IVB–VB transition-metal diboride MB2 (M = Ti, Hf, V, Nb, Ta) are predicted to be a new class of
auxetic materials. They harbor in-plane negative Poisson’s
ratio (NPR) arising mainly from the orbital hybridization between
M d and Boron p orbitals, which is distinct from previously reported
auxetic materials. The unusual NPR and the Dirac transport channel
of these materials are applicable to nanoelectronics and nanomechanics.