BP_5 Monolayer with Multiferroicity and Negative Poisson's Ratio: A Prediction by Global Optimization Method

摘要

Based on variable components global optimization algorithm, we predict astable two-dimensional (2D) phase of boron phosphide with 1:5 stoichiometry,i.e. boron pentaphosphide (BP_5) monolayer, which has a lower formation energythan that of the commonly believed graphitic phase (g-BP). BP_5 monolayer is amultiferroic material with coupled ferroelasticity and ferroelectricity. Thepredicted reversible strain is up to 41.41%, which is the largest among allreported ferroelastic materials. Due to the non-centrosymmetric structure andelectronegativity differences between boron and phosphorus atoms, an in-planespontaneous polarization of 326.0 pC/m occurs in BP_5. Moreover, the recentlyhunted negative Poisson's ratio property, is also observed in BP_5. As anindirect semiconductor with a band gap of 1.34 eV, BP_5 displays outstandingoptical and electronic properties, for instance strongly anisotropicvisible-light absorption and high carrier mobility. The rich and extraordinaryproperties of BP_5 make it a potential nanomaterial for designingelectromechanical or optoelectronic devices, such as nonvolatile memory withconveniently readable/writeable capability. Finally, we demonstrate that AlN(010) surface could be a suitable substrate for epitaxy growth of BP_5monolayer.