Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userBP_5 Monolayer with Multiferroicity and Negative Poissons Ratio: A Prediction by Global Optimization Method
68
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Based on variable components global optimization algorithm, we predict a stable two-dimensional (2D) phase of boron phosphide with 1:5 stoichiometry, i.e. boron pentaphosphide (BP_5) monolayer, which has a lower formation energy than that of the commonly believed graphitic phase (g-BP). BP_5 monolayer is a multiferroic material with coupled ferroelasticity and ferroelectricity. The predicted reversible strain is up to 41.41%, which is the largest among all reported ferroelastic materials. Due to the non-centrosymmetric structure and electronegativity differences between boron and phosphorus atoms, an in-plane spontaneous polarization of 326.0 pC/m occurs in BP_5. Moreover, the recently hunted negative Poissons ratio property, is also observed in BP_5. As an indirect semiconductor with a band gap of 1.34 eV, BP_5 displays outstanding optical and electronic properties, for instance strongly anisotropic visible-light absorption and high carrier mobility. The rich and extraordinary properties of BP_5 make it a potential nanomaterial for designing electromechanical or optoelectronic devices, such as nonvolatile memory with conveniently readable/writeable capability. Finally, we demonstrate that AlN (010) surface could be a suitable substrate for epitaxy growth of BP_5 monolayer.
rate research
Read More
As a basic mechanical parameter, Poissons ratio ({ u}) measures the mechanical responses of solids against external loads. In rare cases, materials have a negative Poissons ratio (NPR), and present an interesting auxetic effect. That is, when a material is stretched in one direction, it will expand in the perpendicular direction. To design modern nanoscale electromechanical devices with special functions, two dimensional (2D) auxetic materials are highly desirable. In this work, based on first principles calculations, we rediscover the previously proposed {delta}-phosphorene ({delta}-P) nanosheets [Jie Guan et al., Phys. Rev. Lett. 2014, 113, 046804] are good auxetic materials with a high NPR. The results show that the Youngs modulus and Poissons ratio of {delta}-P are all anisotropic. The NPR value along the grooved direction is up to -0.267, which is much higher than the recently reported 2D auxetic materials. The auxetic effect of {delta}-P originated from its puckered structure is robust and insensitive to the number of layers due to weak interlayer interactions. Moreover, {delta}-P possesses good flexibility because of its relatively small Youngs modulus and high critical crack strain. If {delta}-P can be synthesized, these extraordinary properties would endow it great potential in designing low dimensional electromechanical devices.
Silicon dioxide or silica, normally existing in various bulk crystalline and amorphous forms, is recently found to possess a two-dimensional structure. In this work, we use ab initio calculation and evolutionary algorithm to unveil three new 2D silica structures whose themal, dynamical and mechanical stabilities are compared with many typical bulk silica. In particular, we find that all these three 2D silica have large in-plane negative Poissons ratios with the largest one being double of penta-graphene and three times of borophenes. The negative Poissons ratio originates from the interplay of lattice symmetry and Si-O tetrahedron symmetry. Slab silica is also an insulating 2D material, with the highest electronic band gap (> 7 eV) among reported 2D structures. These exotic 2D silica with in-plane negative Poissons ratios and widest band gaps are expected to have great potential applications in nanomechanics and nanoelectronics.
Negative Poissons ratio (NPR) materials have attracted tremendous interest due to their unusual physical properties and potential applications. Certain two-dimensional (2D) monolayer materials have also been found to exhibit NPR and the corresponding deformation mechanism varies. In this study, we found, based on first-principles calculations, that the Poissons ratio (PR) sign of monolayer Blue Phosphorus Oxide (BPO) can be tuned by strain: the PR is positive under uniaxial strain <= -1% but becomes negative under > 0. The deformation mechanism for BPO under strain depends on the mutual competition between the P-P attraction and P-O repulsion effect, and these two factors induce two different deformation pathways (one with positive PR, and the other with NPR). Moreover, with increasing of strain, both the decreased strength of P-P attraction and the increased strength of P-O repulsion effect modulate the PR of BPO from positive to negative.
Most materials exhibit positive Poissons ratio (PR) values but special structures can also present negative and, even rarer, zero (or close to zero) PR. Null PR structures have received much attention due to their unusual properties and potential applications in different fields, such as aeronautics and bio-engineering. Here, we present a new and simple near-zero PR 2D topological model based on a structural block composed of two smooth and rigid bars connected by a soft membrane or spring. It is not based on re-entrant or honeycomb-like configurations, which have been the basis of many null or quasi-null PR models. Our topological model was 3D printed and the experimentally obtained PR was$-0.003,pm 0.001,$, which is one the closest to zero value ever reported. This topological model can be easily extended to 3D systems and with compression in any direction. The advantages and disadvantages of these models are also addressed.
We study the elastic response of composites of rods embedded in elastic media. We calculate the micro-mechanical response functions, and bulk elastic constants as functions of rod density. We find two fixed points for Poissons ratio with respect to the addition of rods in 3D composites: there is an unstable fixed point for Poissons ratio=1/2 (an incompressible system) and a stable fixed point for Poissons ratio=1/4 (a compressible system). We also derive an approximate expression for the elastic constants for arbitrary rod density that yields exact results for both low and high density. These results may help to explain recent experiments [Physical Review Letters 102, 188303 (2009)] that reported compressibility for composites of microtubules in F-actin networks.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
