In-plane Negative Poisson's Ratio Research Articles

Bottom-up strategy: A typical way to create multi-directional auxeticity in Si2O-based layered material

Layered auxetic materials have an acute demand for the in-plane negative Poisson's ratio (NPR) due to dimensional restrictions. Yet, it is not yet apparent and developed where the auxeticity in nanomaterials origins from. Aimed at inserting in-plane auxeticity, in this letter, we theoretically propose a series of Si2O-based layer-stacking materials using a bottom-up strategy. As a result of the materials' chemical O absorption, which causes the Pauli repulsion of inter-layer orbits to shift in the direction of the plane, a newly found multi-directional NPR effect is finally realized in II-BK-Si2O. Furthermore, the multilayer structures preserve dispersion of the SL-Si2O while breaking the semi-Dirac semi-metallic conditions and gapped, endowing the materials semiconducting characteristics and strong carrier mobilities. For Si2O-based materials, the aforementioned benefits open up a wide range of application possibilities and research potential.

Switchable hidden spin polarization and negative Poisson's ratio in two-dimensional antiferroelectric wurtzite crystals

Two-dimensional (2D) antiferroelectric materials have raised great research interest over the last decade. Here, we reveal a type of 2D antiferroelectric (AFE) crystal where the AFE polarization direction can be switched by a certain degree in the 2D plane. Such 2D functional materials are realized by stacking the exfoliated wurtzite (wz) monolayers with “self-healable” nature, which host strongly coupled ferroelasticity/antiferroelectricity and benign stability. The AFE candidates, i.e., ZnX and CdX (X = S, Se, Te), are all semiconductors with direct bandgap at Γ point, which harbors switchable antiferroelectricity and ferroelasticity with low transition barriers, hidden spin polarization, as well as giant in-plane negative Poisson's ratio (NPR), enabling the co-tunability of hidden spin characteristics and auxetic magnitudes via AFE switching. The 2D AFE wz crystals provide a platform to probe the interplay of 2D antiferroelectricity, ferroelasticity, NPR, and spin effects, shedding new light on the rich physics and device design in wz semiconductors.

Ultra-high d31 anti-chiral negative Poisson’s ratio BaTiO3 ceramics fabricated by vat photopolymerization 3D printing

In this study, the anti-chiral negative Poisson's ratio structure BaTiO3 piezoelectric ceramics were fabricated by vat photopolymerization 3D printing technology, which obtained an ultra-high transverse piezoelectric coefficient d31. Here, we performed uniaxial compressive load simulations and electric field-driven lattice in-plane strain response simulations, which showed an in-plane negative Poisson's ratio of −1 for the BaTiO3 ceramics. Its strain amplification is about 10 times that of BaTiO3 bulk material. Using the principle of positive and negative piezoelectric effects, we measured effective transverse piezoelectric coefficients d31 for different dimensional parameters. The effective transverse piezoelectric coefficient d31 with a maximum of 599 pm/V was detected at a ligament aspect ratio of 3.6 for the negative Poisson's ratio BaTiO3 piezoelectric ceramics, which is 7.7 times higher than that of the bulk material. For the prepared hydrophone, test results show that the effective hydrostatic strain constant dh and Hydrostatic Figure of Merit (HFOM) of BaTiO3 piezoelectric ceramics with a negative Poisson's ratio structure are 29.6 and 808 times higher than those of bulk BaTiO3.

Metal halide HgI2 monolayer with auxetic property and photocatalysis application

Recently, two-dimensional (2D) metal halides have shown extraordinary performances as photocatalysts, triggering our enormous interest to explore new 2D metal halides for photocatalysis water splitting. Here, based on an unbiased first-principles swarm intelligence structure search, we identified a thermally and dynamically stable HgI2 monolayer. Interestingly, its atomic configuration forms an unusual in-plane negative Poisson's ratio, resulting in an auxetic property. More importantly, the HgI2 monolayer exhibits excellent optoelectronic properties, including suitable direct bandgap (∼2.45 eV), good carrier mobility (×102 cm2 V−1 s−1), excellent light absorption coefficient (×105 cm−1), and suitable band edges for photocatalytic water splitting. These excellent characteristics make the HgI2 monolayer fulfill the basic criteria of efficient photocatalysts for water splitting, supporting it as a promising candidate for photocatalytic materials. Our findings bloom the 2D metal halides family and offer a new candidate material for photocatalysis water splitting.

High out-of-plane negative Poisson's ratios and strong light harvesting in two-dimensional SiS2 and its derivatives.

Two-dimensional (2D) materials with negative Poisson's ratios (NPRs) hold tremendous potential in diverse electronic devices. However, most 2D auxetic materials exhibit small out-of-plane NPRs and materials with bi-directional NPRs are rare. In this work, the SiS2 monolayer and its derivatives MX2 (M = Si, Ge, Sn and X = S, Se, Te) are systematically studied via first-principles simulation. We demonstrate that a SiS2 monolayer possesses a remarkable out-of-plane NPR with a value of -1.09 and an in-plane NPR (-0.13). Furthermore, a higher out-of-plane NPR (-1.79) can be achieved in a SnS2 monolayer by element substitution. Remarkably, SiS2 and its derivative MX2 monolayers exhibit excellent light harvesting over the ultraviolet and visible range, and the corresponding electronic properties show robustness against strains. Our results confirm that MX2 monolayers provide an ideal platform to explore auxeticity in two-dimensional limits.

Negative Poisson's ratio and thickness-dependent optoelectronic response in two-dimensional thermoelectric TlCuSe

In one of the latest accomplishments in the field of materials for energy conversion, layered TlCuSe with a relatively high thermoelectric figure of merit has been designed and successfully fabricated. Inspired by this exciting advance, we herein conduct first-principles calculations to explore the dynamical and thermal stability, mechanical properties, and thickness dependent electronic and optical properties of TlCuSe nanosheets. Analysis of mechanical deformation reveals that TlCuSe monolayer shows a negative in-plane Poisson's ratio of −0.29 and is thus an auxetic material. This novel monolayer also exhibits an intrinsically p-type character with an appreciable hole mobility of 1528 cm2V−1s−1, an HSE06 indirect gap of 1.41 eV, and a multi-valley conduction band. It is found that electronic band gap in TlCuSe considerably decreases with increasing the number of layers and reaches to 0.47 eV for the bulk lattice, indicating strong quantum confinement effects. The mutli-valley character of the conduction and valence bands is also boosted in multilayer TlCuSe systems. Analysis of optical absorption of monolayer to tri-layer TlCuSe indicates that they possess remarkably large absorption coefficients within the visible and UV range of light spectrum. The acquired results provide useful information on physicochemical and electronic properties of TlCuSe nanomaterials for advanced applications.

MgXN2 (X = Hf/Zr) Monolayers: Auxetic Semiconductor with Highly Anisotropic Optical/Mechanical Properties and Carrier Mobility.

Two-dimensional (2D) semiconducting materials with distinct anisotropic physical properties have attracted intense interests. Herein, we show theoretical predictions that MgXN2 (X = Hf/Zr) monolayers are auxetic semiconductors with highly anisotropic electronic, optical, and mechanical properties. The density functional theory calculations coupled with a PSO algorithm (global-minimum search) suggest that both MgHfN2 (MgZrN2) monolayers exhibit orthorhombic symmetry (Pmma) and are direct-gap (indirect-gap) semiconductors with a bandgap of 2.43 eV (2.13 eV). Specifically, the MgHfN2 monolayer exhibits highly anisotropic hole mobility as well as very high electron mobility (∼104 cm2 V-1 s-1). G0W0+BSE calculations indicate that both monolayers bear notable optical anisotropy and relatively large exitonic binding energy (∼0.6 eV). In addition, both monolayers acquire remarkable mechanical anisotropy with a negative in-plane Poisson's ratio (∼-0.2) and high Young's modulus (∼260 N/m). The combination of highly anisotropic electronic, optical, and mechanical properties endows MgXN2 monolayers as potentially useful parts in multifunctional nanoelectronic devices.

Multifunctional PbS2 Monolayer with an In-Plane Negative Poisson Ratio and Photocatalytic Water Splitting Properties.

Designing novel multifunctional materials at the nanoscale is vitally important for flexible electronics. Here, we have uncovered a two-dimensional metal dichalcogenide PbS2 with intriguing negative Poisson ratio behavior and favorable optical and photocatalytic water splitting properties. The calculations indicate that the Poisson ratio of the PbS2 monolayer is -0.061 along both x and y lattice directions, which is attributed to its unique tetrahedral motif and the ligand field of the local PbS4 units in the PbS2 monolayer. The electronic band structures show that the narrow band gap (1.59 eV) of the PbS2 monolayer could be effectively modulated by strain engineering. Most importantly, the strain-induced tunability of optical absorbance and suitable band edge alignment make the PbS2 monolayer a promising catalyst for photocatalytic water splitting, which is further confirmed by the reaction free energies. These findings offer an effective avenue for the design and synthesis of a novel optoelectronic functional material.

Monolayer Ge2S: An auxetic semiconductor with high carrier mobility for metal (Na, K, Mg)-ion battery anodes

Using first-principles calculations, we propose a new two-dimensional Ge2S (space group P21212) with unique mechanical and electronic properties. Monolayer Ge2S has excellent thermal, mechanical, and dynamic stabilities, exhibiting a semiconducting behavior with an indirect bandgap and anisotropic carrier mobility. The uniaxial strain along the zigzag direction can induce an indirect-to-direct bandgap transition. Remarkably, Ge2S possesses large in-plane negative Poisson's ratios, comparable with that of well-known penta-graphene. Moreover, we identify Ge2S as a high-performance anode material for metal-ion batteries. It shows metallic features after adsorbing Na, K, and Mg, providing good electrical conductivity during the charge/discharge process. The diffusion of metal ions on Ge2S is anisotropic with modest energy barriers in the armchair direction of 0.12, 0.39, and 0.76 eV for Na, K, and Mg, respectively. Ge2S can adsorb metal atoms up to a stoichiometric ratio of 1:1, which yields storage capacities of 151.17, 151.17, and 302.35 mA h g−1 for Na, K, and Mg, respectively. The volume of Ge2S shrinks slightly upon the adsorption of metal ions even at high concentrations, ensuring a good cyclic stability. Besides, the average open circuit voltage (0.30–0.70 V) falls within the acceptable range (0.1–1.0 V) of the anode materials. These results make Ge2S a promising anode material for the design of future metal-ion batteries.

Two-dimensional V-shaped PdI2: Auxetic semiconductor with ultralow lattice thermal conductivity and ultrafast alkali ion mobility

Using first-principles calculations, we predicted a multifunctional two-dimensional (2D) semiconductor PdI2 from its van der Walls layered bulk. Monolayer or multilayer PdI2 obtained by mechanical exfoliation exhibit high stability as freestanding 2D materials. Originating from its special corner-shared quasi-plane crystal structure, an amazing in-plane negative Poisson's ratio in monolayer PdI2 has been confirmed. The layer dependent electronic and thermal properties have also been discussed in detail. Encouragingly, it has been found that strong phonon scattering which is induced by low symmetry will further reduce the lattice thermal conductivity in monolayer PdI2 at room temperature. Besides, the monolayer PdI2 is seen as an excellent platform for alkali ions migration with ultralow diffusion barriers, benefiting from its distinctive V-shaped crystal structure. Considering these interesting findings, we believe the 2D PdI2 will be a promising candidate for future's low dimensional electron devices.

The quest for a bidirectional auxetic, elastic, and enhanced fracture toughness material: Revisiting the mechanical properties of the BeH2 monolayers.

Herein we show a density functional theory-based study performed on two recently predicted polymorphs of the BeH2 monolayer, α-BeH2 and β-BeH2 . The α-BeH2 phase possesses an in-plane negative Poisson's ratio (NPR), introducing it into the unique group of auxetic materials. Our assessment delves into the linear-elastic and finite-strain regimes to understand both polymorphs' structural and mechanical responses to deformation. We find that the in-plane NPR is shown to be only parallel to the bonds in α-BeH2 and remains along the uniaxial tensile path. Concomitantly, an out-of-plane transition toward auxetic is also revealed in regions exhibiting conventional Poisson's ratios, making α-BeH2 a bidirectionally auxetic material. While phase transitions in β-BeH2 are triggered at very short strains, α-BeH2 displays excellent elasticity against tension, superior to that of most currently known 2D materials.

2D Janus and non-Janus diamanes with an in-plane negative Poisson's ratio for energy applications

Motivated by the successful synthesis of 2D C2F diamanes [Bakharev, P.V. et al., Nat. Nanotechnol. 15, 59–66 (2020)], we have systematically investigated the structural stability, in-plane mechanical, optoelectronic, photocatalytic, piezoelectric, and thermoelectric properties of non-Janus and Janus diamanes monolayers named as C2H, C2F, C2Cl, C4HF, C4HCl and C4FCl. The structural stability is confirmed by cohesive energy, phonon dispersion spectra, and mechanical properties. The electronic properties has been calculated by HSE06 functional and the band gap are found to be 3.85, 5.64, 2.32, 4.16, 0.73 and 1.91 eV for C2H, C2F, C2Cl, C4HF, C4HCl and C4FCl, respectively. The hydrogen-containing non-Janus and Janus diamanes monolayers have a higher negative Poisson's ratio (NPR) and therefore are good auxetic materials. From the Poisson's ratio and Young's modulus of each configuration of non-Janus and Janus diamanes monolayer, anisotropic behavior was displayed. From the optical properties calculations, the refractive index values are around 1.5, which means that it will be a transparent monolayered materials. Also, C2Cl, C4HCl and C4FCl monolayers displayed high absorption spectra with an order of 105 cm−1 in the visible region, which shows great applications in optoelectronic devices. Additionally, the valence and conduction band-edge positions of 2D Janus and non-Janus diamanes of C2H, C2F, and C2Cl and C4HF monolayers have to straddle the redox potentials of water. It means that the photogenerated electrons and holes are sufficient to drive the overall water splitting. Whereas non-Janus diamanes C4HCl, and C4FCl monolayers displayed only water oxidation. The investigated in-plane piezoelectric coefficient has larger in non-Janus diamanes C4HF, C4HCl, and C4FCl monolayers. Therefore, it is very useful in the field of piezoelectric applications. From the thermoelectric properties, the non-Janus and Janus diamanes monolayers have great thermoelectric efficiency and were found to be 10.52 and 10.63% for C2H and C2F, respectively. Our results demonstrate the new class of 2D carbon-based monolayers has good auxetic materials as well as a wide range of applications in optoelectronics, piezoelectric, and thermoelectric fields.

Novel Braceletlike BiSbX3 (X = S, Se) Monolayers with an In-Plane Negative Poisson's Ratio and Anisotropic Photoelectric Properties.

In this work, we predict two novel two-dimensional (2D) auxetic materials, BiSbX3 (X = S, Se) monolayers, through first-principles calculations. Attributed to their special braceletlike structure, the in-plane negative Poisson's ratio (NPR) of BiSbS3 and BiSbSe3 monolayers are as high as -0.25 and -0.26, respectively. The phonon dispersion calculations, ab initio molecular dynamics simulations, and elastic constants calculations demonstrate that these two monolayers possess excellent dynamic, thermal, and mechanical stabilities. The band gap values of BiSbS3 and BiSbSe3 calculated at the HSE level by considering the spin-orbit coupling (SOC) effect are 1.68 and 1.20 eV. The anisotropic carrier mobility and superior optical absorption indicate that they may shine in the next generation of electronic and optoelectronic devices. All of these discoveries not only enrich the types of auxetic materials but also provide a structural reference for designing new auxetic materials on the molecular level. Furthermore, they can provide theoretical guidance for future applications of BiSbX3 (X = S, Se) monolayers in various fields.

δ-SnS: An Emerging Bidirectional Auxetic Direct Semiconductor with Desirable Carrier Mobility and High-Performance Catalytic Behavior toward the Water-Splitting Reaction.

We propose a novel two-dimensional SnS allotrope (monolayer δ-SnS) based on an auxetic δ-phosphorene configuration using first-principles calculations. This monolayer appears to have outstanding stability as revealed by its energetic, kinetic, thermodynamic, and mechanic calculations, and it can withstand temperatures as high as 900 K. Monolayer δ-SnS is a wide direct-bandgap (2.354 eV) semiconductor, and its electron mobility is as high as ∼1.25 × 103 cm2 V-1 s -1, higher than that of monolayer KTlO (∼450 cm2 V-1 s-1) and MoS2 (∼200 cm2 V-1 s-1). Optical absorption spectra, reaching up to the order of ∼105 cm-1, are obviously excellent in the visible-light region, suggesting efficient harvesting of solar radiation. Because of its unique atomic motif, monolayer δ-SnS presents an unusual bidirectional auxetic effect: a high negative in-plane Poisson's ratio (-0.048 and -0.068), which is larger than those for many recently reported two-dimensional auxetic materials, e.g., black phosphorene (-0.027), borophene (-0.04), and monolayer penta-B2N4 (-0.02). The bandgap and band edge can be substantially manipulated under strain to meet the requirement of the water-splitting reaction. Particularly, when pH = 7, suitable band-edge alignments and small overpotentials of the photocatalytic OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) appear, endowing monolayer δ-SnS with great potential as an efficient visible-light-driven bifunctional photocatalyst for water splitting.

Assessment of negative poisson's ratio effect on thermal post-buckling of FG-GRMMC laminated cylindrical panels

This paper examines the thermal post-buckling behaviors of graphene-reinforced metal matrix composite (GRMMC) laminated cylindrical panels which possess in-plane negative Poisson's ratio (NPR) and rest on an elastic foundation. A panel consists of GRMMC layers of piece-wise varying graphene volume fractions to obtain functionally graded (FG) patterns. Based on the MD simulation results, the GRMMCs exhibit in-plane NPR as well as temperature-dependent material properties. The governing equations for the thermal post-buckling of panels are based on the Reddy's third order shear deformation shell theory. The von Karman nonlinear strain-displacement relationship and the elastic foundation are also included. The nonlinear partial differential equations for GRMMC laminated cylindrical panels are solved by means of a singular perturbation technique in associate with a two-step perturbation approach and in the solution process the boundary layer effect is considered. The results of numerical investigations reveal that the thermal post-buckling strength for (0/90)5T GRMMC laminated cylindrical panels can be enhanced with an FG-X pattern. The thermal post-buckling load-deflection curve of 6-layer (0/90/0)S and (0/90)3T panels of FG-X pattern are higher than those of 10-layer (0/90/0/90/0)S and (0/90)5T panels of FG-X pattern.

Effect of negative Poisson's ratio on the postbuckling behavior of axially compressed FG-GRMMC laminated cylindrical shells surrounded by an elastic medium

Auxetic composites are one of novel metamaterials which exhibit an interesting feature of negative Poisson's ratio (NPR). The current study reports the impact of in-plane NPR on the postbuckling responses of axially loaded cylindrical shells made of graphene-reinforced metal matrix composite (GRMMC) layers. Each layer of a GRMMC laminated cylindrical shell can vary its graphene volume fraction so that a functionally graded (FG) shell is achieved. The GRMMC layers possess temperature-dependent material properties that can be evaluated using an extended micromechanical Halpin–Tsai model. The governing equations for the postbuckling of GRMMC laminated shells are based on the Reddy's third order shear deformation theory. The von Kármán nonlinear strain-displacement relationships together with the foundation support and temperature effects are also included. Analytical solutions are obtained by using a singular perturbation technique in associate with a two-step perturbation approach for the postbuckling of perfect and imperfect FG-GRMMC laminated cylindrical shells. Numerical results explicitly show that the in-plane NPR has a substantial effect on the postbuckling response and imperfection sensitivity of GRMMC laminated cylindrical shells under axial compression.

Giant negative Poisson's ratio in two-dimensional V-shaped materials.

Two-dimensional (2D) auxetic materials with exceptional negative Poisson's ratios (NPR) are drawing increasing interest due to their potential use in medicine, fasteners, tougher composites and many other applications. Improving the auxetic performance of 2D materials is currently crucial. Here, using first-principles calculations, we demonstrated giant in-plane NPRs in MX monolayers (M = Al, Ga, In, Zn, Cd; X = P, As, Sb, S, Se, Te) with a unique V-shaped configuration. Our calculations showed that GaP, GaAs, GaSb, ZnS and ZnTe monolayers exhibit exceptional all-angle in-plane NPRs. Remarkably, the AlP monolayer possesses a giant NPR of −1.779, by far the largest NPR in 2D materials. The NPRs of these MX monolayers are correlated to the highly anisotropic features of the V-shaped geometry. The exotic mechanical properties of the V-shaped MX monolayers provide a new family of 2D auxetic materials, as well as a useful guidance for tuning the NPR of 2D materials.

Computational prediction of a two-dimensional semiconductor SnO2 with negative Poisson's ratio and tunable magnetism by doping

Based on first-principles calculations, we predict a stable two-dimensional semiconductor, namely tin dioxide ${\mathrm{SnO}}_{2}$. By investigating its dynamical, thermal, and mechanical properties, we find that ${\mathrm{SnO}}_{2}$ monolayer is an auxetic material with a large in-plane negative Poisson's ratio. Furthermore, our results show that ${\mathrm{SnO}}_{2}$ is an indirect-gap semiconductor with a band gap in the region of 3.7 eV and an extremely high electron mobility, $\ensuremath{\sim}{10}^{3}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Interestingly, the band structure of ${\mathrm{SnO}}_{2}$ presents double Mexican-hat-like band edges in the valence bands near the Fermi level. Due to such a unique band feature, a ferromagnetic phase transition takes place with a half-metallic ground state that can be induced by hole doping within a very wide concentration range. Such a magnetic phase can be well explained by the Stoner mechanism. A peculiar feature of the magnetic state is the presence of large magnetocrystalline anisotropy that can switch from in-plane to out-of-plane upon hole doping. Hence, ${\mathrm{SnO}}_{2}$ monolayer can be tuned to be either an $XY$ magnet or an Ising one, with a magnetic critical temperature above room temperature at proper hole concentrations. These findings demonstrate that the predicted phase of ${\mathrm{SnO}}_{2}$ is a rare example of $p$-type magnetism and a possible candidate for spintronic applications.

Effect of negative poisson's ratio on the axially compressed postbuckling behavior of FG-GRMMC laminated cylindrical panels on elastic foundations

Auxetic materials are one of the metamaterials that have potential applications in many scientific and engineering fields. In this paper, an investigation is presented on the postbuckling responses of axially loaded graphenereinforced metal matrix composite (GRMMC) laminated cylindrical panels with in-plane negative Poisson's ratio (NPR). The panels are made of GRMMC laminates and rest on an elastic foundation in thermal environments. The graphene volume fraction in GRMMC layer may vary across the panel thickness in order to achieve a piece-wise functionally graded (FG) pattern. The GRMMC layers have in-plane NPR and temperature dependent material properties. The governing differential equations for the GRMMC laminated cylindrical panels are formulated based on the Reddy's third order shear deformation shell theory and are solved by using a singular perturbation technique along with a two-step perturbation approach. Numerical investigation is carried out to study the influence of the in-plane NPR, the FG patterns, the thermal environmental conditions and the foundation stiffness on the postbuckling responses of the GRMMC laminated cylindrical panels under axial compressive load. The results reveal that the in-plane NPR can lead to a substantial change of the postbuckling behaviors of the GRMMC laminated cylindrical panels.

δ-CS: A Direct-Band-Gap Semiconductor Combining Auxeticity, Ferroelasticity, and Potential for High-Efficiency Solar Cells

We propose a two-dimensional material, \ensuremath{\delta}-CS, and show that it is a direct-band-gap semiconductor with strong absorption of solar radiation. Power conversion efficiencies of 7.0% to 20.1% are predicted for solar cells with \ensuremath{\delta}-CS as a donor and a transition metal dichalcogenide as an acceptor. \ensuremath{\delta}-CS also excels in terms of having an exceptionally large negative in-plane Poisson's ratio. Its ferroelasticity with moderate switching barrier is promising for applications in shape memory devices.