RESUMEN
Piezoelectricity has been widely explored for nanoelectromechanical applications, yet its working modes are mainly limited in polar directions. Here we discover the intrinsic electro-mechanical response in crystal materials that is transverse to the conventional polarized direction, which is named unconventional piezoelectricity. A Hall-like mechanism is proposed to interpret unconventional piezoelectricity as charge polarization driven by a built-in electric field for systems with asymmetric Berry curvature distributions. Density functional theory simulations and statistical analyses justify such a mechanism and confirm that unconventional piezoelectricity is a general property for various two-dimensional materials with spin splitting or valley splitting. An empirical formula is derived to connect the conventional and unconventional piezoelectricity. The extended understanding of the piezoelectric tensor in quantum materials opens an opportunity for applications in multidirectional energy conversion, broadband operation, and multifunctional sensing.
RESUMEN
Learning the global crystal symmetry and interpreting the equivariant information is crucial for accurately predicting material properties, yet remains to be fully accomplished by existing algorithms based on convolution networks. To overcome this challenge, here we develop a machine learning (ML) model, named symmetry-enhanced equivariance network (SEN), to build material representation with joint structure-chemical patterns, to encode important clusters embedded in the crystal structure, and to learn pattern equivariance in different scales via capsule transformers. Quantitative analyses of the intermediate matrices demonstrate that the intrinsic crystal symmetries and interactions between clusters have been exactly perceived by the SEN model and critically affect the prediction performances by reducing effective feature space. The mean absolute errors (MAEs) of 0.181 eV and 0.0161 eV/atom are obtained for predicting bandgap and formation energy in the MatBench dataset. The general and interpretable SEN model reveals the potential to design ML models by implicitly encoding feature relationship based on physical mechanisms.
RESUMEN
Two-dimensional piezoelectric materials have been regarded as ideal candidates for flexible and versatile nanoelectromechanical systems, yet their fundamental piezoelectric mechanisms remain to be fully understood. Employing joint theoretical-statistical analyses, we develop universal models for quantifying the piezoelectricity of three-coordinated honeycomb-like monolayers at the atomistic level. The theoretical model within the framework of modern polarization theory suggests that the distribution of effective Berry curvature is essential for interpreting the relation between microscopic/electronic structures and piezoelectric properties. The statistical model based on DFT high-throughput calculation reveals that 2D piezoelectricity crucially depends on the effective mass, bandgap, and atomic distance along the rotation axis. Implementing stress and doping is demonstrated to be effective for optimizing piezoelectricity. Such findings provide valuable guidelines for designing 2D piezoelectric materials.
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Solar energy hydrogen production is one of the best solutions for energy crisis. Therefore, finding effective photocatalytic materials that are able to split water under the sunlight is a hot topic in the present research fields. In addition, theoretical prediction is a present low-cost important method to search a new kind of materials. Herein, with the aim of seeking efficient photocatalytic material we investigated the photocatalytic activity of GaAs monolayer by the first principles calculation. According to the obtained electronic and optical properties, we primarily predicted the photocatalytic water splitting activity of GaAs monolayer, which the result further confirmed by the calculated reaction free energy. More remarkably, predicted carrier mobility of GaAs monolayer 2838 cm2V-1s-1 is higher than 200 cm2V-1s-1 of MoS2. Our finding provides a promising material for the development of renewable energy conversion and a new outlook for better designing of a superior photocatalyst for water splitting.
RESUMEN
Multifunctional monolayer materials with attractive properties and novel applications are of present research interest. In this contribution, we design a new monolayer Be2CO3F2 (BCF) by taking a KBe2BO3F2 unique crystal that is able to produce a high energetic laser by a direct second harmonic generation method, as a parent. The cohesive energy, positive phonon modes, and elastic constants reveal that the BCF monolayer is dynamically and mechanically stable, and the appropriate cleavage energy predicts the experimental realization possibility. The property investigations demonstrated that the monolayer BCF has the significantly superiority in flexibility over the representative flexible optoelectronic material MoS2 based on the calculation of Young's modulus. Additionally, the monolayer BCF possesses both a large band gap (5.2 eV) and a second harmonic generation response. These results demonstrate that the monolayer BCF may provide better applications as a promising multifunctional material in the flexible nonlinear optical fields. We hope that this research will pave a new way for designing new generation multifunctional devices.
RESUMEN
In this study, a new series of NaBaMIIIQ3 (MIII = Al, Ga; Q = S, Se) compounds featuring the first discovered isolated edge-shared (MIII2Q6)6- dimers in known quaternary chalcogenides were synthesized. All compounds showed clear optical anisotropy (Δn = 0.04-0.12) mainly derived from the contribution of isolated (MIII2Q6)6- dimers by the real-space atom-cutting method.
RESUMEN
By the application of cation substitution, five new members of cyclophosphates, RbCdP3O9, CsPbP3O9, CsSrP3O9, RbMgP3O9, and RbCaP3O9, were obtained by a high-temperature melt method and structurally analyzed. The five compounds have identical stoichiometries, and all of them feature a three-dimensional network, which consists of MIIO6 (MII = Cd, Mg, Ca, Pb, Sr) octahedra and cyclic P3O9 units, while alkali-metal atoms are located within the network. However, RbCdP3O9 and CsPbP3O9 belong to the asymmetric space groups P6Ì c2 and Pna21, respectively, and the other three compounds belong to orthorhombic space group Pnma. Detailed structure comparisons in the MI-MII-P-O and (MIMIIP3O9) n ( n = 1, 2, 6) systems are discussed. Remarkably, KMgP3O9 as one of the cyclophosphate members exhibits a second harmonic generation (SHG) intensity about 0.2 times that of KH2PO4 (KDP), RbCdP3O9, and CsPbP3O9 also show SHG responses 0.1 times that of KDP. In addition, the related optical properties are discussed. Furthermore, theoretical calculations and dipole moments were calculated to explain the relation of structure and optical properties.
