Learning physical states of bulk crystalline materials from atomic trajectories in molecular dynamics simulation

Melting of crystalline material is a common physical phenomenon,yet it remains elusive owing to the diversity in physical pictures.In this work,we proposed a deep learning architecture to learn the physical states(solid-or liquidphase)from the atomic trajectories of the bulk crystalline materials with four typical lattice types.The method has ultrahigh accuracy(higher than 95%)for the classification of solid-liquid atoms during the phase transition process and is almost insensitive to temperature.The atomic physical states are identified from atomic behaviors without considering any characteristic threshold parameter,which yet is necessary for the classical methods.The phase transition of bulk crystalline materials can be correctly predicted by learning from the atomic behaviors of different materials,which confirms the close correlation between atomic behaviors and atomic physical states.These evidences forecast that there should be a more general undiscovered physical quantity implicated in the atomic behaviors and elucidate the nature of bulk crystalline melting.

Preparation and Performance Study of Cementitious Capillary Crystalline Waterproof Materials

Cementitious capillary crystalline waterproof materials(CCCW for short)offer durability and excellent waterproofing properties,making them a popular option for building waterproofing.Some scholars have studied the proportioning of such materials.However,these studies lack the relationship between the impermeability pressure of mortar and the components,and the mechanism of action is somewhat debatable.Therefore,we adopted a two-step method in our experiments.Firstly,we screened out the components that significantly impact impermeability from a variety of active components by orthogonal test.We then optimized the design of the active group ratio using the simplex lattice method.Lastly,we conducted a performance test of the optimal ratio and explored the waterproofing mechanism of homemade CCCW.

INTERACTION CURVES OF LINEARLY INTENSIFYING POLYMERIC MATERIALS UNDER TENSILE-TORSIONAL STRESS

Theoretical and experimental research has been performed on the interaction curves and stress paths of crystalline polymeric materials PE and POM under tensile-torsional stress with a linearly intensifying model and in terms of the yield points undergoing Von Mises criterion.

THEORY OF BAINITIC TRANSFORMATION: A MODEL WITH COUPLED FIRST-ORDER PHASE TRANSFORMATIONS

The Ginzbury-Landau theory for bainitic transformation was devised, which contains two first-order phase transformations, one being reconstructive represented by the diffusional proeutectoidal precipitation of ferrite, and the other the displacive transformation. It provides a coupled mechanism for the formation of bainite. With the numerical simulation results, a diffusion-induced nucleation and a diffusion-accompanied growth of displacive transformation were suggested. This theory can be helpful to over- throw the thermodynamic difficulty of displacive transformation above the Ms temperature, and also helpful to understand the Bs temperature, the partial supersaturation, the single variation of bainitic carbides, and the incomplete-reaction phenomenon of bainitic transformation, etc..

Recent Progress in Developing Crystalline Ion Exchange Materials for the Removal of Radioactive Ions

The nuclear fuel cycle inevitably generates a large amount of radioactive waste liquid,which will pose a serious threat to the ecological environment and human health.Ion exchange method has received wide attention for its easy operation,low cost and no secondary pollution.However,the effective removal of radioactive ions from complex solutions still remains a serious challenge due to their environmental mobility and radiotoxicity.We have developed an efficient strategy to construct crystalline ion-exchange materials by inducing layered or three-dimensional microporous anionic frameworks by organic cations that can be effectively exchanged by radioactive metal ions.This type of materials can be applied effectively to the removal of radioactive ions from complex solutions and the removal mechanism has been deeply clarified by means of single crystal structure analyses,theoretical calculations,etc.This review summarizes our recent progress in the study of synthesis,structures and properties of radioactive ion removals for such type of crystalline ion-exchange materials.

Strain tunable band structure of a new 2D carbon allotrope C568

Recently,C568 has emerged as a new carbon allotrope,which shows semiconducting properties with a band gap around 1 eV and has attracted much attention.In this work,the external strain effects on the electronic properties of C568 have been studied theoretically through first-principle calculations.The numerical results show that while in-plane uniaxial and biaxial strains both reduces the band gap of C568 in case of tensile strain,their effects are quite different in the case of compressive strain.With increasing compressive uniaxial strain,the band gap of C568 first increases,and then dramatically decreases.In contrast,the application of compressive biaxial strain up to -10% only leads to a slight increase of band gap.Moreover,an indirect-todirect gap transition can be realized under both types of compressive strain.The results also show that the optical anisotropy of C568 can be induced under uniaxial strain,while biaxial strain does not cause such an effect.These results indicate good strain tunability of the band structure of C568,which could be helpful for the design and optimization of C568-based nanodevices.

Simulation of Polyhedral Crystal Growth Based on the Estimated Surface Energy of Crystallographic Planes

Polyhedral shapes can be found in crystalline materials ranging from macroscopic natural mineral solids to microscopic or nanoscopic particles. These shapes originate from the crystallographic properties of the constituting material, and the outer shape depends on several unique habit planes. In this study, polyhedral crystal growth was simulated considering the surface energy and crystallographic characteristics. A series of polyhedrons, including cube, truncated hexahedron, cuboctahedron, truncated octahedron, and regular octahedron, was targeted. First, the polyhedron’s static surface energy and dynamic energy variation during crystal growth were computed. Then, the crystal-growth process was simulated based on the energy minimization policy. Interestingly, when the simulation began with truncated hexahedral nucleus, the shape changed to a cuboctahedron;however, a certain type of truncated octahedron was obtained when starting with different types of truncated octahedrons. In addition, once converged cuboctahedron abruptly changed the shape to a truncated octahedron as the crystal became larger. These results were supported by the static and dynamic energy curves. Furthermore, the method was applied to different materials by assuming virtual parameters, yielding various morphologies.

Piezoresistivity of Carbon Fiber Graphite Cement-based Composites with CCCW

The electrical conductivity and piezoresistivity of carbon fiber graphite cement-matrix composites（CFGCC） with carbon fiber content（1% by the weight of cement）,graphite powder contents （0%-50% by the weight of cement） and CCCW（cementitious capillary crystalline waterproofing materials,4% by the weight of cement） were studied.The experimental results showed that the relationship between the resistivity of CFGCC and the concentration of graphite powders had typical features of percolation phenomena.The percolation threshold was about 20%.A clear piezoresistive effect was observed in CFGCC with 1wt% of carbon fibers,20wt% or 30wt% of graphite powders under uniaxial compressive tests,indicating that this type of smart composites was a promising candidate for strain sensing.The measured gage factor （defined as the fractional change in resistance per unit strain） of CFGCC with graphite content of 20wt% and 30wt% were 37 and 22,respectively.With the addition of CCCW,the mechanical properties of CFGCC were improved,which benefited CFGCC piezoresistivity of stability.

Recent advances in AIEgen-based crystalline porous materials for chemical sensing

Aggregation-induced emission-based luminogens(AIEgens)have aroused enormous interest due to their unique high fluorescence in a condensed state.To further explore their potential applications,such as chemical monitoring,immobilization of AIE molecules has been widely studied with a variety of supports.Crystalline porous materials,such as metal-organic frameworks,covalent organic frameworks,hydrogen-bonded organic framework,and organic cages,demonstrate well-controlled structures,large surface areas,and promising stabilities,thus providing a perfect platform for AIE agents loading.Outstanding chemical sensing performances are achieved based on these AIE-active crystalline porous materials,such as high sensitivity,short response time,selective identification,and high recyclability,which provide a new alternative to readily detect various hazardous molecules.Furthermore,precise structures of AIEgen-based crystalline porous materials offer an easy way to investigate detection mechanisms.This mini-review will provide a brief overview of AIEgen-based crystalline porous materials for detection and then address how to improve sensing performances remarkably.

Effect of crystalline lens surfaces and refractive index on image quality by model simulation analysis

The surfaces and refractive index of crystalline lens play an important role in the optical performance of human eye. On the basis of two eye models, which are widely applied at present, the effect of lens surfaces and its refractive index distribution on optical imaging is analyzed with the optical design software ZEMAX （Zemax Development Co., San Diego, USA）. The result shows that good image quality can be provided by the aspheric lens surfaces or （and） the gradient-index （GRIN） distribution. It has great potential in the design of intraocular lens （IOL）. The eye models with an intraocular implantation are presented.

Design and synthesis of phosphomolybdate coordination compounds based on {P_(4)Mo_(6)} structural units and their proton conductivity

Developing new low-cost and efficient proton-conducting materials remains an attractive and challenging task.Herein,sodium molybdate dihydrate is used as the source of molybdenum,mixed with transition metal chloride and 2-methylimidazole(2-MI),using the "one-pot method" to synthesize two crystalline proton conducting materials based on {P4Mo6} units:H14[C4H6N2]2[M(H_(2)O)5][M(H_(2)O)_(2)]_(2){M[(PO_(3))_(3)(PO_(4))Mo_(6)O_(15)]_(2)}·4H_(2)O(M=Co and Fe)(1-2).Different from the common{P4Mo_(6)},we use H3PO3to adjust the pH value,resulting in two different coordination modes of P atoms in the crystal structure.The structure is expanded into three-dimensional network by metal ions.At 75℃ and 98% relative humidity,the proton conductivity of compounds 1 and 2 are 1.33 ×10^(-2)S·cm^(-1)and 1.03×10^(-2)S·cm^(-1),respectively.The high proton conductivity is mainly attributed to the free state of 2-methylimidazole as the proton carrier,which has a fast migration rate.At the same time,2-methylimidazole,coordination water,and {P4Mo6} anion form a hydrogen bond network to provide multiple pathways for the transmission of protons.

Phase-selective fluorescence of doped Ge_2Sb_2Te_5 phase-change memory thin films

In this Letter, new concepts of fluorescence phase-change materials and fluorescence phase-change multilevel recording are proposed. High-contrast fluorescence between the amorphous and crystalline states is achieved in nickel- or bismuth-doped Ge;Sb;Te;phase-change memory thin films. Opposite phase-selective fluorescence effects are observed when different doping ions are used. The fluorescence intensity is sensitive to the crystallization degree of the films. This characteristic can be applied in reconfigurable multi-state memory and other logic devices. It also has likely applications in display and data visualization.

Solar cell performance improvement via photoluminescence conversion of Si nanoparticles

Photoluminescence （PL） conversion of Si nanoparticles by absorbing ultraviolet （UV） lights and emitting visible ones has been used to improve the efficiency of crystalline Si solar cells. Si nanoparticle thin films are prepared by pulverizing porous Si in ethanol and then mixing the suspension with a SiO2 sol-gel （SOG）. This SOG is spin-deposited onto the surface of the Si solar cells and dries in air. The short-circuit current as a function of Si nanoparticle concentration is investigated under UV illumination. The maximal increase is found at a Si concentration of 0.1 mg/mL. At such concentration and under the irradiation of an AM0 solar simulator, the photoelectric conversion efficiency of the crystalline Si solar cell is relatively increased by 2.16% because of the PL conversion.

Third-order optical nonlinearities of Zn_(1-x)Mg_xO thin films

The Zn1-xMgxO thin films were deposited on sapphire substrates by reactive electron beam evaporation deposition （REBED）. The X-ray diffraction （XRD） measurement demonstrates that these films undergo phase transition from hexagonal to cubic with increasing the Mg concentration. Absorption coefficients at 532 nm of the samples were obtained from the absorption spectra. Using optical Kerr effect, the thirdorder susceptibilities of the ternary films over a wide range of Mg concentrations were determined. The magnitude of X^（3） of the ternary Zn1-xMgxO films is order of 10^-11 esu at λ = 532 nm. The sample with phase mixture of both hexagonal and cubic structures shows the largest third-order susceptibility. The difference observed in the magnitude of X^（3） of Zn1-xMgxO films is attributed to the different microstructures of the ternary films, such as crystalline phase separation and crystal grains that enhance stimulated scattering.

Three-Dimensional sp^(2) Carbon-Linked Covalent Organic Frameworks as a Drug Carrier Combined with Fluorescence Imaging

Three-dimensional(3D)covalent organic frameworks(COFs)are crystalline porous polymers with potential in numerous high-tech applications,but the linkages involved in their synthesis are still rather limited.Herein,we report novel 3D sp^(2) carbon-linked COFs fabricated by the formation reaction of C=C bonds and their application in fluorescence imaging.These new COFs,namely JUC-580 and JUC-581,show high stability and excellent light-emitting properties in solid state and dispersed in various solvents.Furthermore,we investigate the potential application of JUC-581 as a drug carrier combined with fluorescence imaging.These results indicate that 3D sp^(2) carbon-linked COFs are not only potential drug-loaded and sustained release materials but also promising cell fluorescent stains.This study thus expands the structural categories of 3D COFs based on different linkages,and promotes their prospective applications for biomedicine and fluorescent materials.

Recent Progress of Chiral Hierarchical Assemblies from a Chinese Perspective

Self-assembly of predesigned chiral molecules to form structurally diverse functional materials has been one of the most exciting recent developments in materials science and nanotechnology over the past decade.Particularly,the rationally designed chiral supermolecules and their hierarchical assemblies result in superior microenvironments,in which they interact distinctly with molecularly asymmetric guests for enantiospecific recognition.The chemistry of chiral supermolecule-based materials(CSMs)has become a lively research topic,and thus this review seeks to shed light on a range of synthetic CSMs at differing length scales developed in the past 5 years,with emphasis on the representative work from China.This review includes cavity-containing chiral supermolecules,chiral polymers,and chiral crystalline materials,aiming to tackle important issues from their design,synthesis,and structure to cutting-edge applications.This,in turn,allows for fundamental understanding of the transfer,amplification,and functional expression of chirality from the molecular to the supramolecular to the macroscopic scale.Finally,we provide perspectives on the promises,opportunities,and key challenges for the future development of useful chiral functional materials.