To cooperate with studying the influence of chemical disorder on the conductivity of 6H-SiC, the linear collision cascade of 6H-SiC was simulated by the classical molecular dynamics with LAMMPS. Evolution process of main point defects in 6H-SiC during single linear cascade collision and multiple linear cascade collisions under different energy and different types of PKA (Primary Knock-on Atom) is given, while chemical disorder and the final proportion of each of the point defects are counted. The results show that the Si-Si bond generated by the linear cascade collision is easier to form and more stable than the C-C bond. The Si-Si bond is mainly formed by the antisite defect Si_C, the C-C bond is mainly formed by the C-interstitial cluster. Their chemical disorder and point defect yield are affected by the type and initial energy of PKA. However, the proportion of each point defect is almost unchanged.

Electronic structure and photocatalytic performance of 2D novel Zr₂CO₂/InS heterostructure was systematically investigated using first principle calculations. The calculated results demonstrate that the Zr₂CO₂/InS heterostructure is a direct bandgap semiconductor with a lattice mismatch less than 3% and a formation energy of -0.49 eV, indicating a stable structure. Band gap of the Zr₂CO₂/InS heterostructure is 1.96 eV, which should have a wide visible light absorption range, and the absorption coefficient is up to 10⁵ cm^-1. The heterostructure has a typical type-II band alignment, and its valence band and conduction band offsets are 1.24 and 0.17 eV, respectively, demonstrating the transfer of photo-generated electrons from Zr₂CO₂ layer to InS layer and vice versa for holes, which indicates that the electrons and holes can be separated effectively in space. In addition, InS is an indirect band gap semiconductor material, which can further reduce the recombination of electrons and holes. Therefore, the novel Zr₂CO₂/InS heterostructure is a potential visible-light photocatalyst.

Ceramic coatings can effectively prevent the corrosion of steel bars in marine environments. In this study, we prepared phosphate ceramic coatings on the surface of carbon steel. X-ray diffraction and X-ray fluorescence were used to analyze the phase structure and composition of the ceramic and the results show that the main crystal composition of ceramic is P₂O₅ and SiO₂. Scanning electron microscopy was used to characterize the morphology of the surface and the section and results showed that the surface was cracked, and the thickness of ceramic was 349 μm. Meanwhile, a number of high-resolution images of internal structure of solids were obtained by non-destructive X-ray computed tomography (X-CT). Matlab and Mimics software were used to conduct the three-dimensional reconstruction of the CT images. Matrix and holes are distinguished by threshold segmentation in grayscale images, and the porosity of the ceramic coatings was calculated to be 14.0%. In addition, mercury intrusion porosimetry was used to verify the calculation results. Therefore, X-CT can be a useful and reliable tool for the visualization of the internal structure of ceramic coatings.

In this study, the electronic structure and optical properties of graphene oxide in different structures with single point defect are studied under local density of states approximation and generalized gradient approximation by first-principles calculations based on the density functional theory. The results show that four models are mechanically stable, among which the oxide graphene containing unsaturated oxygen atoms shows an important application potential in water cracking and catalysis. The calculated band structures and partial-wave density of states show that the model containing unsaturated oxygen atoms exhibits indirect band gap, while other models exhibit direct band gap, and the doping type and band gap values vary with different models. The absorption spectrum of graphene oxide is anisotropic, and the absorption edge moves to the near-UV and visible region in the direction perpendicular to the plane. The optical absorption coefficient containing sp ³ hybrid is slightly higher than that containing sp ² hybrid, suggesting that the carbon-oxygen double bond and hanging bond have important influence on the absorption spectrum.

Strontium (Sr) doped hydroxyapatite (HA) has been widely used in diverse biological applications. In this work, hydrothermal synthesis method was used to prepare HA and Sr doped HA nanoparticles. A series of experimental methods and the simulation method based on density functional theory (DFT) were used to investigate the effect of Sr doping on chemical composition, crystallinity, lattice parameters, morphology, and formation energies of HA. The experimental results indicated that the lattice parameters and crystal size of Sr doped HA nanoparticles increased. The crystallinity of Sr doped HA nanoparticles did not change significantly with the increasing concentration of Sr ions. The lattice parameters obtained by the simulation method were in good agreement with the experimental results. The formation energies indicated that Sr ion doping endowed the structure more stable, which also illustrated that the Ca(1) site was the preferential site for Sr doping at 10at% and mixed doping was a more preferred doping mode at 50at%.

To date, solar cells with efficiency of 12.6% has been demonstrated via a hydrazine-based solution approach. Despite this progress, performance of Cu₂ZnSn(S,Se)₄ solar cells remains far lower than the Shockely- Quiser theoretical limit. We performed density functional theory calculations with hybrid functional approach to investigate the Mg-related defects in the kesterite structure of the Cu₂ZnSnS₄ (CZTS) solar cell material. The substitution energies of Mg atom in CZTS were calculated in consideration of the atomic chemical potentials of the constituent elements of Cu, Zn, Sn, and the doping atom of Mg. From our calculation results, Mg doping in CZTS under certain Sn-rich growth condition is expected to convert the conduction from p-type to n-type. The present study provides a theoretical basis for exploring practical applications of Mg doping in CZTS solar cells.

Phase diagrams, also known as equilibrium phase diagrams, serve as a road map for materials design. However, preparation process of coatings (such as Physical Vapor Deposition, PVD) is generally far from equilibrium and results in metastable phases. Thus, the CALPHAD (Calculation of Phase Diagrams) approach faces a challenge in calculating the metastable phase diagrams for PVD coating materials. Here we summarized the development of the modeling methodology for the metastable phase diagrams, where the model with critical surface diffusion distance established in recent years were highlighted. The CALPHAD approach, first-principles calculations coupled with high-throughput magnetron sputtering experiments were used to model the atomic surface diffusion, while only one key combinatorial experiment was performed to obtain the basic data for the computation, and the calculated metastable phase diagrams were confirmed by further experiments. Therefore, the database of the stable and metastable phase diagrams can be established, which will be used to guide the design of the ceramic coating materials by the relationship of composition, processing, microstructure, and performance. This model can also help to achieve the goal to shorten the time and reduce the costs of materials research and development.

As newly-discovered member of the MAB phases, Cr₄AlB₄ has much potential for high-temperature structural applications due to possible formation of a protective oxide scale. By use of “linear optimization procedure” and theoretical model of “bond stiffness” based on first-principle calculations, the phase stability and mechanical behavior of Cr₄AlB₄ were investigated. No imaginary frequencies in phonon dispersion indicate the intrinsic stability. The lower energy as compared with the set of other competing phases also shows the thermodynamic stability. Based on the quantificationally calculated bond stiffness by use of the model of “bond stiffness”, strong covalent bonding is present between Cr and B atoms as well as B and B atoms, while the Cr-Al (625 GPa) and B-Al (574 GPa) bond is relatively weak. It follows that Cr₄AlB₄ can be described as layered structure of strong covalently bonded Cr-B blocks interleaved by Al atomic planes where the bonding is relatively weak, similar to the well-known MAX phases, which demonstrates the similar damage tolerance and fracture toughness of Cr₄AlB₄ with the MAX phases.

Phase diagrams are used as an indicator to estimate the thermodynamic stabilities of the novel MAX phases (Ti₃AuC₂, Ti₃IrC₂, Ti₃ZnC₂, Ti₂ZnC). The phase diagrams of the Ti-Au-C, Ti-Ir-C, and Ti-Zn-C systems were obtained using the CALPHAD (Calculation of Phase Diagrams) approach coupled with ab initio calculations. The calculated results confirmed thermodynamic stabilities of the synthesized Ti₃AuC₂, Ti₃IrC₂, Ti₃ZnC₂, and Ti₂ZnC MAX phases, which is in great agreement with the experiment information. The present work shows a systematic method to calculate the thermodynamic stability of the novel MAX phases, which can be used as guidance to synthesize more undiscovered MAX phases.

The acoustic emission data collected during room temperature tensile test of 2D-C/SiC composites were analyzed by hierarchical clustering and unsupervised pattern recognition method based on an improved genetic algorithm. Combined with the SEM observation on the fracture surface, five damage modes were identified and their typical acoustic emission characteristics were obtained. According to the analysis of energy distribution, cumulative event number and cumulative energy of different damage modes, the damage evolution process of C/SiC composites can be divided into four stages. The first stage (damage initiation stage) shows mainly matrix microcracks and interface debonding. In the second stage, matrix crack reaches saturated and then causes a considerable quantity of interlaminar delamination and fiber failure. The third stage is a gradual damage development stage and all kinds of damage keep occurring except the breakage of fiber bundles. In the last stage, a large amount of fiber bundles break and the sample eventually fails.