A comparative study of the mechanical and thermal properties of defective ZrC, TiC and SiC

Exploring Defect Dynamics and Twin-Layer Interactions in SiC Crystals through Molecular Simulations

Silicon carbide (SiC), a third-generation semiconductor material, is pivotal for applications in new energy vehicles, aerospace, and high-speed electronics, owing to its superior properties. This study delves into the twin-induced growth behaviors of SiC crystals through molecular dynamics simulations at temperatures ranging from 2700 to 3200 K. It focuses on the wurtzite and zinc blende SiC structures, revealing dynamic defect behavior during growth, including an initial rise and subsequent decrease in vacancies, with particular emphasis on prevalent defects within zinc blende twin layers. A significant finding is the direct correlation between temperature and growth rates across different SiC structures, highlighting temperature control as essential for optimizing crystal quality. Furthermore, this work contributes to the analysis of the interactions of twin layers and their impact on structural stability and defect formation in SiC crystals. The insights gained here have substantial implications for the semiconductor industry, potentially enhancing device performance by better controlling growth conditions and defect management in SiC-based electronic and optoelectronic devices.

Photocatalytic CO2 Reduction Using Ti3C2Xy (X = Oxo, OH, F, or Cl) MXene-ZrO2: Structure, Electron Transmission, and the Stability

CO2 photoreduction using a semiconductor-based photocatalyst is a promising option for completing a new carbon-neutral cycle. The short lifetime of charges generated owing to light energy is one of the most critical problems in further improving the performance of semiconductor-based photocatalysts. This study shows the structure, electron transmission, and stability of Ti3C2Xy (X = oxo, OH, F, or Cl) MXene combined with a ZrO2 photocatalyst. Using H2 as a reductant, the photocatalytic CO formation rate increased by 6.6 times to 4.6 μmol h-1 gcat-1 using MXene (3.0 wt %)-ZrO2 compared to that using ZrO2, and the catalytic route was confirmed using 13CO2 to form 13CO. In clear contrast, using H2O (gas) as a reductant, CH4 was formed as the major product using Ti3C2Xy MXene (5.0 wt %)-ZrO2 at the rate of 3.9 μmol h-1 gcat-1. Using 13CO2 and H2O, 12CH4, 12C2H6, and 12C3H8 were formed besides H212CO, demonstrating that the C source was the partial decomposition and hydrogenation of Ti3C2Xy. Using the atomic force and high-resolution electron microscopies, 1.6 nm thick Ti3C2Xy MXene sheets were observed, suggesting ∼3 stacked layers that are consistent with the Ti-C and Ti···Ti interatomic distances of 0.218 and 0.301 nm, respectively, forming a [Ti6C] octahedral coordination, and the major component as the X ligand was suggested to be F and OH/oxo, with the temperature increasing by 116 K or higher owing to the absorbed light energy, all based on the extended X-ray absorption fine structure analysis.

Thermal Expansion of 3C-SiC Obtained from In-Situ X-ray Diffraction at High Temperature and First-Principal Calculations

In situ X-ray crystallography powder diffraction studies on beta silicon carbide (3C-SiC) in the temperature range 25-800 °C at the maximum peak (111) are reported. At 25 °C, it was found that the lattice parameter is 4.596 Å, and coefficient thermal expansion (CTE) is 2.4 ×10-6/°C. The coefficient of thermal expansion along a-direction was established to follow a second order polynomial relationship with temperature (α11=-1.423×10-12T2+4.973×10-9T+2.269×10-6). CASTEP codes were utilized to calculate the phonon frequency of 3C-SiC at various pressures using density function theory. Using the Gruneisen formalism, the computational coefficient of thermal expansion was found to be 2.2 ×10-6/°C. The novelty of this work lies in the adoption of two-step thermal expansion determination for 3C-SiC using both experimental and computational techniques.

Evolution of the oxidation behaviors of highly oxidation-resistant (Ti0.8Nb0.2)C in 1000–1200 °C steam

The evolution of the oxidation behaviors of (Ti0.8Nb0.2)C reveals that the outward diffusion of the metal elements plays a decisive role during oxidation and the diffusion rate disparity gives rise to diverse oxidation behaviors.

Manufacturing ZrB2-SiC-TaC Composite: Potential Application for Aircraft Wing Assessed by Frequency Analysis through Finite Element Model

This study presents a new ultra-high temperature composite fabricated by using zirconium diboride (ZrB₂), silicon carbide (SiC), and tantalum carbide (TaC) with the volume ratios of 70%, 20%, and 10%, respectively. To attain this novel composite, an advanced processing technique of spark plasma sintering (SPS) was applied to produce ZrB₂-SiC-TaC. The SPS manufacturing process was achieved under pressure of 30 MPa, at 2000 °C for 5 min. The micro/nanostructure and mechanical characteristics of the composite were clarified using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and nano-indentation. For further investigations of the product and its characteristics, X-ray fluorescence (XRF) analysis and X-ray photoelectron spectroscopy (XPS) were undertaken, and the main constituting components were provided. The composite was densified to obtain a fully-dense ternary; the oxide pollutions were wiped out. The mean values of 23,356; 403.5 GPa; and 3100 °C were obtained for the rigidity, elastic modulus, and thermal resistance of the ZrB₂-SiC-TaC interface, respectively. To explore the practical application of the composite, the natural frequency of an aircraft wing considering three cases of materials: i) with a leading edge made of ZrB₂-SiC-TaC; ii) the whole wing made of ZrB₂-SiC-TaC; and iii) the whole wing made of aluminum 2024-T3 were investigated employing a numerical finite element model (FEM) tool ABAQUS and compared with that of a wing of traditional materials. The precision of the method was verified by performing static analysis to obtain the responses of the wing including total deformation, equivalent stress, and strain. A comparison study of the results of this study and published literature clarified the validity of the FEM analysis of the current research. The composite produced in this study significantly can improve the vibrational responses and structural behavior of the aircraft's wings.

Materials perspective on new lithium chlorides and bromides: insights into thermo-physical properties

Recently, a new class of lithium chlorides and bromides (e.g., Li3YCl6 and Li3YBr6) were reported to be promising solid-state electrolytes with high ionic conductivity in all-solid-state battery cells. However, their response under mechanical loading is not known which is critical as mechanical properties can play a pivotal role in reducing interfacing resistance between electrolytes and electrodes. To address this issue, herein, we report the thermo-physical properties of these lithium chlorides and bromides using density functional theory calculations. It was found that the new structures possess relatively larger shear moduli than those of thio-phosphate-type solid-state electrolytes and smaller Young's moduli than those of Garnet-type solid-state electrolytes. This suggests that the new halide materials can be more effective in suppressing the formation of lithium dendrites, accommodating volumetric changes of electrode materials and preventing their own degradation. Meanwhile, Poisson's ratio and Pugh's indicator calculations showed that Li3YCl6 and Li3ScCl6 possess improved ductility than other halide candidates, and thus hold promise as solid-state electrolytes. On the other hand, owing to their relatively high thermal conductivities, lithium bromides were found to be more advantageous in conducting heat which is important to ensure safety. These results provide fundamental insights into the mechanical properties of lithium chlorides and bromides and contribute to the rational mechanical design of solid-state electrolytes and the development advanced all-solid-state batteries.