Insights into the Bond Behavior and Mechanical Properties of Hafnium Carbide under High Pressure and High Temperature

Study on the Effect of Temperature and Pressure Environments on the Mechanical and Electronic Properties of Titanium Carbon Nitride Ceramics

As a high-performance cermet, TiCN possesses extensive potential for application in various fields, including coating materials, ceramic products, and electronic materials. Here, the effects of temperature and pressure on the physical properties of the TiCN cermet have been investigated by high-pressure techniques and first-principles calculations. Experimentally, the phase, microstructure, mechanical properties, and electrical conductivity of bulk TiCN ceramics were analyzed. In high-pressure sintering, the sintering temperature rhythmically regulated the porosity and grain size within the ceramics. The TiCN prepared at 5.5 GPa/1200 °C has a Vickers hardness of ∼23.81 GPa, a Young's modulus of 445.24 GPa, and an electrical conductivity of ∼(20.4 ± 0.55) × 105 S/m. Moreover, the responses of the mechanical and electronic properties of TiCN to pressure were evaluated by first-principles, which matched the experimental results. The research findings have revealed that the pressure effects work not only on the microstructure and mechanical properties but also on the atoms and electrons. The study integrates both theoretical and experimental approaches to enhance our comprehension of the microstructure and physical properties of TiCN ceramics, insights that are instrumental in broadening the application scope of TiCN-based ceramic materials.

Fabrication of the SiC/HfC Composite Aerogel with Ultra-Low Thermal Conductivity and Excellent Compressive Strength

Aerogels, as a new type of high-temperature-resistant insulation material, find extensive application in aerospace, high-temperature industrial furnaces, new energy batteries, and various other domains, yet still face some limitations such as inadequate temperature resistance and pronounced brittleness. In this work, SiC/HfC composite aerogels were prepared through a combination of sol-gel method, atmospheric pressure drying technique, and carbothermal reduction reaction. The effects of different molar ratios, calcination time, and temperatures on the microstructural features and physicochemical properties of the resulting SiC/HfC composite aerogels were investigated. The aerogel exhibited an elevated BET-specific surface area of 279.75 m2/g, while the sample displayed an extraordinarily low thermal conductivity of 0.052 W/(m·K). Most notably, the compressive strength reached an outstanding 5.93 MPa after a carbonization temperature of 1500 °C, far exceeding the values reported in prior aerogel studies. This research provided an innovative approach for advancing the development of carbide aerogels in the realm of high-temperature applications.

Preparation of HfCxN1-x Nanoparticles Derived from a Multifunction Precursor with Hf-O and Hf-N Bonds

HfC_xN_1-x nanoparticles were synthesized using the urea-glass route, employing hafnium chloride, urea, and methanol as raw materials. The synthesis process, polymer-to-ceramic conversion, microstructure, and phase evolution of HfC_xN_1-x/C nanoparticles were thoroughly investigated across a wide range of molar ratios between the nitrogen source and the hafnium source. Upon annealing at 1600 °C, all precursors demonstrated remarkable translatability to HfC_xN_1-x ceramics. Under high nitrogen source ratios, the precursor exhibited complete transformation into HfC_xN_1-x nanoparticles at 1200 °C, with no observed presence of oxidation phases. In comparison to HfO₂, the carbothermal reaction of HfN with C significantly reduced the preparation temperature required for HfC. By increasing the urea content in the precursor, the carbon content of the pyrolyzed products increased, leading to a substantial decrease in the electrical conductivity of HfC_xN_1-x/C nanoparticle powders. Notably, as the urea content in the precursor increased, a significant decrease in average electrical conductivity values was observed for the R4-1600, R8-1600, R12-1600, and R16-1600 nanoparticles measured at a pressure of 18 MPa, yielding values of 225.5, 59.1, 44.8, and 46.0 S·cm^-1, respectively.

Pressure-Induced Phase Transition and Compression Properties of HfO2 Nanocrystals

Nanoparticles exhibit unique properties due to their surface effects and small size, and their behavior at high pressures has attracted widespread attention in recent years. Herein, a series of in situ high-pressure X-ray diffraction measurements with a synchrotron radiation source and Raman scattering have been performed on HfO₂ nanocrystals (NC-HfO₂) with different grain sizes using a symmetric diamond anvil cell at ambient temperature. The experimental data reveal that the structural stability, phase transition behavior, and equation of state for HfO₂ have an interesting size effect under high pressure. NC-HfO₂ quenched to normal pressure is characterized by transmission electron microscopy to determine the changing behavior of grain size during phase transition. We found that the rotation of the nanocrystalline HfO₂ grains causes a large strain, resulting in the retention of part of an orthorhombic I (OI) phase in the sample quenched to atmospheric pressure. Furthermore, the physical mechanism of the phase transition of NC-HfO₂ under high pressure can be well explained by the first-principles calculations. The calculations demonstrate that NC-HfO₂ has a strong surface effect, that is, the surface energy and surface stress can stabilize the structures. These studies may offer new insights into the understanding of the physical behavior of nanocrystal materials under high pressure and provide practical guidance for their realization in industrial applications.

Elucidating the Phase Transformation and Metallization Behavior of Zinc Phosphide under High Pressure

Among the family of II₃V₂-type compounds, zinc phosphide (Zn₃P₂) occupies a unique position. As one of the most promising semiconductors well-suited for photovoltaic applications, Zn₃P₂ has attracted considerable attention. The stability of its structure and properties are of great interest and importance for science and technology. Here, we systematically investigate the pressurized behavior of Zn₃P₂ using in situ synchrotron radiation angle-dispersive X-ray diffraction (ADXRD) and in situ electrical resistance measurement under high pressure. The ADXRD experiment shows that Zn₃P₂ undergoes an irreversible structural phase transition under high pressure, beginning at 11.0 GPa and being completed at ∼17.7 GPa. Consistently, the high-pressure electrical resistance measurement reveals a pressure-induced semiconductor-metal transition for Zn₃P₂ near 11.0 GPa. The kinetics of the phase transition is also studied using in situ electrical resistance measurement and can be well described by the classical Avrami model. What's more, the new high-pressure structure of Zn₃P₂ is refined to be orthorhombic with space group Pmmn; the lattice parameters and bulk modulus of this high-pressure phase are determined as a = 3.546 Å, b = 5.004 Å, c = 3.167 Å, and B₀ = 126.3 GPa. Interestingly, we also predict a possible structural phase transformation of orthorhombic phase (Pmmn) to cubic phase (P4₂32) during the decompression process; this cubic Zn₃P₂ is metastable at ambient conditions. These experimental results reveal the unexpected high-pressure structural behaviors and electrical properties of Zn₃P₂, which could help to promote the further understanding and the future applications of Zn₃P₂ as well as other II₃V₂ compounds.

Synthesis and Phase Stability of the High-Entropy Carbide (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C under Extreme Conditions

As a novel ultrahigh temperature ceramic, the stability of a high-entropy transition metal carbide under extreme conditions is of great concern to its application. Despite the intense research, the available high-pressure experimental results are few so far. Here, we synthesized the nanocrystalline (Ti_0.2Zr_0.2Nb_0.2Ta_0.2Mo_0.2)C by a high-pressure solid-state reaction successfully. Meanwhile, synchrotron radiation X-ray diffraction experiments were carried out to explore the phase stability and mechanical response under high pressure. The single cubic B1 phase structure of the high-entropy carbide is retained under extreme hydrostatic pressure. An abnormal cubic-to-cubic phase transition was observed unexpectedly under nonhydrostatic compression. This result reflects the effect of the severe lattice distortion of the initial B1 phase high-entropy carbide and the shear strain caused by deviatoric stress under high nonhydrostatic pressure. The physical mechanism about electronic/magnetic characteristics behind findings is an interesting issue for future studies.