The crystal structure prediction of K₂N₂ in the pressure range of 0–150 GPa using an advanced particle swarm crystal structure search method was conducted. The results show that the stable ground state phase of K₂N₂ is a monoclinic C2/m structure, and three high-pressure structures including Na₂N₂-type, Cmmm, and C2/c are identified at pressures of 1.7, 3.6, 122 GPa, respectively. The volume dependence on pressure shows that the three phase transitions, i. e., C2/m→Na₂N₂-type, Na₂N₂-type→Cmmm, and Cmmm→C2/c, are all first order phase transitions, corresponding to volume collapses of 14.4%, 22.5%, and 4.0%, respectively. During the high pressure phase transitions of K₂N₂, the coordination number of K atom increases from 5 to 10, and a change in the nature of the N-N bonding from N＝N dimmer in the ground state of C2/m structure to N―N single bond chain in the high-pressure C2/c phase is accompanied. The high-pressure C2/c phase exhibits semiconducting properties with a band gap of 2.0 eV, while C2/m, Na₂N₂-type, and Cmmm phases have metallic behaviors. Electronic structure calculation and electron-localized function analysis indicate that the high-pressure structural phase transition of K₂N₂ is due to the K-p lone-pair electrons activation and their participation in bonding with N atoms under high pressure.

In order to investigate the influence of projectile structure design on the detonation reliability, a low-cost and portable static test device for fuze-warhead coordination is designed in this paper to carry out the tests of detonation transfer margin under different conditions. Based on the moving least square method, the multivariable response function is constructed to evaluate the detonation reliability and quantitatively analyze influence of the sensitive factors and coupled effects. The results indicate that the gap distance and the thickness of inert buffer layer have more significant impact on the detonation of the warhead charge while the influence of the interlayer thickness is relatively small within the preset range of 3–5 mm. To ensure the reliability of kinetic energy penetrators under ambient temperature, the relative position of fuze, the interlayer thickness, the gap distance and the thickness of inert buffer layer should not exceed 25, 3.5, 25, and 22 mm, respectively. The test device, analysis method and research results will provide a good reference and guideline for structural design and reliability verification of kinetic energy penetrators.

The high-pressure structure and physical properties of RbNO₃ at zero temperature was systematically explored using first-principles calculations based on density generalized theory combined with CALYPSO crystal structure predictions. The accuracy of four different functionals was compared based on experimental data of the RbNO₃-Ⅳ phase, and the revised PBE for solids (PBEsol) functional was found to be the most reliable. The zero-temperature phase transition sequence of RbNO₃ predicted is R3m→Pnma→Pmmn (experimental phaseⅤ) based on the PBEsol functional, and the two phase transition pressures are 1.7 and 8.2 GPa. The two phase transitions are first-order phase transitions, and the volume collapse rates reach 3.73% and 2.54%, respectively. This suggests that RbNO₃ at low pressure may have new low-temperature phases those are different from P3₁ structure given by experiment in the room temperature and ambient pressure. In the energy-stabilized pressure interval, all three phases satisfy the “Born-Huangkun” elastic stability criteria, and there is no phonon virtual frequency phenomenon in the whole Brillouin zone, which indicates that they are dynamically stable structures. The electronic property analysis showed that the three phases are semiconductors, and the band gap changes caused by the phase transition are generally small, but the pressure generally inhibits the charge transfer from alkali metal ions to nitrate ions. The high-pressure phase transition sequence predicted in this paper and the elasticity, lattice dynamics, and electronic structure properties of the individual phases can provide a reference for subsequent experimental and theoretical studies.

The graphitization process of nano-crystalline diamond (NCD) under high pressure significantly influences the performance of sintered polycrystalline diamond bulks. Here, we investigated the graphitization temperature of both pure nano-diamond, with an average grain size of 50 nm, and a mixture of NaCl and nano-diamond powder in a pressure and temperature range of 5−9 GPa and 600−1500 ℃, respectively. With a quantitative analysis method employing powder X-ray diffraction, we analyzed the graphitization degree of NCD under different pressures and temperatures, examining both non-hydrostatic pressure conditions (pure NCD powder) and quasi-hydrostatic pressure conditions (NaCl-NCD mixed powder). Our findings indicate that the initial graphitization temperature of pure NCD powder exceeds 800 ℃ at 5 GPa, and ranges between 1000 and 1300 ℃ at 9 GPa. Notably, under quasi-hydrostatic pressure conditions at about 7 GPa, the graphitization temperature of NCD increases from 1000 ℃ in non-hydrostatic pressure conditions to 1500 ℃ or higher within a short holding time.

Nitrogen is a highly stable element that exists in the form of nitrogen molecules under ambient pressure. Researchers have found that nitrogen can form polymeric structures under high temperature and pressure, which have extremely high energy density and decompose into pollution-free nitrogen. From the perspective of application, it can be used as a new type of environmentally friendly high-energy-density material. Subsequently, a large number of studies have been conducted on nitrogen, resulting in phase diagrams of nitrogen under high-pressure conditions and the synthesis of structures such as cubic gauche nitrogen and layered polymeric nitrogen. However, the synthesis conditions for pure nitrogen polymeric structures are relatively harsh, and it is also difficult to preserve them under ambient pressure. People have turned to methods such as molecular nitrogen and inert gas nitrides in the hope of obtaining stable high-energy-density nitrogen structures under normal pressure. This article briefly introduces the current theoretical and experimental progress of high-energy-density nitrogen and discusses the future development direction of high-energy-density nitrogen.

In order to investigate the effect of HMX content on the impact sensitivity and non-shock initiation reaction characteristics of PBT based propellants, BAM impact sensitivity tests, friability tests and Susan tests were carried out. The experimental results show that with the increase of HMX content, the characteristic drop height of PBT based propellants at 50% explosion probability (H₅₀) decreases, indicating that the impact sensitivity increases with higher HMX content. In friability tests, the critical non-shock initiation velocities for the PBT based propellants with the HMX mass fraction of 0, 5%, 10%, and 15% are 168, 147, 136, and 131 m/s, respectively, showing a decline in the critical non-shock initiation velocity as HMX content rises. In Susan tests, four different kinds of PBT based propellants react as explosion or partial detonation at velocities range of 120 m/s to 300 m/s. The PBT based propellant with the HMX mass fraction of 10% exhibits more intense reactions compared to the other three PBT based propellants at the same velocity.

High pressure neutron diffractometer (HPND), also known as FENGHUANG, at China Mianyang Research Reactor’s (CMRR) neutron science platform, which include neutron focusing system, detector system, high-pressure devices and integrated system, can be constructed to in situ neutron diffraction experiments under ambient, high/low temperature, and high-pressure conditions. For in situ high-pressure neutron diffraction experiments, the pressure can reach to over 30 GPa at room temperature, and 10 GPa at 2000 K. FENGHUANG diffractometer has been widely applied in the field of materials researches, to provide precise information on atomic occupation, magnetic structure, crystalline structure and phase transitions, such as transition-metal nitrides, Li-containing materials, magnetic materials, energetic materials, ferroelectric ceramics.

Under the conditions of high temperature and high pressure, a series of materials transform into superionic states, which fall between the solid and liquid states and are widely believed to exist in the interior of Earth and exoplanets. Computational research has found that under the temperature and pressure of the Earth’s inner core, iron-hydrogen, iron-carbon, and iron-oxygen alloys transform to superionic states, manifested as elements such as hydrogen, carbon, and oxygen flowing rapidly like liquids in solid iron alloys. The flowing light elements cause softening of Fe alloys and a decrease in seismic wave velocities, explaining the characteristics of core density deficient and low shear wave velocity observed in geophysics. The superionic iron-hydrogen alloy in the core can interact with the geomagnetic field, forming a lattice preferred orientation fiber driven by a dipole geomagnetic field, explaining the origin of the anisotropic structure in the inner core. The discovery of superionic iron-light-element alloys in the inner core has updated our understanding of the state of the inner core, and is of great significance for understanding the structure, composition, and evolution of Earth’s inner core, as well as the relationship between the inner core structure and the Earth’s magnetic field.

An electrochemical accelerated corrosion test was conducted on the Q245R steel sample to simulate the actual corrosion conditions of the carbonization kettle. It was found that corrosion not only causes changes in geometric dimensions, but also causes degradation of the material’s mechanical properties. Tensile tests were conducted on Q235R steel materials at different temperatures, corrosion rates, and strain rates (low strain rate of 10⁻³−1 s⁻¹, medium strain rate of 10−10² s⁻¹, and high strain rate of 10³ s⁻¹). A fitting method was carried out based on the modified Johnson-Cook constitutive equation and MATLAB software, which provides the relationship between its characteristic strength, heat treatment temperature and corrosion rate. According to the results, it can be seen that the fitting curve is in good agreement with the experimental curve.

For energetic materials, the lattice vibration modes in the 6 THz (200 cm⁻¹) range are very sensitive to structural changes caused by external temperature and pressure changes. Therefore, mid- and far-infrared vibrational spectroscopy can be used as a powerful tool to study high-pressure phase transitions in these materials. We have obtained high-pressure vibrational spectra of hydrazine nitrate, using mid- and far-infrared ultra-broadband spectroscopy, whose broadband was generated by air plasma, combined with a diamond anvil cell (DAC). The crystal structure of hydrazine nitrate, as well as the infrared spectrum, were calculated by using the first principle method. Based on the calculation, the intermolecular interactions were analyzed. Combined with the experimental results, it was revealed that the structural changes under pressure alter the strength of intermolecular hydrogen bonds and van der Waals interactions, which in turn affects the low-frequency vibrational modes. And by analyzing the vibrational spectra, we observed the phase transition process of hydrazine nitrate.