[en] The structural phase transition and electronic and elastic properties of CdO have been studied by first-principles pseudopotential calculations. Seven possible potential structures have been considered and our calculations show that there exists a structural phase transition from the NaCl-type (B1) structure to the CsCl-type (B2) structure above 86.6 GPa. The moderately high bulk modulus might partially originate from the strong Cd 5s-O 2p hybridization. The variations of elastic constants (C_ij) with pressure have been presented; C₄₄ decreases gradually with pressure, which implies that the B1 phase of CdO will be unstable with pressure. Moreover, the pressure dependences of the Debye temperature and the longitudinal and transverse elastic wave velocities have been investigated. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

[en] The outer surfaces functional materials of spacecraft are exposed to hypervelocity impacting of micro meteoroids and orbital debris in space. The laser-driven flyer (LDF) system can launch a speed of 3∼10km/s, a thickness of about 5um aluminum flyer under the experimental conditions. It can well simulate the effects of micrometer space debris impact on the outer surfaces functional materials of spacecraft. In this paper, the laser-driven flyer technique and flyer velocity measurement technique are introduced. The quantitative relationships between the flyer velocity and the laser energy, laser pulse width, and the flyer thickness were analyzed. The damage morphology and performance degradation of outer surfaces functional materials (such as K9 glass and OSR) of spacecraft were experimentally studied under the hypervelocity aluminium flyer impacting. (paper)

[en] An investigation into the structural stability, electronic and elastic properties of Ti₃GeC₂ under high hydrostatic pressure was conducted using first-principles calculations based on density functional theory (DFT). From the energy and enthalpy calculations, and the variations of elastic constants with pressure, we conclude that α-Ti₃GeC₂ is most stable upon compression to 100 GPa, which is not consistent with the nonhydrostatic in situ synchrotron X-ray diffraction studies. The higher structural stability was analyzed in terms of electronic level. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of all polymorphs of Ti₃GeC₂. -- Graphical abstract: The less phase stability of β-Ti₃ SiC₂ compared to that of α-Ti₃ SiC₂ can be interpreted by the states between -6.0 and 3.6 eV shift toward the higher energy region for β-Ti₃ SiC₂ Display Omitted Research highlights: → From the energy and enthalpy calculations of polymorphs for Ti₃GeC₂, we can conclude that Ti₃GeC₂ possessed higher stable structural stability under pressure to 100 GPa, which is not consistent with the nonhydrostatic experiments. → The higher stable structure of Ti₃GeC₂ is testified by the calculated variations of elastic constants with pressure. → The reasons for this higher stable phase stability were discussed in terms of the electronic level.

[en] The hypervelocity impact experiments of spherical LY12 aluminum projectile diameter of 6.4 mm on LY12 aluminum target thickness of 23 mm have been conducted using a two-stage light gas gun. The impact velocity of the projectile is 5.2, 5.7, and 6.3 km/s, respectively. The experimental results show that the plasma phase transition appears under the current experiment conditions, and the plasma expansion consists of accumulation, equilibrium, and attenuation. The plasma characteristic parameters decrease as the plasma expands outward and are proportional with the third power of the impact velocity, i.e., (T_e, n_e) ∝ v_p³. Based on the experimental results, a theoretical model on the plasma expansion is developed and the theoretical results are consistent with the experimental data

[en] An investigation into the structural phase transformation, electronic and optical properties of PuSe under high pressure was conducted by using the full potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method, in the presence and in the absence of spin-orbit coupling (SOC). Our results demonstrate that there exists a structural phase transition from rocksalt (B 1) structure to CsCl-type (B 2) structure at the transition pressure of 36.3 GPa (without SOC) and 51.3 GPa (with SOC). The electronic density of states (DOS) for PuSe show that the f-electrons of Pu are more localized and concentrated in a narrow peak near the Fermi level, which is consistent with the experimental studies. The band structure shows that B 1-PuSe is metallic. A pseudogap appears around the Fermi level of the total density of states of B 1 phase PuSe, which may contribute to its stability. The calculated reflectivity R(ω) shows agreement with the available experimental results. Furthermore, the absorption spectrum, refractive index, extinction coefficient, energy-loss spectrum and dielectric function were calculated. The origin of the spectral peaks was interpreted based on the electronic structures. - Abstract: Graphical Abstract Legend (TOC Figure): 5f-electrons are more localized by the analysis of the density of states (SOC). The origin spectra peaks was interpreted based on electronic structures.

[en] The structural stability, electronic and elastic properties of ScN under high pressure were investigated by using full-potential linearized augmented plane-wave (FP-LAPW) method. Our calculations indicate that there exists a pressure-induced structural phase transformation from the ambient rock-salt (B1) phase to CsCl-type (B2) phase above 335 GPa. The origin of moderate high bulk modulus, mechanical and high melting point was analyzed by electronic properties. The variations of elastic constants (C_ij) with volume and pressure have been investigated. Moreover, the volume dependencies of Debye temperature, the longitudinal and transverse elastic wave velocities have been presented.

[en] A two-dimensional numerical model was proposed for the laser-induced temperature field and the acceleration process of laser-driven flyers by a high-intensity laser pulse. This model includes absorption of laser energy, equation of state, thermal parameters and the dynamic rupture strength of the metal film. Assuming that the working vapour can be treated as a typical ideal gas, a dynamics expansion mechanism was established for the vapour generated by laser irradiation. Using the finite difference method, the temperature distributions and the magnitude of flyer velocity with a laser energy up to 10 J were simulated for aluminium films of different thicknesses. The numerical results agreed with the experimental data but systematically underestimated the flyer speeds. The present results can provide some insights into understanding the mechanism of laser-driven flyer plates as well as experimental parameters for flyer plate design.

[en] An investigation into the equation of state (EOS), electronic and elastic properties of Zr₂SC has been conducted by first-principles pseudopotential calculations. The calculated EOS is well consistent with the recent experimental reports. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of Zr₂SC. From the variations of elastic constants with pressure, we find that hexagonal Zr₂SC is most stable in the pressure range from 0 to 100 GPa, which is consistent with the experimental observations. The strong hybridization of Zr 4d states, S 3p states and C 2p states and the presence of pseudogap stabilize the structure of Zr₂SC. By analyzing the ratio between the bulk and shear moduli, we conclude that Zr₂SC is brittle in nature. The mechanism of brittleness of Zr₂SC originated from the large value of Zr atom occupying the internal parameter z.

[en] The equations of state (EOS) and other thermodynamic properties of the hexagonal structure Zr₄Al₂ are investigated by using a first-principles plane wave method plane-wave pseudopotential density functional theory method in the frame of the generalized gradient approximation (GGA). The obtained results are consistent with the experimental data and those calculated by others. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/ V₀ on pressure P, cell volume V on temperature T, and Debye temperature Θ and specic heat C_V on pres- sure P are successfully obtained. The variation of the thermal expansion α as well as Grueneisen paramter γ with temperature and pressure is investigated, which shows the thermal expansion a as well as Grueneisen paramter γ increase with increasing temperature but the temperature has hardly any effect on the thermal expansion a at higher pressure. (authors)

[en] Pressure-induced structural phase transformations, electronic and optical properties of AlN are investigated by first-principles method based on the plane-wave basis set. The wurtzite (B4), zinc-blende (B3), rocksalt (B1), b-β- Sn, NiAs, anti-NiAs, cinnabar, and simple cubic with 16-atom basis (SC16) phases of AlN have been considered. The calculations demonstrate that there exists a phase transition from B4 structure to B1 phase at the transition pressure of 12.7 GPa. Analysis of band structures suggests that the B4-AlN has a direct gap of 4.13 eV, while B1 phase become indirect under high pressure. The mechanism of these changes of band structures is analyzed. The positive pressure derivative of band gap energies for B1 phase might be due to the absence of d occupations in the valence bands. In addition, the imaginary parts of dielectric function for the polarization in the xy plane and average of the imaginary parts of dielectric function over three Cartesian directions were calculated. The origin of the spectral peaks was interpreted based on the electronic structure.