[en] Highlights: • The doping effects of Hf/Nb/Zr on physical properties of Ti3AlC2 and Ti3SiC2 were investigated based on simulations. • Magnetic character was observed in Ti3AlC2 for c-ATi2 site doping of Hf/Zr, which was attributed to electron transfer. • Doping Hf/Nb/Zr at different sites were found to have different effects on Ti3AlC2 and Ti3SiC2. -- Abstract: The effects of doping Hf/Nb/Zr on the structural, electronic, magnetic, mechanical, and thermal properties of Ti₃AlC₂ and Ti₃SiC₂ are investigated based on the density functional theory (DFT). Our calculations show that magnetism can be induced in Ti₃AlC₂ by doping Hf/Zr at c-ATi2 site due to the electron transfer. Doping Hf/Nb/Zr at the Ti1 site has minimal effect on the intrinsic mechanical properties of Ti₃AlC₂ and Ti₃SiC₂, in according with the previous experiment. Whereas doping Hf/Nb/Zr at the interstitial site has adverse effects on the host material, resulting in significantly decreased bulk, shear, Young's moduli and Debye temperature.

[en] Although rare-earth metals have increasingly received attention for use in the storage and transportation of the tritium used in nuclear fusion reactions, they still face great challenges, such as the effect of helium on the mechanical properties of different erbium hydrides. In this work, first principles are used to study the mechanical properties (elastic constants, Young’s modulus, transverse shear modulus and bulk modulus) of different erbium hydrides exposed to helium. The Young’s modulus, the transverse shear modulus and the bulk modulus are given based on the elastic constants calculated according to first principles. It is found that the mechanical properties of all three erbium hydrides decrease in the presence of helium, and the decline of the mechanical properties of ErH₃ is the most serious. To explain the reason for the decrease in the mechanical properties, the densities of the states of erbium hydrides are calculated. During the calculations, helium embrittlement is not found and the ductility of the erbium hydrides improves following the production of helium at the helium concentrations considered in this work. (paper)

[en] Guiding center equations of particle motion under a toroidal magnetic configuration were derived using a new defined magnetic flux coordinates system. A transformation method to Hamiltonian canonical variables is presented in this work. It was found that the newly defined flux coordinates are simple self-consistent, and could be applied to any magnetostatic equilibrium with a nested flux configuration.

[en] Using density functional theory calculation, we show that oxygen (O) exhibits an interesting effect in CuInSe₂ and CuGaSe₂. The Se atoms with dangling bonds in a Se-rich Σ3 (114) grain boundary (GB) create deep gap states due to strong interaction between Se atoms. However, when such a Se atom is substituted by an O atom, the deep gap states can be shifted into valence band, making the site no longer a harmful non-radiative recombination center. We find that O atoms prefer energetically to substitute these Se atoms and induce significant lattice relaxation due to their smaller atomic size and stronger electronegativity, which effectively reduces the anion–anion interaction. Consequently, the deep gap states are shifted to lower energy regions close or even below the top of the valence band.

[en] Highlights: • Irradiation does have an effect on the structure of the fused silica without impurity, making it possible to reduce band gap. This causes it to be more easily to absorb energy of laser. • Structural changes of fused silica are moresever after doping of Fe and Ce, and band gap is further narrowed, resulting in a more obvious decline in resistance to irradiation. • Fe will make the resistance to decline more than Ce. - Abstract: The damages of fused silica surface after laser irradiation can be caused by the impurities introduced during manufacture processes. In this paper, Fe and Ce impurities are considered in fused silica. The first-principles method is employed to simulate the process of high-power ultraviolet laser irradiation to fused silica. The bond angle distribution, pair distribution function, the density of state (DOS) and other information of fused silica structures are calculated. There is a remarkable difference in bond length and bond angle distribution between pure and doped fused silica. New defect states are also observed in DOS with the narrower band gap, and new optical absorption peaks appear in the dielectric function for the fused silica with the dopants after laser irradiation. This means that fused silica with impurities has more significant absorption for laser energy than pure fused silica. FeO bonds are found more stable than CeO ones after irradiation. This indicates the damage of Fe doping is greater than that of Ce doping. So, doping of metal indeed leads to a decrease in damage resistance to laser for fused silica, and Fe is more harmful than Ce.

[en] Highlights: •β-Phase MH_1.5[100] (M = Ti, Zr, Hf) are more stable than other possible structures. •Increasing H concentration in MH_y induces the tetragonal distortion. •Ti_0.75Hf_0.25H_1.5 and Zr_0.75Hf_0.25H_1.5 exhibit the highest mechanical stability. •Systems considered in the present work are anisotropic and show a ductile behavior. •The electronic conductivity of A_1−xB_xH_y exhibits metallic character. -- Abstract: Using ab initio calculations, we investigated the mechanical and electronic properties of Ti_1−xHf_xH_y, Ti_1−xZr_xH_y and Zr_1−xHf_xTH_y (x = 0, 0.25, 0.5, 0.75, 1; y = 1.5, 1.75, 2). The calculated results in binary hydrides show that the β-phase MH_1.5[100] (M = Ti, Zr, Hf) are more stable than other possible structures. At the Fermi level, the density of states for metal d state increases with increasing the H concentration in MH_y (y ranged from 1.5 to 2), which leads to the instability of their fcc structures and induces the tetragonal distortion. Ti_0.75Hf_0.25H_1.5 and Zr_0.25Hf_0.75H_1.5 exhibit the highest mechanical stability, while Ti_0.25Zr_0.75H_1.5 has the lowest mechanical stability among the corresponding ternary systems considered. Moreover, the systems studied in the present work are all anisotropic and show a ductile behavior. The tetragonal distortion in Ti_1−xHf_xH_1.5, Ti_1−xZr_xH_1.5 and Zr_1−xHf_xH_1.5 is not observed, retaining their fcc structures. The electronic structure of A_1−xB_xH_y (A and B = Ti, Hf, Zr) exhibits metallic character