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The effects of seven alloying elements (Co, Cr, Mo, Re, Ru, Ta, and W) on the Ni-vacancy diffusion behavior and the rupture strength of γ-Ni/γ′-Ni3Al interfaces are studied using density functional theory calculations. Our results reveal that all seven solutes prefer to occupy Al sites close to or Ni sites far from the interface. These solutes except for Co could significantly increase the barrier of Ni-vacancy diffusion within the γ/γ′ interface region. The retarding effects are similar when solutes are located at their favored Al and Ni sites, which follows the sequence of Ta > W > Mo > Re > Ru > Cr > Co. Besides, it is found that the presence of solute atoms could always increase the rupture strength of their neighboring interface but reduce that of their next neighboring interface. The best strengthening effects on the neighboring interface are achieved by Re and W. In terms of the entire interface region, alloying at the favored Al site brings a better strengthening effect than that at the favored Ni site. The charge density difference analysis demonstrates that the charge accumulation level at the interface explains the variable strengthening effects among different alloying elements. [ABSTRACT FROM AUTHOR]

High temperature creep deformation of hcp-Mg alloys is dominated by dislocation climb driven by out-of-plane (OOP) vacancy migration. Past experiments and atomistic simulations have indicated that Zn addition reduces vacancy migration tendencies and improves creep resistance. Here, we have compared in-plane (IP) and out-of-plane (OOP) vacancy migration mechanisms in binary Mg–X (Ca, Y, and Gd) and ternary Mg–X (Ca, Y, and Gd)–Zn alloys using density functional theory based first principles computations. Irrespective of Zn addition, the migration barrier for OOP diffusion was consistently higher than IP in our prototype binary and ternary alloys. The presence of Zn in ternary systems, however, substantially increases the OOP activation barrier relative to binary alloys. The higher OOP barrier in Mg–X–Zn was attributed to favorable local relaxation, enhanced charge localization, higher interplanar bond stiffness, and greater s orbital electron occupancy in the peak saddle state. Combined, these factors restrict non-conservative dislocation climb by impeding out-of-plane vacancy movement and improve the creep resistance of ternary Mg–X (Ca, Y, and Gd)–Zn alloys. [ABSTRACT FROM AUTHOR]

The major challenge in the application of Cu2S, as a solar absorber for photovoltaic, is its excessive Cu-vacancy formation tendency within the crystal structure that makes it a degenerate semiconductor. A recent study on Ag alloyed Cu2S acanthite phase has shown a reduced Cu-vacancy formation and a high Cu diffusion barrier. Though low chalcocite is the experimentally known ground state phase at room temperature, its low crystallinity makes it computationally expensive for complex doping modeling. In this work, we first establish the structural correspondence between a newly predicted acanthite and experimentally known low chalcocite phases of Cu2S. This study shows that the acanthite crystal structure of Cu2S can be used to model complex doping in the low chalcocite. The simulated pair distribution functions and diffusions of Cu at room temperature in acanthite and low chalcocite phases of Cu2S show that they have similar structural behavior. Pristine band structures and density of state plots of these two phases also show similarity. Next, we report density functional theory based first-principles investigations of Cu2−xSnxS systems for x = 0 to 0.31 in the acanthite phase for thermodynamic, electronic, and optical properties. We have found that Sn doping coupled with Cu vacancies creates charge-neutral defects and results in higher photoabsorption in the visible light spectra. It was found from these detailed studies that a low concentration of Sn doping is preferable. Then, Sn doping and Cu-vacancy related defects in low chalcocite Cu2S are also studied. Ab initio molecular dynamics simulations show that these compound defects in Cu2S do not negatively affect Cu diffusion inside the crystal. We propose a possible route to synthesize Sn doped acanthite like Cu2S. [ABSTRACT FROM AUTHOR]

In this work, the feasibility of a monolayer Be2C as the anode material for lithium-ion battery (LiB) was investigated using the density functional theory. Our study reveals that the adsorption of Li atoms changes the electronic conductivity of a monolayer Be2C from semiconducting to metallic. This resulted in a low Li diffusion barrier of 0.11 eV, which is highly needed for the fast charge and discharge processes of the LiB. Additionally, the predicted open-circuit voltage was 0.33 V, and the calculated maximum theoretical capacity was impressively high (1785 mAh/g). Our findings suggest that the monolayer Be2C is a promising anode material for high-performance LiB. [ABSTRACT FROM AUTHOR]