First-principles calculations under isotropic tension reveal a common energetic basis for carrier-induced strength modulation in Si, 3C-SiC, and diamond. At ±0.05 e/atom, electron doping reduces the peak tensile stress by 13.7–15.8%, whereas hole doping increases it by 11.7–13.1%. These changes arise from opposite modifications of the bond-formation energy gain, with larger effects at shorter bonds. During bond stretching, the electron-induced energy penalty decreases and the hole-induced stabilization weakens, lowering and raising tensile resistance, respectively. Crystal orbital Hamilton population analysis shows that holes deplete bonding states, so depopulation of antibonding states cannot explain the strengthening. The occupied-level mean energy rises under electron doping and falls under hole doping relative to the neutral state at the same bond length. These differences grow at shorter bonds, paralleling the energetic response and suggesting that the evolution of the occupied-level distribution provides a basis for a common electronic interpretation of strength modulation.
The migration of {1122} twin boundaries (TBs) in alpha-titanium is mediated by twinning disconnections (TDs), yet the origin of high-layer steps remains unclear. Here, atomic-resolution HAADF-STEM reveals distinct immobile high-layer step configurations at TBs and identifies a lower-layer b1/2 disconnection as a pinning precursor. Molecular dynamics (MD) simulations further reveal a feasible origin of this lower-layer interfacial defect, showing that the interaction between a prismatic (c) dislocation and a mobile TD can generate an immobile b1/2 disconnection. Together, these results suggest that dislocation-TB interaction can create the initial immobile b1/2 disconnection, which then promotes continued TD accumulation and subsequent high-layer step development. The resulting high-layer steps provide favorable sites for (c+a) dislocation emission and may facilitate c-axis strain accommodation in alpha-Ti.
