Pressure-driven structural evolution, superconductivity, and anisotropic ideal strength of Nb3Si.

Pressure-induced structural evolution can strongly modify the functional properties of transition-metal silicides, but the pressure response of Nb3Si, particularly the coupling between phase stability, superconductivity, and ideal strength, remains insufficiently clarified. Here, we systematically investigate the structural stability, superconductivity, and mechanical properties of Nb3Si under pressure by combining CALYPSO-based crystal-structure prediction, ACNN-assisted structural screening, and first-principles calculations. We identify a previously unreported orthorhombic Pnma phase that is energetically more favorable than the tetragonal P42/n structure previously regarded as the most stable phase at ambient pressure, thereby revising the phase-stability picture of Nb3Si. Upon compression, the stability hierarchy is reconstructed, and a phase transition to the cubic Pm3̄n phase occurs at about 34 GPa, whereas the Pm3̄m phase is excluded by lattice instability. The stable phases are all metallic, but their superconducting responses differ markedly: the cubic Pm3̄n phase exhibits the highest transition temperature of about 18 K, while the newly identified Pnma and the P42/n phases show much lower Tc values of about 0.5 and 1.5 K, respectively. In parallel, the mechanical response evolves markedly with structure; in particular, the high-pressure Pm3̄n phase develops an exceptionally high ideal compressive strength approaching 100 GPa along the strongest loading direction. These results demonstrate that pressure reconstructs the phase landscape of Nb3Si and thereby governs its superconducting and mechanical properties in a strongly phase-dependent manner, providing a unified understanding of structure-property correlations in transition-metal silicides under compression.