Structural evolution, superconductivity, and high carrier mobility of anti-perovskite Ca3BiX (X = H, N, P): first-principles calculations

Abstract

Through first-principles calculations, the structural evolution, carrier mobility, and superconductivity of anti-perovskite Ca₃BiX (X = H, N, P) have been investigated in the 0–100 GPa range. Results indicate that Pmm, Rm, P6₃/mmc, P4/mmm, Cmcm, Pnma, and C2/m are stable phases in the corresponding pressure regions. Moreover, phase transitions occur in Ca₃BiH from Pnma to Pmm and Rm phases at 8 GPa, in Ca₃BiN from Pmm and P4/mmm to P6₃/mmc phases at 73 GPa, and in Ca₃BiP through three transitions: Pnma → C2/m at 5 GPa, C2/m → Cmcm at 10 GPa, and Cmcm → C2/m at 22 GPa. More importantly, the electron mobility of the Pnma phase of Ca₃BiP is anisotropic and reaches 7.1 × 10⁴ cm² V⁻¹ s⁻¹ in the x direction, exceeding the recently reported result of the anti-perovskite Rb₄I₂O (5.3 × 10⁴ cm² V⁻¹ s⁻¹) in the z direction. Meanwhile, electron–phonon coupling calculations show that the superconducting transition temperature (T_c) of the Pmm phase of Ca₃BiH reaches 7.2 K at 50 GPa, which is higher than that of the comparable Ca-based anti-perovskite Ca₃PN (4 K). These results not only enrich research on Ca-based anti-perovskites under high pressure, but also provide theoretical support for further studies of the mobility and T_c of Ca-based anti-perovskites.