High-Pressure Behavior of MgAgF3 Perovskite: Structural Anisotropy, Pressure-Induced Structural Evolution, and Band Gap Tuning

Abstract

The pressure-dependent structural and electronic properties of the hexagonal perovskite MgAgF3 have been systematically investigated using first-principles density functional theory calculations within the CASTEP code, covering a pressure range of 0–50 GPa. The ambient crystal structure (space group R3 @#x0305;c, a = b = 5.515 Å, c = 13.549 Å) undergoes a complex sequence of pressure-induced phase transitions, with six distinct structural regimes identified from simulated X-ray diffraction patterns and lattice parameter evolution. The material exhibits significant mechanical anisotropy, with the c-axis being more compressible (B₀,c = 185.5 GPa) than the a-axis (B₀,a = 280.6 GPa), resulting in a 19.1% unit cell volume reduction over 50 GPa. Bond analysis reveals that F—Mg bonds become increasingly covalent under pressure (overlap population 0.18 → 0.19), while F—Ag bonds transition from weak covalent to antibonding interactions (0.05 → -0.02). The band gap increases linearly with pressure following E_g = 2.137 + 0.00667 × P (eV), widening from 2.137 eV at ambient pressure to 2.469 eV at 50 GPa (Δ = +15.5%), with no discontinuities at the phase transition pressures. Notably, induced d-states emerge in Mg between −1 and 0 eV under pressure, providing direct electronic evidence for pressure-induced hybridization and enhanced Mg—F covalency. These findings establish a comprehensive pressure-dependent phase diagram for MgAgF₃, positioning this lead-free perovskite as a promising material for optoelectronic applications in the visible to near-UV range, with pressure-tunable electronic properties suitable for strain-engineered devices.