Pressure-induced phase transitions of AX₂-type iron pnictides: An abinitio study

An investigation into the high-pressure behavior of AX₂-type iron pnictides was conducted using first-principles calculations based on density functional theory within the generalized gradient approximation. Our results demonstrate that a phase transition from the marcasite to the CuAl ₂ occurs at 108GPa for FeP₂, at 92GPa for FeAs ₂, and at 38GPa for FeSb₂, accompanying a semiconductor-to-metal crossover. A linear relationship between bulk moduli and the inverse specific volume is proposed to be B₀ = 17 498/V ₀-45.9GPa for the marcasite-type phase and B₀ = 31 798/V₀-67.5GPa for the CuAl₂-type phase. According to the observed structural evolutions, we claim that the regular marcasite transforms to the CuAl₂-type phase and the anomalous marcasite transforms to the pyrite-type phase at high pressures.