Pressure-induced phase transitions of AX(2)-type iron pnictides: an ab initio study.

An investigation into the high-pressure behavior of AX(2)-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 108 GPa for FeP(2), at 92 GPa for FeAs(2), and at 38 GPa for FeSb(2), accompanying a semiconductor-to-metal crossover. A linear relationship between bulk moduli and the inverse specific volume is proposed to be B(0) = 17 498/V(0)-45.9 GPa for the marcasite-type phase and B(0) = 31 798/V(0)-67.5 GPa for the CuAl(2)-type phase. According to the observed structural evolutions, we claim that the regular marcasite transforms to the CuAl(2)-type phase and the anomalous marcasite transforms to the pyrite-type phase at high pressures.