Struture stability and compressibility of iron-based superconductor Nd(O0.88F0.12)FeAs under high pressure.

The high-pressure angle-dispersive X-ray diffraction experiments on the iron-based superconductor Nd(O0.88F0.12)FeAs were performed up to 32.7 GPa at room temperature. An isostructural phase transition starts at approximately 10 GPa. When pressure is higher than 13.5 GPa, Nd(O0.88F0.12)FeAs completely transforms to a high-pressure phase, which remains the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure phase. The ambient conditions isothermal bulk moduli B0 are derived as 102(2) and 245(9) GPa for the low-pressure phase and high-pressure phase, respectively. The structure analysis based on the Rietveld refinement methods shows the difference of pressure dependence of the Fe-As and Nd-(O, F) bonding distances, as well as As-Fe-As and Nd-(O, F)-Nd angles between the low-pressure phase and high-pressure phase.