Pressure and chemical substitution effects in the local atomic structure of BaFe₂As₂

The effects of K and Co substitutions and quasihydrostatic applied pressure (P<9 GPa) in the local atomic structure of BaFe₂As₂, Ba(Fe_0.937Co_0.063)₂As₂ and Ba _0.85K_0.15Fe₂As₂ superconductors were investigated by extended x-ray absorption fine structure (EXAFS) measurements in the As K absorption edge. The As-Fe bond length is found to be slightly reduced (L0.01 Å) by both Co and K substitutions, without any observable increment in the corresponding Debye-Waller factor. Also, this bond is shown to be compressible [κ=3.3(3)×10^-3 GPa^-1]. The observed contractions of As-Fe bond under pressure and chemical substitutions are likely related with a reduction of the local Fe magnetic moments, and should be an important tuning parameter in the phase diagrams of the Fe-based superconductors.