Pressure and chemical substitution effects in the local atomic structure   of BaFe2As2
  The effects of K and Co substitutions and quasi-hydrostatic applied pressure (P<9 GPa) in the local atomic structure of BaFe2As2, Ba(Fe{0.937}Co{0.063})2As2 and Ba{0.85}K{0.15}Fe2As2 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 (<~ 0.01 Angstroms) by both Co and K substitutions, without any observable increment in the corresponding Debye Waller factor. Also, this bond is shown to be compressible (k = 3.3(3)x10^{-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. 
E. Granado, L. Mendonca-Ferreira, F. Garcia, G. de M. Azevedo, G.   Fabbris, E. M. Bittar, C. Adriano, T. M. Garitezi, P. F....
cond-mat.supr-con cond-mat.mtrl-sci