Distortion induced by Zn in La1.85Sr0.15CuO4 superconductor: An XAFS study

XAFS results on Zn-doped La1.85Sr0.15CuO4 system are presented, for doping concentrations of 7% and 13%. The XAFS analysis, at the Cu and Zn K-edges, shows that Zn induces a significant and widespread distortion in the system. Around the Zn impurity, the Zn-O bond-length expands by 0.086 A. The disorder extends to the Cu sites, as marked by (a) 13% deficit of O coordination in the cuprate plane, independent of doping concentration and (b) increasing disorder (Cu-O Debye-Waller factor) along the perpendicular c-axis with increased doping concentration. The relevance of these findings, to the mechanisms of metal-insulator transition and superconductivity suppression in this system, are briefly discussed