Synthesis and Crystal Structure of a New Complex Oxyfluoride La0.813Sr0.187Cu(O,F)3-DELTA

La8-xSrxCu8O20-DELTA (x=1.3, 1.5, and 1.9) compounds were fluorinated using XeF2 as a fluorinating agent. The formation of a new tetragonal complex oxyfluoride La0.813Sr0.187Cu(O, F)3-DELTA was observed. The structure of the new phase was refined using X-ray powder data (a=3.7921(3) ?, c=4.0515(4) ?, S. G. P4/mmm, R1=0.020, RP=0.045, RwP=0.057) and was confirmed by electron diffraction and high-resolution electron microscopy (HREM). The tetragonal distortion of the perovskite unit cell seems to be due to a Jahn–Teller deformation of the copper coordination environment with the formation of four short (1.896 ?) and two long (2.026 ?) Cu–(O, F) distances. Domains of the La0.813Sr0.187Cu(O, F)3-DELTA phase were observed by HREM inside a matrix of a slightly fluorinated initial phase.