Synthesis and crystal structure of a new complex oxyfluoride La_{0.813}Sr_{0.187}Cu(o,F)_{3-\delta}

Abstract La 8− x Sr x Cu 8 O 20− δ ( x =1.3, 1.5, and 1.9) compounds were fluorinated using XeF 2 as a fluorinating agent. The formation of a new tetragonal complex oxyfluoride La 0.813 Sr 0.187 Cu(O, F) 3− δ was observed. The structure of the new phase was refined using X-ray powder data ( a =3.7921(3) A, c =4.0515(4) A, S. G. P 4/ mmm , R 1 =0.020, R P =0.045, R wP =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 A) and two long (2.026 A) Cu–(O, F) distances. Domains of the La 0.813 Sr 0.187 Cu(O, F) 3− δ phase were observed by HREM inside a matrix of a slightly fluorinated initial phase.

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