Superconducting Sr2-xAxCuO2F2+δ (A = Ca, Ba):: Synthetic pathways and associated structural rearrangements

The low-temperature fluorination of a range of insulating alkaline earth cuprates Sr(2-x)A(x)CuO(3) (A = Ca (0 less than or equal to x less than or equal to 2); A = Ba (0 less than or equal to x less than or equal to 0.6)) can result in superconducting oxide fluorides Sr(2-x)A(x)CuO(2)F(2+delta). In contrast, conventional high-temperature solid-state reactions produce thermodynamically more stable mixtures of oxides and fluorides, Various soft-chemistry fluorination pathways (utilizing F-2 gas, NH4F, MF2 [M = Cu, Zn, Ni, Ag]) are compared with respect to their efficacy and mechanisms, Attention is also focused on the structural features of the mixed-oxide precursor and the final-oxide fluorides to highlight the remarkable structural rearrangements that occur during the low-temperature fluorination, The effects of fluorination of other Sr-Cu-O systems are used to identify the structural requirements of the precursor oxide in order to achieve such transformations. (C) 1998 Academic Press.