SUPERCONDUCTING SR(2-X)A(X)CUO(2)F(2- SYNTHETIC PATHWAYS AND ASSOCIATED STRUCTURAL REARRANGEMENTS(DELTA) (A = CA, BA) )

The low-temperature fluorination of a range of insulating alkaline ear th 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 eq ual 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-sta te 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 struc tural features of the mixed-oxide precursor and the final-oxide fluori des to highlight the remarkable structural rearrangements that occur d uring the low-temperature fluorination, The effects of fluorination of other Sr-Cu-O systems are used to identify the structural requirement s of the precursor oxide in order to achieve such transformations. (C) 1998 Academic Press.