AN IMPROVED ROUTE TO THE SYNTHESIS OF SUPERCONDUCTING COPPER OXYFLUORIDES SR(2-X)A(X)CUO(2)F(2+DELTA) (A=CA, BA) USING TRANSITION-METAL DIFLUORIDES AS FLUORINATING REAGENTS

We report here a simple and efficient synthetic route to high temperature superconducting oxyfluorides. Solid phase fluorination of Sr(2-x)A(x)CuO(3) (A = Ca, 0 less than or equal to x less than or equal to 2.0; A = Ba, 0, less than or equal to x less than or equal to 0.6) with the transition metal difluorides, CuF2, ZnF2, AgF2, NiF2, at relatively low temperatures (225-250 degrees C) produces superconducting Sr(2-x)A(x)CuO(2)F(2+delta) with a maximum T-c of 64 K (for A = Ba, x = 0.6). This simple preparation route eliminates the need for F-2 gas, and at the same time produces negligible (Sr/A)F-2 impurity, unlike the corresponding fluorination with NH4F. Using this route the synthesis of the oxyfluoride, Ba2CuO2F2+delta, is also reported for the first time. These studies and the examination of the fluorination of other cuprate systems have shown that this is a powerful and versatile fluorination route.