An improved route to the synthesis of superconducting copper oxyfluorides Sr2-xAxCuO2F2+δ (ACa, Ba) using transition metal difluorides as fluorinating reagents

Slater PR, Hodges JP, Francesconi MG, Edwards PP, Greaves C, Gameson I, Slaski M

We report here a simple and efficient synthetic route to high temperature superconducting oxyfluorides. Solid phase fluorination of Sr2-xAxCuO3 (ACa, 0 ≤ x ≤ 2.0; ABa, 0 ≤ x ≤ 0.6) with the transition metal difluorides, CuF2, ZnF2, AgF2, NiF2, at relatively low temperatures (225-250°C) produces superconducting Sr2-xAxCuO2F2+δ with a maximum Tc of 64 K (for ABa, x = 0.6). This simple preparation route eliminates the need for F2 gas, and at the same time produces negligible (Sr/A)F2 impurity, unlike the corresponding fluorination with NH4F. Using this route the synthesis of the oxyfluoride, Ba2CuO2F2+δ, 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. © 1995.