Jl. Kissick et al., SYNTHESIS, STRUCTURE, AND XPS CHARACTERIZATION OF THE STOICHIOMETRIC PHASE SR2CUO2F2, Physical review. B, Condensed matter, 56(5), 1997, pp. 2831-2835
Thermogravimetric analysis has revealed that reduction of Sr2CuO2F2+de
lta in 10% H-2/90% N-2, occurs in two distinct steps on heating up to
930 degrees C. Whereas reduction to give SrF2, SrO, and Cu is complete
above 800 degrees C, a stable intermediate forms in the region betwee
n 250 and 450 degrees C. This has been identified as a new tetragonal
(I4/mmm) phase, Sr2CuO2F2, with unit-cell dimensions a = 3.967(1) Angs
trom and c = 12.816(2) Angstrom. The structure has been determined fro
m powder x-ray-diffraction data and is related to Nd2CuO4 (T'-type). M
adelung energy, bond valence sum calculations, and F 1s-XPS data clear
ly indicate that the F- ions occupy sites within the fluorite block (S
r2F2) insulating layers. This contrasts with the La2CuO4 (T-type) stru
cture which is adopted by Sr2CuO2F2+delta.