Mossbauer Spectroscopic Study of La 2-2x Sr 2x Cu 1-x Fe x O 4-y (0≤x≤0.5) Solid-solution

Tetragonal K 2 NiF 4 -type La 2 - 2 x Sr 2 x Cu 1 - x Fe x O 4 - y solid-solution have been synthesized by citrate based sol-gel method. The valence state of iron was determined by Mossbauer spectroscopy and subsequent iodometric titration clearly showed that the copper ions in this solid-solution are in the mixed valence state Cu(II/III). When x ≤ 0.3, Fe(III) is competing with the mixture of Cu(II) and Cu(III) and La 2 - 2 x Sr 2 x Cu 1 - x Fe x O 4 - y exhibits a metallic character. No evidence for Cu(II)-O-Fe(IV) ↔ Cu(III)-O-Fe(III) valence degeneracy was observed. In contrast, a small amount of Fe(IV) is observed with increasing x (x=0.4 and 0.5), revealing a semiconducting behavior. These results suggest that the electronic interaction of Cu(III)-O-Fe(III) contributes greatly to the metallic character, while the electronic interaction of Cu(II)-O-Fe(IV) deteriorates the metallic character of La 2 - 2 x Sr 2 x Cu 1 - x Fe x O 4 - y .