Mossbauer Spectroscopic Study of La_2-2xSr_2xCu_1-xFe_xO_4-y (0 ?? x ?? 0

摘要

Tetragonal K₂NiF₄-type La_2-2xSr_2xCu_1-xFe_xO_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_2-2xSr_2xCu_1-xFe_xO_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_2-2xSr_2xCu_1-xFe_xO_4-y.