Room temperature Mössbauer spectra of 57Fe-doped La 2SrCu 2O 6, La 2CaCu 2O 6 and La 1.6Sr 0.4CaCu 2O 6: Structural implications

Abstract

In order to elucidate the properties of iron in the pyramidal Cu(2) sites of YBa 2Cu 3O 7-y, 1% 57Fe was substituted to copper in the simple bilayer compounds La 2SrCu 2O 6 and La 1.6Sr 0.4CaCu 2O 6 (in their insulating forms). It appears that iron enters these systems as high-spin Fe 3+. The room temperature Mössbauer spectra consist of paramagnetic quadrupole doublets, and a magnetic hyperfine structure appears below about 20 K. At RT , two quadrupolar doublets with ΔΔΔ ∼ 1 mm/s and ΔΔ ∼ 0.3 mm/s are observed in variable proportions in all three compounds. They have been interpreted by structural considerations involving, first a small displacement of the iron with respect to the copper position inside the oxygen pyramid, and second the possibility of additional oxygen insertion into 2b vacancy site, leading in some cases to an octahedral oxygen neighbourhood.