X-Ray Absorption Co L Spectra for the Determination of the Charge and Spin States of Cobalt Ions in LnBaCo2O5 + δ Cobaltites (Ln = Eu, Gd, Tb)

Abstract

Co L X-ray absorption spectra were used to determine the charge and spin states of ions in LnBaCo2O5 + δ cobaltites (Ln = Tb, Eu and Gd, 0.08 leqslant delta leqslant 0.55). It is shown that with a decrease in the oxygen content in cobaltites (with a decrease in the average charge state of cobalt ions), the Co {{L}_{3}} maximum shifts linearly towards low photon energies. It was found using Co {{L}_{3}} X-ray spectra that the mechanical action on GdBaCo2O5.5 (uniaxial compression and torsion under pressure) leads to the appearance of divalent cobalt ions, i.e., the CoO phase. The CoO phase appears in the sample under pressure even in the absence of shear deformations. Based on the measurements of X-ray absorption spectra at different temperatures, it was found that at 440 K, which is above the metal–insulator transition point, some of the low-spin Co3+ ions in EuBaCo2O5.52 cobaltite octahedra pass into the high-spin state. No change of the spin state of Co ions in EuBaCo2O5.24 with temperature was found.