X-ray absorption $\mathrm{Co}$ $L$ spectra for the determination of the charge and spin states of cobalt ions in $\mathrm{LnBaCo}_2\mathrm{O}_{5+\delta}$ cobaltites ($\mathrm{Ln} = \mathrm{Eu, Gd, Tb}$)

$\mathrm{Co}$ $L$ X-ray absorption spectra were used to determine the charge and spin states of ions in $\mathrm{LnBaCo}_2\mathrm{O}_{5+\delta}$ cobaltites ($\mathrm{Ln = Tb, Eu}$ and $\mathrm{Gd}$, $0.08 \leqslant \delta \leqslant 0.55$). 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 $\mathrm{Co}$ $L_3$ X-ray spectra that the mechanical action on $\mathrm{GDBaCo}_2\mathrm{O}_{5.5}$ (uniaxial compression and torsion under pressure) leads to the appearance of divalent cobalt ions, i.e., the $\mathrm{CoO}$ phase. The $\mathrm{CoO}$ 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 $\mathrm{Co}^{3+}$ ions in $\mathrm{EuBaCo}_2\mathrm{O}_{5.52}$ cobaltite octahedra pass into the high-spin state. No change of the spin state of $\mathrm{Co}$ ions in $\mathrm{EuBaCo}_2\mathrm{O}_{5.24}$ with temperature was found.