Soft X-ray absorption spectroscopy as a method to study Y$_{1-y}$Ca$_{y}$BaCo$_{4-x}M_x$O$_7$ cobaltites ($M=$ Fe, Zn)

Soft X-ray absorption spectroscopy has been used to determine the charge state and content of cobalt ions in doped cobaltites CaBaCo$_{4}$O$_{7}$, Y$_{0.5}$Ca$_{0.5}$BaCo$_{4}$O$_{7}$, Y$_{0.5}$Ca$_{0.5}$BaCo$_{4-x}$Fe$_x$O$_{7}$, and Y$_{0.5}$Ca$_{0.5}$BaCo$_{4-z}$Zn$_z$O$_{7}$. A method has been proposed to determine the relative concentrations of cobalt ions in barium-containing cobaltites from the relative intensities of X-ray absorption Со $L_3$/Ba $M_5$ spectra, and the relative contents of both Fe and Zn doping elements and Co$^{2+}$ and Co$^{3+}$ ions have been determined. It has been found that the substitution of iron ions for some cobalt ions (cobaltite Y$_{0.5}$Ca$_{0.5}$BaCo$_{4-x}$Fe$_x$O$_{7}$) transforms some Co$^{3+}$ ions to Co$^{2+}$ ions. It has been found that iron ions are in the $3+$ charge state and have tetrahedral coordination with oxygen ions. The substitution of divalent zinc ions for some cobalt ions (cobaltite Y$_{0.5}$Ca$_{0.5}$BaCo$_{4-z}$Zn$_z$O$_{7}$) increases the concentration of high-spin Co$^{3+}$ ions. The tetrahedral coordination of the Co$^{2+}$ and Co$^{3+}$ ions has been confirmed.