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We use x-ray absorption spectroscopy to investigate the local structure andelectronic properties of bulk La$_{1-y}$Sr$_{y}$Co$_{1-x}$Nb$_x$O$_3$ ($y=$2$x$ as LSCNO and $y=$ 0 as LCNO) samples. The x-ray absorption near-edgespectra (XANES) of LSCNO at Co K-edge affirm the valence state of Co in 3+.However, in the case of the LCNO, a subtle variation in the valence state of Coions from 3+ to 2+ is evident with Nb substitution. The detailed analysis ofthe Fourier transform (FT) of the extended x-ray absorption fine structure(EXAFS) for the LSCNO samples exhibit the two groups of the bond-lengths owingto the Jahn-Teller (JT) distortion in the CoO$_6$ octahedra, which manifestthat the Co$^{3+}$ ions exist in the intermediate spin-state(t$^5_{2g}$e$^1_g$) at room temperature. However, we find that the JTdistortion is not present in LCNO samples for $x>$0.025 due to an increase inthe high-spin Co$^{2+}$/Co$^{3+}$ ions accompanied by the Nb--inducedstructural transformation. Intriguingly, the La L$_3$-edge spectra for theLSCNO samples exhibit that the La ions exist in the trivalent state and thelocal disorder around La atoms decreases with Sr and Nb substitution.Interestingly, the simulated FT of the EXAFS spectra at the La L$_3$-edgedemonstrates the three groups of La--O bond lengths, which exhibit a monotonouschange with Sr and Nb substitution. Moreover, the XANES measured at Sr and NbK-edges confirm their oxidation state to be in 2+ and 5+, respectively.

X-ray Absorption Spectroscopy Study of La$_{1-y}$Sr$_{y}$Co$_{1-x}$Nb$_x$O$_3$