Iron perovskites of the ABO₃ type with stoichiometry La_1/2Sr_1/2Fe_(1–x)Me_xO_3−δ have been substituted with 10% Ta and 20% Ti %, and heat treated in air or in argon. 10% substitution of iron by tantalum in the hole-doped La_1/2Sr_1/2FeO₃ decreases the electric conductivity by around 3 orders of magnitude. The conductivity decrease is well correlated with a decrease of the isothermal lattice expansion, a decrease of the formal and actual Fe⁴⁺/Fe³⁺ ratio, and with a shift of the spectral weight within the O(2p)-Fe(3d) mixed states from levels with e_g symmetry near the Fermi energy to levels with t_2g symmetry. Systematic and corresponding differences in the Fe (2p) and O (1s) X-ray absorption spectra reveal that the preparation in an oxygen-rich atmosphere promotes the formation of states with increased covalence in the initial state and states which contain O (2p) character. The electron hole doping peak in the oxygen pre-edge X-ray near edge absorption fine structure (NEXAFS) spectra is virtually absent when the samples were heated in argon. The corresponding Fe core level spectra show no significant differences other than in the branching ratio of L₂ and L₃ peaks, suggesting that the (3d) states are localized, and that hole states are responsible for electric transport changes in the material.