ИСТИНА

The aimes of represented study were to characterize the electronic state and the local surrounding of 57Fe Mössbauer probe atoms within iron-doped layered perovskites La2Li0.5M0.5O4 (M = Co, Ni, Cu) containing transition metal in unusual formal oxidation states “+3”. Despite the fact that these oxides are characterized by the similar crystal structure, the behaviour of the 57Fe probe atoms appears essentially different in these lattices. In the case of La2Li0.5Co0.5O4 and La2Li0.5Ni0.5O4 the observed isomer shift (δ) values correspond to the Fe3+ (3d5) cations located in an oxygen octahedral surrounding. In contrast, for the cuprate La2Li0.5Cu0.5O4, the obtained δ value is comparable to that characterizing the formally tetravalent high-spin Fe4+(3d4) cations in the octahedral coordination. An approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed to explain such a difference. It was shown that electronic states of cobalt and nickel are dominated by the d6(Co) and d7(Ni) configurations corresponding to the ionic “Co3+-O2-“ and “Ni3+-O2-” states for the samples La2Li0.5M0.5O4 (M = Co, Ni). On the other hand, in the case of La2Li0.5Cu0.5O4 a large amount of charge is transferred via Cu-O bonds from the O: 2p bands to the Cu: 3d orbitals and the ground state is dominated by the d9L configuration (“Cu2+-O-” state). The dominant d9L ground state for the (CuO6) sublattice induces in the environment of the 57Fe probe cations a charge transfer Fe3+ + O-(L) → Fe4+ + O2-, which transforms the “Fe3+” into the “Fe4+” state.