Unusual properties and features of oxygen nonstoichiometry of La-Sr manganites with manganese replacement by a combination of nickel and germanium

摘要

When studying manganites of the system La_(1-c)Sr_cMn_(1-x)(Ni~((2+)_(0.5))Ge~((4+)_(0.5)))_xO_(3+γ) (x = 0.05; 0.10; 0.15; 0.15 ≤ c ≤ 0.35), it was experimentally established that after reductive annealing, which leads the oxygen content to the stoichiometric one, unit cell volume (v) of the samples decreases and at c ≥ 0.19 it is less than after annealing in oxygen. Based on the analysis of various charge compensation mechanisms using derived dependences of v on the oxygen content and taking into account the changes in magnetic and electrical parameters, it is established that experimental data can be explained only with the allowance for formation of singly charged oxygen ions. The relationships between magnetic parameters of the manganites and their composition, structural characteristics and deviations from oxygen stoichiometry are explained. The possibility of local ferromagnetic ordering of uncompensated spins of Ni~(2+) ions due to their interaction with singly charged O~- anions is considered.