Abstract
The effect of oxygen stoichiometry on properties of La0.815Sr0.185MnO3+d was studied for samples with oxygen content controlled by quenching from high temperatures (700–1400 °C) in air, cooling under low oxygen partial pressure, and annealing at high oxygen pressure. The oxygen content determined from thermogravimetric analysis was found to vary within a range of 3.00–3.10. At room temperature the lattice parameters of the rhombohedral structure (R3̄c) decrease linearly with increasing oxygen content. The rhombohedral-orthorhombic structural transition temperature decreases abruptly with increasing oxygen content while the Curie temperature increases with increasing oxygen content, reaching a maximum at d∼0.04, and then decreases. The saturation magnetization decreases linearly with increasing oxygen content indicating increasing Mn4+ concentration, i.e., hole doping by cation vacancies. Finally the magnetoresistance effect decreases with increasing d.
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