Neutron diffraction studies of the structure of substituted complex cobalt oxides
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The effect of substitution of manganese and niobium for cobalt on the magnetic and crystal structure of doped cobaltites has been studied by the neutron diffraction method. The Pr0.5Sr0.5Co1 − xMnxO3 samples undergo, with increasing x, a series of transitions of the crystal structure from the monoclinic I2/a to orthorhombic Immm phase, and then, to the high-temperature tetragonal I4/mcm phase and low-temperature orthorhombic Fmmm phase. Undoped Pr0.5Sr0.5CoO3 is a ferromagnet, but the magnetic ordering is destroyed with increasing x. At high degrees of substitution of manganese, the A-type antiferromagnetic ordering is observed. Substitution of niobium for cobalt in La1 − xSrxCoO3 compositions leads to changes in the Co-O bond length and the unit cell volume, which is accompanied by a decrease in the ferromagnetic moment. The Co → Nb substitution prevents the formation of Co4+ and leads to the stabilization of Co3+ in a high-spin state.
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