Neutron diffraction studies of the structure of substituted complex cobalt oxides

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 Pr$_{0.5}$Sr$_{0.5}$Co$_{1-x}$Mn$_x$O$_3$ 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 Pr$_{0.5}$Sr$_{0.5}$CoO$_3$ 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 La$_{1-x}$Sr$_x$CoO$_3$ 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 $\to$ Nb substitution prevents the formation of Со$^{4+}$ and leads to the stabilization of Со$^{3+}$ in a high-spin state.