JOURNAL OF SOLID STATE CHEMISTRY, vol.179, no.5, pp.1434-1444, 2006 (SCI-Expanded)
The effect of replacing Co3+ by Ga3+ and Fe3+ in the perovskite-related tetragonal phase Sr0.75Y0.25CoO2.625 with unit cell parameters: a = 2a(p), and c = 4a(p) (314 phase) has been investigated. The 314 phase is formed by Sr0.75Y0.25Co1-xMxO2.625+delta with x <= 0.375 for M = Ga and x <= 0.625 for M = Fe. High-resolution transmission electron microscopy and electron diffraction revealed frequent microtwinning in the iron-containing compounds, in contrast to the Ga-substituted 314 phases. Diffraction experiments and electron microscope images indicated that at higher Fe contents, 0.75 <= x <= 0.8757 a disordered cubic perovskite structure forms. The crystal structures of Sr0.75Y0.25Co0.75Ga0.25O2.625 and Sr0.75Y0.25Co0.5Fe0.5O2.625+delta were refined using neutron powder diffraction data. It Was found that the oxygen content of Sr0.75Y0.25Co0.5Fe0.5O2.625+delta is higher than in Fe-free 314 phase, so that delta corresponds to 0.076, whereas delta = 0 in Sr0.75Y0.25Co0.75Ga0.25O2.625+delta Magnetization measurements on the unsubstituted Sr0.7Y0.3CoO2.62 and Ga-substituted Sr0.75Y0.25Co0.75Ga0.25O2.625 compounds indicate the presence of a ferromagnetic-like contribution to the measured magnetization at 320 and 225 K, respectively, while replacing Co by Fe leads to the suppression of this contribution. A neutron diffraction study shows that the Si0.75Y0.25Co0.5Fe0.5O2.625+delta compound is G-type antiferromagnetic at room temperature, whereas Sr0.75Y0.25Co0.75Ga0.25O2.625 does not exhibit magnetic ordering at room temperature. (C) 2006 Elsevier Inc. All rights reserved.