Synthesis and structural studies of Sr2Co2-xGaxO5, 0.3≤x≤0.8

The novel oxide Sr2Co2-xGaxO5 with brownmillerite-type structure has been synthesized in the compositional range 0.3less than or equal toxless than or equal to0.8. Rietveld refinements using neutron powder diffraction data have been performed for the end compositions, x = 0.3 and 0.8. The structure is best described in the space-group Icmm (no. 74) with unit cell parameters a = 5.5678(6), 5.6126(7) Angstrom, b = 15.749(2) 15.733(2) Angstrom and c = 5.4599(6), 5.4559(7) Angstrom for the x = 0.3 and 0.8 compositions, respectively. The compounds were found to be G-type antiferromagnetic with the magnetic moments parallel to the c-axis. High-temperature magnetic susceptibility measurements confirmed the samples to be antiferromagnetic with Neel temperatures T-N = 505, 468 and 423 K for the x = 0.3 0.5 and 0.8 samples, respectively. High-resolution transmission electron microscopy and electron diffraction studies confirmed the I-centred structure and revealed the presence of disorder. (C) 2003 Elsevier Science (USA). All rights reserved.