Crystal Structure and Magnetic Properties of La2Co2O5

✍ Scribed by Ole Henrik Hansteen; Helmer Fjellvåg; Bjørn C. Hauback

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 403 KB
• Volume: 141
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7963

✦ Synopsis

The crystal structure of La 2 Co 2 O 5 is determined on the basis of high-resolution powder X-ray diffraction and neutron diffraction data. La 2 Co 2 O 5 adopts the brownmillerite-type structure, where single layers of corner-sharing CoO -octahedra are connected by layers with chains of corner-sharing CoO 4 -tetrahedra running along [100]. Three alternative descriptions of the crystal structure in space groups Pnma, Imma, and Ima2 with slightly different structural distortions and/or atomic disorder are discussed. The unit cell is a ‫؍‬ 544.45(2) pm, b ‫؍‬ 1586.89(4) pm, 569.22(2) pm, R wp (PXD) ‫؍‬ 8.0%, R wp (PND) ‫؍‬ 7.3%, R p (PXD) ‫؍‬ 5.3%, R p (PND) ‫؍‬ 5.6% (space group Pnma). On reducing LaCoO 3 to La 2 Co 2 O 5 there is a 9.8% expansion of the unit cell owing to the increased size of high-spin divalent cobalt atoms, and a significant peak broadening occurs in the high-resolution PXD data. On the basis of powder neutron diffraction data, La 2 Co 2 O 5 is found to order antiferromagnetically (G-type ordering) for temperatures below T N ‫؍‬ 301؎5 K. The magnetic moments for the cobalt atoms are oct. ‫؍‬ 3.0؎0.1 B and tetr. ‫؍‬ 2.5؎0.1 B .