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Synthesis and characterization of cobalt-containing perovskite-type oxides

El-Shinawi, Hany Zakaria Ibrahim (2010)
Ph.D. thesis, University of Birmingham.

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Abstract

A number of cobalt-containing perovskite-type oxides were synthesized and characterized in this study. All materials were half-doped with cobalt in their B-sites, i.e. contain the Co0.5M0.5 B-site state where M = Fe, Mn, Cr, Ni; the materials adopted single layered, double-layered and simple perovskite-type structures. The materials La2 xSrxCo0.5M0.5O4 (M = Fe, Cr) have shown enhanced stability under reducing conditions (10% H2/N2, up to 1000 ºC) with the formation of oxygen deficient compounds, while no evidence for oxygen hyperstoichiometry was observed under oxidizing conditions. Materials such La1.2Sr0.8Co0.5Mn0.5O4.1 and La1.7Sr0.3Co0.5Ni0.5O4.08, however, exhibit oxygen hyperstoichiometry under oxidizing conditions and also withstand reducing conditions via formation of oxygen deficiency. Oxygen vacancies were disordered and confined to the equatorial planes of the single layered structure in all materials, while oxygen hyperstoichiometry was accommodated in the interstitial (0, 0 .5, 0.25) sites of the tetragonal structure. In La1+xSr2 xCoMnO7-δ, oxygen vacancies were confined to the common apex of the double layered structure. The new brownmillerite phase LaSrCoFeO5 was synthesized and fluorination produced the new oxyfluoride LaSrCoFeO5F. Magnetic interactions between Co2+(3+) ions and ions such as Fe3+, Mn3+, Cr3+, Ni2+ in different perovskite-type structures were also studied and a range of magnetically ordered materials, at low and room temperatures, were investigated.

Type of Work:Ph.D. thesis.
Supervisor(s):Greaves, Colin
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Chemistry
Subjects:QD Chemistry
Institution:University of Birmingham
ID Code:625
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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