Synthesis, structure and oxygen thermally programmed desorption spectra of La1-xCaxAlyFe1-yO3-delta perovskites

Perovskites La1-xCaxAlyFe1-yO3-delta (x, y = 0 to 1) were prepared by high-temperature solid-state synthesis based on mixtures of oxides produced by colloidal milling. The XRD analysis showed that perovskites La0.5Ca0.5AlyFe1-yO3-delta with a high Fe content (1-y = 0.8-1.0) were of orthorhombic structure, perovskites with a medium Fe content (1-y = 0.8-0.5) were of rhombohedral structure, and perovskite with the lowest Fe content (1-y = 0.2) were of cubic structure. Thermally programmed desorption (TPD) of oxygen revealed that chemical desorption of oxygen in the temperature range from 200 to 1000 degrees C had proceeded in the two desorption peaks. The low-temperature alpha-peak (in the 200-550 degrees C temperature range) was brought about by oxygen liberated from oxygen vacancies; the high-temperature beta-peak (in the 550-1000 degrees C temperature range) corresponded to the reduction of Fe4+ to Fe3+. The chemidesorption oxygen capacity increased with increasing Ca content and decreased with increasing Al content in the perovskites. The Al3+ ions restricted, probably for kinetic reasons, the reduction of Fe4+ and the high-temperature oxygen desorption associated with it. (c) 2006 Elsevier Ltd. All rights reserved.