Synthesis, structure and oxygen thermally programmed desorption spectra of La1-xCaxAlyFe1-yO3-δ 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. 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, whilst 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 of oxygen revealed that chemical desorption of oxygen in the temperature range 200-1000 C proceeded in two desorption peaks. The low-temperature alpha-peak (in the 200-550 C temperature range) was brought about by oxygen liberated from oxygen vacancies; the high-temperature beta-peak (in the 550-1000 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. Al3+ ions restricted, probably for kinetic reasons, the reduction of Fe4+ and the high-temperature oxygen desorption associated with it. 15 refs.