Syntéza, struktura a kyslíková tepelně programovaná desorpční spektra perovskitů La1-xCaxAlyFe1-yO3-d

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

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Perovskites La1-xCaxAlyFe1-yO3-d (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-d 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 degC had proceeded in the two desorption peaks. The low-temperature alfa-peak (in the 200-550 degC temperature range) was brought about by oxygen liberated from oxygen vacancies; the high-temperature beta-peak (in the 550-1000 degC 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.

Perovskity La1-xCaxAlyFe1-yO3-d (x, y = 0 to 1) byly připraveny vysokoteplotní syntézou v pevné fázi ze směsí oxidů připravených koloidním mletím. Rtg. analýza ukázala, že perovskity La0.5Ca0.5AlyFe1-yO3-d s vysokým obsahem Fe (1 – y = 0.8-1.0) měly orthorhombickou strukturu, perovskity se středním obsahem Fe (1 – y = 0.8-0.5) měly rhombohedrickou strukturu a perovskity s nejnižším obsahem Fe (1 – y = 0.2) měly kubickou strukturu. Tepelně programovaná desorpce (TPD) kyslíku ukázala, že chemická desorpce kyslíku probíhala v teplotním rozsahu od 200 do 1000 degC ve dvou desorpčních pících. Nízkoteplotní alfa-pík (v rozsahu teplot 200-550 degC ) byl způsoben kyslíkem uvolněným z kyslíkových vakancí; vysokoteplotní beta-pík (v teplotním rozsahu 550-1000 degC ) odpovídal redukci Fe4+ na Fe3+. Chemisorpční kyslíková kapacita se zvyšovala s rostoucím obsahem Ca a snižovala se s rostoucím obsahem Al v perovskitech. Al3+ ionty omezovaly, pravděpodobně z kinetických důvodů, redukci Fe4+ a s ní související vysokoteplotní kyslíkovou redukci.

Perovskites La1-xCaxAlyFe1-yO3-d (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-d 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 degC had proceeded in the two desorption peaks. The low-temperature alfa-peak (in the 200-550 degC temperature range) was brought about by oxygen liberated from oxygen vacancies; the high-temperature beta-peak (in the 550-1000 degC 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.

Perovskites; membranes; X-ray methods; powders-solid state reaction; chemisorption

2006

01.01.2006

Elsevier Science

0955-2219

Journal of the European Ceramic Society

26

14

2999–3004

6