Abstract
This article attempts to study changes in the microstructure of solid solutions with the perovskite structure La0.5Ca0.5Mn0.5Fe0.5O3 under the action of the methane oxidation reaction medium. By the methods of XRD, XPS and HRTEM the initial condition of the structure and the surface of the perovskite were both investigated. A feature of the structure of this solid solution is the presence of planar defects in the direction of the planes (101). After the methane oxidation reaction, a similar study of perovskite structure was conducted to obtain the changes. It was shown that under the action of the reaction medium, Ca1−xMnxO particles form on the surface of the perovskite phase, while planar defects in La0.5Ca0.5Mn0.5Fe0.5O3 structure remain. In situ XRD experiments on perovskite calcination in helium current up to 750 °C showed the formation of a similar Ca1−xMnxO phase on the perovskite surface.
Highlights
Solid solutions with perovskite structure have been intensively studied in recent decades due to a wide and unique set of their physical and chemical properties [1,2,3,4,5]
Measurement of the specific surface area by thermal desorption of argon showed a surface value of 9.3 m2 /g, which is the average value for perovskites synthesized by Pechini method at temperatures of 900 ◦ C [35]
According to XRD pattern (Figure 1) La0.5 Ca0.5 Mn0.5 Fe0.5 O3 is a well-crystallized solid solution with a perovskite structure (PDF Number: 70-2665) having orthorhombic modification, which corresponds to the data obtained in Reference [36] for CaLaMnFeO6 and for La0.6 Ca0.4 Mn1−x Fex O3 [37] structures
Summary
Solid solutions with perovskite structure have been intensively studied in recent decades due to a wide and unique set of their physical and chemical properties [1,2,3,4,5]. Materials based on La1−x Mx MeO3 (M = Ca, Sr, Ba, Me = Mn, Fe, Co) at high temperatures have mixed ionic and electronic conductivity and can be used in high-temperature electrochemical devices such as gas sensors, oxygen permeable membranes and electrodes of solid-state fuel cells and catalysts of high-temperature oxidizing processes [12,13,14]. Catalytic oxidation of methane has been the subject of numerous publications in recent decades [15]
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