Mohamed Anis Silakhal Calcination temperatures beyond 600°C can lead to unintended side reactions. At higher temperatures,perovskite may decompose or react with impurities. in your case, the formation of CeO₂ (cerium dioxide) and Fe₂O₃ (iron(III) oxide) suggests that the perovskite partially decomposed or reacted with other species.

• Boumaza, S., Boudjellal, L., Brahimi, R., Belhadi, A., & Trari, M. (2020). Synthesis by citrates sol-gel method and characterization of the perovskite LaFeO 3: application to oxygen photo-production. Journal of Sol-Gel Science and Technology, 94, 486-492.
• Zhang, Z., Zhang, H., Hou, Y., Liu, P., Hao, X., Liu, Y., ... & Guo, J. (2022). One-step synthesis of CeFeO 3 nanoparticles on porous nanocarbon frameworks derived from ZIF-8 for a boosted oxygen reduction reaction in pH universal electrolytes. Journal of Materials Chemistry A, 10(24), 13013-13020.

Dear Mohamed Anis Silakhal

A useful reference is DOI:10.3390/catal7020045 Aqueous and Surface Chemistries of Photocatalytic Fe-Doped CeO2 Nanoparticles, January 2017, Catalysts 7(2):45. (It's available for free download.)

Please pay attention in particular to figures 2 and 3 there, charting respectively the stability of Ce species and of Fe species as a function of temperatures and oxygen partial pressures. At 600 degC, practically all Ce is in the 4+ state unless -logP(O2) in atm is 30, and at the same time for mostly Fe(3+) you need -logP(O2) < 22. Obviously the two conditions are incompatible assuming the authors' calculations are correct (I didn't attempt to check).

So, should we give up? Not so fast. The product of Ce2O3 and Fe2O3 should have extra stability relative to the combination of CeO2 and either Fe2O3 or FeO, because of what I would call simplistically acid-base affinity. Ce2O3 is a moderately basic oxide, much more than CeO2, while Fe2O3 is a slightly acidic one (FeO is moderately basic). So their reaction should have a significant negative free energy of formation, and the product may well have some range of stability. However, in order to give yourself the best chance, you should try to reach the desired -logP(O2) of roughly 26 +/- 4 by working in a "buffered" oxygen concentration, probably in a CO2/CO atmosphere. I'll leave to you to find the optimal ratio of CO2 to CO (I'm sure there is significant literature about this system, which is sometimes called an oxygen buffer).

Dear Silakhal,

During calcination, the transition elements i.e Ce and Fe is oxidised partially and changed their oxidation states. So they formed two different products.