Low Temperature Formation of Ruddlesden–Popper-Type Layered La2CoO4±δ Perovskite Monitored via In Situ X-ray Powder Diffraction

Article abstract of DOI:10.1002/ejic.201801162

In this contribution low temperature formation of Ruddlesden–Popper (RP)-type layered La₂CoO_4±δ perovskite was optimized via in situ X-ray powder diffraction (XRPD). Starting from LaCoO₃ a stoichiometric transformation to La₂CoO_4±δ and CoO can be achieved by controlled reduction with H₂. The challenge of this reaction is the use of appropriate amounts of H₂ in a defined temperature region. If the amount of H₂ is too high, complete reduction of the perovskite occurs. If temperatures are not appropriate, intermediate phases seem to hinder the transformation to La₂CoO_4±δ or lead to a complete decomposition to simple oxides. Based on in situ XRPD experiments, the temperature window and required amount of H₂ for the transformation of LaCoO₃ to La₂CoO_4±δ were determined. Systematic experiments reveal that 650 °C is the optimal temperature for the complete transformation of LaCoO₃ into La₂CoO_4±δ and CoO/Co⁰. The information was then transferred to realize bulk synthesis of La₂CoO_4±δ at 650 °C in a tube furnace without extended heat treatments at elevated temperatures.