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Free keywords:
Ruddlesden-Popper phases; Perovskite phases; Structure elucidation; Phase transitions
Abstract:
In this contribution low temperature formation of Ruddlesden–Popper (RP)-type layered La2CoO4±δ perovskite was optimized via in situ X-ray powder diffraction (XRPD). Starting from LaCoO3 a stoichiometric transformation to La2CoO4±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 La2CoO4±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 La2CoO4±δ were determined. Systematic experiments reveal that 650 °C is the optimal temperature for the complete transformation of LaCoO3 into La2CoO4±δ and CoO/Co0. The information was then transferred to realize bulk synthesis of La2CoO4±δ at 650 °C in a tube furnace without extended heat treatments at elevated temperatures.
