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

In this contribution low temperature formation of Ruddlesden-Popper (RP)-type layered La2CoO4 +/-delta perovskite was optimized via in situ X-ray powder diffraction (XRPD). Starting from LaCoO3 a stoichiometric transformation to La2CoO4 +/-delta and CoO can be achieved by controlled reduction with H-2. The challenge of this reaction is the use of appropriate amounts of H-2 in a defined temperature region. If the amount of H-2 is too high, complete reduction of the perovskite occurs. If temperatures are not appropriate, intermediate phases seem to hinder the transformation to La2CoO4 +/-delta or lead to a complete decomposition to simple oxides. Based on in situ XRPD experiments, the temperature window and required amount of H-2 for the transformation of LaCoO3 to La2CoO4 +/-delta were determined. Systematic experiments reveal that 650 degrees C is the optimal temperature for the complete transformation of LaCoO3 into La2CoO4 +/-delta and CoO/Co-0. The information was then transferred to realize bulk synthesis of La2CoO4 +/-delta at 650 degrees C in a tube furnace without extended heat treatments at elevated temperatures.