Thermal stability and high temperature polymorphism of topochemically-prepared Dion-Jacobson triple-layered perovskites

The thermal stability of six Dion-Jacobson-related triple layered perovskites, ACa2Nb3O10 (A = H, NH4, Li, Na, K, CuCl), was explored to 1000 °C. Each compound was produced topochemically by low-temperature (<500 °C) ion exchange from RbCa2Nb3O10. The thermal behavior of the series was examined by variable temperature X-ray powder diffraction experiments in tandem with thermogravimetric analysis and differential scanning calorimetry. Five of the species were found to be low temperature/metastable phases, decomposing below 900 °C, where the stability of the series decreased with decreasing interlayer cation size. The compounds, A = Li, Na, K, exhibited high temperature polymorphism, with a completely reversible transition evident for KCa2Nb3O10.