Reinvestigation of Dion-Jacobson phases CsCa2Nb 2MO9 (M = Fe and Al)

Abstract

Dion-Jacobson phases CsCa2Nb2FeO9 and CsCa2Nb2AlO9 were reinvestigated by the Rietveld analysis of powder X-ray diffraction (XRD) method, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). These nominal compounds, previously known as the oxygen-deficient layered perovskites with the sequences of NbO6-MO4-NbO6 in tripled slab, in fact, were mixed phases of n = 3 Dion-Jacobson phases and impurities such as Ca2NbFeO6 and Ca3Al2O6. The difference of morphology and chemical in-homogeneity between Dion-Jacobson phases and impurities could be clearly identified by scanning electron microscopy with energy-dispersive X-ray spectroscopy. The chemical composition of CsCa2Nb2FeO9 was calculated into Cs 0.59Ca2.64Nb2.92Fe0.81 in small agglomerate crystals and Cs0.95Ca1.97Nb 3.08Fe0.15 in long plate-like crystals.