Preparation method investigation and structure identification by XRD and Raman techniques for A₂B₂O₇ composite oxides

Abstract

A2B2O7 oxides comprise four subcrystalline phase structures, which include the layered perovskite, pyrochlore, disordered defect fluorite, and rare‐earth C‐type structures. Herein, a series of A2B2O7 oxides have been synthesized using simple methods, and the X‐ray diffraction (XRD) and Raman spectroscopic characteristics of their subcrystalline phase structures are systematically summarized. It was found that the rA/rB ratio can be used to correctly determine the subcrystalline phase structure of the A2B2O7 oxides when the A‐site ions are rare‐earth ions. Although the A‐site ions are the main‐group metal ions, the rA/rB ratio cannot be used to accurately determine probably due to f electrons. Raman spectroscopy proves to be the most effective method for determining the subcrystalline phase structure, which is followed by XRD. The characteristic Raman spectral bands of disordered defect fluorites are closely related to their B‐site ion oxides with fluorite phase structures. For these A2B2O7 oxides with rA/rB ratios located at the edge value possessing the same elemental composition, different subcrystalline phase structures have been prepared by adopting different synthesis methods and calcination temperatures. The crystal phase of A2B2O7 oxides comprising two types of subcrystalline structures with a lower disorder degree is more stable at high temperatures.