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

A(2)B(2)O(7) 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 A(2)B(2)O(7) 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 r(A)/r(B) ratio can be used to correctly determine the subcrystalline phase structure of the A(2)B(2)O(7) oxides when the A-site ions are rare-earth ions. Although the A-site ions are the main-group metal ions, the r(A)/r(B) 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 A(2)B(2)O(7) oxides with r(A)/r(B) 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 A(2)B(2)O(7) oxides comprising two types of subcrystalline structures with a lower disorder degree is more stable at high temperatures.