Combining Raman spectroscopy and synchrotron X‐ray diffraction to unveil the order types in A3CaNb2O9 (A = Ba, Sr) complex perovskites

The structural ordering process in complex perovskites has a pivotal role for tuning many physical properties for broad applications, ranging from microwave technology, proton‐conduction, multiferroicity, and so on. Therefore, the characterization of order type in these materials is essential for designing new devices with high‐performance. Here, the coexistence of B‐site 1:1 and 1:2 order types in mixed ordered A3CaNb2O9 (A = Ba, Sr) perovskite was investigated by combining Raman spectroscopy and high‐resolution synchrotron X‐ray powder diffraction. High‐wavenumber interval 700–825 cm−1 exhibits two bands concerning the symmetric breathing modes of [NbO6] octahedra in A3CaNb2O9, which were ascribed to the 1:1 and 1:2 domain regions in coexistence. This model was fully corroborated using two phases for describing the synchrotron X‐ray pattern of the Ba3CaNb2O9 sample. Therefore, the Raman spectroscopy can be indeed applied as a rapid tool for probing the achievement of ordered, partially ordered, or disordered structures in complex perovskites. For the first time, BaLaCaNbO6 was synthesized and structural characterized, being indexed by the monoclinic unit cell belonging to the space group I2/m. We have investigated the Raman spectra of complex perovskites and their nonstoichiometric variations in order to clarify the occurrence of different order types as induced by thermal treatments. High resolution synchrotron X‐ray powder diffraction unveiled the coexistence of two order types in mixed ordered Ba3CaNb2O9, that is, 1:1 Ca/Nb (cubic) and 1:2 Ca/Nb (trigonal). Our result has consequences for using the Raman technique as a quality control tool during the preparation of niobate‐based microwave ceramics.