Synthesis of CaNb₂O₆ with a Rynersonite-like Structure: Morphology, Rietveld Refinement, Optical, and Vibrational Properties

In this study, we report the easy and low-cost synthesis of calcium niobate (CaNb2O6) with the isomorphic structure of the Rynersonite mineral for CaTa2O6. The samples were prepared by the ball milling method at room temperature at a synthesis time of 0.5, 1, 2, 3, and 4 h. The structural analysis by XRD, Rietveld refinement, and vibrational Raman spectroscopy confirms all diffraction peaks and active mode characteristics of the pure phase of CaNb2O6 for the 3-h and 4-h samples, with a crystallite size of 22.5 and 23.2 nm, respectively. The optical band gap obtained was 3.18(2) eV (3-h sample), lower than the optical band gap for niobium oxide, characteristic of materials with strong photon absorption in the UVA region of the spectrum. The surface analysis by scanning electron microscopy reveals the obtention of several agglomerates of irregular particles ranging in the submicro and micro scales. Therefore, the present approach successfully obtained calcium niobate with the formula CaNb2O6 at a short synthesis time and room temperature.