Crystallographic, structural, and electrical characteristics of a new molybdate crystalline phase within the NaNbO₃-BaNb₂O₆-MoO₃ system

The tetragonal tungsten bronze structural type (TTB) is one of the interesting family where the structure is compatible with a wide variety of cationic substitution that permits tailoring physical properties including ferroelectricity, piezoelectricity, nonlinear optics, and energy storage properties. Over the past years, major consideration was devoted to niobate based- tetragonal tungsten bronze, as promising materials for electronic components. In the present work, the conventional solid-state method was used to prepare samples within the NaNbO₃−BaNb₂O₆−MoO₃ system. The structural refinement performed by the Rietveld method and using GSAS-II software, showed that this sample is constituted by two crystalline phases namely Ba₂Mo_0.80NaNb_4.20O₁₅ and Ba₂Mo_0.40NaNb_4.60O₁₅. The first one crystallizes in the P4bm- tetragonal structure with cell parameters of a = b = 12.3762Å and c = 3.98587Å. However, the second was found to crystallize in the orthorhombic symmetry with Pba2 as space group and a = 12.5260 Å, b = 12.42936 Å, and c = 3.97861 Å. Raman spectroscopy was used to get complementary comments on the structure of the BNMO ceramic. The dielectric measurements were carried out from 25 °C to 550 °C and in a frequency range of (10 Hz–1 MHz).