Influence of processing conditions on crystal structure of BiNbO4 ceramics

Bismuth niobate (BiNbO4) has attracted attention as a low-fired ceramics with promising microwave application potential. It belongs to the bismutocolumbite oxides with similarly to scheelite-like stibiotantalite structure (SbTaO4) A3+B5+O4. The aim of the present research was to fabricate BiNbO4 ceramics by solid state reaction route from the mixture of simple oxides viz. Bi2O3, and Nb2O5, and study its phase composition as well as crystal structure by X-ray diffraction method. The Rietveld refinement method was utilized for analysis of diffraction patterns. It was found that the mass change effects finished at temperature T=500°C and the total mass change was about Δm=-0.78%. It was found that BiNbO4 ceramics sintered in ambient air exhibited multiphase composition, i.e., apart from the major α-BiNbO4 phase, the orthorhombic Bi5Nb3O15, Bi3Nb17O47 and cubic Bi3NbO7 phases were present. An increase in sintering temperature caused an increase in the amount of major α-BiNbO4 phase which adopted an orthorhombic symmetry described well by Pnna(52) space group.