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.