Structural, morphological and dielectric properties of BiNbO4 ceramics prepared by the sol-gel method

• The thermal treatment at 1200 °C generates a non-stoichiometric secondary phase.
• The secondary phase Bi3.54Nb7.09O22.7, is responsible for the highest Q × f and density.
• The samples with triclinic BiNbO4 have the highest ε′.

BiNbO4 ceramic powders were prepared using the sol-gel method. The fine particles were pressed into cylinders and, then, they were treated at temperatures between 500 and 1150 °C.The structure was studied by X-ray diffraction and Raman spectroscopy and the morphology was observed by scanning electron microscopy.The measurements of the complex permittivity were made in a resonant cavity operating at 2.7 GHz, using the small perturbation method.The reversible phase transformation between β-BiNbO4 and α-BiNbO4 was observed.The density, dielectric constant (ε') and the dielectric loss (tg δ) of the prepared powders increase with the sintering temperature, and the sample treated at 1150 °C shows the highest ε' and the highest Q × f.

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