Nanopowder preparation and dielectric properties of a Bi₂O ₃-Nb₂O₅ binary system prepared by the high-energy ball-milling method

The high-energy ball-milling (HEM) method was used to synthesize the compositions of BiNbO₄, Bi₅Nb₃O₁₅, and Bi₃NbO₇ in a Bi₂O₃-Nb ₂O₅ binary system. Reagent Bi₂O₃ and Nb₂O₅ were chosen as the starting materials. The X-ray diffraction patterns of the three compositions milled for different times were studied. Only the cubic Bi₃NbO₇ phase, Nb ₂O₅, and amorphous matters were observed in powders after being milled for 10 h. After heating at proper temperatures the amorphous matters disappeared and the proleptic phases of BiNbO₄ and Bi ₅Nb₃O₁₅ could be obtained. The Scherrer formula was used to calculate the crystal size and the results of nanopowders are between 10 and 20 nm. The scanning electron microscopy photos of Bi ₃NbO₇ powders showed drastic aggregation, and the particle size was about 100 nm. The dielectric properties of ceramics sintered from the nanopowders prepared by HEM at 100-1 MHz and the microwave region were measured. Bi₃NbO₇ ceramics showed a good microwave permittivity ε_r of about 80 and a Q × f of about 300 at 5 GHz. The triclinic phase of BiNbO₄ ceramics reached its best properties with ε_r=24 and Q × f=14 000 GHz at about 8 GHz.