Barium niobate formation from mechanically activated BaCO3-Nb2O5 mixtures

The effect of high-energy ball milling and subsequent annealing on a mixture of Nb2O5 and BaCO3 has been investigated. DTA results show that the decomposition temperature of BaCO3 decreases with the increase of ball milling time duration. X-ray diffraction (XRD) measurement indicates that the nanocrystalline powder mixture is produced and no BaNb2O6 is formed during a high-energy ball milling process after milling for 30 h. Significant crystallization of a intermediate Ba5Nb4O15 from the nanocrystalline powder mixture milled for 5, 15, 30 h is observed after annealing at 750 °C, while some amount of BaNb2O6 is formed and Nb2O5 still exists at this temperature. With an increase of calcining temperature, the intensity of the diffraction peaks of the dominating crystalline phase BaNb2O6 clearly increases; the intensity of the diffraction peak of the secondary crystalline phase Ba5Nb4O15 and Nb2O5 obviously decreases. Single phase BaNb2O6 can be obtained for the sample milled for 30 h at 900 °C, which is at least 100 °C lower than that used in the traditional solid-state method. Comparatively, the secondary crystalline phase Ba5Nb4O15 and Nb2O5 exist for the physical mixture at 900 °C. With an increase of ball milling time and holding temperature time, the grain growth slightly increases for the milled powders annealed at 900 °C and the average grain size is about 0.3-0.6 μm.