Papers by Keyword: Sol-Gel Auto-Ignition Synthesis

Abstract: The Nb and Co doped barium titanate was synthesized by sol-gel auto-ignition synthesis process (abbreviated SAS) and compared with the doped powder of the same composition prepared by conventional ball milling process. The phase structure, morphology of the two as-obtained powders and correlative dielectric properties of sintered BaTiO3-based ceramics were measured. The XRD analysis demonstrated that the SAS powder was the Ba(M0.047Ti0.953)O3(M=Nb, Co) solid solution based on BaTiO3; it further suggested that Nb and Co cations could replace the Ti ions and reach reciprocal balance of acceptors and donors during the decomposition step of the organic fuel by igniting the dried gel. TEM observation showed that the Ba(M0.047Ti0.953)O3(M=Nb, Co) particles were spherical with the size ranged from 30 to 110nm. Furthermore, it was found that the value of the Curie temperature of both the doped powders was being lowered in comparison with pure BaTiO3 (Tc≈128°C ); and the dielectric constant at room temperature of the SAS powder was 5840, which was much higher than that of the conventional ball milling doped powder(3013). It was attributed to the maximum homogeneous distribution of dopants in Ba-Ti initial solution at atomic level via the SAS process.

Abstract: Non-agglomerated nano-sized BaTiO3 powders were prepared by a 3 step decomposition of barium titanyl citric acid chelate derived from Ba(NO3)2-TiO(NO3)2-citric acid-NH4NO3 based complex compound system. The 1st step was the thermal treatment of chelate wet gel at 150°C for 40min to remove water and non-bridging hydroxyl groups and to form expanded gel intermediate. The 2nd step was the decomposition of the organic fuel by igniting expanded gel intermediate at 300°C. The 3rd step was the formation of the high purity BaTiO3 by calcining the decomposed powders at 700°C for 2 hours. The most expanded gel intermediate was found to be a decisive factor for the elimination of hard agglomerate. In addition, the initial oxidant/fuel molar ratio was shown to strongly influence the characteristics of the powders thus obtained. The optimum oxidant/fuel value was 3 for obtaining non-agglomerated pure BaTiO3 powders with a particle size of 50 nm. The agglomerate degree of BaTiO3 powders was determined by particle morphology and uniformity of the green compact microstructure observed by field emission scanning electron microscopy and scanning electron microscope.