Alkyl groups effect on the formation of ultrafine Nb2O5-doped SrTiO3 powders by sol-precipitation process

Nb2O5-doped SrTiO3 can be obtained from titanyl acylate precursors by using acetic acid chelating titanium alkoxides in a strong alkaline solution (pH>13) without external heating. Fourier transfer infrared spectroscopy (FTIR), differential scanning calorimetry (DSC)/thermogravimetric analysis (TGA) and X-ray diffraction (XRD) were used to investigate the effects of the alkyl chain length of the alkoxide on the morphology of the powder and its sinterability. It was found that a longer alkyl chain length (Ti(O-n-C4H9)4), and a more electronegative alkoxide group, leads to a slower rate of hydrolyzation, and a slower shift rate in the condensation. Furthermore, less cross-linking of smaller particles is observed. In contrast, a shorter alkyl chain, Ti(OC2H5)4, and a less electronegative alkoxide group, cause much more network cross-linking in the structure of larger particles. Therefore, the particle size of the precursor gel obtained from the longer alkyl chain length alkoxide was smaller, and the formation rate of the powder was quicker. The powder obtained from Ti(O-n-C4H9)4 at boiling contained ultrafine particle sizes (0.03–0.04 μm) and readily sintered at 1150–1250°C.