Synthesis And Characterization Of Nanosized Barium Titanate Powders

Nano-sized BaTiO₃ powders were prepared by an alkoxide-hydroxide process and a solvothermal recrystallization route, respectively.Firstly, in the alkoxide-hydroxide process Ba(OH)₂·8H₂O, Ti(i-OC₃H₇)₄ and hydrous ethanol were acted as barium source, titanium source and reactive medium, respectively. The results showed that higher reaction temperature or titanium alcoholic concentration tended to increase the particle size of powders and siutbale reaction time and Ba/Ti were benifit to obtain finer powders. Under refluxing conditions, when added Ba(OH)₂·8H₂O to Ti alcoholic solution and reacted for 8h, nanosized BaTiO₃ particles with mean size of-13 nm, few aggregates and cubic structure was obtained. HRTEM revealed single-crystal particles existed in powders. Calcining the as-prepared powders at 800, tetragonal BaTiO₃ (c/a=1.0097) with particle size of 60nm could be obtained.Furthmore, BaTiO₃ powders were synthesized by a modified AH route, that was replacing part of the Ba(OH)₂·8H₂O by hydrous Ba(OH)₂ to change the water content of the reaction system. It was found that the powders particle size increased with reduce of R in barium sources and AH route was a sol-precipitation process. Hydrolysis of titanium alkoxide depended on the release of water molecules in situ Ba(OH)₂·8H₂O dissolved in the alcoholic solution. Thus, smaller R in barium source or lower reaction temperature would slow down the hydrolysis rate of Ti alkoxide.In order to process the crystallinity of the BaTiO₃ obtained by AH process, a novel solvothermal recrystallization (SV) route was developed to obtain finer BaTiO₃ nanocrystals. The results showed that the SV-BaTiO₃ powders had much less hydroxyl lattice defects, higher purity and better crystallinity than AH-BaTiO₃. Higher solvothermal treatment temperature and time were favorable for the preparation of nice crystallinity and larger particle size of BaTiO₃ powder. Higer Ba/Ti of the precursor was benefit to produce tetragonal BaTiO₃. When fixed the ammonia/enthnal of 2/3, Ba/Ti molar ratio in precursor of 2, solvothermal temperature of 190℃, recrystalling time of 3h and the concentration of BaTiO₃ slurry of 0.4g/ml, tetragonal BaTiO₃ powders with mean size of 25nm could be obtained.Finally, the sintering reactivity and delectric properties of BaTiO₃ ceramic were investigated. It was found that AH-BaTiO₃ ceramics had a relative low sintering temperature and could be sintered at 1000℃with relative density of 94.5%, which was lower than that obtained by solvothermal recrystallization route. Compared with the untreated powders, due to the less hydroxyl lattice defects content and higher density of crude pellet, the dielectric constant of BaTiO₃ ceramics increased from 2055 to 2608 at room temperature, while the delectric loss reduced from 0.035 to 0,02,...