均匀共沉淀法制备钛酸钡-钡铁氧体核-壳结构粒子

Preparation of BaTiO_3-BaFe_(12)O_(19) Core-Shell Structure Particles by Homogeneous Coprecipitation

用均匀共沉淀法制备了钛酸钡-钡铁氧体核-壳粒子,研究了沉淀反应温度、尿素/金属离子摩尔比值(R)和BaTiO3浓度对核-壳粒子形貌和结构的影响,探讨了钛酸钡-钡铁氧体核-壳粒子在焙烧时的形成过程及其磁性能.采用透射电子显微镜(TEM)、X射线衍射(XRD)分析仪对钛酸钡-钡铁氧体前驱物核-壳粒子及钛酸钡-钡铁氧体核-壳粒子的形貌和结构进行了表征,采用振动样品磁强计(VSM)研究了钛酸钡-钡铁氧体核-壳粒子的磁性能.结果表明:当沉淀反应温度为100°C,R为180,BaTiO3浓度为2.5g·L-1时,金属离子沉淀完全,得到的钛酸钡-钡铁氧体前驱物核-壳粒子包覆层均匀、完整、光滑,厚度约为10nm.过高的温度和R值都会导致大量独立颗粒杂质的生成;随着BaTiO3浓度的增大,包覆层厚度有减小的趋势.当焙烧温度为900°C时,壳层中开始形成BaFe12O19相,其形成过程为晶态的α-Fe2O3和BaCO3首先生成中间相BaFe2O4,然后由BaFe2O4和α-Fe2O3反应得到最终的BaFe12O19.当焙烧温度为1000°C时,壳层完全转化为BaFe12O19相.随着焙烧温度从900°C升高到1000°C,所得BaTiO3-BaFe12O19核-壳粒子的饱和磁化强度从16.5A·m2·kg-1增加到39.5A·m2·kg-1,矫顽力从340kA·m-1略微降低到316kA·m-1.

BaTiO3-BaFe12O19 core-shell structure particles were obtained using the homogeneous coprecipitation method. The effects of temperature, molar ratio of urea to metal ions （R）, and BaTiO3 concentration on the morphology and structure of the core-shell particles were investigated. The mechanism of formation for the BaTiO3-BaFe12O19 core-shell structure particles and their magnetic property were also discussed. Transmission electron microscopy （TEM） and X-ray diffraction （XRD） were used to characterize the morphology and structure of the BaTiO3-BaFe12O19 precursor core-shell structure particles and the BaTiO3-BaFe12O19 core-shell structure particles. A vibrating sample magnetometer （VSM） was used to characterize the magnetic property. The results indicated that the obtained sample possessed an integrated and smooth shell of about 10 nm in size and the metal ions precipitated completely after homogeneous coprecipitation when the sample was synthesized under the following conditions： 100 °C, R=180, and a BaTiO3 concentration of 2.5 g·L-1. A large amount of free particle impurities appeared if the temperature and R value were too high. The shell thickness of the BaTiO3-BaFe12O19 precursor core-shell structure particles tended to decrease as the BaTiO3 concentration increased. The BaFe12O19 phase in the shell began to form when the calcination temperature reached 900 °C. The mechanism of formation included the formation of BaFe2O4 by the reaction of crystalline α-Fe2O3 and BaCO3 initially, and this was followed by the reaction of BaFe2O4 and α-Fe2O3 to form the final BaFe12O19. As the temperature increased to 1000 °C, a complete BaFe12O19 shell was obtained. The saturation magnetization and coercivity of the BaTiO3-BaFe12O19 core-shell structure particles increased and decreased from 16.5 to 39.5 A·m2·kg-1 and from 340 to 316 kA·m-1, respectively, as the calcination temperature increased from 900 to 1000 °C.