纳米BaTiO_3陶瓷的超高压烧结

Fabrication of Nanocrystalline BaTiO_3 Ceramics by Ultra-High Pressure Sintering

将10 nm钛酸钡粉在6 GPa超高压条件下进行烧结,得到了晶粒大小约为30 nm的钛酸钡陶瓷。用扫描电子显微镜和原子力显微镜观测了样品的微观结构。研究表明,由于超高压能够压碎纳米粉体中的团聚体,而且能增加烧结的驱动力,降低成核的势垒,从而使成核速率增加;同时由于扩散能力的降低而使生长速率减小,所以超高压烧结能在较低的温度和较短的时间内得到致密的纳米陶瓷。用压电力显微镜对样品的压电性能进行了检测。在30 nm钛酸钡陶瓷的不同区域内,都存在完整的压电响应回线,说明在30 nm钛酸钡陶瓷中存在压电性。此外,由于超高压的还原性气氛,使钛酸钡陶瓷在烧结过程中产生了氧空位,氧空位俘获电子而形成F+色心,使钛酸钡陶瓷颜色变黑。

10nm raw BaTiO3 powder was sintered by ultra-high pressure assisted method at 6GPa.The grain size of sintering samples is about 30nm.The microstructures of sintering samples were studied by scanning electron microscope and atomic force microscopy.The results indicated that owing to the ultra-high pressure,the agglomerates in nano powders were broken down,and the densification was significantly increased.Additionally,the nucleation rate was increased due to reducing the energy barrier for nucleation and the growth rate was reduced due to the decrease of diffusivity.Thus,ultra-high pressure enables the specimen to be fabricated under relatively lower temperature and shorter period that assures to obtain dense nanocrystalline ceramics.The piezoelectricity was investigated by piezoelectric force microscopy.There existed some full piezoresponse hysteresis loops at different areas in 30nm BaTiO3 ceramics,indicating the presence of piezoelectricity.In addition,oxygen vacancies were produced in strongly reducing atmosphere during ultra-high pressure sintering.F＋ centers were formed because oxygen vacancies caught electrons,and therefore,the color of BaTiO3 ceramics became block.