铋掺杂钛酸锶陶瓷晶界纳米颗粒的平衡形状分析

Analysis on Equilibrium Shape of Nano-precipitations at Grain Boundaries in Bismuth Doped Strontium Titanate Ceramics

利用透射电子显微镜对铋掺杂钛酸锶陶瓷晶界结构进行表征,在某些晶界处观测到不连续分布的纳米颗粒,尺寸为十几至一百多纳米,形状各有迥异.能谱分析结果表明这些纳米颗粒为金属铋.采用Cahn-Hoffmanξ矢量构建模型可以把晶界纳米颗粒形状定性地描述为相邻晶粒内两个独立平衡形状(Wulff形状)在晶界处的交集,两个平衡形状中心间的距离与晶界能相当.晶界纳米颗粒的平衡形状与两个独立平衡Wulff形状本身特征、相邻两侧晶粒的晶体学取向、晶界能和晶界的倾转以及颗粒本身尺寸等因素相关.

Grain boundary structures in Bi-doped strontium titanate ceramics were characterized by transmission electron microscope（TEM）.Discontinuous nano-precipitations（NPs）,whose sizes ranged from ten to over one hundred nanometers,were observed aligning along some grain boundaries.The composition of NP was detected as pure bismuth by spatial difference energy dispersive X-ray spectra（EDXS） method.Different shapes with facets were possessed by the NPs,indicating the anisotropy of NPs.The Cahn-Hoffman ξ-vector construction based on anisotropic surfaces was successfully applied to qualitatively describe the equilibrium shape of NP,which can be regarded as the intersection of two Wulff shapes at the grain boundaries.The distance between the two Wulff shapes centers is equal to the grain boundary energy.The Wulff shape itself,orientation of neighboring grains,grain boundary energy and grain boundary twist are considered as the important factors to affect the equilibrium shape of NP.Besides these,the size of NP will also influence the faceting of NP.This work is helpful to deepen the understanding of the microstructure evolvement during the sintering.