纳米催化剂Pt/C的X射线衍射线形分析

X-ray diffraction line-profile analysis of nanocatalyst Pt/C

X射线衍射线形与晶体材料的微观结构密切相关.在晶粒尺寸衍射线形和微应变衍射线形可由Voigt函数近似描述的前提下,本文较详细地论述了由X射线衍射线形分析获取晶粒尺寸和位错等微观结构信息的方法.采用这种方法,对乙二醇还原法制备的Pt/C催化剂进行了X射线衍射线形分析.样品晶粒尺寸分布的对数正态均值为0.95 nm,对数正态方差为0.37.X射线衍射线形分析所得晶粒尺寸分布与透射电镜的测试结果符合较好.对样品的衍射线形积分宽度进行细致的比较,发现存在各向异性展宽现象.如果衍射线的各向异性展宽主要是由伯格斯矢量为1/2〈110〉的位错引起,可进一步计算位错密度值.结果表明,位错组态无论是螺型位错还是刃型位错,位错密度值的量级均约为1015/m2.

X-ray diffraction line-profile is closely related with microstructure of crystalline material. Under the assumption that crystallite size and microstrain diffraction line-profiles can be approximated with the Voigt function, the method of X-ray diffraction line-profile analysis, used to determine, microstructural information of crystallite size and dislocation, is described in detail. With this procedure, nanocatalyst Pt/C produced by glycol synthesis method is investigated by X-ray diffraction line-profile analysis. The lognormal mean of the sample crystallite size is 0.95 nm, and the lognormal variance is 0.37. The crystallite size distribution from X-ray diffraction line-profile analysis is well consistent with transmission electron microscopy observations. The integral breadths of the sample diffraction line-profiles are compared, anisotropic diffraction line broaden- ing is found. If such a phenomenon is caused by the dislocations of Burgers vector 1/2（110）, the value of the dislocation density can be calculated. The results show, whether the dislocation character is screw or edge, the order of the dislocation density is about 1015/m^2.