XAFS研究Ni-P和Ni-Ce-P超细非晶合金的退火晶化

采用原子配位分布函数为Gaussian函数Ｐ_G和指数函数P_E直积的非 对称模型进行拟合计算，XAFS定量地研究化学还原法制备的Ni-P和Ni-Ce-P超细非晶合金大 无序度体系中Ni原子的局域环境结构随退火温度升高而产生的变化.结果表明Ni-P和Ni-Ce-P 原样的Ni-Ni配位的平均键长Ｒ_j、配位数N、热无序度σ_T、结构无 序度σ_S分别为0271nm，100，00060nm，0028n 关键词： XAFS Ni-P Ni-Ce-P 超细非晶合金 局域结构

ANNEALED CRYSTALLIZATION OF ULTRAFINE Ni-P AND Ni-Ce-P AMORPHOUS ALLOYS STUDIED BY XAFS

XAFS technique has been used to quantitatively determine the local structure evo lutions of ultrafine Ni-P and Ni-Ce-P amorphous alloys prepared by chemical redu ction during the annealing process.Using an asymmetric atom distribution functio n model of convolution of a Gaussian function P_G and an exponential f unction P_E for XAFS data analysis,we obtained that the average bond l ength Ｒ_j,coordination N,thermal disorder factor σ_T,and s tatic disorder factor σ_S for the Ni-Ni first neighbor shell are 0.27 1nm,10.0,0.0060nm and 0.028nm in the Ni-P and 0.271nm,10.6,0.0070nm and 0.030nm in the Ni-Ce-P initial samples,respectively.It indicates that the σ_S is rather large and about three times larger than that of σ_T.The Ni -P sample crystallized under the annealing temperature of 573K,while the crystal lizing temperature of Ni-Ce-P sample is about 100K higher.The result suggests th at the thermal stability of Ni-Ce-P sample is significantly increased by the add ition of 2% Ce element.After being annealed at 773K,both Ni-P and Ni-Ce-P sample s are fully crystallized as metallic Ni and an amount of crystalline Ni_{3P.Furthermore,we have found that the static disorder σs of Ni-Ni coordination shell is 0.011nm for the Ni-P and still larger for the Ni-Ce-P samp les annealed at 773K,despite their radial distribution functions around Ni atoms are similar to that of Ni foil.It implies that the Ni lattice obtained from the crystallized Ni-P and Ni-Ce-P amorphous alloys is significantly distorted by th e interaction of P element.}