同步辐射软X-ray吸收精细结构-研究生组会presentation课件.ppt

1、一、XAFS技术简介uXAFS定义：X射线吸收精细结构 X-ray Absorption Fine StructureuXAFS是用于描绘局部结构最强有力的工具之一。在此技术中，我们将X射线能量调整至与所研究的元素中内电子层一致，再用于探测样品，然后监测吸收的X射线数量与其能量的函数关系。随着同步辐射的发展，XAFS已成为研究凝聚态物质，特别是长程无序,短程有序的非晶态、液态、熔态的原子、电子结构的有力工具。一、XAFS技术简介uXAFS分类：EXAFS XANES l EXAFS(Extended x-ray absorption fine structure)元素的X射线吸收系数 在吸收边

2、高能侧 30-1000 eV 范围出现的振荡，称为EXAFS。它含有吸收原子的近邻原子结构信息（近邻原子种类、配位数、配位距离等）。EXAFS方法的特点主要是可以对不同种类原子分别进行测量，给出指定元素原子的近邻结构,也可区分近邻原子的种类。()E一、XAFS技术简介l XANES（X-ray absorption near edge structure）元素的X射线吸收系数 在吸收边高能侧 30-50 eV 范围出现的振荡，称为EXAFS。它不仅反映吸收原子周围环境中原子几何配置，而且反映凝聚态物质费米能级附近低能位的电子态的结构，因此成为研究凝聚态物质的有用工具。XANES作为研究和表征催

3、化剂的有力工具，可以确定价态、表征d-带特性、测定配位电荷、提供包括轨道杂化、配位数和对称性等结构信息。()E二、文献阅读the Brazilian Synchrotron Light Laboratory(LNLS,Brazil),under proposals D04B-XAFS1-13435 二、文献阅读1、样品制备u 样品：u 制备方法：l microwave assisted hydrothermal homogeneous co-precipitation（HMW）nanostructured spheresl cation complexation（CC）nanopowders二

4、、文献阅读2、XANES studiesNormalized XANES spectra obtained at room temperature atthe Ce L3-edge for(a)TbDC10-HMW(b)TbDC10-CC(c)TbDC20-HMW(d)TbDC20-CCthe experimental data(empty circles),four Gaussian peaks(AD),and one arctangent function obtained by least-squares fitting and the sum of all five functions

5、(continuous black lines).二、文献阅读2、XANES studiesFraction of Ce present as Ce3+in TbDC10 and TbDC20 samples at room temperature,estimated from fittings to the Ce L3-edge XANES spectra二、文献阅读2、XANES studiesNormalized XANES spectra obtained at room temperature in air at the Tb L3-edge for(a)TbDC10 and(b)T

6、bDC20 obtained by cation complexation(black line)and microwave assisted hydrothermal homogeneous co-precipitation(red line).Spectra of Tb(NO3)3(Tb3+;dotted line)are included for comparison.二、文献阅读2、situ XANES studiesFraction of Ce present as Ce3+in TbDC10 and TbDC20 samples under reducing and oxidizi

7、ng conditions at 500,estimated from fittings to the Ce L3-edge XANES spectra二、文献阅读2、situ XANES studiesNormalized XANES spectra at the Tb L3-edge obtained at 500 under(a)reducing and(b)subsequent oxidizing conditions for TbDC10-HMW(continuous red line),TbDC20-HMW(dotted red line),TbDC10-CC(continuous

8、 blue line)and TbDC20-CC(dotted blue line).Spectra for Tb(NO3)3(Tb3+;dotted black line)are included for comparison.二、文献阅读3、Preliminary in situ EXAFS studiesFourier Transforms(FTs)of the EXAFS signal corresponding to the Tb L3-edge for TbDC20 samples synthesized by the CC(a)and HMW(b)methods at room

9、temperature(blue line),at 500 in 5%H2/He(red line)and at 500 in air(green line).The calculated FT of the theoretical EXAFS signal of a fluorite-like structure is included(black dotted line)for comparison.二、文献阅读3、Preliminary in situ EXAFS studiesFourier Transforms(FTs)of the EXAFS signal correspondin

10、g to the Ce L3-edge for TbDC20 synthesized by CC(a)and HMW(b)and recorded in air at room temperature(blue line)and in 5%H2/He(red line)and in synthetic air(green line),both at 500.For comparison,the theoretical FTs for CeO2 with the space group(dashed line)and the experimental FTs of CeO2 synthesize

11、d by the HMW method(black line)are also included.二、文献阅读4、总结l Ce与Tb的L3边的XANES实验表示了含Tb样品中还原形成的Tb3+比Ce3+更容易，支持了以前报道过的Tb3+在某种程度上加固了Ce4+离子。l 初步的Ce和Tb的L3边EXAFS图谱表示了Tb的氧化态的变化对阳离子周围局部序有影响，但对Tb的影响比Ce更大。EXAFS图谱表示Tb周围的局部序在纳米粉末与纳米球之间存在质的差异。在室温与高温下都做了还原和氧化的EXAFS实验。纳米球结构下的结构无序的程度比纳米粉末更显著。在所有的情况下，阳离子局部序都比荧石结构有着质的不同。