X射线衍射（PPT课件讲稿）X-ray Diffraction（XRD）

Characteristic X-ray Lines Kβ and o2 will cause Extra peaks in XRD pattern, but can be eliminated by adding Ka1filters <0.001A ---- is the mass Ko absorption coefficient of zr 久=2dsin WAVELENGTH (angstroms Spectrum of Mo at 35kV

Characteristic X-ray Lines Spectrum of Mo at 35kV K1 K K I  (Å) <0.001Å K2 K and K2 will cause Extra peaks in XRD pattern, but can be eliminated by adding filters. ----- is the mass absorption coefficient of Zr. =2dsin

Absorption of X-ray All x-rays are absorbed to some extent in passing through matter due to electron ejection or scattering The absorption follows the equation I=Io 0e( where I is the transmitted intensity Io is the incident intensity x is the thickness of the matter u is the linear absorption coefficient u(element dependent) p is the density of the matter; (u/p)is the mass absorption coefficient(cm2/gm)

• All x-rays are absorbed to some extent in passing through matter due to electron ejection or scattering. • The absorption follows the equation where I is the transmitted intensity; I0 is the incident intensity x is the thickness of the matter;  is the linear absorption coefficient  (element dependent);  is the density of the matter; (/) is the mass absorption coefficient (cm2/gm). Absorption of x-ray x x I I e I e             − − = 0 = 0 I0  I ,  x

Effect of l, u/p(z)and t on Intensity of Diffracted X-ray Xray source Mo wavelength= 0.07 nm incident beam crystal diffracted beam film Specimen water Thickness =4000 um Intensity of Transmitted Xrays=96.08% http://www.matter.orguk/diffraction/x-ray/x_ray_diffraction.htm

Effect of , / (Z) and t on Intensity of Diffracted X-ray incident beam diffracted beam film crystal http://www.matter.org.uk/diffraction/x-ray/x_ray_diffraction.htm

Absorption of x-ray · The mass absorption coefficient is also wavelength Absorption edges dependent. Discontinuities or ∥P Absorption edges" l can be seen on the absorption coefficient VSwavelength plot. · These absorption edges mark the point 00.102030405060708091.01.11.21.31415 Wavelength(A) on the wavelength scale where the x Absorption coefficients of Pb, rays possess showing k and l absorption edges sufficient energy to eject an electron from one of the shells

• The mass absorption coefficient is also wavelength dependent. • Discontinuities or “Absorption edges” can be seen on the absorption coefficient vs. wavelength plot. • These absorption edges mark the point on the wavelength scale where the x￾rays possess sufficient energy to eject an electron from one of the shells. Absorption of x-ray Absorption coefficients of Pb, showing K and L absorption edges.  / Absorption edges

Filtering of X-ray The absorption behavior of X-ray by matter can be used as a means for producing quasi monochromatic x-ray which is essential for XRD experiments The rule :Choose for the filter an element whose K absorption edge is just to the short wavelength side of the Ko line of the target material arget g materi Filter Pd|Nb.Ni‖co‖Fe Mn material

Filtering of X-ray • The absorption behavior of x-ray by matter can be used as a means for producing quasi￾monochromatic x-ray which is essential for XRD experiments. • The rule: “Choose for the filter an element whose K absorption edge is just to the short￾wavelength side of the K line of the target material.” Target material Ag Mo Cu Ni Co Fe Cr Filter material Pd Nb, Zr Ni Co Fe Mn V