Theoretical Analysis Of Rietveld Method And Its Application In Phase Analysis

The Rietveld method of X-ray polycrystalline diffraction is a widely used method in the field of material structure analysis.In this paper,the principle of Rietveld method is clearly explained by the simulation of XRD pattern,and the crystal structure of some alloy phases was studied by this method.1.Simulation of the XRD patternAccording to the theory of X-ray diffraction intensity,the diffraction pattern of Ti powder was calculated by using different peak shape functions and the diffraction pattern of cool-rolled Ti sheet was also calculated after adding the preferred orientation factor.On the whole,the calculated pattern agrees well with the experimental pattern.2.Crystal structure refinementThe structure of ternary compound Zn_55.24Al_18.86Zr_25.9 was studied by Rietveld method.The reliability factor for Rietveld refinement is Rp=7.15%,Rwp=9.56%.The alloy crystallizes in a tetragonal structure with space group P4/mmm.The lattice constant is a=b=4.07080?3????,c=4.07366?9????.In the structure,Zr atoms occupy the position of 1a,part of the Zn atoms occupy 2e position,the other part of the Zn atoms and Al atoms mixed occupy 1c position.The rationality of the obtained structure is verified by the theoretical calculation.The crystal structure and phase transition of ternary boride Mo₂NiB₂ were studied by Rietveld method.The results show that after doped V the crystal structure of Mo₂NiB₂ has changed from Orthorhombic to Tetragona.The lattice constant of Mo₂NiB₂ is a=7.0914?2????,b=4.5639?9????,c=3.1787?8????,The reliability factor for the refinement is Rp=6.74% and Rwp=8.52%.The lattice constant of V doped Mo₂NiB₂ is a=b=5.8244?5????,c=3.1239?6????,The reliability factor is Rp=5.69% and Rwp=7.41%.The structure of three Fe-Zn intermetallic phases contained in the galvannealed coating was refined by Rietveld method.The results show that FeZn₁₃ crystallizes in a monoclinic structure with space group C12/m1,lattice constant is a=13.41049?1????,b=7.60535?2????,c=5.07590?4????.As the use of three different sets of original structure data can meet the requirements of refinement,the location of the Fe atoms in FeZn₁₃ phase need to be further confirmed by experiment.Fe₁₁Zn₄₀ crystallizes in a cubic structure with space group F-43 m,the lattice constant is a=b=c=17.96867?8????.FeZn₁₀ crystallizes in a hexagonal structure with space group P63/mmc,the lattice constant is a=b=12.79683?7????,c=57.03453?4????.Some atomic coordinates of FeZn₁₀ phase has big difference with the original data.3.Quantitative phase analysisThe Rietveld quantitative analysis of the samples containing FeZn₁₃,Fe₁₁Zn₄₀ and FeZn₁₀ was carried out.The calculated results were in good agreement with the actual ratios.The feasibility of the Rietveld method for determining the phase content of galvannealed steel sheet was proved.