Applications Of Rietveld Method In Inorganic Materials

Rietveld whole-pattern fitting method using X-ray powder diffraction data is an efficient method in materials science research. In this paper, the computer program GSAS and X'pert plus which based on this principle were used to explore some of the applications of the Rietveld method in the field of inorganic materials, including refinement of crystal structure, phase transition and quantitative phase analysis (QPA).1.Refinement of crystal structureThe crystal structure of Li9Ga3(P2O7)3(PO4)2 was refined by GSAS using X-ray powder diffraction data. The compound crystallizes in the trigonal space group P3c1(158) with the following crystallographic parameters: a=9.72879 (13) ?, c=13.5827 (3) ?, V=1113.36 (3) ?3, Z=2. There are 65 parameters to be used in refinement. The profile function set up for this Rietveld refinement is the one with the pseudo-Voigt description of the profile shape. March–Dollase formulation was used for preferred orientation correction. The final refinement gives results with Rp=4.7%, Rwp=6.1%, Rexp=4.9%, S=1.24. The structure consists of∞2 [(GaP2 O 7 ) 3 (PO 4 ) 2]9- corrugated layers, parallel to (001), separated by lithium ions. The layers are built up of [GaO6] octahedra sharing corners with [PO4] tetrahedra and [P2O7] groups.2.Phase transition researchX-ray powder data of DyVO4 have been collected by in situ XRD from room temperature down to 8K, and a reversible displacive phase transition was observed at 14K. By contrast with high temperature phase of DyVO4, the space group of low temperature phase was lowered from I41/amd to Imma. The crystal structure of its low temperature phase has been ab initio determined by EXPO and GSAS. ao (orthorhombic phase at 8K) is about 0.016 ? shorter than at (tetragonal phase at 200K), and bo is about 0.016 ? longer than bt, co is almost the same with ct.3.Quantitative phase analysisThe quantitative analysis of specimens which were the mixture powder of quartz and corundum with the different weight ratios, were studied by using X'pert plus computer program. The results are almost consistent with the original weight ratios of quartz and corundum in the specimens. It means Rietveld whole-pattern fitting method can validly be used for the quantitative phase analysis of multiphase powder. Based on this method, we determined the quantity of Anatase and Rutile in TiO2 which produced by China National Pharmaceutical Group Corporation.