Crystal structure refining by X-ray diffraction and least square method using experimental data of polycrystalline sample

The crystal structure of the florencita was refined by least squares using experimental data obtained with the Debye-Scherrer method. An automatic optical microdensitometer was used for the data collection from powder difractogram and numerical analysis methods for the integration of the function (2 theta, Y) which is tabulated at equidistant points. 14 diffraction peaks were observed, reflections which superpose contributing to the same peak were identified and their contributions were taken in account using multiplicity factors. The program POWLS (Powder Least Squares) was used for the refinement and initially the positional parameters of the atoms of the Goyazite, which is isomorfous with the florencita were used. Intensities were corrected for the Lorentz, polarization and absortion factors. The final R factor for the 14 peaks was of 0.097. The molecular formula of the florencita is CeAl3(PO4)2(OH)6. It crystallizes in the hexagonal system, space group R3 sup(-)m with cell parameters a0 = 6.96 A; c0 = 16.33 A; α = β = 900; γ = 1200; V = 685.07 A3 and the calculated density is of 3.67 g.cm-3. (Author)