X-ray crystallographic analysis of a Heusler (Co2 Sc Sn) alloy and bioceramic material using the Rietveld method

Two polycrystalline materials were analysed by X-ray diffraction: a Heusler alloy (Co2 Sc Sn), where samples originating from the same preparation were submitted to several different thermal treatments, and a bioceramic material. The Rietveld method was employed for the refinement. The analysis of the Heusler alloy clearly revealed the presence of a second phase: Co2 Sn, which was not refined due to the absence of a structural model. Thus, the refinement was performed, only for the component with known structural model, choosing several alternative profiles functions such as Gaussian, pseudo-Voigt and Thompson-Cox Hastings modified pseudo-Voigt. The background radiation also was refined using a fifth order polynomial. The results obtained were equivalent. From the results obtained by the refinement it can be concluded that the preparation conditions of sample F 117 (arising from the original sample treated at 6000 C for 60 hours, ground, treated at 2000 C for 80 hours and annealed) and A 117 (arising from the original sample treated at 8000 C for 48 hours and annealed) were more satisfactory. The samples F 117 and A 117 were more satisfactory, respectively, according to the disagreement factors goodness of fit, pattern and weighted pattern, and according to the disagreement factors Bragg and structure factor. The analysis of the bioceramic material clearly revealed the presence of two crystalline phases: hydroxyapatite [Ca10 (P O4) 6(OH)2] and whitlockite [β-Ca3 (P O4) 2] and via the refinement it was possible to calculate its composition. The procedure used to obtain sample HAIII103, proved to be the most adequate since this sample was richer in hydroxyapatite. (author). 64 refs., 41 figs., 32 tabs