Investigation Of The Crystallographic Structures Of LaNi_5-xAl_xD_y By Means Of Neutron Powder Diffraction

The crystallographic structures of the compounds LaNi5-xAlxDy have been investigated systematically by means of neutron powder diffraction. Meanwhile, the corresponding research on the data alalysis technique of neutron powder diffraction has been also peformed, which including mainly two aspects: the analysis of the influence of peak shape selections on the values of the crystal structure parameters when using Rietveld method, and the implementation of the anisotropic strain broadening model for activated LaNi5 into the open source codes of LHPM 6.5.Rietveld method plays an important role in extracting structural informations from powder diffraction data. For a successful refinement, a suitable description of the shape of the peaks is necessary. Results given by refinements of data for PbSO4 with different peak shape functions show the variation of peak shape functions does not affect the unit cell and atomic positional parameters, however, to which the thermal parameters are sensitive.Severe anisotropic peak broadening which leads considerable difficulties to Rietveld analysis has been observed in powder diffraction patterns of activated LaNis. Optimal fits to data showing anisotropic strain broadening could be achieved using a few of parameters from the phenomenological model devised by Rodriguez-Carvajal. Based on the principles of the model mentioned above, in the study an anisotropic strain broadening model for activated LaNi5has been implemented into the open source codes of LHPM 6.5. And the results given by LHPM 6.5 modified are compared with those by FullProf 2000.The conclusion that Al atoms occupy mainly the 3g site on the Ni sublattice is derived from Rietveld refinements of neutron powder diffraction data collected for the compounds LaNi4.75Al0.25 LaNi4.25Al0.75. Significance tests on the refinement results reveal Al atoms only lie in the z=l/2 plane for LaNi4.75Al0.25, while for LaNi4.25Alo.75, besides the substitution of Ni by Al in the 3g site, there is still a small amount of Al atoms lies in the z=0 plane. It is emphasized that a need still exists for a confirmation of the Al occupancy in the z=0 plane for LaNi4.25Alo.75 due to the large standard deviation of it. From Rietveld analysis, D atoms all enter the 12n site for LaNi5D0.3 LaNi5D0.8 and LaNi4.25Al0.75D0.3, for LaNi4.25Al0.75D3.03 12n and 6m sites are occupied. In addition, a detailed description of structural parameters for all commounds above has been given.