engleski

Application of Rietveld method to XRD and SAED pattern of nanocrystalline TiO2 samples

Two kinds of nanocrystalline TiO2 samples were synthesised by the sol-gel method: iron doped TiO2 (contains iron as a solid solution and poly(ethylene)glycol in anatase matrix) and undoped TiO2. They were characterised by means of X-ray diffraction measurements (XRD) and selected area electron diffraction (SAED). Rietveld refinement of XRD and SAED data was applied in order to extract structural parameters such as unit cell parameters, bond lengths and angles. The obtained unit cell parameters a, c, bond lengths and angles from Rietveld refinement of XRD pattern are in a good agreement with obtained parameters from SAED pattern. Comparing our results with previous results obtained from neutron diffraction on coarse-grained TiO2 powders, we found evident decrease of lattice parameter c and slight increase of lattice parameter a and enhancement of Debye-Waller parameters. The grain-size (in the range from 3 to 12 nm) dependencies of structural parameters can be explained by two-state model (presence of significant amount of grain boundaries in samples with nanocrystalline grains). Significant changes of lattice parameters were found between undoped and iron doped samples in parameter a for 0.4 % and c 0.5 % (XRD) and a 1.6 %, c 0.5 % (SAED). The changes are observed in bond lengths and angles. This can be explained by substitutional role of iron ions within unit cell of anatase. The reliability factor of the refinement is on average Rwp=10 % (XRD) and 15 % (SAED), indicating a good fit.

Rietveld; SAED; XRD

nije evidentirano