Investigating the effect of dopant type and concentration on TiO2 powder microstructure via rietveld analysis

The influence of dopant types (anion: Cl and F; cation: Fe and Zn) on the phase transformation, crystallite size, lattice parameters, and lattice strain of TiO2 powder is investigated by Rietveld refinement of X-ray powder diffraction (XRD) data. Undoped and doped powders are synthesized by using a sol-gel route and heat treated for different times and temperatures. In general, dopants diminish the phase transformation rate and decrease particle size (FESEM data support), but F doping demonstrates the strongest effect. Cation doping induces defects and distortion in the lattice and increases strain both in anatase and rutile phases, but anion doping enhances strain in anatase only. The decreasing order of the dopants inducing strain in anatase and rutile phases is observed as F > Zn10% > Cl > Zn5%> Fe10% > Fe5% ≈Zn1%>Fe1%>UD, and Zn10% > Fe10% > Zn5%>Fe5%> Zn1%> Fe1%> UD > Cl > F, respectively. This could be explained from EDX study, which shows that the anion dopants, irrespective of the amount, abandon the material at a treatment temperature ≥400 °C. This may create high defect density in anatase, influence phase transformation, and particle size. But, the high temperature ion mobility annihilates the point defects and shows less strain in rutile. Whereas, the cations assimilate in structure and show similar effects in both the phases.