Structural and electronic modifications on TiO2 anatase by Li, K or Nb doping below and above the solubility limit

Official URL: http://dx.doi.org/10.1007/s10853-016-9893-8

Undoped and Nb, K or Li doped TiO2 nanopowders were synthesized using a buttom-up approach by sol-gel method. The changes of crystal structure in TiO2 upon Nb, K or Li doping were followed with X-Ray Diffraciton (XRD) and Raman Spectroscopy techniques. XRD results have shown that anatase to rutile phase transition as a function of temperature was suppressed by Potassium and Niobium incorporation whereas it was facilitated by Lithium incorporation. X-ray detectable secondary phases were not observed in any of the cases. Additional Raman lines were observed at 362 cm-1, 323 cm -1 and 242 cm-1 for K or Nb doped anatase, which were missing in both Li-doped and undoped anatase TiO2. Those additional lines were attributed to brookite phase or brookite-like distortions introduced to Ti-O octahedra in anatase. Solubility limits of the aforementioned cations were determined with depth profiling by using a surface etching technique. ICP-OES results of etched powders have shown that most of the K or Li was on the surface of the particles and only 0.2% at K and 0.7% at Li have been incorporated into bulk anatase. A wedge shaped specimen was utilized for chemical analysis of Nb-doped anatase. EDXS measurements in a TEM were carried out above and below solubility limit. Strong surface accommodation took place in the sample doped above the solubility limit.