Surface characteristics of zirconia-coated TiO2 and its phase transformation

Recently, zirconia has been considered as a suitable material for surface coating nanosized TiO2 for use as an electrode in a solar cell application. In this study, the TiO2 (P-25) coated ZrO2 was synthesized from P-25 TiO2 and coated with zirconium n-propoxide in the range of 2.5-50 wt.%. The surface of the TiO2 coated with ZrO2 were examined by X-ray diffraction (XRD) analysis, high resolution transmission electron microscope (HRTEM), which showed zirconia could coat onto the P-25 TiO2 surface. Any excess of zirconia has been deposited as separated particles. Peaks for tetragonal zirconia were observed from the XRD patterns in zirconia-coated P-25 containing more than 20 wt.% of zirconia after calcinations at 500 degrees C, 800 degrees C and 1300 degrees C. In addition, peaks of anatase could be observed from XRD patterns of the samples after calcination at 1300 degrees C. The results show that coating zirconia onto the TiO2 grain surfaces may act to retard the phase transformation from anatase to rutile.