Room temperature stabilized TiO2 doped ZrO2 thin films for teeth coatings–A sol-gel approach

Abstract

Zirconia (ZrO2) is a strong, osseoconductive, transparent ceramic thus can be used as protective coatings. Moreover, its ivory color makes it suitable for teeth coatings. The aim of this study is to prepare transparent, dense and single-phase coatings. Sol-Gel spin coating method is used to synthesize TiO2 doped ZrO2 coatings. Dopant concentration is varied in the range of 1 to 5 wt%. Rietveld refined X-ray diffraction results of as-deposited thin films depict the formation of phase pure tetragonal zirconia (t-ZrO2) at 3 wt% of TiO2 content. Crystallite size for phase pure t-ZrO2 is observed to be ∼13 nm with reduced unit cell volume of 136.5 Å3. High X-ray density (∼5.75 g/cm3) and low porosity (∼6%) of thin films result in high value of hardness (∼1363HV). Phase pure t-ZrO2 thin films, with 3 wt% TiO2 doping, show ∼80% transmission along with direct energy band gap value of 5.15eV. Shift in fundamental absorption edge from 220 nm to 240 nm has been observed revealing the band gap in the range of 5.15–5.6eV for 1 to 5 wt% TiO2 content. The high refractive index is an indication of high x-ray density of doped ZrO2 coatings. FTIR and Raman fundamental tetragonal bands appearing at 470 cm−1 and 148 cm−1, respectively, confirm the formation of t-ZrO2 for 3 wt% TiO2 content. High grain-boundary resistance (0.597MΩ) and high dielectric constant (∼36) along with low tangent loss are observed at 3 wt% TiO2 concentration. Here we report TiO2 stabilized t-ZrO2, at room temperature with high density, low porosity, high hardness and better transparency, a potential material for teeth coatings. To the best of our knowledge TiO2 doped ZrO2 thin film with pure tetragonal phase (t-phase), at very low dopant concentration (3 wt%), under as deposited conditions is one of its kind report.