Densification and porosity evaluation of ZrO2–3 mol.% Y2O3 sol–gel thin films

Abstract Densification of ZrO 2 –3 mol.% Y 2 O 3 sol–gel thin films after heating in air at 100 °C≤ T ≤1100 °C is investigated, with particular emphasis on porosity evaluation. For this purpose, the refractive index and thickness of the films are determined from transmission spectrometry. Three densification regimes were clearly identified: T T ≤ 800 °C and T >800 °C. For porosity evaluation, a simple strategy based only on film thickness measurements is used. These porosity values are compared with those obtained from refractive index measurements, applying commonly used analytical expressions. Our results clearly show that the porosity of thin films is underestimated when the Lorentz–Lorenz expression is used. Implications for preparation of ZrO 2 sol–gel thin films are also discussed.