Effect of capping agent on microwave assisted sol-gel synthesized zirconia coatings for optical applications

Abstract

Conventional heating techniques used to synthesize zirconia may not provide uniform heating resulting in microstructural flaws in the finally achieved material / product. In this study, effect of both capping agent and microwave powers on the stability of zirconia coatings have been studied. Honey added zirconia sols are synthesized using microwave-powers (200–1000 W). As-synthesized zirconia sols are deposited onto glass substrates to obtain thin films. Structural analysis shows the formation of phase pure tetragonal zirconia (t-ZrO2) at microwave powers of 200 W and 600–1000 W under as-deposited conditions. Phase pure tetragonal zirconia coatings are comprised of smaller crystallite size with higher value of X-ray density (∼5.23gm/cm3) and relatively higher surface hardness (∼1347 HV). Fundamental band observed at 490cm−1 in FTIR spectrum confirms the formation of t-ZrO2. Optical spectra reveal higher value of transparency (75–90 %) for phase pure films whilst in the other case it is ∼62 %. Direct energy band gap values are in the range of 4.7–4.82 eV for phase pure t-ZrO2. The refractive index values vary between 2.03–2.17 for the phase pure zirconia while it is 1.95 (λ = 500) for mixed phases. Real part of optical dielectric constant values is 4.12–4.72 for phase pure and 3.83 (λ = 500) for mixed phases.