Optical properties of Zr and ZrO₂

Highlights: • Optical surface characterization of metal tubes. • Reference dielectric functions for Zr (E110G) and ZrO₂. • Depth profiling of ZrO₂ by ellipsometry and XPS. • Oxidation kinetics of Zr (E110G) in steam. • Multi-sample evaluation for the determination of reference dielectric functions. - Abstract: Optical properties of Zr and its oxide have been measured on the surface of nuclear fuel cladding tubes. It has been shown that ellipsometry with focusing can routinely be used to measure thin layers and surface properties on Zr tubes with a diameter as small as 9.1 mm. Multi-sample and depth profiling models have been used to determine reference dielectric function spectra for both the Zr substrate and its oxide. Temporal behavior of the oxide thickness has been measured for oxidation temperatures of 600 °C and 800 °C. A vertical inhomogeneity of the oxide properties has been found by the optical measurements as well as by depth-profiling X-ray photoelectron spectroscopy investigations that revealed the formation of sub-oxides at the interface region of Zr and its surface oxide.