Growth of Zr/ZrO_(2) core-shell structures by fast thermal oxidation

Abstract

This research has been conducted to characterize and validate resistive heating as a synthesis method for zirconium oxides (ZrO_(2)). A wire of Zr has been oxidized to form a core-shell structure, in which the core is a metal wire, and the shell is an oxide layer that is around 10 mu m thick. The characterization of the samples has been performed by means of several techniques based on Scanning Electron Microscopy (SEM). The topography images show that thermal gradient appears to have little influence on morphology, unlike time, which plays an important role. The chemical composition was analyzed by X-ray spectroscopy (EDX) and X-ray diffraction (XRD), and Raman spectroscopy has been used to assess crystallinity and crystal structure. The oxide layer is mainly formed by monoclinic ZrO_(2), alongside other, less significant, phases. Photoluminescence (PL) and cathodoluminescence (CL) measurements have allowed us to study the distribution of defects along the shell and to confirm the degree of uniformity. The oxygen vacancies, either as isolated defects or forming complexes with impurities, play a determinant role in the luminescent processes. Color centers, mainly electron centers such as F, F-A and F-AA, give rise to several visible emissions extending from blue to green, with main components at around 2 eV, 2.4-2.5 eV and 2.7 eV. The differences between PL and CL in relation to distinct recombination paths are also discussed.