Yttria-stabilized zirconia microspheres: novel
building blocks for high-temperature photonics
Zirconia-based ceramics cover a huge variety of applications, including refractories, electro- and
bioceramics, fuel cells, catalysts, and many more. For various photonic applications considered for
energy systems and heat management, zirconia microspheres are interesting building blocks due to their
high refractive index, as well as their chemical and mechanical robustness. However, instabilities caused
by thermally-induced phase transitions and grain growth at temperatures above B1000 1C preclude
high-temperature applications of pure zirconia particles. Here, we present a synthetic route for yttriastabilized
zirconia microparticles with significantly improved thermal stability. With these particles we
conducted the first study on their thermal stability as a function of the yttrium content and at
temperatures up to 1500 1C. Using X-ray diffraction and scanning electron microscopy, the optimum
Y content was determined to be 8–۱۰%, which was marked by stabilization of the tetragonal or cubic
phase and significantly attenuated grain growth. Furthermore, with diameters ranging from 2 to 5 mm,
the particles covered a size range perfectly suited for photonic applications in the IR spectral range.
To demonstrate this, photonic glass coatings were prepared with these particles and their IR reflectivity
and microstructural stability was studied after subjecting them to various heating cycles. While heating
beyond 1200 1C led to failure and delamination of undoped particle films, films doped with 6 and 10% Y
displayed quite stable broadband IR reflection of up to 80% in the wavelength range from 1–۵ mm, even
after prolonged heating at 1400 1C. A detailed analysis of the X-ray diffraction patterns revealed that
prolonged heating at 1400 1C resulted in phase decomposition due to Y segregation into Y-lean and
Y-rich domains, confirming the presence of the solute-drag effect.
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