Effect of Zr⁴⁺+La³⁺ sintering aid on the microstructure and optical properties of transparent Y₂O₃ ceramics

DOI: 10.62564/M4-AB2148

Anton Balabanov, Ihor Vorona, Oksana Matvienko, Arsenii Tymoshenko, Olexander Tolmachev, Roman Yavetskiy

“Institute for Single Crystals” of National Academy of Sciences of Ukraine


The synthesis of Y2O3 ceramics using a complex admixture of La2O3+ZrO2 has been described [1-3]. However, most authors use high concentrations of additives, which promote sintering (6–13 at.%). Such high concentrations of additives can lead to the formation of color centers, disruption of stoichiometry, formation of secondary phases, segregation of additives along grain boundaries, thereby limiting the optical quality and functional characteristics of the ceramics. Therefore, recently, the main trend of consolidating optical ceramics is towards reducing the concentration of additives used. Ceramics were synthesized with Zr4+ ion concentrations of 0, 1, 1.5, and 2.5 at.%, while the La3+ ion concentration was constant at 0.5 at.%. The average grain size of the unalloyed ceramics is greater than 100 µm and significantly decreases with the introduction of zirconium ions to 5-10 µm. Thus, Zr4+ ions effectively inhibit recrystallization processes during the sintering of Y2O3 ceramics. Ceramics containing Zr4+ ions demonstrate high optical transmittance overall (approximately 78% at a wavelength of 1.1 µm). The introduction of zirconium ions Zr4+ requires compensation of excess charge, which occurs according to the following mechanisms 1, 2 [4]. $2ZrO_{2} + 2Y_{Y}^{X}\Leftrightarrow 2Zr_{\dot{Y}} + {O}''_{i} + Y_{2}O_{3}$ (1) $3ZrO_{2} + 4Y_{Y}^{X}\Leftrightarrow 3Zr_{\dot{Y}} + {V}'''_{Y} + 2Y_{2}O_{3}$ (2) The most energetically favorable is the incorporation of Zr4+ ions into the 24d non-centrosymmetric position of yttrium Y3+ according to equation (1) [4]. Such a defect has a larger specific volume compared to the regular position of the yttrium ion. Another charge compensation mechanism involves the formation of yttrium vacancies (2). Considering the X-ray diffraction data on the reduction of the lattice parameter of yttrium oxide ceramics upon the introduction of tetravalent zirconium ions, it can be concluded that the formation of substitution solid solutions occurs according to mechanism 2. The study shows that the complex addition La3++Zr4+ effectively suppresses the mobility of grain boundaries in Y2O3 ceramics while simultaneously activating diffusion transport along the branched system of grain boundaries.

Keywords
Infrared-traNanoceramics; microstructure; sintering aids; vacuum sintering; optical spectroscopy.

Acknowledgments
Тhe work was carried out during the NFSU project, competition "Supporting research of leading and young scientists" (2020-2023, state registration number 0123U102633)

References
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