Transparent ceramics are polycrystalline inorganic bodies that transmit light in the visible or the infrared, made possible by reducing the residual porosity to a level where scattering becomes negligible. Pores are the dominant scatterer because their refractive index differs sharply from that of the grains, so the processing target is full densification without grain growth, and pressure-assisted sintering is the route most taken to reach it [1]. Hot isostatic pressing after sintering closes the remaining closed porosity, and the order in which the two steps are applied changes both the trajectory and the final in-line transmittance [2]. Reactive sintering from mixed powders, followed by a short hold, is an alternative that avoids a separate calcination [3]. The optical and the mechanical properties do not improve together: the conditions that give the highest transmittance are not those that give the highest strength, and in laminated bodies the two are often traded against each other deliberately [4]. The same approach extends to infrared-transmitting chalcogenide hosts [5]. Grain-boundary phases and dopant segregation, rather than porosity, then set the remaining loss.
- optical ceramics
- in-line transmittance
- residual porosity
- spark plasma sintering
- hot isostatic pressing
- grain boundary
References
- Ratzker, B.; Wagner, A.; Sokol, M.; Kalabukhov, S.; Dariel, M.P.; Frage, N.; Optical and mechanical properties of transparent alumina fabricated by high-pressure spark plasma sintering. Journal of the European Ceramic Society 2019, 39, 2712-2719, 10.1016/j.jeurceramsoc.2019.03.025.
- Chrétien, L.; Bonnet, L.; Boulesteix, R.; Maître, A.; Sallé, C.; Brenier, A.; Influence of hot isostatic pressing on sintering trajectory and optical properties of transparent Nd:YAG ceramics. Journal of the European Ceramic Society 2016, 36, 2035-2042, 10.1016/j.jeurceramsoc.2016.02.021.
- Irankhah, R.; Rahimipour, M.R.; Zakeri, M.; Razavi, M.; Optical and mechanical properties of transparent YAG ceramic produced by reactive spark plasma sintering (RSPS). Materials Research Express 2018, 5, 095206, 10.1088/2053-1591/aad60e.
- Liu, L.; Morita, K.; Effect of sintering conditions on optical and mechanical properties of MgAl2O4/Al2O3 laminated transparent composite fabricated by spark-plasma-sintering (SPS) processing. Journal of the European Ceramic Society 2022, 42, 2487-2495, 10.1016/j.jeurceramsoc.2021.12.045.
- Yu, S.; Carloni, D.; Wu, Y.; Microstructure development and optical properties of Fe:ZnSe transparent ceramics sintered by spark plasma sintering. Journal of the American Ceramic Society 2020, 103, 4159-4166, 10.1111/jace.17144.