Optical and thermo-mechanical properties of fine-grained transparent yttria ceramics fabricated by hot-press sintering for infrared window applications

In this work, highly transparent yttria ceramics Φ = 55 mm in size were fabricated by a hot-pressing method with 1 at.% ZrO2 or 12 at.% La2O3 as a sintering additive. For a 4-mm-thick specimen doped with ZrO2, the in-line transmittance reaches 71.1% at 400 nm and 80.9% at 1100 nm, and the transmittance of the La2O3-doped specimen is comparable to that of the ZrO2-doped specimen. By means of the relatively low sintering temperature of 1600 °C, the present samples exhibited very fine microstructures (<2 μm), giving rise to excellent mechanical strength levels (∼200 MPa). With regard to the 1 at.% ZrO2-doped specimen, the combination of high strength and high thermal conductivity (∼10 W/m K) substantially improved parameters related to the thermal shock resistance. The results of this study indicate that the hot-pressed transparent yttria ceramic doped with 1 at.% ZrO2 is optically, mechanically, and thermally suitable for high-temperature IR window applications.