Highly transparent yttria ceramics with Nb2O5/Ta2O5 as novel sintering additives by pressureless vacuum sintering

Highly transparent yttria ceramics were fabricated by pressureless sintering with Nb2O5 or Ta2O5 as a novel sintering additive. The optical transmittance, microstructural evolution, and thermo‐mechanical properties of the samples were investigated. The optimal doping concentrations of Nb2O5 and Ta2O5 are 0.3 and 0.2 at.%, respectively, which are much lower compared to those of previously reported counterparts. The transmittance of the sample with 0.3 at.% Nb2O5 reaches 81.6% at 1100 nm and 72.4% at 400 nm (2 mm in thickness), similar transmittance was obtained in the sample with 0.2 at.% Ta2O5. The microhardness (∼7 GPa), fracture toughness (∼0.85 MPa·m1/2), and biaxial strength (∼200 MPa) of the present samples were confirmed to be comparable or even better compared to those of previously reported transparent yttria ceramics fabricated by pressureless sintering. Furthermore, the present samples, by virtue of the low doping concentrations, possessed relatively high thermal conductivity values (>10 W/m·K), which substantially guaranteed high thermal shock resistance.