The densities of the specimens as a function of the sintering conditions are presented in Fig. 8. The density was measured using the Archimedes method and the theoretical density was 5.01 g/cm3 [41]. Specimens with yttrium nitrate showed higher densities than the others due to the higher packing density resulting from the formation of very fine Y2O3 particles at 600 °C in the YN specimens. Since the increased packing density further enhanced the densification with increasing temperature, the YN specimens with higher packing density also showed higher values at 1400℃ [42, 43]. In particular, the 20YN specimen displayed the highest density of ~99% at 1400 °C.