Differential densification in Ho:Y₂O₃ transparent ceramics

Differential densification has been observed in the sintering of Ho:Y2O3 ceramics at heating rates of <= 3 degrees C. The temperature gradients in compacts during the heating process were simulated using ANSYS software. At a heating rate of 3 degrees C/min, the simulation results indicate a small temperature discrepancy of about 2 degrees C between the surface and the center area of the samples. Compared with those in the near-center (NC) area of the compact, the grain coarsening and rearrangement in the near-surface (NS) area are more pronounced during the initial and intermediate sintering stages. As a consequence, both the pore distribution and microstructure in the NS area were more uniform, which accelerated the elimination of pores in the subsequent sintering stage. This obser-vation suggests that particle rearrangement in the early sintering stage is one of the main reasons for the enhancement in the ultimate densification of the ceramics. The NC area could be fully densified by using hot isostatic pressing (HIP). After HIP, the Ho:Y2O3 ceramics have high in-line transmittance of 80% at the wave-length of 500 nm.