Enhancement of the optical transmittance of hot-pressed transparent yttria ceramics by a multi-step sintering process

In this work, we report the enhancement of the optical transmittance of yttria ceramics via a ‘pre-sintering/hot-pressing/hot-isostatic pressing’ multi-step process. The in-line transmittance reaches 78.0% at 400 nm and 83.2% at 1100 nm with an average grain size of approximately 1 µm. This sintering route is derived and upgraded from our previously reported one-step hot-pressing method for the fabrication of transparent yttria ceramics. Through the enhanced strength of the green body by pre-sintering, the formation of cracks and the breaking up of the as-hot-pressed samples can be effectively suppressed, leading to sound or crack-free but less transparent samples. After a post-HIPing treatment, the optical transmittance of the samples with a pre-sintering step was substantially improved to higher levels in the visible and the IR wavelengths compared to that of a sample which does not undergo pre-sintering. The corresponding mechanism was revealed by microstructural analyses.