Improving optical transmission of spark-plasma-sintered yag ceramics: Effect of powder conditioning and post-treatments

Three YAG powders were densified by means of spark plasma sintering (SPS), with the aim of developing optically transparent ceramics. The influence of the physico-chemical characteristics of the powders (purity, agglomeration state and stoichiometry) on the sintering and the optical transmission was investigated. Depending on the powder type, different pre-treatments and/or post-treatments were necessary to increase both homogeneity and optical transmission of the densified parts. In the case of agglomerated powders, dispersion by ultrasonication was efficient and led to better homogeneity and higher optical transmission. Post-treatments such as annealing and post-hipping in air were helpful to reduce oxygen vacancies and residual porosities and improved the optical transmission of the ceramics. The highest values of real in-line transmission (RIT) were obtained under SPS conditions of 50 MPa at 1500 °C and after annealing in air at 1150 °C for 12 h. The achieved RIT value was equal to 66 % at the wavelength of 600 nm.