Effect of the spark plasma sintering (SPS) parameters and LiF doping on the mechanical properties and the transparency of polycrystalline Nd-YAG

Transparent 1 at.% Nd:YAG ceramics were fabricated by spark plasma sintering (SPS) from nanometric Nd:YAG powders, both undoped and pre-mixed with 0.25 wt.% LiF additive. The mechanical and optical properties of the consolidated samples were determined as a function of the processing parameters, namely holding time, peak sintering temperature and heating rate. The presence of LiF accelerates densification and grain growth. Hardness and bending strength are decreased in the presence of the LiF additive, in consistence with the increase of the grain size. The optical transmittance in the doped samples sintered at 1400 °C, reaches 97% of the theoretical transmission and is significantly higher than that of the undoped samples. The increased optical transmittance of the doped samples is attributed to pore elimination by enhanced mass transport and cleansing of the carbon contamination by the fluorine component of the LiF additive. The presence of the latter has no effect on the absorption spectrum of the Nd:YAG ceramic.