Transparent YAG ceramics - the effect of doping ions

Transparent YAG ceramics doped with active ions have become a valuable alternative to single crystals in solid state lasers in the last 10 years. The dopant ion substitutes Y3+ in the crystal, and despite low concentration it influences the sintering process. It has been shown for example that, differently to Yb, Nd fastens sintering, and this is related to the ionic radius. This work describes the influence of doping ions on the microstructure evolution of transparent YAG ceramics and on the material properties. Variously doped YAG ceramics have been prepared by solid state reaction under high vacuum and characterized in terms of microstructure and thermal and mechanical properties. A model relation approximating the optical transmittance is provided. Transmittance is then presented not only as a material characteristic, but also as an indicator of microstructure development. The sintering and densification is discussed in relation to the transmittance and to material properties, in all cases considering the effect of the doping ions. It is interesting to show the sensitivity of various properties on the microstructural homogeneity and the small differences in porosity lying between nearly dense, translucent and transparent material. The influence of the active ions on the sintering evolution and consequently final properties highlighted in the present work can be exploited for the optimization of the processing conditions.