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Abstract
Transparent yttrium aluminium garnet (YAG) polycrystal can be used as a host material for a solid state laser. In the present study, the authors prepared completely transparent YAG ceramics from active powder. The optical and mechanical properties of YAG ceramics are very sensitive to point defects. In order to examine the relationship between these properties and point defects, it is first necessary to characterise the defects. The authors report the effect of doping on oxygen diffusivity in several YAG ceramics, doped with various elements. Although Nd doping slightly increases the oxygen diffusion coefficient and the number of oxygen vacancies increases with increasing Nd concentration in as sintered materials, the variation of the oxygen diffusion coefficient in well annealed samples is small. These results suggest that the oxygen vacancies exist in non-equilibrium. However, grain boundary diffusivity was not influenced by preannealing before the oxygen diffusion experiments. The oxygen defect structure in transparent YAG ceramics is also discussed.