Solid-state reactive sintering of transparent polycrystalline Nd:YAG ceramics

Transparent polycrystalline Nd:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al ₂O ₃, Y ₂O ₃, and Nd ₂O ₃ powders. The powders were mixed in methanol and doped with 0.5 wt tetraethoxysilane (TEOS), dried, and pressed. Pressed samples were sintered from 1700° to 1850°C in vacuum without calcination. Transparent fully dense samples with average grain sizes of ∼50 μm were obtained at 1800°C for all Nd ₂O ₃ levels studied (0, 1, 3, and 5 at.). The sintering temperature was little affected by Nd concentration, but SiO ₂ doping lowered the sintering temperature by ∼100°C. Abnormal grain growth was frequently observed in samples sintered at 1850°C. The Nd concentration was determined by energy-dispersive spectroscopy to be uniform throughout the samples. The in-line transmittance was >80 in the 350-900 nm range regardless of the Nd concentration. The best 1 at. Nd:YAG ceramics (2 mm thick) achieved 84 transmittance, which is equivalent to 0.9 at. Nd:YAG single crystals grown by the Czochralski method.