Fabrication of Tb3Al5O12 transparent ceramics using co-precipitated nanopowders: The influence of ammonium hydrogen carbonate to metal ions molar ratio

Terbium aluminum garnet (Tb 3 Al 5 O 12 , TAG) nanopowders were synthesized by the co-precipitation method using ammonium hydrogen carbonate (NH 4 HCO 3 , AHC) as the precipitant. The influence of ammonium hydrogen carbonate to metal ions molar ratio (AHC/M 3+ , R value) on the properties of TAG precursors and powders was investigated by FTIR, XRD and FESEM. It is found that the compositions of the precursors are nearly the same, and all the 1100°C-calcined powders exhibit a pure TAG phase. However, the R value has a significant influence on the morphology and agglomeration degree of TAG precursors and final powders. The precursor with R=3.6 shows a strong agglomeration, which is retained in the resultant powder. For the TAG precursors and powders with R=4.0, 4.4 and 4.8, they show better dispersity and homogeneity. Using the obtained powders as starting materials, TAG transparent ceramics were successfully fabricated by pre-sintering at 1700   °C for 20   h and then HIP post-treating at 1700   °C for 3   h. The ceramic sample with R=4.0 shows the best transparency, and its in-line transmittance exceeds 55% in the region of 500–1600   nm, reaching about 64% at 1450   nm. The microstructures and the magneto-optical properties of the TAG ceramics with different R values were also studied.