Co-precipitation synthesis and sintering of yttrium aluminum garnet (YAG) powders: The effect of precipitant

YAG precursors were co-precipitated from a mixed solution of aluminum and yttrium nitrates using ammonia water and ammonium hydrogen carbonate as precipitants, respectively. Phase evolution of the precursors during calcination and sinterability of the resultant YAG powders were compared between the two methods. The use of ammonia water produced a hydroxide precursor with an approximate composition of Al(OH)₃·0.3[Y₂(OH)₅(NO₃)·3H₂O] which transformed to pure YAG at about 1000°C via YAlO₃ phase. Severe agglomeration caused poor sinterability of the resultant YAG powders. The use of ammonium hydrogen carbonate produced a carbonate precursor with an approximate composition of NH₄AlY_0.6(CO₃)_1.9(OH)₂·0.8H₂O. The precursor directly converted to pure YAG at about 900°C. The precursor was loosely agglomerated and the resultant YAG powders showed good dispersity and excellent sinterability. For the same calcination temperature of 1100°C, YAG powders from the hydroxide precursor and the carbonate precursor densified to ~81.2 and ~99.8% of the theoretical, respectively, by vacuum sintering at 1500°C for 2 h. (C) 2000 Elsevier Science Ltd. All rights reserved.