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[Y-2(OH)(5)(NO3). 3H(2)O] which transformed to pure YAG at about 1000 degreesC 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). 08H(2)O The precursor directly converted to pure YAG at about 900 degreesC. The precursor was loosely agglomerated and the resultant YAG powders showed good dispersity and excellent sinterability. For the same calcination temperature of 1100 degreesC, YAG powders from the hydroxide precursor and the carbonate precursor densified to similar to 81.2 and similar to 99.8% of the theoretical, respectively, by vacuum sintering at 1500 degreesC for 2 h. (C) 2000 Elsevier Science Ltd. All rights reserved.