Seeding and the Non-Hydrolytic Sol-Gel Synthesis of ZrW2O8 and ZrMo2O8

The unseeded non-hydrolytic sol-gel synthesis of ZrW₂O₈ and ZrMo₂O₈ produces trigonal ZrM₂O₈ (M = W, Mo) at 740 and 300–400°C, respectively. Cubic ZrW₂O₈ can be prepared using non-hydrolytic sol-gel methods by seeding with small amounts of preprepared cubic material, and the formation of the trigonal polymorph can be suppressed completely. Seeds with a small particle size are necessary for the preparation of cubic ZrW₂O₈. In contrast, seeding of ZrMo₂O₈ gels with either cubic ZrMo₂O₈ or cubic ZrW₂O₈ only lowers the temperature at which the trigonal phase crystallizes.