Rapid synthesis of ZrW2O8 and related phases, and structure refinement of ZrWMoO8

Six different synthesis routes to ZrW2O8 and related phases ale described and compared. A new combustion route requires a synthesis time of less than 15 min and a furnace temperature of 773 K. The reactants were ammonium tungstate, zirconium oxynitrate, 3 N nitric acid, and urea as a fuel. Synthesis by a coprecipitation route is complete in just a few hours but requires a final calcination temperature of about 1425 K. The sol-gel route gives the desired crystalline phases with calcination temperatures of about 875 K, but this route requires more than 1 week for good results. A fourth hydrothermal route also starts with solution precursors. Finally, for purposes of comparison, syntheses were performed by direct calcination of ZrO2 and WO3 or zirconium oxynitrate and ammonium metatungstate. In addition to ZrW2O8, samples of isostructural WfW(2)O(8), Zr0.5Hf0.5W2O8 ZrW1.5Mo0.5O8, HfW1.5Mo0.5O8 and ZrWMoO8, were prepared by the combustion route. Sintered pellets of ZrW2O8 prepared from powders produced by the combustion or hydrothermal syntheses were 90% dense. A room-temperature structural refinement of ZrWMoO8 using a combination of X-ray and neutron powder diffraction data confirmed that it has the beta-ZrW2O8 structure. (C) 2000 Elsevier Science Ltd. All rights reserved.