Combustion synthesis and properties of fine-particle rare-earth-metal zirconates, Ln2Zr2O7

Abstract

Fine-particle rare-earth-metal zirconates, Ln₂Zr₂O₇, where Ln = La, Ce, Pr, Nd, Sm, Gd and Dy having the pyrochlore structure have been prepared using a novel combustion process. The process employs aqueous solutions of the corresponding rare-earth-metal nitrate, zirconium nitrate and carbohydrazide/urea in the required molar ratio. When the solution is rapidly heated to 350–500 °C it boils, foams and burns autocatalytically to yield voluminous oxides. The formation of single-phase Ln₂Zr₂O₇ has been confirmed by powder X-ray diffraction, infrared and fluorescence spectroscopy. The solid combustion products are fine, having surface areas in the range 6–20 m² g^–1. The cold-pressed Pr₂Zr₂O₇ compact when sintered at 1500 °C, 4 h in air, achieved 99% theoretical density.