PREPARATION OF METAL RUTHENATES BY SPRAY-PYROLYSIS

Submicrometer crystalline metal ruthenate powders with perovskite structure, MRuO(3) (M = Sr, La), and pyrochlore structure, M'2Ru2O7-x(0.5 < x < 1; M' = Bi, Ph, Y, Eu, Gd, Tb, Dy, Ho, Er, Tm), were prepared by spray pyrolysis using metal nitrates and glycolates under an oxygen-gas atmosphere at temperatures up to 1100 degrees C. Submicrometer-sized solid single crystals (SrRu(O)3), submicrometer-sized hollow spheres consisting of nanocrystallites (pyrochlore rare-earth ruthenates, Bi2Ru2O7, and Pb2Ru2O6.5 below 1000 degrees C), and nanometer-sized particles (Pb2.31Ru1.69O6.5 and Bi-Pb-O above 1000 degrees C) were observed. Particle formation proceeded by intraparticle reaction and intraparticle reaction followed by evaporation of volatile metal oxides to form metal oxide vapors followed by condensation and reaction to form particles. The former was observed for systems where no volatile metal oxides were formed, whereas the latter occurred for the Pb-Ru-O and Bi-Ru-O systems, where volatile metal oxides, such as Bi2O3, PbO, and RuOx could occur. Particle morphology depended strongly on precursor properties. Submicrometer-sized single-crystal SrRuO3 particles could be formed from the metal nitrates but not from Sr(NO3)(2) and ruthenium glycolate, which gave hollow polycrystalline particles. In general, crystallite size could be controlled by varying precursor properties and reactor temperature, with higher temperatures giving larger crystallite sizes.