Phase evolution and gas-phase particle size distributions during spray pyrolysis of (Bi,Pb)SrCaCuO and Ag(Bi,Pb)SrCaCuO powders

Abstract

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)SrCaCuO powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi 1.8Pb 0.44Sr 2Ca 2.2Cu 3O x composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)SrCaCuO powders were (Bi,Pb) 2Sr 2CuO x (2201), Ca 2PbO 4 (plumbate), (Bi,Pb) 2Sr 2CaCu 2O x(2212), and (Bi,Pb) 3Sr 2Ca 2Cu 1O x(3221). For T≥800° C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900° C, a large number of ultrafine particles (<30 nm) were formed, probably from the PbO vapor released from the reactor walls. Using spray pyrolysis, it is easy to control stoichiometry and limit the phase segregation at the nanometer-scale so that homogeneous and phase-pure materials can be obtained rapidly during subsequent processing.