Oxalate-precursor processing for high quality BaZrO3

Abstract

BaZrO3 is by far the most inert crucible material that has been used for melt processing of high quality single crystal YBCO superconductors. To overcome the processing difficulties of existing solid-state methods, solution processing methods are increasingly important in powder synthesis. This study investigates several methods of producing oxalate precursors for subsequent thermal decomposition to BaZrO3 with a view to producing high quality BaZrO3 ceramics. The most favourable system used barium acetate, ammonium oxalate and zirconium oxychloride, which unlike other previously reported oxalate processes allowed near stoichiometric precipitation without requiring a large excess of Ba reagents, elevated precipitation temperatures or slow addition of reagents. Precise control over precipitate stoichiometry was achieved by variation of the solution Ba:[Zr+Hf] mole ratio without requiring accurate control over oxalate addition. XRF, XRD, N2 BET adsorption, DTA/TGA and TEM analysis showed this process to be capable of producing BaZrO3 powders suitable for ceramics applications. The phase purity, particle size and surface areas of BaZrO3 powders produced by calcination of these precursors can be adjusted by variation of stoichiometry and calcination temperature. Crucibles formed from oxalate precursors have been able to contain Y2O3-BaCuO2-CuO melts for up to seven days.