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.