Solid-state processing of BaZrO3 for crucibles used in the growth of YBCO single crystals

Abstract

BaZrO3 is by far the most inert crucible material that has been used for flux growth of high qualitysingle crystal YBCO superconductors. The performance of this otherwise resilient materialis primarily determined by secondary phases, hence high chemical purity, veryhigh phase purity, and high sintered density are required for sustained corrosionresistance (Erb et al 1995 Physica C 245 245–51, Liang et al 1998 Physica C 304105–11). In this paper we report new data on the solid-state processing properties ofBaZrO3, showing strong effects of stoichiometry and processing conditions onthe physical properties of powders. If the constituents are reacted fullythere is a sharp transition in the particle size and surface areas of theBaZrO3 powders obtained near to the phase boundary where theBa/Zr mole ratio is unity. Repeated calcination and regrinding of powders was shown toincrease the phase purity of processed powders. Precise control over stoichiometry isrequired to produce crucibles with corrosion resistance adequate for single crystalgrowth experiments. Optimal corrosion resistance was observed over a narrowBa:[Zr+Hf] mole ratio range between 1.001 and 1.007(± 0.002). The corrosionresistance of BaZrO3 is acutelysensitive to residual ZrO2, whose phase abundance must be very strictly minimized by control of stoichiometry andprocessing conditions, whereas tolerances for Ba-rich phases are less demanding.Measurements of YBCO single crystals grown in one of these crucibles have been made fora range of oxygen contents, i.e. hole concentrations. These show that the crucibles aresuitable for growing high quality single crystals.