Synthesis of Y _3Ba 5Cu _8O _(18) superconductor powder by auto-combustion reaction: Effects of citrate-nitrate ratio

摘要

In this experiment, nanocrystalline Y _3Ba _5Cu _8O _(18) superconductor powder was prepared by citrate-nitrate auto-combustion reaction. A series of Y _3Ba _5Cu _8O _(18) precursor gels with different citrate-nitrate ratio ranged from 0.3 to 1.0 have been prepared by varying the amount of citric acid added. The auto-combustion reaction during drying process transformed the precursor gels into ashes powder that upon calcinations at 900°C yield Y _3Ba _5Cu _8O _(18) nanocrystalline powders. The TG/DTA analysis reveals that the precursor gels with 0.3 ≤ c < 1.0 decomposed in a single-step reaction combusted at temperature of around 230°C. Established from XRD and SEM characterization, the Y 3Ba _5Cu _8O _(18) calcined powder prepared from c = 0.7 precursor gels has got the orthorhombic structure with smallest particle size (～10 nm) compared to the rest of the batches. Samples with c = 0.5 and 0.7 appeared in this work to be electrically superconducting at temperature above 100 K as measured using standard four-probe technique. This emphasized on maintaining a stoichiometric or near stoichiometric reaction for the analysis.