Optimization of superconducting critical temperatures by control of cation and anion stoichiometry in Bi2Sr2CaCu2Oδ-based solid solutions
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Tc data are reported for powders of cation-stoichiometric Bi2Sr2CaCu2Oδ and for nonstoichiometric samples based on the three mechanisms Bi⇄Sr, Sr⇄Ca and Sr vacancy. For each, the Tc values depend critically on the final oxygen contents, which were varied by heating samples in either O2 or N2 at different temperatures. Stoichiometric Bi2Sr2CaCu2Oδ has the highest Tc, 92 K, obtained after heating in O2 at ∼ 820 °C. Heating in O2 at lower temperatures gives rise to overdoping and Tc decreases to 60 K. The other cation compositions show a smaller maximum Tc but also less reduction in Tc on overdoping. Under-doped samples, with reduced Tc values were obtained on heating in N2. These data, together with selected literature results, lead to a unified picture of the variation of Tc with cation composition and oxygen content.
KeywordsOxygen Polymer Solid Solution Oxygen Content Critical Temperature
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