Abstract
Sr is doped into Ba 2Ca 2+ x Cu 3+ y O z ( T c=126 K) to improve its chemical stability. A solubility limit of Sr/(Ba+Sr+Ca)∼0.3 was observed under our synthesis conditions. Below this limit, Sr is equally distributed among the Ca and Ba sites, and does not affect the superconductivity significantly. Unfortunately, improvement in the chemical stability of the compound is limited. Above the solubility limit, however, a new compound with an as-synthesized T c of 106 K becomes the major phase. This phase decomposes into another new compound with T c∼80 K after exposure to humid air. A 0212-type model is proposed, with both Ba and Sr located in the rock-salt layers. The model can accommodate both the local cation stoichiometry and the XRD pattern for this new 106 K-phase.
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