Abstract
THE 'infinite-layer' parent structure1 of the copper oxide superconductors (Fig. 1) is the simplest structure containing the CuO2 sheets that are apparently essential to high-transition-temperature (high-Tc) superconductivity. At ambient pressure only Ca1-x SrxCuO2 with x≈O.l can be stabilized in this structure1,2but at high pressures and temperatures compounds ranging from Ba1/3Sr2/3CuO2 to Ca2/3Sr1/3CuO2 through SrCuO2 can be synthesized3. We have previously reported superconductivity with Tc = 40–100 K in the Ba–Sr–Cu–O system4,5 but have not until now been able to isolate a superconducting phase. Here we report the isolation of an alkaline-earth-deficient infinite-layer phase, (Ca1-xSrx)1-yCuO2 (y~O.l), with Tc up to 110 K. In contrast to Sr1-xRxCuO2 (with R a rare-earth element and Tc⩽43 K), which from the composition dependence of the lattice constants is thought to be an n-type superconductor6,7 our data suggest that the present superconductor is of p-type, with the carriers arising from calcium and strontium vacancies. High-resolution electron micrographs reveal defect layers, which we suggest are where the calcium and strontium vacancies are concentrated.
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Azuma, M., Hiroi, Z., Takano, M. et al. Superconductivity at 110 K in the infinite-layer compound (Sr1-xCax)1-yCuO2. Nature 356, 775–776 (1992). https://doi.org/10.1038/356775a0
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DOI: https://doi.org/10.1038/356775a0
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