Crystal substructure and physical properties of the superconducting phase<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Bi</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">r</mml:mi><mml:mo>,</mml:mo><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">a</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mn>6</mml:mn><mml:mo>+</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>

We have isolated a high-${T}_{c}$ phase in the Bi-Sr-Ca-Cu-O system of composition ${\mathrm{Bi}}_{4}{(\mathrm{S}\mathrm{r},\mathrm{C}\mathrm{a})}_{6}{\mathrm{Cu}}_{4}{\mathrm{O}}_{16+x}$. The crystal substructure has a tetragonal unit cell $a=3.817$ \AA{}, $c=30.5$ \AA{}) with similarities to both the oxygen-defect perovskites $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ and the ${\mathrm{K}}_{2}$Ni${\mathrm{F}}_{4}$ structure of ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$. The oxygen content, determined by titration and thermogravimetric analysis experiments, corresponds to a formal oxidation state Cu(2.15). Oxygen can be reversibly depleted in an argon ambient in an amount corresponding to the reduction of the Cu(III) into Cu(II). The compound has a metalliclike resistance above its ${T}_{c}$ near 85 K. Processing this precursor compound by heating to temperatures near its melting point (885 \ifmmode^\circ\else\textdegree\fi{}C) produces a sharp resistivity drop near 110 K that we show by ac susceptibility and Meissner effect is due to a superconducting transition.

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