A new family of C-free high-temperature superconducting oxides in the Ba-Ca-Cu-O system showing a Tc up to 107 K has been synthesized under high pressure. Structural analyses, based on X-ray and electron diffractions and high resolution electron microscopy, have revealed that these oxides can be represented by CaBa2Ca2Cu3O9-δ [Ca-1223-Ba] with a tetragonal subcell that has lattice constants α approximately 3.85 angstroms and c approximately 16.5 angstroms and is isostructural to Tl-1223-Ba with the Tl sites occupied mainly by Ca. These oxides have the same active block of [(CuO2)(Ca)(CuO2)(Ca)(CuO2)] but with cation mixing and substitution of Ca by Cu within the charge reservoir block [(BaO)(CaO)(BaO)]. This results in the observed variations in composition and superstructure but has only minor influence on Tc.
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