New superconducting oxides that have a composition of Ba2Ca2Cu3(CaxCuy)O 8+δ with 0.4 ≥ x ≥ 0.9 and 0.7 ≥ y ≥ 0, and show an optimum Tc ∼ 126 K were identified. Structural analysis, based on X-ray diffraction, indicated a common tetragonal unit cell among these oxides, which has lattice constants a = 3.85 Å and c = 28.2 Å with an I/4mmm symmetry. The cell consists of a rock-salt (BaO)2 block sandwiched between two perovskite Ca2Cu3O6 blocks with interstitial Ca+2x and Cu+2y located, e.g. at the 4d site between the two BaO planes. In other words, a so-called 0223 cell with interstitial CaxCuy. The oxides differ from one another by the amounts of the inserted cations, i.e. the values of x and y. The presence of these interstitial cations offers a new way to adjust the carrier concentration. These oxides are unstable against the incorporation of H2O and CO2 in open air. The decayed products (Ca,Cu,H,CO2)2Ba2Ca2Cu 3O8+δ have an expanded lattice constant c ∼ 33.8 Å and a lower Tc ∼ 90 K. A structure model for the decayed phases was also proposed.
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