Superconductivity in multiple phase Sr2Ln1−xCaxGaCu2O7 and characterization of La2−xSrxCaCu2O6+δ

Superconductivity at 28 K in a cuprate with a niobium oxide intermediary layer

“…In the past two years the discovery of new cuprate superconductors has become more difficult, as simple combinations of elements and standard processing techniques have become exhausted in the search. Complex chemistry, high oxygen pressures or high hydrostatic pressures have been employed recently to discover new materials [1][2][3][4][5][6][7]. Here we report the discovery of bulk superconductivity at 28 K in Sr 2 Nd 1.5 Ce 0.5 NbCu 2 -O 10-δ (and the Ta analog), a previously reported compound [8,9] with a single Nb(Ta)O 6 octahedral layer between the apices of pyramidal (CuO 5 ) ∞ planes.…”

“…The Nb(Ta)O 6 octahedral layer is a new kind of intermediary layer for high-T c copper oxides, and the Nb and Ta charges of +5 are the highest yet on cations to be accommodated in such a layer. The (Nb, Ta-O) octahedral layers join (Tl-O) and (Pb, Cu-O) octahedral layers, (PbOCu-PbO) and (Bi-O) distorted pyramids, Cu-O sticks and chains, and possibly GaO 4 tetrahedra [6,7], as building blocks for new materials. The octahedra in the new layer share corners, not edges as [8,9] and the expected optimal concentration for superconductivity, x 0.6 (which corresponds to a nominal hole concentration of 0.2/Cu).…”