Phase identification of the new 126 K Ba-Ca-Cu-O superconductor
Journal
Physica C: Superconductivity and its Applications
Journal Volume
294
Journal Issue
3-4
Pages
316-326
Date Issued
1998
Author(s)
Xue, Y.Y.
Sun, Y.Y.
Rusakova, I.
Ross, D.K.
Du, Z.L.
Wu, N.L.
Cao, Y.
Gao, L.
Hickey, B.
Chu, C.W.
Abstract
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. © 1998 Elsevier Science B.V.
Type
journal article