Neutron structural study of the Bi-monolayer compound (Bi{sub 0.5}Cu{sub 0.5})Sr{sub 2}(Y{sub 0.8}Cu{sub 0.2})Cu{sub 2}O{sub 7+{delta}} - the role of excess oxygen in superconductivity
- Bhabha Atomic Research Centre, Bombay (India); and others
Comparative neutron structural investigations are made on nonsuperconducting (slow-cooled) and superconducting (liquid-nitrogen quenched; T{sub c}{sup onset} = 70 K and R = 0 at 20 K) samples of (Bi{sub 0.5}Cu{sub 0.5})Sr{sub 2}(Y{sub 0.8}Cu{sub 0.2})Cu{sub 2}O{sub 7+{delta}} in order to examine the role of excess oxygen on the superconducting behavior of this {open_quotes}1212{close_quotes}-phase compound. Analysis of refined structural parameters shows that the two main factors which influence the superconductivity in (Bi, Cu)-1212 are: (i) the extent of occupancy of excess oxygen at O(5), the 2(e) site located in between the two CuO{sub 2} pyramidal layers, and (ii) the length of the apical Cu(2)-O(2) bond. The (Bi, Cu)-O monolayer plays the role of the {open_quotes}charge reservoir{close_quotes} quite effectively as reflected by the substantial increase in the length of the apical (bridging) Cu(2)-O(2) bond due to depletion of excess oxygen in this layer. Surprisingly, vacancies at as many as 10% of the O(1) site belonging to the CuO{sub 2} planes do not appear to disrupt the flow of current in the Cu(3d)-O(2p) planar network in the superconducting state. Relevant features of the structure of the (Bi,Cu)-1212 phase, in particular the role of excess oxygen and its occupancy at different sites, are discussed in the light of the available data on the isostructural (Pb,Cu)-1212 phase and the (La,Sr,Ca){sub 3}-Cu{sub 2}O{sub 6+{delta}} phase superconductors.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 106863
- Journal Information:
- Journal of Superconductivity, Vol. 7, Issue 5; Other Information: PBD: Oct 1994
- Country of Publication:
- United States
- Language:
- English
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