The structure of superconducting Pb 2Sr 2Y 0.73Ca 0.27Cu 3O 8 by single-crystal neutron diffraction
Abstract
The structure of superconducting Pb 2Sr 2Y 0.73Ca 0.27Cu 3O 8 has been refined by single-crystal neutron diffraction data. It has been found to belong to space group Pman with lattice parameters: a=5.3835(8), b=5.4091(8), c=15.784(2) Å determined by the use of a Guinier focusing camera, λ Fe Kα, and a silicon standard. The large single crystal used for the neutron experiment, prepared by the flux method, was twinned by reticular merohedry and contained two individuals related by the (110) pseudo mirror plane. The final R-factor based on F 2 was 6.33%. The most important structural feature of the superconducting Ca-doped compound with respect to the undoped non-superconducting one is the increase of the apical Cu(2)O(1) distance on going from the latter to the former. This is contrary to what occurs in YBa 2Cu 3O 6+ x where the appearance, as a function of x, of the superconducting state is accompanied by a decrease of the apical CuO distance indicating a charge transfer from the chain Cu cations to the planar ones. In Pb 2Sr 2Y 0.73Ca 0.27Cu 3O 8 the charge transfer takes place from the (Y,Ca) layers to the CuO 2 layers and the apical CuO distance is not implicated in the charge transfer.
- Publication:
-
Physica C Superconductivity
- Pub Date:
- April 1991
- DOI:
- 10.1016/0921-4534(91)90600-4
- Bibcode:
- 1991PhyC..175..293C