Crystal structure of 1–2–3 superconductor precursor material: Vacancy distribution and lattice relaxation
- 1 October 1988
- journal article
- research article
- Published by Taylor & Francis in Philosophical Magazine Letters
- Vol. 58 (4) , 173-181
- https://doi.org/10.1080/09500838808214750
Abstract
The crystal structure of tetragonal YBa2Cu3O7-δ, with δ close to the critical composition for the tetragonal–orthorhombic transition, has been refined. The oxygen deficiency δ = 0·65(10) is accommodated by both the O(1) and O(2) sites which coordinate the ‘square planar’ Cu(1) site. Structural relaxation around the vacancies is indicated by large anisotropic Debye-Waller ellipsoids in the structural layer formed by these atomic sites. The Y, Ba, Cu(2) and O(3) sites are not involved in the relaxation mechanism. On comparing this structure with the δ ≈ 0 and δ ≈ 1 end-members, we find that with decreasing oxygen content of the structure the Cu(2) valence type transforms from square-pyramidal character towards square-planar character. This effect gives the main contribution to the increase of the c 0 lattice constant with decreasing oxygen content.Keywords
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