J. Phys. I France
Volume 2, Numéro 6, June 1992
Page(s) 887 - 898
DOI: 10.1051/jp1:1992186
J. Phys. I France 2 (1992) 887-898

Incommensurability and transfer mechanism in bismuth high ${T}_{\rm c}$ superconductors

G. Pan1, S. Megtert1 and G. Collin2

1  Laboratoire de Physique des Solides, Bt. 510, Université Paris-Sud, 91405 Orsay Cedex, France
2  Groupe C.P.C.M., L.L.B., CEN Saclay, 91191 Gif sur Yvette Cedex, France

(Received 2 March 1992, revised and accepted 2 April 1992)

The structure of bismuth high ${T}_{\rm c}$ superconductors is investigated. A correlation is found between incommensurate modulations and transport properties : Bi 2Sr 2CuO 6 is not a good metal because the transfer of electrons from the Cu-O 2 layers into the Bi-O bi-layers induces an incommensurate and monoclinic distortion, responsible for the localization of carriers. Substitution of Sr 2+ by La 3+ reduces the transfer degree and the distortion : a superconductive transition is therefore observed with the remaining carriers after a monoclinic-orthorhombic phase transition. Futher substitution tending to a complete compensation of transfer leads to a compensated insulator. It is suggested that the $c^{\ast}$ component of the modulation is linked to the lattice distortion and the $b^{\ast}$ component to the charge transfer degree. Similar changes are observed in Bi 2Sr 2(Ca 1-zY z)Cu 2O 8 except that the monoclinic distorsion is never present.

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