ICIFUAS 11
Eleventh International Conference on Internal Friction and Ultrasonic Attenuation in Solids

J. Phys. IV France 06 (1996) C8-469-C8-472
DOI: 10.1051/jp4:19968101

Low-Activation Energy Relaxations in Oxide Superconductors

G. Cannelli¹, R. Cantelli², F. Cordero³, F. Trequattrini² and M. Ferretti<sup>4

1</sup>  Università della Calabria, Dip. di Fisica, Arcavacata di Rende (CS), 87036, Italy
²  Università di Roma "La Sapienza", Dip. di Fisica, P. le A. Moro, 00185 Roma, Italy
³  CNR, Istituto di Acustica "O.M. Corbino", Via Cassia 1216, 00189 Roma, Italy
⁴  Università di Genova, Dip. di Chimica e Chimica Industriale, Via Dodecanneso 31, 16146 Genova, Italy

Abstract
A brief survey is made of the numerous anelastic relaxation processes with activation energies below 0.2 eV, which are found in the oxide superconductors with the 123 and 214 structure. Up to now there is no general agreement on their mechanisms, although some kind of electronic relaxation is often invoked. New measurements are presented of the process with the lowest activation energy, ≈80 meV, in superconducting YBa₂Cu₃O_6+x. It is shown that the intensity of this peak is maximum at the maximum oxygen stoichiometry, x = 1, and steeply decreases in the restricted range 0.9<x<1, disappearing below it. It is proposed that the anelastic relaxation is caused by the reorientation of pairs of the P_z holes, which are observed at p_Z by X-ray absorption spectroscopy.

© EDP Sciences 1996