Oxygen mobility in RBa2Cu3O6+x by anelastic relaxation.

Abstract

The electric properties of the oxide superconductors of the RBa2Cu3O6+x family are determined by the stoichiometry and ordering of oxygen in their CuOX planes. These O atoms are also very mobile even at room temperature and below, as demonstrated by the change of the electric properties of O deficient samples with aging at room temperature. Detailed information on the atomic mobility can be obtained by anelastic relaxation experiments (acoustic absorption), and here is made a short review of the main results obtained by this technique on the mobility of O in RBa2Cu3O6+X. Three elastic energy loss peaks as a function of temperature are attributed to jumps of O in different environments. The O atoms near a O vacancy in the OI domains (x=1) can jump with an activation energy of 1.1eV, those in the OII domains (x=0.5) or in disordered chains cause a separate relaxation process with a similar activation energy (-1.2eV). The isolated O atoms are much more mobile, and they are supposed to be the cause of a relaxation process with an activation energy of only 0.1eV in the highly O deficient samples. The apparent contrast between such a high mobility and the slow time constants for reaching equilibrium in O deficient samples is discussed.