Anelastic creep and aftereffect studies of oxygen relaxation in YBa2Cu3O7−δ

Abstract

It is desirable to better understand the atomic mobility of oxygen in YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] because the oxygen stoichiometry and thus the superconducting properties are determined by diffusion of oxygen into the bulk. Anelastic relaxation studies, especially those which involve jumping of atoms between sites, have in the past been important to the understanding of atomic mobility in many materials. The focus for this paper is to extend earlier anelastic investigations of oxygen mobility in YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] to a new regime of relaxation times, those greater than 100 s. The authors use the anelastic creep and aftereffect (ACA) method which complements internal friction (IF) studies by measuring relaxation times at much lower temperatures. Results form a typical ACA experiment on YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] are given, which is a plot of the fractional anelastic strain [epsilon][sub an] at 79.8C versus time on a logarithmic scale. That the ACA data span a much longer time than for a single relaxation time can be seen by comparing the time span of the measured data with that for the dashed curve which is for an anelastic relaxation having a single relaxation time of 5,500 s. For ACA the strength ofmore » the relaxation is given by [Delta]=[epsilon][sub anelastic]/[epsilon][sub elastic]. For the isothermal measurements in Fig. 1 [Delta] = 0.172. This agrees with [Delta] = 0.166 and the monotonic decrease of [Delta] with temperature reported for the same sample using an IF measurement with peak temperature of 211 C.« less