A positron annihilation study of the decomposition of Y₁Ba₂Cu₃O_7-x

Abstract

Measurements of the positron lifetime and the angular correlation of positron annihilation radiation have been carried out on oxygen off-stoichiometric Y₁Ba₂Cu₃O_7-x as a function of ageing time at 150°C, 200°C and 250°C. A two-component analysis of the positron lifetime data indicates that the second component of lifetime, τ₂=280±20 ps, develops in intensity with ageing time. The positron lifetime in the bulk is seen to increase from 185±2 ps to 210±2 ps. The results are interpreted in terms of increasing positron trapping and annihilation from oxygen deficient regions in the sample and from interfacial defects that form due to the decomposition of YBCO during the heat treatment. The results of the positron experiments are discussed in the light of the phase diagram of YBCO.