Positron annihilation study of oxygen vacancies in Y₁Ba₂Cu₃O_7-x

Abstract

Positron lifetime and Doppler broadened lineshape parameter have been measured as a function of quench temperature in Y₁Ba₂Cu₃O_7-x. The mean lifetime, τ̅, and the peak parameter of the Doppler broadened lineshape, I, are observed to decrease as the quench temperature (T_Q) is lowered from 925 ° C to 325 ° C. The variations in τ̅ and I with T_Q are observed to correlate with the oxygen deficiency (x) measured at a various quench temperatures. The positron lifetime component, τ₂, attributed to trapping at oxygen vacancies, is observed to decrease from (200 ± 1) ps in the tetragonal phase (x=0.5) to (190 ± 1) ps in the orthorhombic phase (x = 0.0). The variation in positron annihilation parameters with T_Q is qualitatively explained in terms of a change in the charge state of oxygen vacancies.