Positron lifetime spectroscopy in Y1Ba2Cu3O6+x

Positron annihilation in sintered Y1Ba2Cu3O6+x was investigated by measuring the positron lifetime in the temperature range between 80 K and 1200 K. Two lifetime components could be determined from those spectra under 450 K: τ1 increased linearly with increasing temperature, τ2 was found to be constant by 192 ps. The intensity I2 increased with decreasing temperature. This behaviour indicated the occurrence of a localized positron state, which could be identified with positrons trapped at twin boundaries. The corresponding binding energy was calculated to Eb = 0.16 eV. In order to investigate the influence of oxygen content x on the positron annihilation spectra were accumulated with a 58Co source under various oxygen partial pressures up to 1200 K. Only one lifetime component anti τ, which increased linearly with temperature above 700 K was found. Only a small oxygen partial pressure dependence of anti α was observed. In combination with thermodynamical and structural investigations the results of this work show, that the positron wave function is not localized at oxygen vacancies