Positron annihilation measurements of Pr-containing superconductor compounds

Abstract

Positron annihilation lifetime and Doppler broadening energy spectra have been measured in Pr-containing YBa2Cu3O7−δ as a function of temperature between 18 and 295 K. The defect-related positron lifetime component τ2 was independent of temperature for the PrBa2Cu3O7−δ compound and was very close to the value τ1 associated with bulk or defect-free material. These results indicate that the structure of this compound is nearly free of defects which trap positrons and that there is no electronic structure change during cooling. There was a slight temperature dependence below Tc for the Y0.5Pr0.5Ba2Cu3O7−δ compound. It was also found that a change in the positron Doppler line-shape parameter S occurred at the superconducting transition temperature for 0.5 Pr-containing compound but not for the 1.0 Pr-containing compound. These results show that the average electron momentum at the annihilation sites increases as temperature is lowered across the superconducting transition range for the 0.5 Pr-containing compound but not for the PrBa2Cu3O7−δ compound.