Positron Annihilation at Defects in Sintered High Tc Perovskite Superconductors

摘要

We report positron lifetime measurements in sintered superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ and GdBa/sub 2/Cu/sub 3/O/sub 7-x/ oxides. It is shown that the thermal behavior of the positron lifetime spectra strongly depends on the preparation of the ceramics. A lifetime of 190+-3 ps is attributed to oxygen deficient regions. Two lifetimes of 251+-7 ps and 225+-5 ps are attributed to a cation vacancy presenting a temperature dependent atomic arrangement. The lifetime transition (251 -> 225 ps) occurs during decreases in temperature across the resistivity superconducting transition. This lifetime change indicates that the volume of the cation vacancy decreases in the superconducting state. (ERA citation 14:015256)