Abstract
In this paper, we report the positron lifetime data in high- T c cuprate perovskite YBa 2Cu 3− x M x O y (M=Al, Sn) systems with different dopant concentration x. A significant substitution dependence of the positron lifetime parameters was observed, and the local electron density n e and defect concentration C v were also evaluated as a function of substitution content x. The results show that in the region of known structural transition from orthorhombic to tetragonal phase, n e and C v present an large anomalous change. Here, n e is decreased and C v increases. These can be interpreted by electronic weak localization in Cu–O chains and would affect on the charge transfer in superconducting state. The mechanisms of positron annihilation were also discussed.
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