Background-suppressed Doppler broadening spectroscopy, using two detector coincidence technique of the electron-positron annihilation γ-radiation, has been employed on tetragonal La 0.7Y 0.3Ca 0.5Ba 1.5Cu 3O z polycrystalline high-Tc superconductor to study the changes in the electron momentum distributions due to superconducting transition. The temperature-dependent (298 K to 60 K) S-parameter graph shows a sharp peak at the superconducting transition temperature, Tc, region. The spectra at different sample temperatures have been compared with the spectra of defect-free 99.9999% pure Al and Cu metals by constructing ratio-curves. The results indicate a decrease of the annihilation of positrons with 3d electrons of Cu ions just above Tc. © 2004 Elsevier B.V. All rights reserved.