We have measured the positron-lifetime spectra of oxygen-deficient ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$ for 6.3<x<6.9. It is found that the lifetime parameters ${\mathrm{\tau }}_{\mathit{m}}$, ${\mathrm{\tau }}_1$, ${\mathrm{\tau }}_2$, and ${\mathit{I}}_2$ have a significant oxygen-content dependence. It is suggested that there are many kinds of positron states in polycrystalline ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$, the disordering of O(1) vacancies strongly affects positron lifetime, and with gradually decreasing x the average electronic density decreases and the configuration and/or the charge states of the oxygen vacancies change in the region containing Cu(1)-O(1) chains.

• Received 21 March 1990

DOI:https://doi.org/10.1103/PhysRevB.42.8078