Doppler-broadened positron annihilation studies in Y-Ba-Cu-O, Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O superconductors
Doppler-broadened annihilation radiation spectra have been measured as a function of temperature from 77 K to 300 K, for several high temperature oxide superconductors viz single-phase YBCO, single- and mixed-phase Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O compounds. The temperature-dependent parameters extracted respond to a change at the onset of superconducting transition. The observations point to involvement of oxygen valence electrons at the onset of superconducting transition. Also a possible structural change and/or increase in electron density at the oxygen vacancy/defect sites seem to accompany the transition. In addition, the parameters derived are seen to be sensitive to the presence of more than one superconducting phases in mixed phase samples.
Volume 42 | Issue 6
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