Thermal expansion in the F-doped Bi(Pb)-2:2:2:3 superconductor studied by positron annihilation.

Abstract

Results of positron lifetime measurements as a function of temperature from 80 to 300 K for the F-doped Bi(Pb)-2:2:2:3 superconductor (${\mathit{T}}_{\mathit{c}}$=118 K) are presented. The lifetime ${\mathrm{\ensuremath{\tau}}}_{1}$ is about 200 ps and nearly temperature independent. The lifetime ${\mathrm{\ensuremath{\tau}}}_{2}$ fluctuates around 310 ps but its intensity ${\mathit{I}}_{2}$ increases slightly and the mean lifetime ${\mathrm{\ensuremath{\tau}}}_{\mathit{m}}$ increases continuously from 212 to 217 ps as the temperature is increased from 80 to 300 K. We discussed the possible effect of fluorine doping on the structural properties in this system and interpreted the temperature dependence of ${\mathrm{\ensuremath{\tau}}}_{\mathit{m}}$ in terms of a simple thermal expansion. An average linear expansion coefficient \ensuremath{\alpha}\ensuremath{\sim}35\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$ for this system is obtained.