Out-of-plane thermal conductivity of the layered thermoelectric oxideBi2−xPbxSr2Co2Oy

摘要: The out-of-plane thermal conductivity $({\ensuremath{\kappa}}_{c})$ of ${\mathrm{Bi}}_{2\ensuremath{-}x}{\mathrm{Pb}}_{x}{\mathrm{Sr}}_{2}{\mathrm{Co}}_{2}{\mathrm{O}}_{y}$ is measured and analyzed. A low value $4--8\phantom{\rule{0.3em}{0ex}}\mathrm{mW}∕\mathrm{cm}\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ observed at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which close to the minimum conductivity. This implies phonon mean-free path order $c$-axis lattice parameter. temperature dependence also anomalous, positive coefficient $d{\ensuremath{\kappa}}_{c}∕dTg0$ observed. These features can be understood semiquantitatively by a phenomenological expression $\ensuremath{\kappa}$ including contribution optical phonons.