THERMAL-CONDUCTIVITY OF YBA2CU4O8 UNDER HIGH-PRESSURE

The thermal diffusivity a of YBa2Cu4O8 (1-2-4) has been measured as a function of pressure p and temperature T over the range 85<T<310 K and up to 1 GPa (10 kbar). From the data obtained we have calculated the pressure dependence of the thermal conductivity K as a function of T. Kappa increases slowly with increasing p above 150 K but decreases below this value. Most of the high-T increase with p is caused by an increase in the electronic thermal conductivity kappa(e). For the phonon thermal conductivity, which dominates kappa in 1-2-4, we find that charge transfer with p causes a strong increase in electron-phonon scattering with p, while the p dependence of the boundary scattering and phonon-phonon scattering is in reasonable agreement with the behaviour predicted by simple models.