THERMAL-CONDUCTIVITY OF YBA2CU4O8 DOMINATED BY PHONON-PHONON INTERACTIONS

The thermal conductivity kappa of dense sintered ceramic YBa2Cu4O8 in the range 30-310 K has been measured. At 100 K, kappa is 10 W m-1 K-1, approaching the in-plane kappa of single crystals of other high-T(c) materialS. Kappa decreases rapidly with increasing T to 7.4 W m-1 K-1 at 300 K. Fitting standard models for kappa(T) to the data we find that kappa is limited mainly by phonon-phonon interactions. Depending on the model used, the best fit is found for effective values of THETA(Debye) between 155 and 185 K, characteristic for the acoustic phonon branches, indicating that such phonons carry most of the heat. Finally, we suggest a possible way to test the electron-phonon model for the electrical and thermal conductivities in high-T(c) materials.