Abstract
Understanding the mechanism of thermal conduction and its modulation strategy is a threshold task in the search of advanced multifunctional thermal and environmental barrier coating materials (TEBCs). We herein disclose the hierarchical features in the thermal transport of a typical TEBC material, Yb2Si2O7, using the state-of-the-art dual-phonon theory. Large amounts of vibrational modes transport heat in a diffusive feature, different from the propagative feature for normal phonons, and make significant contribution to the lattice thermal conductivity (κL) at high temperatures (T). This mechanism drives a weak κL~T dependence at high temperatures, deviating from the κL~T−1 trend predicted by the phonon Boltzmann transport equation (BTE) theory. The present study indicates that modulating the κL of complex-structure low-κL TEBC materials requires wisdoms beyond the BTE theory and considering the joint effects from different thermal transport channels.
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