Mechanism of Thermal Transport in Zirconia and Yttria‐Stabilized Zirconia by Molecular‐Dynamics Simulation

We present results of molecular‐dynamics simulations of the thermal conductivity, κ, of ZrO 2 and Y 2 O 3 ‐stabilized ZrO 2 (YSZ). For both pure ZrO 2 and YSZ with low concentrations of Y 2 O 3 , we find that the high‐temperature κ is typical of a crystalline solid, with the dominant mechanism being phonon‐phonon scattering. With increasing Y 2 O 3 concentration, however, the mechanism changes to one more typical of an amorphous system. In particular, phononlike vibrational modes with well‐defined wave vectors appear only at very low frequencies. As in amorphous materials, the vast majority of vibrational modes, while delocalized, do not propagate like ordinary phonon modes but transport energy in a diffusive manner. We also find that the few highest frequency modes are localized and do not contribute to κ.