Thermal conductivity modeling on highly disordered crystalline Y1− x Nb x O1.5+ x : Beyond the phonon scenario

Understanding the thermal conductivity of highly disordered materials has received growing interest. However, conventional thermal conductivity models fail in these materials due to the breakdown of the “phonon” image caused by the disorder of interatomic force constant. In this work, a quantitative thermal conductivity model is proposed based on “propagon” and “diffuson,” which can better describe the lattice vibrational modes in disordered materials. Lattice dynamics analysis is performed to investigate the vibrational modes in the disordered solid solution Y1−xNbxO1.5+x. The contribution to thermal conductivity from the propagons, which exhibit phonon-like high eigenvector periodicity, is calculated by the Debye–Klemens–Callaway equation. The contribution from diffusons, which exhibit low eigenvector periodicity, is calculated by Cahill's equation. The proposed thermal conductivity model produces an accurate temperature dependence for the Y1−xNbxO1.5+x that cannot be attained in the conventional models. Both the lattice dynamics analysis and thermal conductivity fitting suggest a decreasing trend with the Nb content for the propagon modes in Y1−xNbxO1.5+x.