Resolving Basis Dependence in Point‐Defect Scattering Models for Thermal Conductivity in Multi‐Sublattice Ceramics

ABSTRACT Alloying is a widely used strategy for reducing lattice thermal conductivity through phonon scattering induced by mass and strain fluctuations. However, the evaluation of disorder‐scattering parameters in multi‐sublattice compounds remains inconsistent because both atomic‐ and unit‐cell‐based formulations are used in the literature. In this work, the origin of these discrepancies is systematically examined using ZrC and ZrB 2 as model systems. We show that the two approaches yield equivalent predictions only when a consistent basis is maintained throughout the calculation and the alloyed site has a degeneracy of unity. For compounds containing multiple sublattices or higher site degeneracy, the formulations diverge and can lead to substantially different estimates of alloying‐induced phonon scattering. To address this issue, a generalized framework incorporating sublattice‐selective disorder scattering is proposed. The formulation preserves basis consistency while accounting for the localized nature of disorder in complex compounds. The model is applied to W‐doped ZrB 2 ceramics and compared with experimental thermal conductivity measurements. Improved agreement is obtained relative to conventional treatments. The proposed framework provides a physically consistent methodology for evaluating point‐defect scattering in multi‐sublattice solid solutions and enables more reliable prediction of lattice thermal conductivity in complex ceramic materials.