Evolution of phonon transport across structural phase transitions in MgAgSb

MgAgSb, a promising thermoelectric material, undergoes reversible phase transitions that drastically alter its thermal transport behavior. Using first-principles calculations, we systematically investigate the lattice thermal conductivity (κL[jls-end-space/]) of its three phases: α[jls-end-space/], β[jls-end-space/], and γ[jls-end-space/], revealing a progressive increase following (Formula presented). This trend originates from distinct scattering mechanisms. Four-phonon scattering substantially suppresses the particle-like conductivity (κp[jls-end-space/]) in the β and γ phases, while phonon-electron scattering provides a minor additional reduction. In contrast, the wave-like conductivity (κc[jls-end-space/]) from coherent phonon tunneling is highest in the complex α phase, contributing up to 44% of κL[jls-end-space/]. Notably, the temperature dependence of κL differs fundamentally between phases: in β[jls-end-space/], the weak κp variation arises from a decreasing Grüneisen parameter with temperature; in α[jls-end-space/], the strong rise in κc with temperature counteracts the decay of κp[jls-end-space/]. Our findings establish a comprehensive picture of thermal transport in MgAgSb, highlighting the phase-dependent interplay between particle-like and wave-like phonon contributions.