Reduction of lattice thermal conductivity from planar faults in the layered Zintl compound SrZnSb₂

The layered Zintl compound SrZnSb₂ is investigated using transmission electron microscopy (TEM) to understand the low lattice thermal conductivity. The material displays out-of-phase boundaries with a spacing from 100 down to 2 nm. Density functional theory calculations confirm that the TEM-derived defect structure is energetically reasonable. The impact of these defects on phonon scattering is analyzed within the Debye-Callaway model, which reveals a significant reduction in the acoustic phonon mean free path. This enhancement in phonon scattering leads to an ∼30 reduction in lattice thermal conductivity at 300 K.