Understanding the Extremely Poor Lattice Thermal Transport in Chalcogenide Perovskite BaZrS₃

Combining first-principles calculations with the solution to the Boltzmann transport equations, we examine the lattice thermal transport for the orthorhombic perovskite BaZrS3 through analyses of phonon group velocities, lifetimes, average Grüneisen parameter, and Debye temperature. An extremely low lattice thermal conductivity (LTC) of 1.16 Wm–1 K–1 at 300 K is obtained with phonons at 0–4 THz being the main contributors. The acoustic phonons contribute ∼30% to the LTC, while the lower frequency range of the optical modes contributes the most. Nearly 83% of the accumulated LTC is contributed by phonons with MFP < 5 nm. Since the lattice parameter (9.98 Å) of BaZrS3 is not significantly different from the calculated MFP, we corroborate that nanostructuring might be ineffective to reduce LTC.