Fig. 5: Lattice thermal conductivity and phonon-related calculations.

a Lattice thermal conductivity, κL. b T dependence of Cp/T3. The circle is the experimental data and the line is established by using a Debye and three Einstein modes. c Phonon dispersions and atom-projected phonon DOS of the low-frequency phonons up to f = 1.0 THz. Transverse acoustic phonons, TA1 and TA2 are plotted in red and orange colors. Longitudinal acoustic phonon, LA, is in the blue line. Optical phonons are in black lines. In the low-frequency region, the dominant contribution stems from Pb atoms. d Grüneisen dispersions. Displacement patterns of e the low-frequency optical phonon at Γ point, and f low-frequency TA1 mode at Γ point.