fig6

Figure 6. (A) Distribution of normal strains in the GeTe and high-entropy Ge_0.61Ag_0.11Sb_0.13Pb_0.12Bi_0.01Te samples. Left images and green lines are from GeTe samples, and right images and pink lines are from the Ge_0.61Ag_0.11Sb_0.13Pb_0.12Bi_0.01Te sample. The value of σ is the root mean square; (B) Raman intensity and FWHM of the GeTe (left) and high-entropy Ge_0.61Ag_0.11Sb_0.13Pb_0.12Bi_0.01Te (middle) samples; (C) Measured sound velocities of the transverse (ν_t) and longitudinal (ν_l) waves and the calculated Grüneisen parameter (γ) and lattice thermal conductivity (κ_l) values at room temperature, where ν₀ is the measured sound velocity of the GeTe sample. Copyright 2022, AAAS^[97]; (D) Measured neutron-weighted phonon DOSs of the Nb_0.9X_0.1FeSb compounds. The error bars represent one standard deviation from counting statistics. Copyright 2023, Han et al.^[98]; (E) A reduction of κ_l upon the introduction of micro/nano structural defects. The lines show the κ_l= Av_s³T^-1 model describing phonon thermal conductivity in the high-T limit where the only scattering mechanism is phonon-phonon scattering. A is normalized to the Na-PbTe sample and fixed. The shaded region shows the reduction in κ_l expected from lattice softening alone, without assuming an increase in phonon-defect scattering centers. Phonon scattering mechanisms could account for the remaining reduction in κ_l, depicted by the cross-hatched region. The speed of sound (v_s) reduction, measured in this study, is given in the legend. The circles are data for a Na-doped (0.75% Na) sample synthesized and measured in this study. The square data points are a low dislocation density sample from reference (Na_0.015Eu_0.03Pb_0.955Te). Copyright 2019, Wiley^[28]; (F) Lattice thermal conductivity versus temperature under different biaxial tensile strains (δ = 0%, 2%, 4%, 6%, and 8%) of unstrained and strained 1T-SnSSe monolayers. Copyright 2022, Elsevier^[92]; Phonon dispersion relations for (G) Mg2Si; (H) Mg₂Si_0.375Sn_0.625; and (I) Mg₂Sn; the gradually changing colors indicate the group velocity for the corresponding phonon branches; (J) shows their acoustic phonon branches along the “Γ-X” direction. Copyright 2017, AIP Publishing^[99]. FWHM: Full width at half maximum.