Anharmonicity-induced phonon broadening in aluminum at high temperatures

Thermal phonon broadening in aluminum was studied by theoretical and experimental methods. Using second-order perturbation theory, phonon linewidths from the third-order anharmonicity were calculated from first-principles density-functional theory (DFT) with the supercell finite-displacement method. The importance of all three-phonon processes were assessed and individual phonon broadenings are presented. The good agreement between calculations and prior measurements of phonon linewidths at 300 K and new measurements of the phonon density of states to 750 K indicates that the third-order phonon-phonon interactions calculated from DFT can account for the lifetime broadenings of phonons in aluminum to at least 80% of its melting temperature.

Figure 1

(Color online) Neutron scattering $I\left(Q,E\right)$ from aluminum at 300 K. The vertical axis of the color scale is linear in intensity.

Figure 2

(Color online) (a) Calculated phonon dispersion at 0 K with DOS shown at right and (b) correspondent linewidth at 300 K (solid lines), in comparison with neutron spectroscopy measurement from Ref. 17 (symbols). Linewidth distribution over high-symmetry planes are shown in (c)–(e) for LA, ${\text{TA}}_1$, and ${\text{TA}}_2$ modes.

Figure 3

(Color online) Up-conversion $\left(D_1\right)$ processes in blue and down-conversion $\left(D_2\right)$ processes in red for three branches along high-symmetry directions. Individual scattering channels are shown by dashed lines.

Figure 4

(Color online) Distribution of phonon broadenings versus phonon energy at 300 K with ${\text{TA}}_1$ phonons shown in green, ${\text{TA}}_2$ phonons in blue, and LA phonons in red.

Figure 5

Comparison of phonon DOS between calculation (solid lines) and inelastic neutron-scattering measurements (points).