Mode-Resolved Phonon Damping and Anharmonicity in Mo2C: Insights from Temperature-Dependent Raman Spectroscopy

The lattice dynamics of metallic molybdenum carbide (Mo2C) is investigated through mode-resolved temperature-dependent Raman spectroscopy over the range of 80–296 K. The Raman-active modes at ∼143 and ∼223 cm–1 and the high-frequency mode at ∼658 cm–1 exhibit systematic frequency softening and line width broadening with an increase in temperature. The line width evolution is adequately described by a three-phonon anharmonic decay model, with normalized residuals below 5%, indicating that anharmonic phonon–phonon interactions provide the dominant contribution to the temperature-dependent line width within the investigated range. The temperature-independent residual line width is analyzed using an Allen-type framework to obtain effective upper-bound estimates of electron–phonon coupling λeff, which may include contributions from defect scattering and other temperature-independent broadening mechanisms. The extracted values decrease from 0.081 and 0.026 for the low- and intermediate-frequency modes, respectively, to 0.0019 for the high-frequency mode. This hierarchy reflects the mode dependence of the residual line width-derived effective parameters and is qualitatively consistent with the predominantly Mo-derived electronic states near the Fermi level and reported density functional perturbation theory (DFPT) calculations. The results establish anharmonic phonon interactions as the dominant temperature-dependent contribution to the line width, while the intrinsic electron–phonon contribution cannot be uniquely separated from other sources of residual broadening.