Mn+1AXn Phonon Density of States: Ti3AlC2 and Ti3SiC2 Simulation and Experimentation Results

For the first time detailed measurements of the DOS (density of states) for Ti 3 AlC 2 and Ti 3 SiC 2 are presented at temperatures between T = 10 and 100 K.For Ti 3 AlC 2 a DFT (density functional theory) simulation of lattice dynamics is compared to experimental data demonstrating a noticeable difference between the spectra especially below 40 meV.In the case of Ti 3 SiC 2 the DFT model is augmented with MD (molecular dynamics) simulations resulting in the measured and simulated spectra resembling one another more closely but still having significant differences below 40 meV.Within the experimental spectra, there are features up to and including 20 meV which are unaccounted for by the simulation.Tracing individual atoms generated by the computer models suggests anharmonic motion of Si within the Ti 3 SiC 2 .The results presented could explain differences between calculated elastic moduli using DFT harmonic lattice dynamics simulations and results from recent experiments.