Structural and optical properties of the recently synthesized (Zr3−x Ti x )AlC2 MAX phases

In the present study we investigate the structural, Fermi surface and optical properties of the recently synthesized (Zr3−x Ti x )AlC2 MAX phases using density functional theory. The inclusion of Ti in the M site causes a reduction of both the a and c lattice parameters. The reduction of the a lattice parameter with respect to Ti content is more significant and this is reflected in the increase of the c/a ratio. The Fermi surfaces are formed mainly due to the low-dispersive transition metal d-like orbitals, which are responsible for the conductivity in the compounds. The energy loss spectra reveals that the two end members of (Zr3−x Ti x )AlC2 (x = 0 and 3) change from metallic to dielectric response at incident light energies 11.9, 13.4 and 10.8, 13.5 eV for [100] and [001] polarization directions, respectively. The reflectivity spectra indicate the ability of two end compounds Zr3AlC2 and Ti3AlC2 to be candidate materials for coatings to reduce solar heating. The calculated optical functions show the dependence on the polarization directions.