Structure, electronic and optical properties of (Cr1-xMnx)2GeC MAX phase: DFT calculations and epitaxial film synthesis

https://doi.org/10.1016/j.mtcomm.2025.114184

The energy and electronic characteristics, as well as crystal parameters of the (Cr_1-xMn_x)₂GeC MAX phase with x = 0.00, 0.25, 0.33, 0.50, 0.67, 0.75, and 1.00 were determined using quantum chemical calculations. As the manganese concentration increases, the stability of the compound is expected to decrease. However, the possibility of experimentally realizing a structure with x > 0.25 has been shown. Epitaxial thin (Cr_1-xMn_x)₂GeC MAX films with x up to 0.33 were synthesized by magnetron co-deposition at an increased technological carbon concentration. The samples were studied using electron spectroscopy, high-energy electron diffraction, X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy and reflection spectral ellipsometry. The additional graphitic carbon is identified in the films and is attributed to the peculiarities of the deposition method. An increase in x results in an increase in the parameters of the crystal lattice, a deterioration of the crystalline order, and a decrease in optical conductivity. However, a low manganese concentration (x = 0.25) enhances epitaxy compared to Cr₂GeC. A threefold increase in the thickness of the (Cr_0.75Mn_0.25)₂GeC film results in an increase in the fraction of the secondary (013) structure and a weakening of the primary (00L) structure, though the single-phase nature of the film is preserved.