Phase formation of Nb2AlC investigated by combinatorial thin film synthesis and ab initio calculations

Abstract

The phase formation of Nb2AlC was studied by combinatorial thin film synthesis and ab initio calculations. Thin films with lateral chemical composition gradients were synthesized by DC magnetron sputtering at substrate temperatures of 710–870°C. The lowest formation temperature for Nb2AlC is between 710 and 750°C. A predominantly single phase Nb2AlC region where 99% of the X-ray diffraction intensity originate from Nb2AlC was identified. Furthermore, selected area electron diffraction analysis reveals the local formation of single phase Nb2AlC. The limited Al solubility in Nb2AlC compared with Cr2AlC can be understood by comparing the defect formation energy of Al substituting Nb and Cr in Nb2AlC and Cr2AlC, respectively. This methodology may serve as indicator for the magnitude of the A-element homogeneity range in Mn+1AXn phases. The structural and elastic properties of Nb2AlC determined experimentally are in very good agreement with the ab initio calculated data.