Vegard’s law deviating Ti₂(Sn_xAl_1−x)C solid solution with enhanced properties

The achievement of chemical diversity and performance regulation of MAX phases primarily relies on solid solution approaches. However, the reported A-site solid solution is undervalued due to their expected chemical disorder and compliance with Vegard’s law, as well as discontinuous composition and poor purity. Herein, we synthesized high-purity Ti₂(Sn_xAl_1−x)C (x = 0–1) solid solution by the feasible pressureless sintering, enabling us to investigate their property evolution upon the A-site composition. The formation mechanism of Ti₂(Sn_xAl_1−x)C was revealed by thermal analysis, and crystal parameters were determined by Rietveld refinement of X-ray diffraction (XRD). The lattice constant (a) adheres to Vegard’s law, while the lattice constant (c) and internal free parameter (z_M) have noticeable deviations from the law, which is caused by the significant nonlinear distortion of Ti₆C octahedron as Al atoms are substituted by Sn atoms. Also, the deviation also results in nonlinear changes in their physicochemical properties, which means that the solid solution often exhibits better performance than end members, such as hardness, electrical conductivity, and corrosion resistance. This work offers insights into the deviation from Vegard’s law observed in the A-site solid solution and indicates that the solid solution with enhanced performance may be obtained by tuning the A-site composition.