Influence of synthesis routes on oxygen content, crystallography, and thermal stability of Ti3AlC2 MAX phases and resulting MXenes

Abstract

Current MXene research focuses on synthesising high-quality MAX phases with minimal O substitution in the C sublattice. This study provides insights into how different ball milling techniques and elemental compositions used in Ti₃AlC₂ MAX phase synthesis affect the O incorporation into the lattice structure, which directly impacts the MAX phases’ and the resulting MXenes’ thermal stability. The unit cell lattice parameters (LPs) of a MAX phase are well-established indicators in determining the degree of O substitution. The presence of O reduced the a and c LPs of the MAX phase unit cell. However, the corresponding MXenes exhibited similar a LP (a = 3.05 Å) values regardless of the LP values of their MAX phases. The LP observations are validated by correlative thermogravimetric analysis (TGA) carried out in air atmosphere. With the decreasing O incorporation in the MAX phase, an increase in the oxidation temperature was observed from 450 °C to 780 °C. However, the corresponding MXenes showed an average oxidation onset around 460 °C. Thus, this study reveals an important structure–property relationship between the Ti₃AlC₂ MAX phase and the resulting Ti₃C₂ MXenes.