Structural and Phase Stability of the $\text{Ti}_{3} \mathrm{C}_{2} \mathrm{T}_{\mathrm{x}}$ MXene at Elevated Temperatures: in-situ X-Ray Diffraction Investigation

This study investigates the structural and phase stability of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ti}_{3} \mathrm{C}_{2}$</tex> MXene synthesized via selective etching of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ti}_{3} \text{AlC}_{2}$</tex> MAX-phase powder in mixed HCl and HF acids. Flexible nanostructured films were prepared by vacuum filtration of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ti}_{3} \mathrm{C}_{2}$</tex> colloidal solution In-situ X-ray diffraction analysis revealed that initial heating triggers deintercalation and decomposition of intercalated water and hydroxyl groups, with accelerated kinetics in air due to ambient oxygen. Above 600° C, pronounced oxidation forms <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{TiO}_{2}$</tex>, persisting under vacuum via residual surface-bound oxygen and trace atmospheric oxygen. Post <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-800^{\circ} \mathrm{C}$</tex> exposure, both air and vacuum-treated samples exhibited loss in plasticity and altered surface morphology by formation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{TiO}_{2}$</tex> crystals, with no detectable phase transformation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ti}_{3} \mathrm{C}_{2}$</tex> to cubic TiC. Heat treatment in vacuum and in air leading to reduction of interplanar distance of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ti}_{3} \mathrm{C}_{2}$</tex> MXene related to changes in functional surface groups of MXene. These results underscore environmental oxygen's critical role in MXene's thermal degradation pathways, necessitating stringent atmospheric control for high-temperature applications to mitigate oxidation-driven structural changes.