Facile Synthesis of Ti₂AC (A = Zn, Al, In, and Ga) MAX Phases by Hydrogen Incorporation into Crystallographic Voids

While using hydride precursors, such as TiH₂, can promote the formation of some MAX phases, the mechanism for this stabilization effect by hydrogen has been unsolved. Herein, we report a facile synthesis method of Ti₂AC (A = Zn, Al, In, and Ga) MAX phases using hydrogen as the phase stabilizer at their crystallographic voids. DFT calculations revealed that hydrogen could be incorporated in the center of the Ti₃A (A = Zn, Al, Ga, and In) cages of Ti₂AC MAX phases. The hydrogen is accommodated as an anion as a result of electron transfer from the surrounding Ti and A to H, leading to the stabilized state through Coulomb interaction between (Ti₃A)^δ+ and H^-. Consequently, high-purity Ti₂AC (A = Zn, Al, Ga, and In) was directly synthesized under pressure-less and milder temperature conditions by simply employing TiH₂ as the precursor. These findings indicate that utilizing hydrogen could be one of the experimental parameters to facilitate the formation of materials having crystallographic voids.