Structural transitions and mechanical properties of Zr₂C under ambient and high-pressure conditions

Transition metal carbides have attracted considerable attention and are widely used in machining tools, hard coatings and aerospace components, owing to their excellent mechanical and thermal properties. The Zr–C system is a typical refractory and hard transition-metal carbide, and its structural integrity and stability under extreme conditions are critical for practical applications. Here, a computational study focusing on the structural stability and crystal evolution pattern of Zr₂C under ambient and high-pressure conditions was performed using a particle-swarm optimization algorithm, in combination with first-principles calculations. The calculations identified seven_ viable stable or metastable crystalline phases of Zr₂C, exhibiting Fd3m, R3m, Cmcm, Cmca, Pbcn, Pnma and I4/mcm symmetries; further, a series of structural phase transitions were determined as the pressure increased: Fd3m ! R3m ! Cmcm ! Cmca. In addition, the mechanical and dynamical stabilities of these phases were verified, and their structural properties were investigated. Overall, this work reveals valuable information concerning the structural, mechanical and electronic properties of Zr₂C, providing key insights into the mechanisms underlying its crystal evolution behavior.