Ab initio Monte Carlo prediction of order-to-disorder transitions in multicomponent MXenes

Abstract

This letter predicts unprecedented order-to-disorder transition behaviors in multicomponent MXenes using an integrated and improved first-principles Monte Carlo (MC) framework. The improvements include (i) structural relaxation and (ii) selective atom swapping during MC iterations for more accurate and efficient predictions. Using (TiMo)-based double transition metal (DTM) carbide MXenes as a model system, ab initio MC simulations reveal that surface termination and coordination environments play critical roles in governing chemical ordering in MXenes. Specifically, the formation of out-of-plane MXene (o-MXenes) with Mo segregation to outermost metallic layers (M') is only driven by the oxygen (O) termination at prismatic sites. In contrast, O termination at octahedral sites and fluorine (F) termination at both prismatic and octahedral sites always promote the formation of o-MXenes with Ti-segregated to M' layers. Furthermore, changing the F/O ratio at prismatic termination sites or alternating the atomic coordination within the MXene lattices can induce an order-to-disorder transition in DTM MXenes.