Atomic level decomposition mechanism of Ti2AlC into TiCx

Abstract

It has proved that outwards diffusion of Al from A layers of Ti2AlC and Ti3AlC2 leads to the formation of Al2O3 layer and TiC during oxidation above 800 °C. While, no atomic level observation was conducted to reveal this transformation process. We demonstrated that the replacement of Al by Ti atoms in A planes leads to the formation of TiCx rather than the connection of two adjacent Ti2C or Ti3C2 layers after the outwards diffusion of Al atoms from A layers. This replacement arouses an adjustment of atomic distance between two adjacent Ti layers and produces one local strain. This further induces one rotation of lattice and TiCx formation instead of the twin formation Ti2C or Ti3C2 along A layer. Due to the lack of one Ti or Al layer, Edge-like structure similar to out-of-plane dislocations formed at the junctions of Ti3C2 and Ti3AlC2 or Ti2AlC and Ti3AlC2. Our observations prove that it is impossible to produce MXene at 800 °C or even high temperature.