Phase transition at 350 K in the Ti₃ C₂ T_x MXene: Possible sliding or moiré ferroelectricity

A phase transition is found in Ti3C2Tx MXene at 350 K, by measuring the complex Young's modulus of self-standing thick films. A steplike softening and increase of the mechanical losses is found below 350 K, indicative of a phase transition, where the square of the order parameter is coupled to strain. It is argued that it should be a ferroelectric transition, most likely of the sliding (moiré) type, due to charge transfer between facing flakes sliding with respect to each other. If the transition will be confirmed to be ferroelectric, Ti3C2Tx will be added to the class of metallic ferroelectrics and open new perspectives of applications, in addition to the numerous already studied.