Pressure-induced shear and interlayer expansion in Ti₃C₂ MXene in the presence of water

Pseudo-negative compressibility in layered materials is a phenomenon typically limited to in situ high-pressure experiments in some clay minerals and carbon-based materials. We show that the MXene Ti₃C₂T expands along its crystallographic c direction when compressed in the presence of H₂O. This expansive effect occurs when a mixture of powders and excess water is quasi-hydrostatically compressed in a diamond anvil cell; it also occurs to a much larger extent when powders are pressed uniaxially into discs and, notably, persists after pressure is released. We attribute the expansion to the insertion of H₂O molecules and have identified shear-induced slipping of the nanosheets comprising multilayered MXene particles as a possible cause of this behavior in the latter case. This both has implications for the processing of MXenes and contributes to the field of materials with pseudo-negative compressibility by adding a new member for further investigation.