Oxidation Pathways of Ti₃C₂T_x MXenes to Titanium Oxides

The quasi-two dimensional Ti₃C₂T_x system is commonly prepared by chemical etching of the aluminum layers in the stable Ti₃AlC₂ MAX phase. The freshly exposed metal ions stabilize by attracting termination groups, but the resulting MXene is still susceptible to degradation under elevated temperature, humidity, and oxidizing environments. In this talk, I will show that in situ Raman spectroscopic measurements track the evolution and growth of new vibrational peaks corresponding to polymorphs of titanium oxides.  The particular etching method in MXene synthesis promotes the bonding of particular T_x termination groups can be seen through X-ray photoelectron spectroscopy, and that these features can influence the structural favorability of forming rutile and anatase TiO₂. This oxide formation leads to observable changes in spin dynamics and transport properties characterized by temperature dependent electron spin resonance, microwave conductivity, and impedance spectroscopy techniques. Understanding MXene stability in damaging conditions, which can be present in ambient surroundings, is important if MXenes are to be deployed in real applications.