Highly Stable Nanolamellar MXene-Derived Carbides by Phase Transformation of Ti₃C₂T_x and Mo₂TiC₂T_x MXenes for Extreme Environments

Two-dimensional transition metal carbides, nitrides, and carbonitrides, known as MXenes, have a wide array of impressive material properties due to their inherent transition metal carbide and nitride core with abundant surface functionalities. Although MXenes’ properties have been extensively investigated for energy storage and catalysis, few studies take advantage of the inherent stability of the interior transition metal carbide core for use in inert extreme environment conditions. In this study, we investigated the high-temperature behavior of Ti₃C₂T<i>_x</i> from room temperature to 2,000 °C using <i>in-situ </i>annealing of Ti₃C₂T<i>_x</i> up to 1,100 °C using two-dimensional x-ray diffraction (XRD²) and <i>ex-situ </i>XRD²sintered Ti₃C₂T<i>_x</i> up to 2,000 °C annealed via spark plasma sintering. We utilize cross-sectional scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) methods to analyze the formed microstructures of Ti₃C₂T<i>_x</i> MXene films annealed up to 2,000 °C. The combination of these methods identified the transformation of hexagonal ordered carbon vacancy Ti₃C₂T<i>_x</i> to nanolamellar cubic disordered carbon vacancy TiC<i>_y</i> with strong preferential (111) plane orientation. In addition, our studies identify that these preferentially ordered lamellar phases are stable up to 2,000 °C in inert environments. We also expand these methods with other <i>in-situ</i> techniques to measure the micro- and nano-scale structure to characterize the phase transformation behavior in the more exotic ordered double-transition metal MXene Mo₂TiC₂T<i>_x</i>. These findings identify a unique capability of MXenes for future studies, which utilize their transition metal carbide and nitride core to form highly stable MXene-derived carbides and nitrides with controlled morphology for extreme environment applications.