Interfacial Polytype Engineering of Polymer-Derived SiC via Compositionally Complex MXene Templating.

Controlling polytype selection in polymer-derived silicon carbide (SiC) remains challenging since stacking sequences are determined locally at the nucleation front. Here, we investigate an interface-based strategy for influencing SiC polytype evolution by introducing compositionally complex TiVCrMoC3 MXene nanosheets at the preceramic stage. Under spark plasma sintering (1900 °C, 70 MPa), which typically stabilizes cubic 3C-SiC (β-SiC), the MXene partially transforms into multicomponent (Ti,V,Cr,Mo)Cx carbide structures, while MXene-derived layered regions are also locally observed. Local HRTEM observations show reconstructed carbide/SiC interfaces adjacent to 6H-SiC regions and MXene-derived layered phase/SiC interfaces adjacent to 3C-SiC regions, revealing heterogeneous interfacial configurations within the SiC matrix. Mechanical testing further reveals peak performance at an optimal MXene loading where interfacial reconstruction is most pronounced, with an ∼82% increase in Young's modulus and ∼42% improvement in fracture toughness. These findings highlight interfacial polytype engineering via two-dimensional carbide templates as a promising route for directing crystal structure evolution in polymer-derived ceramics.