Multicomponent alloying has displayed extraordinary potential for producing exceptional structural and functional materials. However, the synthesis of single-phase, multi-principal covalent compounds remains a challenge. Here, we present a diffusion-controlled alloying strategy for the realization of covalent multi-principal transition metal carbides (MPTMCs) with a single face-centered cubic phase. The increased interfacial diffusion promoted by the addition of a nonstoichiometric compound leads to rapid formation of the single phase at much lower sintering temperature. Direct atomic-level observations via scanning transmission electron microscopy demonstrate that MPTMCs are composed of a single phase with a random distribution of all cations, which holds the key to the unique combinations of improved fracture toughness, superior Vickers hardness, and extremely lower thermal diffusivity achieved in MPTMCs. The present discovery provides a promising approach toward the design and synthesis of next-generation high-performance materials.

The discovery of electrides, in particular, inorganic electrides where electrons substitute anions, has inspired striking interests in the systems that exhibit unusual electronic and catalytic properties. So far, however, the experimental studies of such systems are largely restricted to ambient conditions, unable to understand their interactions between electron localizations and geometrical modifications under external stimuli, e.g., pressure. Here, pressure‐induced structural and electronic evolutions of Ca₂N by in situ synchrotron X‐ray diffraction and electrical resistance measurements, and density functional theory calculations with particle swarm optimization algorithms are reported. Experiments and computation are combined to reveal that under compression, Ca₂N undergoes structural transforms from R m symmetry to I 2d phase via an intermediate Fd m phase, and then to Cc phase, accompanied by the reductions of electronic dimensionality from 2D, 1D to 0D. Electrical resistance measurements support a metal‐to‐semiconductor transition in Ca₂N because of the reorganizations of confined electrons under pressure, also validated by the calculation. The results demonstrate unexplored experimental evidence for a pressure‐induced metal‐to‐semiconductor switching in Ca₂N and offer a possible strategy for producing new electrides under moderate pressure.