Abstract
<jats:p>Single-phase high- and medium-entropy carbides typically require synthesis temperatures above ~2000 °C due to sluggish cation interdiffusion in the carbide lattice. Here, we demonstrate a precursor-engineering strategy using compositionally complex La2Zr2O7-based pyrochlores, in which transition-metal cations are pre-homogenized within a single oxide lattice prior to carbothermal reduction. Single-phase (Zr,Hf,Ta)C is obtained at 1600 °C, while directly mixed oxide systems remain phase-separated under identical conditions due to diffusion-limited interdiffusion among separately formed carbides. DFT calculations confirm that the reaction is thermodynamically favorable and largely composition-insensitive, indicating that single-phase formation is governed by precursor-controlled kinetics rather than thermodynamics. Comparative studies across multiple pyrochlore systems further establish precursor phase purity as the critical requirement, with competing oxide phases reverting the system to conventional diffusion-controlled behavior. These results identify a precursor-controlled pathway for lowering synthesis temperature and improving phase control in compositionally complex carbides.</jats:p>