A carbon-nitride compound with defect zincblende structure (P4¯3m) has been discovered in samples prepared by a chemical precursor route. Crystallographical (high-resolution electron microscopy and electron nanodiffraction) and electron energy loss measurements has been performed to identify the material as cubic zincblende with C3N4composition. Nanoindentation indicates a high elastic recovery and hardness. The results agree with detailedab initiocalculations on metastable structures and compressibility. Our synthesis method is projected to be a process that could produce large quantities of material by controlling the chemical strategy. The new compound has potential applications for high hardness, elasticity and thermal conductivity materials and thin films. ©1997 American Institute of Physics.