Fine‐Grain Densification in Faceted Grain Ceramics Via Chemical Modification

Densification of faceted grain ceramics, exemplified by lead‐free piezoelectric potassium sodium niobate (KNN), remains a longstanding challenge due to preferential grain growth and directional diffusion, which degrade performance and hinder practical applications. Here, chemical modification via single‐element Ti doping enables high densification (98% relative density) with submicron grains (0.36 µm) in KNN ceramics. Substitution of Ti 4+ at Nb 5+ sites generates both oxygen vacancies and substitutional defects, which reshape the energy landscape by elevating crystallographic plane interfacial energy while suppressing step free energy. This strategy redirects sintering driving forces toward densification over grain growth, enabling fine‐grain densification. This work develops a disorder‐mediated framework‐integrating defect chemistry, interfacial energy anisotropy, and grain growth kinetics‐to decipher densification mechanisms of faceted grain ceramics. The approach not only deepens fundamental insights but also provides a scalable method to manufacture high‐quality faceted grain ceramics for industrial processing.