Cold sintering of ceramics: interfacial mechanisms, structure–property relationships, and multifunctional applications

The cold sintering process (CSP) has emerged as a promising ceramic processing route capable of achieving densification at temperatures far below those required for conventional sintering. The process relies on the combined effects of transient liquid phases, external pressure, dissolution-precipitation reactions, and subsequent thermal activation, resulting in distinctive microstructural and interfacial characteristics. Beyond low-temperature densification, CSP offers opportunities to tailor dielectric, thermal, ionic, ferroelectric, piezoelectric, and energy-storage properties through control of grain boundaries, residual phases, and defect chemistry. Despite significant progress, important questions remain regarding interfacial transport mechanisms, transient phase evolution, grain-boundary behavior, and long-term stability. Unlike previous reviews that primarily focus on densification mechanisms or specific material systems, this article establishes an interface-centered framework linking grain-boundary chemistry, defect evolution, and coupled transport phenomena to multifunctional performance in cold-sintered ceramics. This review examines the physicochemical mechanisms governing CSP and their relationships with microstructural development and functional performance. Particular attention is given to ionic transport, thermal conduction, dielectric polarization, and defect-mediated electrical behavior. Alongside the process-interface-transport-property paradigm, emerging applications, characterization approaches, modeling efforts, and challenges associated with scalability and sustainable manufacturing are also discussed.