Cold Sintering Breaks Temperature Barriers: Aqueous‐NaOH‐Driven Densification of Amorphous SiHfBN Ceramics at 250°C

ABSTRACT

Conventional ceramic processing often requires temperatures above 1500°C, locking the field into high energy costs and limited compositional flexibility. Here, we defy this paradigm by demonstrating the cold sintering of amorphous SiHfBN ceramics at only 250°C. Using a transient aqueous NaOH medium, amorphous SiHfBN powders derived from a single‐source polymeric precursor are transformed into dense monoliths (≈ 88% relative density) through a synergistic combination of lubrication‐assisted particle rearrangement and surface‐driven hydrolysis‐condensation reactions. The resulting ceramics achieve a Vickers hardness of 2.8 GPa and compressive strength of 114 MPa, rivaling porous Si ₃ N ₄ processed above 1700°C. They also exhibit good thermal stability and oxidation behavior, achieving a mass loss of only 0.25% at 1000°C in air. Their ultralow thermal conductivity (0.7–1.3 W m ⁻¹ ·K ⁻¹ ), structural integrity, and stability up to 700°C establish a new processing frontier for amorphous Si‐based ceramic materials. This work redefines the boundaries of ceramic fabrication, positioning cold sintering as a viable route for future energy‐efficient manufacturing of high‐performance nonoxide ceramics.