Air-Sensitive Material Synthesis via Liquid Metal Shielding.

Air-sensitive solid-state reactions typically require complex encapsulation or inert atmospheres to prevent oxidation at elevated temperatures. Here we introduce a liquid metal shielding strategy that enables high-temperature solid-state reactions to be carried out under ambient conditions. Owing to its near-room-temperature melting point and low viscosity, liquid gallium forms a conformal and hermetic sealing barrier that prevents oxygen transport throughout thermal processing. We demonstrate the gram-scale synthesis of nanocrystalline refractory borides including WBx, ReB2, ZrB2, and FeB, layered WS2, and bronze oxides (KxWO3). Mechanistic investigations reveal that gallium primarily serves as a physical shield, while also modifying local redox chemistry and phase evolution in certain systems. While limitations exist for reactions producing large gas volumes or involving gallium-soluble elements, this approach provides a practical encapsulating strategy for efficient, high-temperature, air-sensitive solid-state synthesis. This methodology offers a powerful platform to expand the toolkit for advanced materials synthesis.