Switchable Electromagnetic Absorption and Shielding in Liquid Metal‐ZnO Ceramics via Ultralow‐Electric‐Field

ABSTRACT Conventional electromagnetic shielding and absorbing materials are constrained by intrinsic dielectric and magnetic responses, rendering them inadequate for multi‐band communication, reconfigurable electronics, and adaptive stealth technologies. Here, we report a ZnO–liquid Ga composite ceramic that enables electric‐field‐driven switching between electromagnetic absorption and shielding under ultralow external electric fields. By tailoring interfacial reactions during cold sintering, a hierarchical ZnO/ZnGa 2 O 4 /Ga 2 O 3 /Ga heterointerface network is constructed. This architecture synergistically regulates interfacial polarization and field‐dependent carrier transport, enabling simultaneously ultrahigh‐intensity and broadband electromagnetic absorption (reflection loss of −70.1 dB at 1.91 mm with an effective bandwidth exceeding 6 GHz), together with outstanding electrical nonlinearity (α ≈ 445) and an ultralow threshold field (<45 V mm −1 ). Below the threshold field, electromagnetic attenuation is dominated by interfacial polarization loss, whereas exceeding the threshold induces a sharp conductivity increase via interfacial barrier modulation, driving a transition to a shielding‐dominated state. In this regime, the composite exhibits a theoretically estimated shielding effectiveness exceeding 35 dB across 2–18 GHz based on experimentally measured conductivity, thereby realizing dynamic switching between absorption and shielding modes. This work establishes a new paradigm for heterointerface‐engineered, cold‐sintered ceramics toward intelligent electromagnetic protection materials with externally controllable functionality.