When trace water dominates: Hydration-mediated dielectric and transport behaviour in BiFeO₃

Trace amounts of water can profoundly alter the dielectric response of functional oxides, yet such effects remain largely unrecognized in systems where colossal dielectric behaviour is widely reported. Here, we investigate the impact of sub-percent hydration (∼0.14 wt%) on dielectric relaxation, charge transport, and interfacial polarization in porous BiFeO₃ ceramics. Broadband dielectric spectroscopy reveals, in the hydrated state, a dominant relaxation with anomalously large dielectric strength and a pronounced saddle-point deviation from Arrhenius dynamics, indicating non-Arrhenius behaviour. These features appear only in the hydrated state and vanish upon dehydration, while intrinsic activation barriers governing the thermally activated relaxation timescale remain comparable. Comparison with layered clay minerals, which typically contain 2–15 wt% water, shows similar behaviour at substantially lower water content (∼0.14 wt%), highlighting the effectiveness of confined water at grain boundaries and internal interfaces. These results demonstrate that trace confined water provides a dominant extrinsic contribution to dielectric and transport anomalies.