Ultrahigh dielectric permittivity in oxide ceramics by hydrogenation

Boosting dielectric permittivity representing electrical polarizability of dielectric materials has been considered a keystone for achieving a new stage of scientific breakthroughs as well as technological advances in various multifunctional devices. In this work, we demonstrate the significant enhancement of low-frequency dielectric constant in oxygen-deficient oxide ceramics via the hydrogenation induced by water dissociation. In the as-sintered state, the initial dielectric constant in Ni-substituted BaTiO₃ ceramics is very low (~10³ at 1 Hz, the off-state). When ceramics are exposed to high humidity, a giant dielectric constant (~10⁶ at 1 Hz, the on-state) is obtained, which is three orders of magnitude higher than that in the pristine state. It appears that the ultrahigh dielectric permittivity in the on-state is restored to the original value in the off-state via the thermal annealing. The conversion between these two dielectric states via the ambient-environment-mediated treatments and the successive application of external stimuli allows us to realize reversible control of dielectric relaxation characteristics in oxide ceramics. The achieved huge dielectric permittivity in the ambient-environment-treated Ni-substituted BaTiO₃ ceramics would originate from spatial inhomogeneity of electrical polarizability induced by the hydrogenation. Conceptually, our work is of potential interest for realizing a new concept of ceramic-based dielectric sensors (e.g., hygrometers), which are able to detect water vapor in ambient air with high efficiency and sensitivity.