Water ice becomes a superionic phase under the high pressure and temperature conditions of deep planetary interiors of ice planets such as Neptune and Uranus, which affects interior structures and generates magnetic fields. The solid Earth, however, contains only hydrous minerals with a negligible amount of ice. Here we combine high pressure and temperature electrical conductivity experiments, Raman spectroscopy and first-principles simulations to investigate the state of hydrogen in the pyrite-type FeO₂H_x (x ≤ 1), which is a potential H-bearing phase near the core–mantle boundary. We find that when the pressure increases beyond 73 GPa at room temperature, symmetric hydroxyl bonds are softened and the H⁺ (or proton) becomes diffusive within the vicinity of its crystallographic site. Increasing temperature under pressure, the diffusivity of hydrogen is extended beyond the individual unit cell to cover the entire solid, and the electrical conductivity soars, indicating a transition to the superionic state, which is characterized by freely moving protons and a solid FeO₂ lattice. The highly diffusive hydrogen provides fresh transport mechanisms for charge and mass, which dictate the geophysical behaviours of electrical conductivity and magnetism, as well as geochemical processes of redox, hydrogen circulation and hydrogen isotopic mixing in Earth’s deep mantle.

水冰在海王星、天王星等冰行星的深层行星内部的高压和高温条件下变成超离子相，影响内部结构并产生磁场。然而，固体地球只包含含水矿物和微量冰。在这里，我们结合高压和高温电导率实验、拉曼光谱和第一性原理模拟来研究黄铁矿型 FeO ₂ H _x ( x  ≤ 1) 中的氢状态，这是靠近核心的潜在含氢相——地幔边界。我们发现，当压力在室温下超过 73 GPa 时，对称的羟基键会软化，H ⁺（或质子）在其结晶位置附近变得扩散。在压力下升高温度，氢的扩散率扩展到单个晶胞之外以覆盖整个固体，电导率飙升，表明向超离子态的转变，其特征是自由移动的质子和固体 FeO ₂晶格。高度扩散的氢为电荷和质量提供了新的传输机制，这决定了电导率和磁力的地球物理行为，以及地球深部地幔中氧化还原、氢循环和氢同位素混合的地球化学过程。