Under high pressures and temperatures, molecular systems with substantial polarization charges, such as ammonia and water, are predicted to form superionic phases and dense fluid states with dissociating molecules and high electrical conductivity. This behaviour potentially plays a role in explaining the origin of the multipolar magnetic fields of Uranus and Neptune, whose mantles are thought to result from a mixture of H₂O, NH₃ and CH₄ ices. Determining the stability domain, melting curve and electrical conductivity of these superionic phases is therefore crucial for modelling planetary interiors and dynamos. Here we report the melting curve of superionic ammonia up to 300 GPa from laser-driven shock compression of pre-compressed samples and atomistic calculations. We show that ammonia melts at lower temperatures than water above 100 GPa and that fluid ammonia’s electrical conductivity exceeds that of water at conditions predicted by hot, super-adiabatic models for Uranus and Neptune, and enhances the conductivity in their fluid water-rich dynamo layers.

在高压和高温下，具有大量极化电荷的分子系统，如氨和水，预计会形成超离子相和致密流体状态，具有离解分子和高导电性。这种行为可能在解释天王星和海王星多极磁场的起源方面发挥了作用，它们的地幔被认为是由 H ₂ O、NH ₃和 CH _{4的混合物产生的}冰。因此，确定这些超离子相的稳定域、熔化曲线和电导率对于模拟行星内部结构和发电机至关重要。在这里，我们通过预压缩样品的激光驱动冲击压缩和原子计算报告了高达 300 GPa 的超离子氨的熔化曲线。我们表明，在高于 100 GPa 的温度下，氨的熔化温度低于水，并且在天王星和海王星的热超绝热模型预测的条件下，液态氨的电导率超过水的电导率，并增强了它们富含流体的发电机层的电导率.