Most experimentally known high-pressure ice phases have a body-centred cubic (bcc) oxygen lattice. Our large-scale molecular-dynamics simulations with a machine-learning potential indicate that, amongst these bcc ice phases, ices VII, VII′ and X are the same thermodynamic phase under different conditions, whereas superionic ice VII″ has a first-order phase boundary with ice VII′. Moreover, at about 300 GPa, the transformation between ice X and the Pbcm phase has a sharp structural change but no apparent activation barrier, whilst at higher pressures the barrier gradually increases. Our study thus clarifies the phase behaviour of the high-pressure ices and reveals peculiar solid–solid transition mechanisms not known in other systems.

大多数实验上已知的高压冰相具有体心立方（bcc）氧晶格。我们具有机器学习潜力的大规模分子动力学模拟表明，在这些 bcc 冰相中，冰 VII、VII' 和 X 在不同条件下是相同的热力学相，而超离子冰 VII" 具有一级相与冰 VII' 的边界。此外，在大约 300 GPa 时，冰 X 和 P bcm相之间的转变具有急剧的结构变化，但没有明显的活化势垒，而在较高压力下，势垒逐渐增加。因此，我们的研究阐明了高压冰的相行为，并揭示了其他系统中不知道的特殊固固转变机制。