Direct evidence of the proton-dynamics crossover in ice VII from high-pressure dielectric measurements beyond 10 GPa

We have conducted dielectric measurements of ice VII at pressures up to 12.2 GPa, and verified a dominant-dynamics change from a molecular rotation to a proton translation at approximately 10 GPa, using a newly developed high-pressure cell. Based on relaxation times of the two motions, which have a crossover point between 9 and 10 GPa, we show that the change in the disordered states in ice VII can be characterized by the time scale of the motions. Our results provide a suitable explanation of the long-standing problem of the anomalous behavior of ice VII at around 10 GPa.