Quantum Nuclear Dynamics of Protons within Layered Hydroxides at High Pressure
Résumé
Studies of the structure of hydroxides under pressure using neutron diffraction reveal that the high
concentration of hydrogen is distributed in a disordered network. The disorder in the hydrogen-bond
network and possible phase transitions are reported to occur at pressures within the range accessible to
experiments for layered calcium hydroxides, which are considered to be exemplary prototype materials.
In this study, the static and dynamical properties of these layered hydroxides are investigated using a
quantum approach describing nuclear motion, shown herein to be required particularly when studying
diffusion processes involving light hydrogen atoms. The effect of high-pressure on the disordered
hydrogen-bond network shows that the protons tunnel back and forth across the barriers between
three potential minima around the oxygen atoms. At higher pressures the structure has quasi twodimensional
layers of hydrogen atoms, such that at low temperatures this causes the barrier crossing
of the hydrogen to be significantly rarefied. Furthermore, for moderate values of both temperature
and pressure this process occurs less often than the usual mechanism of proton transport via vacancies,
limiting global proton diffusion within layers at high pressure
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