Quantum Nuclear Dynamics of Protons within Layered Hydroxides at High Pressure

International audienceStudies of the structure of hydroxides under pressure using neutron diffraction reveal that the highconcentration of hydrogen is distributed in a disordered network. The disorder in the hydrogen-bondnetwork and possible phase transitions are reported to occur at pressures within the range accessible toexperiments 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 aquantum approach describing nuclear motion, shown herein to be required particularly when studyingdiffusion processes involving light hydrogen atoms. The effect of high-pressure on the disorderedhydrogen-bond network shows that the protons tunnel back and forth across the barriers betweenthree potential minima around the oxygen atoms. At higher pressures the structure has quasi twodimensionallayers of hydrogen atoms, such that at low temperatures this causes the barrier crossingof the hydrogen to be significantly rarefied. Furthermore, for moderate values of both temperatureand pressure this process occurs less often than the usual mechanism of proton transport via vacancies,limiting global proton diffusion within layers at high pressur