Orientational Disorder Drives Site Disorder in Plastic Ammonia Hemihydrate - Tout INSP
Article Dans Une Revue Physical Review Letters Année : 2024

Orientational Disorder Drives Site Disorder in Plastic Ammonia Hemihydrate

Résumé

In the 2–10 GPa pressure range, ammonia hemihydrate H$_2$⁢O:(NH$_3$)$_2$ (AHH) is a molecular solid in which intermolecular interactions are ruled by distinct types of hydrogen bonds. Upon heating, the low-temperature ordered $P2_1/c$ crystal (AHH-II) transits to a bcc phase (AHH-$p$ ⁢bcc) where each site is randomly occupied by water or ammonia. In addition to the site disorder, experiments suggest that AHH-$p$ bcc is a plastic solid, but the physical origin and mechanisms at play for the rotational and site disordering remain unknown. Using large-scale (∼10$^5$  atoms) and long-time (>10  ns) simulations, we show that, as temperature rises above the transition line, orientational disorder sets in, breaking the strongest hydrogen bonds that provide the largest contribution to the cohesion of the ordered AHH-II phase and enabling the molecules to migrate from a crystal site to a neighboring one. This generates a plastic molecular alloy with site disorder while the solid state is overall maintained until melting at a higher temperature. The case of high (P,T) plastic ammonia hemihydrate can be extended to other water-ammonia alloys where a similar interplay between distinct hydrogen bonds occurs
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Dates et versions

hal-04698682 , version 1 (16-09-2024)

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Citer

Niccolò Avallone, Simon Huppert, Philippe Depondt, Leon Andriambariarijaona, Frédéric Datchi, et al.. Orientational Disorder Drives Site Disorder in Plastic Ammonia Hemihydrate. Physical Review Letters, 2024, 133 (10), pp.106102. ⟨10.1103/PhysRevLett.133.106102⟩. ⟨hal-04698682⟩
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