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Detailed crystallographic analysis of the ice VI to ice XV hydrogen ordering phase transition

Salzmann, CG; Slater, B; Radaelli, PG; Finney, JL; Shephard, JJ; Rosillo-Lopez, M; Hindley, J; (2016) Detailed crystallographic analysis of the ice VI to ice XV hydrogen ordering phase transition. The Journal of Chemical Physics , 145 (20) , Article 204501. 10.1063/1.4967167. Green open access

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Abstract

The D2O ice VI to ice XV hydrogen ordering phase transition at ambient pressure is investigated in detail with neutron diffraction. The lattice constants are found to be sensitive indicators for hydrogen ordering. The a and b lattice constants contract whereas a pronounced expansion in c is found upon hydrogen ordering. Overall, the hydrogen ordering transition goes along with a small increase in volume which explains why the phase transition is more difficult to observe upon cooling under pressure. Slow-cooling ice VI at 1.4 GPa gives essentially fully hydrogen-disordered ice VI. Consistent with earlier studies, the ice XV obtained after slow-cooling at ambient pressure is best described with P-1 space group symmetry. Using a new computational approach, we achieve the atomistic reconstruction of a supercell structure that is consistent with the average partially ordered structure derived from Rietveld refinements. This shows that C-type networks are most prevalent in ice XV but other structural motifs outside of the classifications of the fully hydrogen-ordered networks are identified as well. The recently proposed Pmmn structural model for ice XV is found to be incompatible with our diffraction data and we argue that only structural models that are capable of describing full hydrogen order should be used.

Type: Article
Title: Detailed crystallographic analysis of the ice VI to ice XV hydrogen ordering phase transition
Open access status: An open access version is available from UCL Discovery
DOI: 10.1063/1.4967167
Publisher version: http://doi.org/10.1063/1.4967167
Language: English
Additional information: Published by AIP Publishing.
Keywords: Cond-mat.mtrl-sci, cond-mat.mtrl-sci
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/1504250
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