title: Nuclear dynamics and phase polymorphism in solid formic acid.
abstract: We apply a unique sequence of structural and dynamical neutron-scattering techniques, augmented with density-functional electronic-structure calculations, to establish the degree of polymorphism in an archetypal hydrogen-bonded system - crystalline formic acid. Using this combination of experimental and theoretical techniques, the hypothesis by Zelsmann on the coexistence of the β1and β2phases above 220 K is tested. Contrary to the postulated scenario of proton-transfer-driven phase coexistence, the emerging picture is one of a quantitatively different structural change over this temperature range, whereby the loosening of crystal packing promotes temperature-induced shearing of the hydrogen-bonded chains. The presented work, therefore, solves a fifty-year-old puzzle and provides a suitable framework for the use neutron-Compton-scattering techniques in the exploration of phase polymorphism in condensed matter.
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. matthew.krzystyniak@stfc.ac.uk and School of Science and Technology, Nottingham Trent University, Clifton Campus, Nottingham, NG11 8NS, UK.
authors.forename: Maciej
authors.identifier: http://orcid.org/0000-0003-0307-6871
authors.initials: M
authors.lastname: Krzystyniak
authors.affiliation: Faculty of Physics, Adam Mickiewicz University, Umultowska St. 85, 61-614 Poznan, Poland.
authors.forename: Kacper
authors.initials: K
authors.lastname: Drużbicki
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. matthew.krzystyniak@stfc.ac.uk.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Romanelli
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. matthew.krzystyniak@stfc.ac.uk.
authors.forename: Matthias J
authors.initials: MJ
authors.lastname: Gutmann
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. matthew.krzystyniak@stfc.ac.uk.
authors.forename: Svemir
authors.identifier: http://orcid.org/0000-0003-3023-8565
authors.initials: S
authors.lastname: Rudić
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. matthew.krzystyniak@stfc.ac.uk.
authors.forename: Silvia
authors.initials: S
authors.lastname: Imberti
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK. matthew.krzystyniak@stfc.ac.uk and Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK.
authors.forename: Felix
authors.initials: F
authors.lastname: Fernandez-Alonso