title: Structure of the X-phase of 38% brominated betaine calcium chloride dihydrate.
abstract: The structures of the high- and low-temperature phases of 38% brominated BCCD [betaine (trimethylammonioacetate) calcium chloride dihydrate], the latter being known as the X-phase, have been determined by single-crystal neutron diffraction at 295 and 20 K, respectively. The symmetry of the X-phase is described by the P2(1)2(1)2(1) space group. The distortion with respect to the high-temperature Pnma phase is characterized by anti-symmetric displacements of the betaine molecules as well as of the Ca octahedra. On the basis of a symmetry-mode analysis, we propose an interpretation of the direct phase transition that occurs around 80 K between these two phases.
authors.affiliation: Departamento de Física, Universidade do Minho, 4709 Braga codex, Portugal.
authors.forename: L G
authors.initials: LG
authors.lastname: Vieira
authors.forename: O
authors.initials: O
authors.lastname: Hernandez
authors.forename: J L
authors.initials: JL
authors.lastname: Ribeiro
authors.forename: A
authors.initials: A
authors.lastname: Cousson
authors.forename: J M
authors.initials: JM
authors.lastname: Kiat
authors.forename: M R
authors.initials: MR
authors.lastname: Chaves
authors.forename: A
authors.initials: A
authors.lastname: Almeida
authors.forename: A
authors.initials: A
authors.lastname: Klöpperpieper