title: Nuclear and magnetic structures and magnetic properties of synthetic brochantite, Cu4(OH)6SO4.
abstract: Cu4(OH)6SO4 (1) and Cu4(OD)6SO4 (2) were obtained by hydrothermal syntheses from copper sulfate and sodium hydroxide in H2O and D2O, respectively. They crystallize in the monoclinic system, space group P2(1)/a (14), a = 13.1206(5), b = 9.8551(3), c = 6.0295(2) Angstroms, beta = 103.432(3) degrees, V = 758.3(1) Angstroms(3), Z = 4 and a = 13.1187(5), b = 9.8552(3), c = 6.0293(2) Angstroms, beta = 103.410(3) degrees, V = 758.3(1) Angstroms(3), Z = 4, respectively. They are iso-structural to the mineral brochantite and consist of double chains of edge-sharing copper octahedra that are connected to one another by corners to form corrugated planes along bc; these planes are in-turn bridged by the unprecedented mu7-sulfate tetrahedra to give a 3D-structure. All the hydrogen atoms were precisely located from refinement of the neutron powder diffraction data of the deuterated sample. Magnetic susceptibility data reveal a low-dimensional behavior at high temperature and the presence of both ferromagnetic and antiferromagnetic super-exchanges resulting in a 3D long-range antiferromagnetic ordering at 7.5 K accompanied by a small canting of the moments. The transition is confirmed by a lambda-peak in the specific heat. The magnetic structure at 1.4 K shows the moments are oriented perpendicular to the corrugated planes with alternation along +/-a for neighboring chains within the double chains. The enhanced incoherent scattering at low-angle suggests the existence of short-range ferromagnetic clusters.
authors.affiliation: Groupe des Matériaux Inorganiques, IPCMS, CNRS-ULP UMR-7504, Strasbourg, France. vilminot@ipcms.u-strasbg.fr
authors.forename: Serge
authors.initials: S
authors.lastname: Vilminot
authors.forename: Mireille
authors.initials: M
authors.lastname: Richard-Plouet
authors.forename: Gilles
authors.initials: G
authors.lastname: André
authors.forename: Dariusz
authors.initials: D
authors.lastname: Swierczynski
authors.forename: Françoise
authors.initials: F
authors.lastname: Bourée-Vigneron
authors.forename: Mohamedally
authors.initials: M
authors.lastname: Kurmoo