title: An open framework crystal structure and physical properties of RbCuAl(PO4)2.
abstract: The novel phosphate RbCuAl(PO4)2 was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F(2) to R = 0.026. The compound crystallizes in the monoclinic space group P21/c, with unit-cell parameters a = 5.0723(8) Å, b = 14.070(2) Å, c = 9.352(1) Å, β = 100.41(1), V = 656.4(2) Å(3), and Z = 4. The crystal structure is based on an open 3D aluminophosphate framework built by AlO5 bipyramids and PO4 tetrahedra sharing oxygen vertices. Channels in the [100] and [001] directions accommodate Rb(+) cations and chains of Cu-centered octahedra alternatively sharing cis- and trans-edges. The new phase is characterized by the structure type established for isotypic iron phosphates KMFe(PO4)2, where M = Fe/Ni, Ni, Mg or Co. It also shows topological relationships with Pb2Ni(PO4)2 and Fe(3+)Fe(2+)0.5(H2O)2(HPO4)2 structures. The RbCuAl(PO4)2 exhibits rather peculiar physical properties evidenced in specific heat and magnetization measurements. It releases a significant part of magnetic entropy well above the Neel temperature TN = 10.5 K and possesses a spontaneous magnetic moment at lower temperatures. The origin of the spontaneous moment is ascribed to the canting of a pristine antiferromagnetic structure due to the interchain Dzyaloshinskii-Moriya exchange interaction.
authors.affiliation: M.V. Lomonosov Moscow State University, Moscow 119991, Russia. yakubol@geol.msu.ru.
authors.forename: Olga V
authors.initials: OV
authors.lastname: Yakubovich
authors.forename: Galina V
authors.initials: GV
authors.lastname: Kiriukhina
authors.forename: Olga V
authors.initials: OV
authors.lastname: Dimitrova
authors.forename: Elena A
authors.initials: EA
authors.lastname: Zvereva
authors.forename: Larisa V
authors.initials: LV
authors.lastname: Shvanskaya
authors.forename: Olga S
authors.initials: OS
authors.lastname: Volkova
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Vasiliev