The crystal chemistry of Bi6TP2O15+x, T=Fe, Ni, Zn: Isomorphism and polymorphism, structural relationship to Bi6TiP2O16 |
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Authors: | N Arumugam H Steinfink |
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Affiliation: | a Department of Chemical Engineering and Texas Materials Institute, University of Texas at Austin, 1 University Station C0400, Austin, TX 78712, USA b Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX 78712, USA |
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Abstract: | The crystal structures of compounds with nominal compositions Bi6FeP2O15+x (I), Bi6NiP2O15+x (II) and Bi6ZnP2O15+x (III) were determined from single-crystal X-ray diffraction data. They are monoclinic, space group I2, Z=2. The lattice parameters for (I) are a=11.2644(7), b=5.4380(3), c=11.1440(5) Å, β=96.154(4)°; for (II) a=11.259(7), b=5.461(4), c=11.109(7) Å, β=96.65(1)°; for (III) a=19.7271(5), b=5.4376(2), c=16.9730(6) Å, β=131.932(1)°. Least squares refinements on F2 converged for (I) to R1=0.0554, wR2=0.1408; for (II) R1=0.0647, wR2=0.1697; for (III) R1=0.0385, wR2=0.1023. The crystals are complexly twinned by 2-fold rotation about , by inversion and by mirror reflection. The structures consist of edge-sharing articulations of OBi4 tetrahedra forming layers in the a-c plane that then continue by edge-sharing parallel to the b-axis. The three-dimensional networks are bridged by Fe and Ni octahedra in (I) and (II) and by Zn trigonal bipyramids in (III) as well as by oxygen atoms of the PO4 moieties. Bi also randomly occupies the octahedral sites. Oxygen vacancies exist in the structures of the three compounds due to required charge balances and they occur in the octahedral coordination polyhedron of the transition metal. In compound (III), no positional disorder in atomic sites is present. The Bi-O coordination polyhedra are trigonal prisms with one, two or three faces capped. Magnetic susceptibility data for compound (I) were obtained between 4.2 and 350 K. Between 4.2 and 250 K it is paramagnetic, μeff=6.1 μB; a magnetic transition occurs above 250 K. |
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Keywords: | Crystal structures: Bi6(Fe0 68Bi0 32)P2O15 5 Bi6(Ni0 46Bi0 54)P2O15 2 Bi6ZnP2O15 magnetic susceptibility Bi6(Fe0 68Bi0 32)P2O15 5 Bismuth transition metal phosphate Oxygen vacancies |
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