The crystal chemistry of Bi6TP2O15+x, T=Fe, Ni, Zn: Isomorphism and polymorphism, structural relationship to Bi6TiP2O16

✍ Scribed by N. Arumugam; V. Lynch; H. Steinfink

• Publisher: Elsevier Science
• Year: 2007
• Tongue: English
• Weight: 564 KB
• Volume: 180
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1016/j.jssc.2007.02.018

✦ Synopsis

The crystal structures of compounds with nominal compositions Bi 6 FeP 2 O 15+x (I), Bi 6 NiP 2 O 15+x (II) and Bi 6 ZnP 2 O 15+x (III) were determined from single-crystal X-ray diffraction data. They are monoclinic, space group I2, Z ¼ 2. The lattice parameters for (I) are

1023. The crystals are complexly twinned by 2-fold rotation about ½10 1, by inversion and by mirror reflection. The structures consist of edge-sharing articulations of OBi 4 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 PO 4 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, m eff ¼ 6.1 m B ; a magnetic transition occurs above 250 K.