摘要
Single crystals of PrNb_5O_(14) were prepared by solid state reaction from PrOBr/Nb_2O_5/NH_4Br system at 950℃. Compound PrNb_5O_(14) (M_r=829. 43) crystallized in orthorhombic Pmmn (No. 59) with cell parameters of a=7. 758 (3), b= 20. 092(6), c=6. 241(1) A, V=972. 8(5) A￣3: Z=4; F(000)=1504; Dc=5. 66 g/cm￣3;μ(MoKa)=104. 39 cm￣(-1).The final structure factors are R=0. 063 and R_w=0. 073 respectively for 1747 observed reflections with I>3σ(I). The structure consists of two types of NbO polyhedra, Nb (1) and Nb (3) pentagonal bipyramids and Nb (2)O6 octahedron. Chains of edge sharing pentagonal NbO_7-bipyramids are connected by corner-sharing NbO_6-octahedra. Tunnels running in a-direction are created by this framework of NbO_6 and NbO_7-polyhedra. Praseodymium atoms are 9-coordinated with tricapped trigonal prism polyhedron, and are located in these tunnels at levels between the niobium atoms.
Single crystals of PrNb_5O_(14) were prepared by solid state reaction from PrOBr/Nb_2O_5/NH_4Br system at 950℃. Compound PrNb_5O_(14) (M_r=829. 43) crystallized in orthorhombic Pmmn (No. 59) with cell parameters of a=7. 758 (3), b= 20. 092(6), c=6. 241(1) A, V=972. 8(5) A￣3: Z=4; F(000)=1504; Dc=5. 66 g/cm￣3;μ(MoKa)=104. 39 cm￣(-1).The final structure factors are R=0. 063 and R_w=0. 073 respectively for 1747 observed reflections with I>3σ(I). The structure consists of two types of NbO polyhedra, Nb (1) and Nb (3) pentagonal bipyramids and Nb (2)O6 octahedron. Chains of edge sharing pentagonal NbO_7-bipyramids are connected by corner-sharing NbO_6-octahedra. Tunnels running in a-direction are created by this framework of NbO_6 and NbO_7-polyhedra. Praseodymium atoms are 9-coordinated with tricapped trigonal prism polyhedron, and are located in these tunnels at levels between the niobium atoms.
