NiAs (Nickel Arsenide) Nickel Arsenide(NiAs) Structure An alternative unit cell origin is at As (rather than Ni) LAttice Constant: a=.602A. c=5.009A sHCP As with Ni in all Octahedral holes The coordination of Ni and As is 6, but their structures =b,c=8/3 Motf2Niat(0,0.0)&(0,0,2 /ne hep of As, and As exist in the trigonal prism of n os 2Asat(14)&Q2234) share face. The distance of Ni-Ni is only 2.50 A, close to 2NiAs in unit cell hat in metallie Ni, thus NiAs crystal shows obvious metalli cOordination: Ni 6(octahedral: As 6(trigonal en the cdirection. the NrN Structures of lonic Solids based on hcp also 6 bu HCP I with Cd in Octahedral holes of alternate tThe niAs structure is a com structure in metallic compounds CdI o oe made from (a) transition metals with 11u -block elements such a lodide As Sb. Bi. S. Se ooe mOtif Cd at(0.0.0) lCdI in unit ce cOordination: Cd-6(Octahedral) I-3(base pyramid) Structures of lonic Solids Based on HCP Structures of lonic solids based on hcp Cal, Cdl, Cadmium lodide Polyhedral representation is most useful using Cdl lodide ctahedra (compare with NiAs) Cdl NIAs Comparison ACBACB Cd(OH): Mnlg, Mn(OH), Fe(OH): CoBr. TiS, ZrS, Sns. HCPI with Cd in octahedral holes of alternate lavers TiTe, Ni(OHda9 An alternative unit cell origin is at As (rather than Ni) NiAs (Nickel Arsenide) HCP As with Ni in all Octahedral holes Lattice: Hexagonal - P a = b, c =8/3a Motif: 2Ni at (0,0,0) & (0,0,1 / 2 ) 2As at (2 / 3 , 1 / 3 , 1 / 4 ) & (1 / 3 , 2 / 3 , 3 / 4 ) 2NiAs in unit cell Coordination: Ni 6 (octahedral) : As 6 (trigonal prismatic) vLattice Constant: a=3.602 Å, c=5.009 Å vThe coordination of Ni and As is 6，but their structures are different：Ni fill in the octahedronal coordination from the hcp of As, and As exist in the trigonal prism of Ni. vIn NiAs structure, the neighboring octahedra of Ni atoms share face. The distance of Ni-Ni is only 2.50 Å，close to that in metallic Ni, thus NiAs crystal shows obvious metallic. Nickel Arsenide (NiAs) Structure In the c-direction, the Ni-Ni distance is rather short. Overlap of 3d orbital gives rise to metallic bonding. The NiAs structure is a common structure in metallic compounds made from (a) transition metals with (b) heavy p-block elements such as As, Sb, Bi, S, Se. Coordination of As is also 6 but as a trigonal prism: CdI2 Cadmium Iodide Structures of Ionic Solids Based on HCP HCP I with Cd in Octahedral holes of alternate layers Lattice: Hexagonal - P Motif: Cd at (0,0,0); 2I at (2 / 3 , 1 / 3 , 1 / 4 ) & (1 / 3 , 2 / 3 , 3 / 4 ) 1CdI2 in unit cell Coordination: Cd - 6 (Octahedral) : I - 3 (base pyramid) CdI2 Cadmium Iodide Structures of Ionic Solids Based on HCP HCP I with Cd in Octahedral holes of alternate layers A c B A c B… … Polyhedral representation is most useful using CdI6 octahedra (compare with NiAs) CdI2 Cadmium Iodide Structures of Ionic Solids Based on HCP CdI2 structure: CaI2 ,Ca(OH)2 , MgBr2 ,MgI2 , Mg(OH)2 , Cd(OH)2 , MnI2 , Mn(OH)2 , Fe(OH)2 , CoBr2 ,TiS2 , ZrS2 , SnS2 , TiTe2 , Ni(OH)2