ChemInform Abstract: CRYSTAL STRUCTURE OF EQUIATOMIC TERNARY COMPOUNDS: LANTHANIDE-TRANSITION METAL ALUMINIDES

1984 ◽  
Vol 15 (50) ◽  
Author(s):  
A. E. DWIGHT
Keyword(s):  
Crystal Structure ◽  
Transition Metal ◽  
Ternary Compounds ◽  
Metal Aluminides

Ternäre Nitride des Lithiums mit den Elementen Cr, Mo und W / Ternary Lithium Nitrides with Elements Cr, Mo and W

1990 ◽  
Vol 45 (2) ◽  
pp. 111-120 ◽  
Author(s):  
Axel Gudat ◽  
Sabine Haag ◽  
Rüdiger Kniep ◽  
Albrecht Rabenau
Keyword(s):  
Crystal Structure ◽  
Transition Metal ◽  
Transition Metals ◽  
Ternary System ◽  
Crystal Structures ◽  
Ternary Compounds ◽  
Metal Atoms ◽  
Transition Metal Atoms ◽  
Fluorite Type ◽  
Nitride Oxide

The ternary compounds were prepared by reaction of the transition metals with Li3N melt under nitrogen. The crystal structures of Li6MeN4 (P42/nmc, Z = 2; Me = Mo: a = 667.3(1) pm, c = 492.5(3) pm; Me = W: a = 667.9(1) pm, c = 492.7(1) pm) and Li15Cr2N9 (P4/ncc, Z = 4; a = 1023.3(5) pm, c = 938.9(7) pm) can be described as fluorite-type superstructures with the lithium and transition metal atoms in tetrahedral holes of the nearly fcc nitrogen arrangement and with an ordered distribution of defects within the cation substructure. In addition, the ternary system Li–Cr–N contains the compound Li6CrN4 with a crystal structure which is not quite clear at present, but which shows close relations to the structures of Li6MeN4 (Me = Mo, W). The previously reported compounds Li9MeN5 (Me = Cr, Mo, W) have not been observed during this study. The respective Cr compound in fact is a nitride-oxide (nitride-imide) of composition Li14Cr2N8(O,NH) with a crystal structure (P3̄, Z = 1, a = 579.9(1) pm, c = 826.3(6) pm) also showing a fluorite-type superstructure.

Electron energy loss near edge structures of intermetallic alloys and grain boundaries in NiAl

1996 ◽  
Vol 54 ◽  
pp. 522-523
Author(s):  
G.A. Botton ◽  
C.J. Humphreys
Keyword(s):  
High Temperature ◽  
Transition Metal ◽  
Energy Loss ◽  
Grain Boundaries ◽  
Industrial Applications ◽  
Edge Structure ◽  
Structural Applications ◽  
Yield Behaviour ◽  
Late Transition ◽  
Metal Aluminides

Transition metal aluminides are of great potential interest for high temperature structural applications. Although these materials exhibit good mechanical properties at high temperature, their use in industrial applications is often limited by their intrinsic room temperature brittleness. Whilst this particular yield behaviour is directly related to the defect structure, the properties of the defects (in particular the mobility of dislocations and the slip system on which these dislocations move) are ultimately determined by the electronic structure and bonding in these materials. The lack of ductility has been attributed, at least in part, to the mixed bonding character (metallic and covalent) as inferred from ab-initio calculations. In this work, we analyse energy loss spectra and discuss the features of the near edge structure in terms of the relevant electronic states in order to compare the predictions on bonding directly with spectroscopic experiments. In this process, we compare spectra of late transition metal (TM) to early TM aluminides (FeAl and TiAl) to assess whether differences in bonding can also be detected. This information is then discussed in terms of bonding changes at grain boundaries in NiAl.

Crystal chemistry of transition metal diarsenates M 2As2O7 (M = Mn, Co, Ni, Zn): variants of the thortveitite structure

2010 ◽  
Vol 66 (6) ◽  
pp. 603-614 ◽  
Author(s):  
Matthias Weil ◽  
Berthold Stöger
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Transition Metal ◽  
Basic Structure ◽  
Structure Type ◽  
Ambient Conditions ◽  
Modulated Structure ◽  
Triclinic Crystal System ◽  
Space Groups ◽  
Unit Cells

The structures of the 3d divalent transition-metal diarsenates M 2As2O7 (M = Mn, Co, Ni, Zn) can be considered as variants of the monoclinic (C2/m) thortveitite [Sc2Si2O7] structure type with a ≃ 6.7, b ≃ 8.5, c ≃ 4.7 Å, α ≃ 90, β ≃ 102, γ ≃ 90° and Z = 2. Co2As2O7 and Ni2As2O7 are dimorphic. Their high-temperature (β) polymorphs adopt the thortveitite aristotype structure in C2/m, whereas their low-temperature (α) polymorphs are hettotypes and crystallize with larger unit cells in the triclinic crystal system in space groups P\bar 1 and P1, respectively. Mn2As2O7 undergoes no phase transition and likewise adopts the thortveitite structure type in C2/m. Zn2As2O7 has an incommensurately modulated crystal structure [C2/m(α,0,γ)0s] with q = [0.3190 (1), 0, 0.3717 (1)] at ambient conditions and transforms reversibly to a commensurately modulated structure with Z = 12 (I2/c) below 273 K. The Zn phase resembles the structures and phase transitions of Cr2P2O7. Besides descriptions of the low-temperature Co2As2O7, Ni2As2O7 and Zn2As2O7 structures as five-, three- and sixfold superstructures of the thortveitite-type basic structure, the superspace approach can also be applied to descriptions of all the commensurate structures. In addition to the ternary M 2As2O7 phases, the quaternary phase (Ni,Co)2As2O7 was prepared and structurally characterized. In contrast to the previously published crystal structure of the mineral petewilliamsite, which has the same idealized formula and has been described as a 15-fold superstructure of the thortveitite-type basic structure in space group C2, synthetic (Ni,Co)2As2O7 can be considered as a solid solution adopting the α-Ni2As2O7 structure type. Differences of the two structure models for (Ni,Co)2As2O7 are discussed.

scholarly journals First-principle investigations of structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides

2015 ◽  
Vol 33 (2) ◽  
pp. 251-258
Author(s):  
Bendouma Doumi ◽  
Allel Mokaddem ◽  
Mustapha Ishak-Boushaki ◽  
Miloud Boutaleb ◽  
Abdelkader Tadjer
Keyword(s):  
Transition Metal ◽  
Electronic Properties ◽  
Density Functional ◽  
First Principle ◽  
Generalized Gradient ◽  
Metallic Behavior ◽  
Plane Wave Method ◽  
Structural And Electronic Properties ◽  
The Difference ◽  
Metal Aluminides

AbstractIn the present work, we have investigated the structural and electronic properties of TMAl (TM = Fe, Co, and Ni) transition metal aluminides in the B2 structure, using first-principle calculations of the density functional theory (DFT) based on the linearized augmented plane wave method (FP-LAPW) as implemented in the WIEN2k code, in which the energy of exchange and correlation are treated by the generalized gradient approximation (GGA), proposed in 1996 by Perdew, Burke and Ernzerhof (PBE). The ground state properties have been calculated and compared with other calculations, and the electronic structures of all FeAl, CoAl, and NiAl compounds exhibited a metallic behavior. It was depicted that the density of states is characterized by the large hybridization between the s-p (Al) and 3d (Fe, Co, and Ni) states, which creates the pseudogap in the region of anti-bonding states. Moreover, the band structures of FeAl, CoAl, and NiAl are similar to each other and the difference between them is in the energy level of each band relative to the Fermi level.

Sign in / Sign up

Export Citation Format

Share Document