NiAs Structure Research Articles

Bonding, Ion Mobility, and Rate-Limiting Steps in Deintercalation Reactions with ThCr2Si2-type KNi2Se2

Here, we study the nature of metal-metal bonding in the ThCr(2)Si(2) structure type by probing the rate-limiting steps in the oxidative deintercalation of KNi(2)Se(2). For low extents of oxidation, alkali ions are removed exclusively to form K(1-x)Ni(2)Se(2). For greater extents of oxidation, the rate of the reaction decreases dramatically, concomitant with the extraction of both potassium and nickel to form K(1-x)Ni(2-y)Se(2). The appreciable mobility of transition metal ions is unexpected, but illustrates the relative energy scales of different defects in the ThCr(2)Si(2) structure type. Furthermore, the fully oxidized compounds, K(0.25)Ni(1.5)Se(2), spontaneously convert from the tetrahedral [NiSe(4)]-containing ThCr(2)Si(2) structure to a vacancy-ordered NiAs structure with [NiSe(6)] octahedra. From analysis of the atom positions and kinetic data, we have determined that this transformation occurs by a continuous, low-energy pathway via subtle displacements of Ni atoms and buckling of the Se sublattice. These results have profound implications for our understanding of the stability, mobility, and reactivity of ions in materials.

Phases of the NiAs family in Cu-Pd-Sn and Au-Pd-Sn systems

Phases with with a NiAs-based structure have been studied in Au-Pd-Sn and Cu-Pd-Sn systems at 500°C using powder X-ray diffraction, X-ray structure analysis, and energy-dispersive X-ray microanalysis. In the Cu-Pd-Sn system, binary phases γ-Pd2Sn and Cu6Sn5 both having the Ni2In structure form a phase region (Pd,Cu)2 − x Sn, which preserves the Ni2In structure and is confined at 500°C by an L + (Pd,Cu)2 − x Sn + ɛ-Cu3Sn three-phase region. In the Au-Pd-Sn system, the δ-AuSn phase with the NiAs structure and γ-Pd2Sn with the Ni2In structure form a single phase region (Pd,Au)2 − x Sn, which is bounded at 500°C by an L + (Pd,Au)2 − x Sn two-phase region; the structure of the ternary phase changes from Ni2In with incompletely filled trigonal-prismatic interstices to NiAs. The Pd20Sn13 phase, which crystallizes in the GaGe2Ni4 type structure, penetrates into both ternary systems up to ∼5 at % of the third component. The solubilities of copper and gold in PdSn and Pd2Sn phases, which have structures based on orthorhombically distorted NiAs and Ni2In lattices, respectively, do not exceed 2 at %.

Half-metallic Ferromagnetism in the Rocksalt and Zincblende NaX (X=O, S, Se, Te, and Po)

The first-principles full potential linearized augmented plane wave method within spin-polarized density functional theory was used to investigate the structural, electronic, and magnetic properties of NaX compounds in the NiAs, rocksalt (RS), and zincblende (ZB) phases. The results showed that in all compounds, the stable state phase is a nonmagnetic (NM) NiAs structure except for NaO in which the stable state phase is a ferromagnetic (FM) RS structure. The ZB NaX (X=O, S, Se, Te, and Po) and RS NaX (X=O, S, and Se) structures are half-metallic (HM) ferromagnets with an integer magnetic moment of 1μB per formula unit. The half-metallicity originates from hybridization between X p and Na s and p states. The ZB NaO compound is a very robust half-metal which has the HM band gap of 1.25 eV and maintains HM characteristic up to above 40% of the lattice constant contraction. The half-metallicity is also found up to the lattice constant contraction of about 26.3%, 19.6%, 10.4%, and 7.5% for ZB NaS, NaSe, NaTe, and NaPo and 27.1%, 6.4%, and 1.7% for RS NaO, NaS, and NaSe, respectively. The robustness of half-metallicity with respect to the lattice contraction in the HM NaX compounds and their compatibility with the binary semiconductors make them suitable candidates in spintronic applications.

ChemInform Abstract: New Mixed Palladium—Lead and Palladium—Tin Tellurides of the NiAs Type.

AbstractNew phases of the Pd—Pb—Te and Pd—Sn—Te systems belonging to the NiAs structure type are synthesized from the elements (750 °C, 8—10 h) and characterized by powder XRD.

Structural and magnetic properties of CrSb compounds: NiAs structure

The structural and magnetic properties of CrSb compounds with NiAs structure have been studied by means of the Korringa–Kohn–Rostoker (KKR) band structure method. An analysis of the structural and magnetic stability has been performed on the basis of total energy calculations for various magnetic states. The magnetic properties at finite temperature have been investigated by means of Monte Carlo simulations on the basis of a classical Heisenberg Hamiltonian and the exchange coupling parameters calculated from first principles. This approach allowed us to determine the critical temperature in good agreement with experiment.

Half-metallic ferromagnetism in the zincblende TiTe

The first-principle calculations based on spin-polarized density functional theory were performed to investigate the structural, electronic and magnetic properties of TiTe compound. The results showed that the ground state phase of TiTe is a non-magnetic NiAs structure and the zincblende (ZB) TiTe structure becomes stable at −5.2 GPa. It was predicted that the ZB structure is a half-metal ferromagnet with a magnetic moment of 2 μ B per formula unit for the equilibrium lattice parameter. The minority- spin and spin-flip gaps were calculated equal to 2.84 eV and 0.2 eV, respectively. In addition, the reasons for appearance of half-metallicity and magnetism in the ZB TiTe were discussed. It was noted that the half-metallicity characteristic exists within a wide range of lattice constant which makes the ZB TiTe an interesting material in the field of spintronics.

Phase relations in the Nb-Cr-Sb and Nb-Mn-Sb systems

The 970-K phase relations in the Nb-Cr-Sb and Nb-Mn-Sb systems have been studied by X-ray diffraction. The systems contain no ternary compounds. There are substitutional solid solutions based on binary antimonides. The Nb5Sb4-based solid solution (Ti5Te4 structure) extends to the composition Nb4.1Mn0.9Sb4; the Nb3Sb-based solid-solution series (Cr3Si structure) is bounded by the compositions Nb2.6Cr0.4Sb and Nb2.4Mn0.6Sb; the Cr1.04 − xSb0.96 + x-based solution with x = 0.08 (NiAs structure) exists between the compositions Cr0.94Nb0.10Sb0.96 and Cr0.70Nb0.30Sb1.00; and the Mn1.00 + xSb1.00 − x-based solution with x = 0.1 extends to the composition Mn0.9Nb0.2Sb0.9. In addition, there is an interstitial solid solution (Ni2In structure), which extends to MnNb0.25Sb. The 970-K isothermal sections of the Nb-Cr-Sb and Nb-Mn-Sb phase diagrams are mapped out in the region 0–80 at % Sb.

Metal‐Organic Niccolite: Synthesis, Structures, Phase Transition, and Magnetic Properties of [CH3NH2(CH2)2NH2CH3][M2(HCOO)6] (M=divalent Mn, Fe, Co, Ni, Cu and Zn)

We report the synthesis, crystal structures, thermal and magnetic characterizations of a family of metal-organic frameworks adopting the niccolite (NiAs) structure, [dmenH(2)(2+)][M(2)(HCOO)(6)(2-)] (dmen=N,N'-dimethylethylenediamine; M=divalent Mn, 1Mn; Fe, 2Fe; Co, 3Co; Ni, 4Ni; Cu, 5Cu; and Zn, 6Zn). The compounds could be synthesized by either a diffusion method or directly mixing reactants in methanol or methanol-water mixed solvents. The five members, 1Mn, 2Fe, 3Co, 4Ni, and 6Zn are isostructural and crystallize in the trigonal space group P31c, while 5Cu crystallizes in C2/c. In the structures, the octahedrally coordinated metal ions are connected by anti-anti formate bridges, thus forming the anionic NiAs-type frameworks of [M(2)(HCOO)(6)(2-)], with dmenH(2)(2+) located in the cavities of the frameworks. Owing to the Jahn-Teller effect of the Cu(2+) ion, the 3D framework of 5Cu consists of zigzag Cu-formate chains with Cu-OCHO-Cu connections through short basal Cu-O bonds, further linked by the long axial Cu-O bonds. 6Zn exhibits a phase transition probably as a result of the order-disorder transition of the dmenH(2)(2+) cation around 300 K, confirmed by differential scanning calorimetry and single crystal X-ray diffraction patterns under different temperatures. Magnetic investigation reveals that the four magnetic members, 1Mn, 2Fe, 3Co, and 4Ni, display spin-canted antiferromagnetism, with a Néel temperature of 8.6 K, 19.8 K, 16.4 K, and 33.7 K, respectively. The Mn, Fe, and Ni members show spin-flop transitions below 50 kOe. 2Fe possesses a large hysteresis loop with a large coercive field of 10.8 kOe. The Cu member, 5Cu, shows overall antiferromagnetism (both inter- and intra-chains) with low-dimensional characteristics.

Crystallographic and magnetic properties of (Cu 1− xV x)V 2S 4 ( x≈0.3) single crystals with the layered defect NiAs structure synthesized under high pressure

We report on the reproducible growth of (Cu 1− x V x )V 2S 4 single crystals of sizable dimensions (∼0.3 mm) and homogeneous composition ( x≈0.3) by means of high-pressure synthesis. The refinement of single crystal X-ray diffraction data indicates that the crystal structure is of the monoclinic defect NiAs-type, which consists of a stacking of VS 2 layers with CdI 2-type structure and chains of edge-sharing (Cu 1− x V x )S 6 octahedra. Layers and chains form a network of face-sharing octahedra with no Cu–V intra-chain ordering. A combined X-ray photoelectron spectroscopy and bond valence sum analysis indicates that the valence of the V and Cu ions are 3+ and 1+, respectively. Magnetic susceptibility measurements unveil the coexistence of a large Pauli-like and of a small Curie-like paramagnetic contributions, with no evidence of any long range order down to 2 K. This result suggests a picture of predominantly itinerant 3 d V electrons with significant electron–electron correlations.

Spin correlations and electron transport in MnBi:Au films

The structural, magnetic, and electron transport properties of Mn55−xAuxBi45 (x = 0, 4.5) thin films prepared by magnetron sputtering have been investigated. The magnetization of the MnBi films decreases and the coercivity increases due to Au doping. The temperature dependence of resistivity between 2 to 300 K shows that the films are metallic but the 4.5% Au-doped film shows a Kondo behavior with resistance minimum at 10.2 K. The magnetoresistance is anisotropic and the positive transverse magnetoresistance is significantly enhanced (16.3% at 70 kOe) by Au doping. We interpret these data in terms of a model in which Au atoms preferentially substitute for Mn atoms on the Mn lattice, and some Mn atoms are displaced to interstitial sites in the NiAs structure. These interstitial Mn atoms are coupled antiferromagnetically to the Mn atoms on the original Mn lattice leading to the large decrease in magnetization, Kondo effect, and the positive magnetoresistance.

New mixed palladium—lead and palladium—tin tellurides of the NiAs type

New ternary mixed nickel arsenide-type palladium and platinum—Group 14 metal tellurides were searched for by the high-temperature ampoule synthesis combined with the X-ray powder diffraction analysis. As a result, new phases of the ternary Pd—Pb—Te and Pd—Sn—Te systems belonging to the NiAs structure type were synthesized. The crystal structure of the compound PdPb0.304(5)Te0.695(5) was determined by the Rietveld method (P63/mmc, a = 4.151(1) A, c = 5.680(1) A, Z = 2, R1 = 0.032, Rp = 0.075, wRall = 0.025). It was shown that no ordering exists in the occupancy of the main-group atom site by lead and tellurium. In the Pd—Sn—Te system, a phase isostructural with the above-mentioned compound was found. In the latter phase, there is also no ordering in the occupancy of the main-group atom site. According to the electron diffraction data, a superstructure derived from the NiAs type exists in a narrow range of the compositions PdSn0.3Te0.7—PdSn0.4Te0.6.

THE ELECTRONIC STRUCTURE AND MAGNETISM OF CrSb WITH LATTICE CONSTANTS

The electronic structure and magnetism of CrSb compounds have been studied by a periodic quantum-mechanical calculation based on density functional theory. The results show that a ferrimagnetic ordered phase of CrSb in the Zinc-blende structure (ZB) is stable with half metallic properties, whereas the antiferromagnetic phase of CrSb in the NiAs -type crystal structure is energetically favored with no-gap band. The lattice constants have significant influence on the magnetism of CrSb . The band gap and the magnetic moment of Cr atom increase with increasing lattice constant in ZB CrSb . The effects on magnetic moment in the NiAs -type crystal structure are more sensitive substantially to the change of lattice constant a as compared with that of the lattice constant c. It is found that apart from ionic or metallic bonds there are covalent bonds between Cr d and Sb p orbitals in ZB CrSb , while bonding between Cr and Sb atoms is mainly ionic or metallic in CrSb of NiAs structure.

High-pressure electrical resistivity, Mossbauer, thermal analysis, and micro-Raman spectroscopic investigations on microwave synthesized orthorhombic cubanite (CuFe 2S 3)

We present here the powder X-ray diffraction, micro-Raman, thermal, Mössbauer and high-pressure electrical resistivity properties of microwave synthesized orthorhombic cubanite CuFe 2S 3. The unique physico-chemical conditions required for the formation of orthorhombic cubanite CuFe 2S 3 prevents its successful synthesis under the normal laboratory conditions. However, in natural occurrence, the mineral occurs in orthorhombic structure along with chalcopyrite (CuFeS 2) and pyrrhotite (Fe 1 − x S). A successful attempt to synthesize orthorhombic CuFe 2S 3 is reported using microwave heating. The DTA and Micro-Raman and Mössbauer spectroscopic measurements on the synthesized sample confirm that the synthetic sample is orthorhombic cubanite. High pressure electrical resistivity measurements on the sample show an irreversible first order phase transformation of orthorhombic cubanite to NiAs structure at ~ 4 GPa. The high-pressure recovered sample has been characterized by micro-Raman spectroscopy and exhibits Raman bands at 349 and 387 cm − 1 , characteristic of isocubanite phase. The present high-pressure and temperature studies on the orthorhombic cubanite may be useful in understanding the thermodynamic behavior of cubanite and its paragenesis in carbonaceous chondrite.

Ab initio calculation of pressure-induced phase transition of TiN polytypes

Based on a plane wave pseudopotential method within the framework of density functional theory, equilibrium structure, bulk modulus, and relative stability were calculated for 6 kinds of TiN polytypes including B1 (NaCl structure), B2 (CsCl structure), B3 (zincblende structure), Bk (hexagonal BN structure), Bh (WC structure) and B81 (NiAs structure). Theoretical calculation also showed that TiN can not exist in B4 (wurtizite) structure. Through geometry optimization under hydrostatic pressure, the enthalpy of each TiN phase at different pressures was obtained. It was found that TiN with B1 structure is the most stable phase at pressure lower than about 345 GPa, whereas B2 TiN is the most stable at pressure above 345 GPa. Volume discontinuity and bulk modulus change can be observed during the transition from B1 to B2 phase.

The phase transition and elastic property of osmium carbide under pressure

First-principles calculations of the stabilities, the mechanical properties, and the elastic properties of osmium carbide (OsC) in tungsten carbide (WC) and nickel arsenide (NiAs) structures have been carried out with the plane-wave pseudopotential density functional theory method. WC-OsC is stable in the ground state. The phase-transition pressure from WC structure to NiAs structure is about 7.2 GPa. The pressure dependence of the elastic constants, the aggregate elastic moduli (B, G and E), Poisson's ratio, the Lamè constants, the compressibility, and the elastic anisotropy of these two structures are calculated and compared; many differences can be found in the two structures.

Energetic, mechanical, and vibrational stability of metastable OsC phase

The assessment of experimental and theoretical results shows controversy about the mechanical stability of OsC phases. The stability of WC-structured, NiAs-structured, and CoSn-structured OsC phases has been investigated by using first-principles calculations. Present results show that WC–OsC and NiAs–OsC are both unstable, energetically and vibrationally, at zero pressure. Further calculations show WC–OsC can be stabilized under high pressure but not NiAs–OsC, which is unstable even under very high pressure. It is found that the interaction between Os atoms in parallel x-y plane is responsible for the deep instability of NiAs structure, while the greatly increased interaction under high pressure between nearest C–Os atoms is responsible for the stabilization of WC–OsC under high pressure.

ChemInform Abstract: (Et3P)6Co6Te8 and a Connection Between Chevrel Clusters and the NiAs Structure.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

First Principles Study of Half Metallic Properties of VSb Surface and VSb/GaSb (001) Interface

The structural, electronic, and magnetic properties of VSb in zincblende, and NiAs phases, VSb (001) film surfaces and its interfaces with GaSb (001) have been investigated within the framework of the density functional theory using the FPLAPW+lo approach. The NiAs structure is more stable than the ZB phase, ZB VSb is found to a half-metallic ferromagnetic. The V-terminated surfaces retain the half-metallic character, while the half-metallicity is destroyed for Sb-terminated surfaces due to surface states, which originate from p electrons. The phase diagram obtained through the ab-initio atomistic thermodynamics shows that the formation energy of ZB VSb is about 0.1 Ryd. The half-metallicity character is also preserved at VSb/GaSb (001) interface. The conduction band minimum (CBM) of VSb in the minority spin case lies about 0.47 eV above that of GaSb, suggesting that the majority spin can be injected into GaSb without being flipped to the conduction bands of the minority spin.

Magnetic Sensor Devices Based on Ordered Planar Arrangements of MnAs Nanocluster

We propose planar magneto-electronic devices based on accurately positioned and shaped ferromagnetic MnAs nanoclusters in NiAs structure. The prototype discussed consists of a small hexagon-shaped cluster sandwiched between two elongated clusters with fixed magnetic orientations. The magnetization of the center cluster is free and can be rotated by an external magnetic field. Our ab initio calculations yield a strong dependence of the conductance as a function of the direction of the external magnetic field which exhibits an in-plane symmetry of 360 degrees.

Structure of pyrrhotite 5C(Fe9S10)

The distribution of vacancies throughout the underlying NiAs structure of pyrrhotite 5C was analysed through the application of vacancy avoidance and the closeness condition in conjunction with order-disorder layering. Two crystallographically equivalent structure solutions (chiral enantiomers) were produced consisting of layers containing one vacancy in every eight iron sites broken by a fully occupied layer every fifth iron layer, and best described by monoclinic statistical models. The statistical 5C structures were verified using synchrotron powder diffraction data as well as published electron-diffraction patterns. An order-disorder structure description is proposed for the intermediate pyrrhotites of which pyrrhotite 5C is an end-member.