NiAs Research Articles

Pressure-induced structural phase transition, elastic and thermodynamic properties of ReC under high pressure

The pressure-induced structural phase transition of rhenium monocarbon (ReC) is investigated via the projector augmented wave (PAW) method with the generalized gradient approximation (GGA). Using the first-principles calculations, the equilibrium structural parameters of ReC in rocksalt (NaCl), cesium chloride (CsCl), zinc blende (ZB), wurtzite (WZ), nickel arsenide (NiAs) and tungsten carbide (WC) types are successfully obtained, and the results are well consistent with other theoretical data. It is firstly noted that WC-ReC translates into CsCl-ReC at 510.50 GPa by analyzing the enthalpy difference versus pressure. From the calculated elastic constants, the aggregate elastic modulus (B, G, E), the Poisson's ratio (σ) and the Debye temperature ΘD of WC-type are also derived. It is observed that all the data of WC-ReC obtained increase monotonically with increasing pressure. Meanwhile, the thermodynamic properties of WC-ReC under high temperature and high pressure are investigated applying nonempirical Debye model in the quasi-harmonic approximation.

Structural, electronic, mechanical and superconducting properties of ReC and TcC

The structural, electronic, mechanical and superconducting properties of rhenium carbide (ReC) and technetium carbide (TcC) are investigated using first principles calculations based on density functional theory (DFT). The computed ground state properties like equilibrium lattice constants and cell volume are in good agreement with the available experimental and theoretical data. It is observed that tungsten carbide phase (WC) is the most stable phase for ReC and TcC at normal pressure. Pressure induced structural phase transitions are observed from tungsten carbide to zinc blende phase and then zinc blende to wurtzite phase in rhenium carbide while tungsten carbide to zinc blende phase and then zinc blende to nickel arsenide phase in technetium carbide. Electronic structure reveals that these materials are metallic at ambient condition. The high bulk modulus (B) value of WC phase of both ReC (438GPa) and TcC (368GPa) suggests that they are ultra hard and incompressible materials. Also, the superconducting transition temperature is estimated for ReC and TcC at normal pressure.

Phase transition and thermodynamic properties of beryllium telluride under high pressure

A theoretical investigation on structural, dynamical, phase diagram and thermodynamic properties of beryllium telluride (BeTe) under high pressure and temperature is presented in the framework of density functional theory. The calculated structural parameters of BeTe in both zinc blende (ZB) and nickel arsenide (NiAs) structures are in reasonable agreement with available experimental data and previous theoretical work. The phonon dispersion relations, dielectric tensor and Born effective charge are investigated within the density functional perturbation theory (DFPT). The investigation of the phase diagram indicated that the NiAs structure BeTe becomes stable at high pressure and temperature. Based on the quasiharmonic Debye model, the pressure and temperature dependences of bulk modulus, Grüneisen parameter, Debye temperature, specific heat and thermal expansion coefficient are all successfully obtained. We hope that the theoretical results reported here can give more insight into the structural and thermodynamic properties of other semiconductors at high temperature and pressure.

A Hydrothermal Ni-As-PGE Geochemical Halo Around the Miitel Komatiite-Hosted Nickel Sulfide Deposit, Yilgarn Craton, Western Australia

The remobilization of metals during postdeposition hydrothermal alteration of magmatic sulfide ores has the potential to result in large haloes, the recognition of which could potentially enlarge the detectable footprint of this ore type. The Miitel komatiite-hosted nickel sulfide deposit in Western Australia was used as a case study to investigate the nature and 3-D geometry of the geochemical halo created by the remobilization of base metals, gold, and platinum group elements (PGE) into the rocks surrounding the mineralization. At Miitel, anomalous metal enrichment is found in the country rocks surrounding the massive sulfides, up to 250 m away from the ore. This enrichment, detected using portable X-ray fluorescence (pXRF) and backed up by laboratory analyses, occurs in the Mount Edwards footwall basalt within decimeters of the contact with the overlying Widgiemooltha komatiites. It is associated with the presence of nickel arsenides. Gersdorffite and minor nickeline are concentrated within small quartz and carbonate veinlets, and are interpreted to form during the circulation of arsenic-rich hydrothermal fluids. Results of lead fire assay analyses and in situ laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS) analyses indicate high PGE concentrations (Pd and Pt) and minor gold associated with the observed nickel and arsenic enrichment. Results from a larger, regional-scale study, combined with this PGE enrichment, suggest that the massive nickel sulfides from the Miitel ore are the source of the remobilized nickel in the country rocks. The presence of Pd- and Pt-enriched trace arsenide phases in country rocks and shear zones may be a generally applicable proximity indicator for nickel sulfides in hydrothermally altered terranes.

First-principles calculation of structural stability, lattice dynamic and thermodynamic properties of BeX (X = S, Se and Te) compounds under high pressure

The phase transitions, lattice dynamical and thermodynamic properties of BeS, BsSe and BeTe at high pressure have been investigated with the density functional theory. The calculated equilibrium structural parameters agree well with the available experimental and theoretical values. The phase transition pressures from the zinc-blende (ZB) to the nickel arsenide (NiAs) phase of these compounds are determined. The calculated phonon dispersion curves of these compounds in ZB phase at zero pressure do not show any anomaly or instability. Dynamically, the ZB phase of BeS, BeSe and BeTe is found to be stable near transition pressures PT. Within the quasiharmonic approximation, the thermodynamic properties including the thermal expansion coefficient, heat capacity at constant volume, heat capacity at constant pressure and entropy are predicted.

Dearsenization of nickel-based catalysts: Thermal behaviour of nickel arsenide in oxygen and in air

The arsenic present in the spent Ni-catalysts of petroleum industries is supposed to form arsenides. It must be removed for the catalysts regeneration or for recycling nickel. In air or Ar/O2, a partial dearsenization of Ni11As8 occurs, giving Ni5As2, between 580 and 650°C. Ni5As2 forms AsO(g) and a NiO layer that blocks the arsenic elimination (passivation layer). The reaction mechanism is complex, dearsenization being governed by the surface oxidation of arsenic, and oxidation being rate-limited by the Ni outward diffusion. This work shows that the industrial process of regeneration does not eliminate arsenides, but only the physisorbed arsenic.

Ab Initio Calculations of Structural, Electronic, and Mechanical Stability Properties of Magnesium Sulfide

The structural, electronic, and mechanical stability properties of magnesium sulfide in different phases are presented using the plane wave pseudopotential method within the generalized gradient approximation. Eight different phases such as rocksalt (B1), zincblende (B3), wurtzite (B4), nickel arsenide (B8), cesium chloride (B2), PH4I-type (B11), FeSi-type (B28), and MnP-type (B31) are considered in great detail. The calculated ground-state properties of these phases are consistent with available experimental and theoretical data. It is found that MgS in the B1 and B8 phases are indirect band gap materials, the B3, B4, B11, B28, and B31 phases are all direct gap materials, while the B2 phase displays the metallic character. The B1, B3, B4, B8, B28, and B31 phases are mechanically stable at ambient conditions, but the B2 and B11 phases are mechanically unstable under zero pressure and zero temperature

Non-stoichiometric nickel arsenides in nature: The structure of orcelite, Ni5−xAs2 (x = 0.25), from the Bon Accord oxide body, South Africa

The crystal structure of the mineral orcelite, a rare nickel arsenide reported in the literature with the formula Ni5−xAs2 (with x=0.23), was refined using intensity data collected from a crystal from the Bon Accord body, South Africa. This study revealed that the structure is hexagonal, space group P63mc, with a=6.7922(2), c=12.4975(5)Å, and V=499.31(3)Å3. The refinement of an anisotropic model led to an R index of 0.028 for 412 independent reflections. The orcelite structure can be described as a distorted variant of the Pd5Sb2 structure. The smaller As atoms are in the centres of distorted tetragonal antiprisms, formed by only Ni atoms. The coordination sphere is completed with two additional Ni atoms opposite to the rectangular faces. Electron microprobe data carried out on the same crystal used for the structural study point to the following formula [on the basis of Σ(As+Fe+Sb)=2]: Ni4.75(As1.93Fe0.05Sb0.02). According to the high-quality structure refinement, the minor elements were found to replace As in the structure. An atomic position for Ni was found to be partially occupied (75%), thus confirming the non-stoichiometry for the mineral orcelite previously reported in literature. Such a deviation from the stoichiometry could represent the driving force favouring disorder phenomena during the growth of the mineral.

First-Principles Study of Pressure-Induced Structural and Magnetic Phase Transitions of Binary Ferromagnets: MnSn and MnSb

First-principles calculations within density functional theory have been performed to study the structural and magnetic phase transitions of two 3d compounds (MnSn and MnSb) under pressure. We consider the rocksalt (B1), cesium chloride (B2), zinc-blende (B3), nickel arsenide (B81) modifications of MnSn and MnSb. Both spin-polarized and nonspin-polarized calculations are carried out for ferromagnetic (FM) and paramagnetic (PM) states, which can be used to distinguish the ground-state magnetic configuration with increasing pressure. The crystal structure preferences and the possible phase transitions among them have been studied. We report FM B81⟶14GPaFM B2⟶145GPaPM B2 phase transition for MnSn, FM B81⟶23GPaPM B2 for MnSb. Phonon band dispersions, density of phonon states, and elastic stiffness constants are given and used to analyze the lattice dynamical and mechanical stability for the pressure-induced phase. Electronic band structures and density of states at different pressures are given to discuss the detailed electronic and magnetic properties.

Study of the structural and electronic properties of YC using DFT: The true ground state is a NiAs-like structure

We study the structural and electronic properties of YC in volume using density functional theory (DFT) within the generalized gradient approximation (GGA), using the scheme of Wu-Cohen 2006 and Tran et al. 2007. Several crystal structures were considered: Nickel Arsenide (NiAs), Sodium Chloride (NaCl), Cesium Chloride (CsCl), and zincblende (ZB). A new fact that we present in this paper is the inclusion of the NiAs-like structure, which is the true ground state (GS) for YC. We calculated the density of states (DOS) and the band structure and found that YC is non-magnetic and its behavior is metallic-like. The lattice parameter alatt is 3.69 Å and the c/a = 1.47. Cohesion energy (Ecoh) is −12.90 eV, which is very close to Ecoh of the NaCl structure. Therefore, YC exists in these two structures. Our results with respect to alatt, bulk modulus (B), Ecoh, and the main features of the electronic properties are in good agreement with those found by other researchers. Other researchers found a transition from NaCl to CsCl, but we found a new transition from NiAs to CsCl, where the volume diminishes ~10% and its transition pressure (PT ~79 GPa) is very close to the 80 GPa of the former. The contraction can fracture the material if it is worked on near the transition. For pressures before and after the transition, YC maintains non-magnetic and metallic behaviors.

Fractionation of platinum, palladium, nickel, and copper in sulfide–arsenide systems at magmatic temperature

Experimentally derived phase relations of arsenide in sulfide melt are presented to quantify the fractionation paths of As-bearing sulfide melts. When a natural sulfide melt reaches arsenide saturation, a separate Ni–PGE-rich arsenide melt exsolves. The arsenic saturation concentration in an Fe–Ni–Cu sulfide melt is between 0.5 and 1.5 wt%. The affinities of the chalcophile metals for an immiscible arsenide melt follow the order Pt > Pd > Ni ≫ Fe ≈ Cu. In natural systems, arsenide exsolution will be triggered by the activity of the nickel arsenide components dissolved in sulfide melt, Ni being the most common base metal with strong affinity to the Asn− anionic species. Arsenic may have a major effect on the fractionation paths of sulfide melts even if no separate arsenide phase forms. Arsenic, and probably many other chalcogens and metalloids in magmatic melts, may undergo associations with Pt and Pd well before discrete PGE minerals become stable phases.

Electronic structure, optical properties and the mechanism of the B3–B8 phase transition of BeSe: insights from hybrid functionals, lattice dynamics and NPH molecular dynamics

We have investigated the electronic structure and the mechanism of the pressure induced phase transition of beryllium selenide (BeSe) by employing a first-principles pseudopotential method within the framework of density functional theory. Our study demonstrates that use of the hybrid PBE0 functional (PBE stands for Perdew, Burke and Ernzerhof) leads to significant improvement in the band gap calculations, compared to those using either of the common density functionals (local density approximation (LDA) and generalized gradient approximation (GGA)), which severely underestimate the band gap of BeSe. The band gap obtained from the hybrid PBE0 functional shows excellent agreement with available experimental data. A constant-pressure (NPH) first-principles molecular dynamics (FPMD) approach has been adopted to characterize the first-order pressure induced phase transition from the zinc blende (ZB) to the nickel arsenide (NiAs) structure. We have shown that the FPMD simulation overestimates the transition pressure PT (compared to static enthalpy and experimental data) due to overpressure in the simulation box. The MD simulation reveals the structural pathway (cubic → orthorhombic → monoclinic → hexagonal), leading from the ZB phase to the NiAs phase. To find an explanation for the phase transition we calculated the vibrational and elastic properties under pressure. Negative Grüneisen parameters were obtained for the transverse acoustic phonon modes at the X and L high symmetry points. However, no mechanical instability or imaginary frequencies were found at pressures near PT. Thus the transition results from a thermodynamic instability rather than an elastic/dynamical one. We have also calculated the optical properties of both the B3 and B8 phases, such as the real and imaginary parts of the dielectric constant, reflectivity, loss function and refractive index, and compared them with the existing experimental and theoretical data. An abrupt decrease is obtained from the reflectivity spectrum of the NiAs phase at PT, which is supported from the peaks in the loss function.

THE FIRST-PRINCIPLES STABILITY STUDY OF PdC AND CdC COMPOUNDS

We have studied structural, mechanical and dynamical properties of PdC and CdC compounds to predict the most stable structure. We have focused on seven binary structure types as rock salt (RS), caesium chloride ( CsCl ), zinc blende (ZB), wurtzite (WZ), tungsten carbide (WC), cadmium telluride ( CdTe ) and nickel arsenide ( NiAs ). For modelling exchange-correlation effects we have used generalized gradient (GGA) approximation based on Perdew–Burke–Ernzhorf functional (PBE). The polycrystalline elastic moduli such as Young's and shear moduli, Poisson's ratio, sound velocities, Debye temperatures and shear anisotropic factors have been presented for mechanically stable structures using second-order elastic constants calculated from the stress-strain relations. The results show that PdC is thermodynamically, mechanically and dynamically stable in ZB structure. On the other hand, while CdC is energetically in favor of RS structure, it is mechanically and dynamically stable in ZB structure.

The pressure dependences of elastic and lattice dynamic properties of AlAs from ab initio calculations

Ab initio calculations, based on norm-conserving nonlocal pseudopotentials and density functional theory (DFT), are performed to investigate the structural, elastic, dielectric, and vibrational properties of aluminum arsenide (AlAs) with a zinc-blende (B3) structure and a nickel arsenide (B81) structure under hydrostatic pressure. Firstly, the path for the phase transition from B3 to B81 is confirmed by analyzing the energies of different structures, which is in good agreement with previous theoretical results. Secondly, we find that the elastic constants, bulk modulus, static dielectric constants, and the optical phonon frequencies vary in a nearly linear manner under hydrostatic pressure. What is more, the softening mode of the transversal acoustic mode at the X point supports the phase transition in AlAs.

New type of possible high-pressure polymorphism in NiAs minerals in planetary cores

The nickel arsenide (B81) and related crystal structures are among the most important crystallographic arrangements assumed by Fe and Ni compounds with light elements such as Si, O, S, and P, expected to be present in planetary cores. Despite the simple structure, some of these materials like troilite (FeS) exhibit complex phase diagrams and rich polymorphism, involving significant changes in interatomic bonding and physical properties. NiP (oP16) represents one of the two principal structure distortions found in the nickel arsenide family and is characterized by P–P bonding interactions that lead to the formation of P2 dimers. In the current study, the single-crystal synchrotron X-ray diffraction technique, aided by first principles density functional theory (DFT) calculations, has been applied to examine the compression behavior of NiP up to 30 GPa. Two new reversible displacive phase transitions leading to orthorhombic high-pressure phases with Pearson symbols oP40 and oC24 were found to occur at approximately 8.5 and 25.0 GPa, respectively. The oP40 phase has the primitive Pnma space group with unit cell a = 4.7729(5) A, b = 16.6619(12) A, and c = 5.8071(8) A at 16.3(1) GPa and is a superstructure of the ambient oP16 phase with multiplicity of 2.5. The oC24 phase has the acentric Cmc21 space group with unit cell a = 9.695(6) A, b = 5.7101(9) A, and c = 4.7438(6) A at 28.5(1) GPa and is a superstructure of the oP16 phase with multiplicity of 1.5. DFT calculations fully support the observed sequence of phase transitions. The two new phases constitute logical next stages of P sublattice polymerization, in which the dilution of the P3 units, introduced in the first high-pressure phase, decreases, leading to compositions of Ni20(P3)4(P2)4 and Ni12(P3)4, and provide important clues to understanding of phase relations and transformation pathways in the NiAs family.

Ab-initio study of structural and electronic properties of AlAs

The structural properties, i.e. equilibrium lattice constant, transition pressure, bulk modulus and its pressure derivatives, together with electronic properties, i.e. energy bands, Compton profile and autocorrelation function, of AlAs are presented in this work. The linear combination of atomic orbitals (LCAO) method of the CRYSTAL code was applied considering the Perdew–Burke–Ernzerhof correlation energy functional and Becke's ansatz for the exchange. The total energy of AlAs as a function of primitive cell volume has also been calculated for the zincblende (B3), nickel arsenide (B8), sodium chloride (B1) and cesium chloride (B2) phases. Structural parameters of the B3, B8, B1 and B2 phases are determined. The calculated structural parameters are found to be in good agreement with the results of previous investigations. The spherically averaged theoretical values of Compton profile are in good agreement with an earlier measurement. The LCAO calculation shows an indirect band gap of 1.85 eV, in reasonable agreement with earlier data. On the basis of the equal-valence-electron-density Compton profile, it is found that AlAs is more ionic compared to AlSb.

First-Principles Studies on Magnetic Stability of SrC and BaC in Rocksalt, Zincblende, and Nickel Arsenide Phases Under Pressure

Using the first-principles method based on the density functional theory, we investigated the magnetic stability of sp half-metal ferromagnets SrC and BaC in rocksalt (RS), zincblende (ZB), and nickel arsenide (NA) structures under external pressure. The magnetic moments, total energy of magnetic and nonmagnetic phases, and lattice constants are calculated as a function of the applied pressure. The calculations show the occurrence of pressure-induced magnetic phase transitions which are mainly resulted from the band widening of anion p states. It is also confirmed that for both SrC and BaC, the rocksalt structure is the most stable phase among the three phases.

Combined intensive nutrition education and micronutrient powder supplementation improved nutritional status of mildly wasted children on Nias Island, Indonesia.

To assess the impact of intensive nutrition education (INE) with or without the provision of micronutrient powder (MNP) on the nutritional status of mildly wasted children in Nias, Indonesia, two groups of mildly wasted (>=-1.5 to <-1.0 WHZ) children aged >=6 to <60 months in the Church World Service (CWS) project areas were assigned by village randomization to receive INE (n=64) or INE+MNP (n=51) in a weekly program. Another two groups of mildly wasted children who were living at a clear distance from INE and INE+MNP villages were selected to receive a monthly non-intensive nutrition education program (NNE) with or without MNP (n=50 both respectively). WHZ, weight, height, haemoglobin (Hb) level, and morbidity data were assessed at admission, during the study, and at individual discharge. Children's weight gain (g/kg body weight/day) was highest in INE+MNP group (2.2±2.1), followed by INE (1.1±0.9), NNE+MNP (0.3±0.5) and NNE (0.3±0.4) group. In both MNP intervention groups (INE+MNP, NNE+MNP), supplements significantly increased Hb value (g/L) of respective children (10.0±10.0; p<0.001 and 3.0±8.0; p<0.05 respectively). Proportion of children who reached discharge criterion was highest among the INE+MNP (70.6%; n=36), followed by INE (64.1%; n=41), NNE+MNP (26.0%; n=13), and NNE (20.0%; n=10) groups (p<0.001). Shortest length of stay until recovery was observed among children in the INE+MNP group (29.9 days), followed by INE (40.0 days), NNE+MNP (80.6 days), and NNE (86.2 days) respectively (p<0.001). Weekly intensive nutrition education supported by MNP supplementation produced the best results regarding weight gain and haemoglobin status of mildly wasted children.

Effect of Heat Treatment Solution on the Size and Distribution of Gamma Prime (γ´) of Super-alloy INCONEL 738

ABSTRACTNickel base superalloys, which are gamma prime γ‘(Ni3Al, Ti) precipitation strengthened, is largely responsible for the elevated-temperature strength of the material and the higher resistance to creep deformation. The amount of γ’ depends on the chemical composition and temperature, heat treatment, these alloy are widely used in hot sections of aero-engines, land based turbines, stator parts, nozzle guide vanes, blades and integral wheels, due to its excellent elevated temperature strength and hot corrosion resistance. The γ‘ size decreases not only by the high temperature of heat treatment solution (1120 °C), the cooling environment and cooling rate are important parameter to decrease γ’ size to 0.65 μm. This paper presents the effect of heat treatment solution in base nickel IN 738 superalloy under service conditions, on the size and morphology of the gamma phase γ’ Ni3 (Al, Ti), main phase in the nickel base superalloys. Also shown coarse carbide and precipitates gamma prime size distributed and improve interdentritic spacing in the matrix after heat treatment solution.

Kinetic Growth of Self-Formed In2O3 Nanodots via Phase Segregation: Ni/InAs System

Highly compact In(2)O(3) nanodots with uniform size were synthesized by a novel approach via direct annealing of Ni/InAs samples at temperatures over 250 °C. The In(2)O(3) nanodots were formed by solid diffusion between nickel and indium arsenide (InAs) and phase segregation via a catalyst-assisted kinetic process. By controlling the annealing time and ambient conditions, the size and density of In(2)O(3) nanodots can be controlled. From photoluminescence (PL) measurements, two distinct peaks located at ∼430 and ∼850 nm, corresponding to 2.9 and 1.5 eV for In(2)O(3) nanodots, can be observed. The peaks originate from radioactive recombination centers such as oxygen vacancies or indium interstitials inside In(2)O(3) nanodots. The periodic array of Ni microdiscs with diameters and interdisc spacing of ∼5 and ∼10 μm on InAs substrate surface prepared by a photolithography process demonstrated the precise control of In(2)O(3) nanodots at a specific position. Applications for precisely locating optoelectronic nanodevices in combination with electronic nanodevices are envisioned.