Properties Of Silicides Research Articles

Microstructure and mechanical properties of magnesium silicide prepared via spark plasma assisted combustion synthesis

The current study reports the swift synthesis of high strength nanocrystalline magnesium silicide (Mg2Si) doped with bismuth (Bi) of 0–0.025 at.% via spark plasma assisted combustion synthesis. The proposed synthesis approach is rapid (∼54 min) against the conventional liquid and solid state synthesis routes which warrants prolong duration. XRD and TEM studies reveal the in-situ evolution of Mg2Si phase and substantial doping of Bi. The synthesized Mg2Si compound exhibits higher density (>95). Mg2Si0.975-Bi0.025 demonstrates the benchmarked Vickers hardness of 484.2 ± 15.44 Hv1 and un-doped Mg2Si shows the excellent fracture toughness of 2.09 ± 0.03 MPa√m.

Crystal Structure and Thermoelectric Properties of Lightly Substituted Higher Manganese Silicides.

The dissipation of MnSi layered precipitates during solidification is critical for further enhancement of the thermoelectric properties of the higher manganese silicides. We have investigated the effects of partial substitution of V in Mn sites and of Ge in Si sites on the crystal structures and thermoelectric properties of these silicides in detail. As previously reported, a small amount of V-substitution is quite effective in completely dissipating the MnSi striations; in contrast, a small proportion of these MnSi striations always remains present in the Ge-substitution case, even in the vicinity of the Ge solubility limits. For completely MnSi-dissipated samples, domain separation of the regular and highly strained arrangements of the Si atoms is realized. This domain separation suppresses the deterioration of the carrier mobility of the partially V-substituted samples and maintains even higher electrical conductivity to yield a high thermoelectric power factor of ∼2.3 mW/Km at higher temperatures.

Magnetic Binary Silicide Nanostructures.

In spite of numerous advantageous properties of silicides, magnetic properties are not among them. Here, the magnetic properties of epitaxial binary silicide nanostructures are discussed. The vast majority of binary transition-metal silicides lack ferromagnetic order in their bulk-size crystals. Silicides based on rare-earth metals are usually weak ferromagnets or antiferromagnets, yet both groups tend to exhibit increased magnetic ordering in low-dimensional nanostructures, in particular at low temperatures. The origin of this surprising phenomenon lies in undercoordinated atoms at the nanostructure extremities, such as 2D (surfaces/interfaces), 1D (edges), and 0D (corners) boundaries. Uncompensated superspins of edge atoms increase the nanostructure magnetic shape anisotropy to the extent where it prevails over its magnetocrystalline counterpart, thus providing a plausible route toward the design of a magnetic response from nanostructure arrays in Si-based devices, such as bit-patterned magnetic recording media and spin injectors.

First-Principles Investigation of Mechanical and Thermodynamic Properties of Nickel Silicides at Finite Temperature

First-principles calculations are performed to investigate lattice parameters, elastic constants and 3D directional Young’s modulus E of nickel silicides (i.e., β-Ni3Si, δ-Ni2Si, θ-Ni2Si, e-NiSi, and θ-Ni2Si), and thermodynamic properties, such as the Debye temperature, heat capacity, volumetric thermal expansion coefficient, at finite temperature are also explored in combination with the quasi-harmonic Debye model. The calculated results are in a good agreement with available experimental and theoretical values. The five compounds demonstrate elastic anisotropy. The dependence on the direction of stiffness is the greatest for δ-Ni2Si and θ-Ni2Si, when the stress is applied, while that for β-Ni3Si is minimal. The bulk modulus B reduces with increasing temperature, implying that the resistance to volume deformation will weaken with temperature, and the capacity gradually descend for the compound sequence of β-Ni3Si > δ-Ni2Si > θ-Ni2Si > e-NiSi > θ-Ni2Si. The temperature dependence of the Debye temperature ΘD is related to the change of lattice parameters, and ΘD gradually decreases for the compound sequence of e-NiSi > β-Ni3Si > δ-Ni2Si > θ-Ni2Si > θ-Ni2Si. The volumetric thermal expansion coefficient αV, isochoric heat capacity and isobaric heat capacity C p of nickel silicides are proportional to T3 at low temperature, subsequently, αV and C p show modest linear change at high temperature, whereas Cv obeys the Dulong-Petit limit. In addition, β-Ni3Si has the largest capability to store or release heat at high temperature. From the perspective of solid state physics, the thermodynamic properties at finite temperature can be used to guide further experimental works and design of novel nickel–silicon alloys.

First-principles investigation of mechanical and thermodynamic properties of nickel silicides at finite temperature -=SUP=-*-=/SUP=-

AbstractFirst-principles calculations are performed to investigate lattice parameters, elastic constants and 3D directional Young’s modulus E of nickel silicides (i.e., β-Ni_3Si, δ-Ni_2Si, θ-Ni_2Si, ε-NiSi, and θ-Ni_2Si), and thermodynamic properties, such as the Debye temperature, heat capacity, volumetric thermal expansion coefficient, at finite temperature are also explored in combination with the quasi-harmonic Debye model. The calculated results are in a good agreement with available experimental and theoretical values. The five compounds demonstrate elastic anisotropy. The dependence on the direction of stiffness is the greatest for δ-Ni_2Si and θ-Ni_2Si, when the stress is applied, while that for β-Ni_3Si is minimal. The bulk modulus B reduces with increasing temperature, implying that the resistance to volume deformation will weaken with temperature, and the capacity gradually descend for the compound sequence of β-Ni_3Si > δ-Ni_2Si > θ-Ni_2Si > ε-NiSi > θ-Ni_2Si. The temperature dependence of the Debye temperature ΘD is related to the change of lattice parameters, and ΘD gradually decreases for the compound sequence of ε-NiSi > β-Ni_3Si > δ-Ni_2Si > θ-Ni_2Si > θ-Ni_2Si. The volumetric thermal expansion coefficient αV, isochoric heat capacity and isobaric heat capacity C _ p of nickel silicides are proportional to T ^3 at low temperature, subsequently, αV and C _ p show modest linear change at high temperature, whereas C _v obeys the Dulong-Petit limit. In addition, β-Ni_3Si has the largest capability to store or release heat at high temperature. From the perspective of solid state physics, the thermodynamic properties at finite temperature can be used to guide further experimental works and design of novel nickel–silicon alloys.

First-principles investigation of new structure, mechanical and electronic properties of Mo-based silicides

The adjustment of strength and ductility of high-temperature ceramics is still a big challenge. Although Mo-based silicides are promising high-temperature materials, the influence of Mo concentration on the mechanical and electronic properties of Mo-based silicides is unclear. In addition, it is necessary to explore the novel Mo-based silicides. In this paper, we present results of novel phases, mechanical and electronic properties of the stable Mo-based silicides within various stoichiometries. Two new Mo-based silicides: MoSi (Cmcm and Pnma) and Mo2Si (I4/mcm) are predicted. The calculated results show that the volume deformation resistance of Mo-based silicides increases with increasing Mo concentration. MoSi2 shows the strongest elastic stiffness and shear deformation resistance due to the strong Mo-Si bonds. The calculated intrinsic hardness of MoSi2 (37.7GPa) is much larger than that of other Mo-based silicides. In particular, MoSi2 and MoSi show brittle behavior. However, other silicides exhibit ductility. We further find that high concentration of Mo can improve the electronic properties of Mo-based silicides because of the formation of Mo-Mo metallic bond. Finally, our works indicate that the adjustment of the Mo stoichiometric ratio to improve the mechanical and electronic properties of Mo-based silicides.

Insight into the influence of alloying elements on mechanical and thermodynamic properties of Nb3Si: A first-principles calculations

Abstract

Ni and Ti silicide oxidation for CMOS applications investigated by XRD, XPS and FPP

Although silicide oxidation was studied 20 years ago, the interest of obtaining a robust process for new application appears significant today. Indeed, for the new architectural development process are required dense and narrow spaces. This paper focuses to bury a silicide layer under a protective layer such as silica in order to keep constant the physical and electrical properties of silicide after oxidation. Earlier works show the possibility to oxidize preferably the silicon (Si) in metal contained silicide rather than a pure crystalline Si at high temperatures. Thus, we first tried to reproduce and study these conditions and once acquired, targeted to decrease the oxidation temperature in order to fit with industrial requirements. Titanium (Ti) and Nickel (Ni) are chosen for their metallurgical interest and their integration capability in devices. Thus, four different group/phases (TiSi, TiSi2, Ni2Si, NiSi) of silicide were targeted by adjusting the temperature. In situ X-ray diffraction (XRD), photoelectron spectroscopy and sheet resistance (four point probe) measurements were carried out simultaneously before and after oxidation of silicide to characterize the phase and chemical composition. After silicide formation last three phases (TiSi2, Ni2Si, NiSi) were confirmed by XRD and G1(Ti/Si) was unknown, where only for NiSi was observed the low sheet resistance (≈7.3Ω/□) and resistivity (18μΩ·cm). After (dry, wet and plasma) oxidation, the phases of TiSi2 and Ni2Si changed and only NiSi was observed the constant phase, even pure SiO2 was noted on NiSi after wet oxidation.

염료감응형 태양전지용 니켈실리사이드 촉매재료의 물성 연구

염료감응형 태양전지용 니켈실리사이드 촉매재료의 물성 연구

Unraveling the effect of uniaxial strain on thermoelectric properties of Mg2Si: A density functional theory study**Kulwinder Kaur thanks Council of Scientific & Industrial Research (CSIR), India for providing fellowship.

In this work, the effect of uniaxial strain on electronic and thermoelectric properties of magnesium silicide using density functional theory (DFT) and Boltzmann transport equations has been studied. We have found that the value of band gap increases with tensile strain and decreases with compressive strain. The variations of electrical conductivity, Seebeck coefficient, electronic thermal conductivity, and power factor with temperatures have been calculated. The Seebeck coefficient and power factor are observed to be modified strongly with strain. The value of power factor is found to be higher in comparison with the unstrained structure at 2% tensile strain. We have also calculated phonon dispersion, phonon density of states, specific heat at constant volume, and lattice thermal conductivity of material under uniaxial strain. The phonon properties and lattice thermal conductivity of Mg2Si under uniaxial strain have been explored first time in this report.

Influence of native defects on structural and electronic properties of magnesium silicide

The narrow-gap semiconductor magnesium silicide (Mg2Si) is a promising candidate for mid-temperature (500–800 K) thermoelectric applications. Mg2Si exhibits intrinsic n-type conductivity because of its interstitial Mg defects and is generally doped with n-type dopants; however, the synthesis of p-type Mg2Si has proven difficult. In the present study, we examined several types of defects, such as vacancies and the insertion of constituent atoms (Mg and Si) into crystals, to elucidate their stability in Mg2Si and their influence on its electronic states. A first-principles calculation has revealed that the insertion of Mg into a cell is the most stable and causes n-type conductivity in terms of formation energy. In contrast, the vacancy of Mg produces hole doping although its formation energy per conventional unit cell is approximately 0.07 eV higher than that of the insertion of Mg, at their concentration of 1.04 at. %. Furthermore, the insertion and vacancy of Si atoms generate electrons with higher formation energies compared to the Mg-related defects. As these defects alter the carrier concentration, they can compensate for intentional doping because of the added impurity atoms.

Role of Si concentration on the thermodynamic properties of molybdenum silicides

Thermal stability of high-temperature materials plays an important role for high-temperature application. Although molybdenum silicides(Mo-Si) are promising ultrahigh-temperature materials, the thermodynamic properties of Mo-based silicides are unknown. In this letter, we apply the first-principles calculations to investigate the influence of Si concentration on thermodynamic properties of Mo-based silicides. We find that the Debye temperature and heat capacity of Mo-based silicides depend on the Si concentration. The Debye temperature of Mo-based silicides increases with increasing Si concentration. The calculated Debye temperature of MoSi2 is 576 K. The reason is attributed to the vibration of Si atom and Si-Si covalent bonds.

Effect of Si content on the thermoelectric transport properties of Ge-doped higher manganese silicides

Polycrystalline bulks of Si-content tuned Ge-doped higher manganese silicides (HMSs) were fabricated to elucidate the effects of Si content on the phase formation behavior and thermoelectric properties. The phase formation and electronic transport characteristics of HMSs were significantly dependent on Si content. Improved power factor was obtained at higher Si contents because of an enhanced Seebeck coefficient due to the increase in density of states effective mass, maintaining electrical conductivity. Furthermore, the lattice thermal conductivity was reduced through Si-content tuning, which suppressed the formation of secondary phases. Thus, a maximum ZT of 0.61 at 823K was obtained in MnSi1.77Ge0.027.

Silicides and Nitrides Formation in Ti Films Coated on Si and Exposed to (Ar-N2-H2) Expanding Plasma

The physical properties including the mechanical, optical and electrical properties of Ti nitrides and silicides are very attractive for many applications such as protective coatings, barriers of diffusion, interconnects and so on. The simultaneous formation of nitrides and silicides in Ti films improves their electrical properties. Ti films coated on Si wafers are heated at various temperatures and processed in expanding microwave (Ar-N2-H2) plasma for various treatment durations. The Ti-Si interface is the centre of Si diffusion into the Ti lattice and the formation of various Ti silicides, while the Ti surface is the centre of N diffusion into the Ti film and the formation of Ti nitrides. The growth of silicides and nitrides gives rise to two competing processes which are thermodynamically and kinetically controlled. The effect of thickness on the kinetics of the formation of silicides is identified. The metastable C49TiSi2 phase is the main precursor of the stable C54TiSi2 phase, which crystallizes at about 600 °C, while TiN crystallizes at about 800 °C.

Mechanical properties of microconstituents in Nb-Si-Ti alloy by micropillar compression and nanoindentation

The micromechanical properties of both Nb solid solution (Nbss) and (Nb,Ti)3Si silicide in a ternary Nb-16Si-22Ti (in at%) alloy were evaluated by nanoindentation and micropillar compression techniques. Nanoindentation tests showed that (Nb,Ti)3Si possesses much higher hardness (15.6±0.6GPa) and Young's modulus (253.3±8.4GPa) than Nbss (5.2±0.4GPa and 124.9±5.1GPa, respectively). Stress-strain curves of each constituent were obtained by micropillar compression. The stress-strain behavior showed that (Nb,Ti)3Si exhibited a brittle fracture mode, while Nbss was able to bear large ductile deformation. The compressive failure strength of (Nb,Ti)3Si intermetallic and yield strength of Nbss were found to be 8.4±1.2GPa and 0.9±0.1GPa, respectively. The fracture toughness of the (Nb,Ti)3Si phase evaluated by cracks emanating from nanoindentation, was measured to be ~2.3MPa-m1/2.

Thermodynamic Assessment of the Possibility of the Deposition of Silicon Borides from Their Halogenides

The results of the predictive calculation of thermodynamic properties (enthalpy, entropy, and heat capacity) of boron silicide required for a thermodynamic analysis of the Si–B–Cl–H system performed with the help of the TERRA software complex are presented. Cases of the formation of condensed phases SiB4 and SiB6 in the reaction mixture are considered. To evaluate process parameters (temperature, pressure, and ratio of initial reagents) of deposition from the gas phase of silicon borides, thermodynamic calculations of the Si B–Cl–H system formed by SiCl4, BCl3, and H2 for a temperature range of 1000–2200 K and pressure range of 0.00001–0.1 MPa are performed. It is shown that the thermodynamic stability of higher chlorides in the Si–B–Cl system drops with a decrease in pressure and the fraction of lower chlorides increases; i.e., initial silicon and boron chlorides destruct. However, no condensed phases SiB4 and SiB6 is formed, because their formation requires the introduction of hydrogen. It is determined that, varying the parameters of chemical deposition from the gas phase, it is possible to fabricate both single-phase and multiphase coatings. The results found in this study are of scientific and practical interest for developers of various production processes (gas-phase, liquid-phase, etc.) of silicon borides.

High-Temperature Silicides: Properties and Application

The overview presents a historic retrospective and current state of research of structure, properties and application of hightemperature silicide materials in science and engineering. These materials, particularly construction and functional materials based on or involving silicide refractory metals, are a most important alternative class of materials which adequately complete with special alloys, intermetallic metals, and ceramics that are traditionally used at high (above 15000C) temperatures in oxidizing and other aggressiveenvironments. The paper analyzes the data available on constitutional diagrams, particularly on molybdenum-silicon and tungsten-silicon systems. Also, it shows differences in descriptions of diagrams given by different authors and considers some crystallochemical and physical properties of some high-temperature silicides. The paper reviews areas of application of high-temperature silicide materials of various types (layered and multiple-phase composites, consolidated powders, film structure, three-dimensional materials), and presents details of the challenges encountered in the process of creation and application of high-temperature protectingsilicide coatings, as well as possible ways to improve their performance. It is noted that lack of unified approach to presentation and correlation of research results as well as to description of real performance of materials is a substantial problem in creating new high-temperature silicide materials.

Meta-study: Analysis of thermoelectric figure of merit parameters for silicides with various doping agents

Thermoelectric (TE) materials are increasingly promising for power generation in medium to high-temperature environments. Recent research on thermoelectric generators (TEGs) has determined the thermodynamic properties which impact the total efficiency and figure of merit (ZT) of these materials. A large Seebeck coefficient, high electrical conductivity and low thermal conductivity optimise ZT. This meta-study investigates silicides for potential TEG applications due to their high chemical stability and higher natural abundance than other TE materials. Data on the thermoelectric properties of CrSi2, FeSi2, Mg2Si and MnSi2, with a range of dopants, was sourced from a wide scope of literature and is analysed. The above thermodynamic properties contributing to ZT for each of these materials are graphed between 300 and 1000 K. It was found that chromium silicides are most effective at a temperature range of 600-800 K, and undoped magnesium silicides are most effective around 900 K. Oxide addition to β-FeSi2 produced relatively high ZT scores (ZT ≈ 0.5) among iron silicides. Rhenium substitution in manganese silicides produced a maximum figure of merit (1.05) at 900 K. Supersaturation via liquid quenching was determined to maintain high rhenium substitution and this technique may be the key to further improving the thermoelectric properties of other silicides.

Effect of pressure on electronic and thermoelectric properties of magnesium silicide: A density functional theory study**Project supported by the Council of Scientific & Industrial Research (CSIR), India.

We study the effect of pressure on electronic and thermoelectric properties of Mg2Si using the density functional theory and Boltzmann transport equations. The variation of lattice constant, band gap, bulk modulus with pressure is also analyzed. Further, the thermoelectric properties (Seebeck coefficient, electrical conductivity, electronic thermal conductivity) have been studied as a function of temperature and pressure up to 1200 K. The results show that Mg2Si is an n-type semiconductor with a band gap of 0.21 eV. The negative value of the Seebeck coefficient at all pressures indicates that the conduction is due to electrons. With the increase in pressure, the Seebeck coefficient decreases and electrical conductivity increases. It is also seen that, there is practically no effect of pressure on the electronic contribution of thermal conductivity. The paper describes the calculation of the lattice thermal conductivity and figure of merit of Mg2Si at zero pressure. The maximum value of figure of merit is attained 1.83×10−3 at 1000 K. The obtained results are in good agreement with the available experimental and theoretical results.

A special issue on silicon and silicon-related materials for thermoelectricity

Over the last years interest on thermoelectricity for microharvesting or for prospective large-scale conversion of heat into electric power has revamped. This was mostly due to the tremendous impact of nanotechnology onto the conversion rate achievable by thermoelectric generators [1], grown up by almost a factor three over the last two decades. Novel classes of thermoelectric materials have appeared – but also old materials have rejuvenated. Nanowires and nanolayers, along with multilayered structures, have imparted new improved characteristics to many age-old materials [2–4]. Two avenues were actually explored, namely reducing the thermal conductivity κ and increasing the power factor σα (where σ is the electrical conductivity and α is the Seebeck coefficient). Both approaches lead to an increase of the thermoelectric figure of merit ZT = σαT/κ (where T is the absolute temperature) – and thus of the thermoelectric efficiency with which heat is converted into electric energy [5]. As thermoelectric performances have remarkably enhanced, much attention is now dedicated to selecting materials and technologies that could be scaled up and brought to bulk production. On this avenue, geo-abundance and low material costs are key issues. Thus, it is not surprising that thermoelectric properties of silicon, silicon-germanium alloys, and silicides had been the subject of more than 700 publications over the last five years. This Special Issue is devoted to cover the most important advances in this field through some mini-review papers and a selected number of research contributions, spanning from theoretical and experimental research on silicon-based nanostructured materials to the technology enabling their implementation in actual thermoelectric generators. Possibly, a key date in the history of nanostructured thermoelectric silicon may be set at 2008, when Nature published back-to-back two seminal papers by Hochbaum et al. [6] and by Boukai et al. [7] on nanowires. Both