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High entropy silicide (Mo 0.2 Cr 0.2 Ta 0.2 Nb 0.2 W 0.2)Si 2 (named as MeSi 2) coating was successfully prepared on Ta substrate by slurry sintering method. Firstly, precursor powders were initially obtained through mechanical alloying of silicide powders. Then powder slurry was coated on Ta substrate, and then the samples were sintered. For comparison, TaSi 2 coating prepared by halide-activated pack cementation method was synthesized. Subsequently, the static oxidation resistance of both MeSi 2 coating and TaSi 2 coating was examined at 1200 °C, results revealing that the MeSi 2 coating demonstrates an effective protection time of more than 60 h. The protective effect and duration of the MeSi 2 coating on Ta substrate are significantly greater than that of TaSi 2 , indicating an improvement oxidation resistance due to the high entropy effect of the silicide coating. After oxidation, the coating evolved an outer SiO 2 layer, followed by MeSi 2 , Me 5 Si 3 , TaSi 2 , and Ta 5 Si 3 layers. As the oxidation progressed, MeSi 2 gradually transformed into Me 5 Si 3 , leading to a loss of the coating's antioxidant capacity. [ABSTRACT FROM AUTHOR]

Nickel films of 40 nm thickness were obtained by means of magnetron sputtering on a single-crystalline silicon substrate. The films were subjected to rapid thermal treatment (RTT) for 7 s until the temperature increased from 200 to 550 °C. By means of the X-ray diffraction method, the structural-phase composition of nickel films before and after RTT was explored. The atomic force microscopy method due to direct contact with the surface under study, made it possible to accurately define the microstructure, roughness, specific surface energy and grain size of the nickel films before and after RTT, as well as to establish the relationship of these parameters with the phase composition and electrical properties of the films. Surface specific resistance was measured using the four-probe method. Based on XRD results, formation of Ni2Si and NiSi phases in the film was ascertained after RTT at 300 °C. At RTT 350–550 °C, only the NiSi phase was formed in the film. The microstructure and grain size significantly depend on the phase composition of the films. A correlation has been established between specific surface energy and resistivity with the average grain size after RTT at 350–550 °C, which is associated with the formation and constant restructuring of the crystal structure of the NiSi phase. [ABSTRACT FROM AUTHOR]

Ceramic-metal corrugated structures have attracted extensive attention because of their strong penetration resistance. In this study, the effects of geometric features and boundary constraints on corrugated structures consisting of a TC4 frame and five SiC ceramic prisms were explored by performing a series of ballistic tests. Deformation results were obtained using a three-dimensional scanner, and the dynamic response was observed using a high-speed imaging system. Numerical models of these tests were established and validated using experimental results. The results suggest that increasing the support and confining strength of ceramics delay their failure and increase their degree of breakage, thereby increasing the internal energy conversion ratio of the projectile and the energy absorption ratio of ceramics by 14% and 10%, respectively. Notably, a reasonable reduction in the strength of the frame partition expands the plastic deformation range of the frame and increases its energy absorption ratio by 10%. The conclusions of this study provide a reference for designing corrugated composite structures. [ABSTRACT FROM AUTHOR]

The surface reconstruction of electrochemically activated catalysts is an effective way to improve performance. However, there is currently a dearth of study on the surface reconstruction of silicide catalysts for hydrogen evolution reactions (HER). Here, a new HER electrocatalyst, LaRuSi3, is synthesized and electrochemically triggered it to produce Ru clusters on its surface. Experimental data and theoretical simulations reveal that Ru clusters optimize the charge distribution of LaRuSi3, which promotes the adsorption of water by Ru sites and improves the adsorption of hydrogen by Si sites. The conductivity and electrochemical active sites of the catalysts are also enhanced. The catalyst has an overpotential of 45 mV to attain a current density of 10 mA cm−2 in alkaline media, which exceeds the majority of other Ru‐based compounds. This work contributes to the exploration of more efficient novel silicides HER electrocatalysts and broadens the application of surface reconstruction techniques. [ABSTRACT FROM AUTHOR]

Multi-component high entropy oxides (HEOs) have attracted enormous attention due to their unique structures and potential applications. The conventional selection strategy to obtain HEOs is to search for equimolar cationic systems to maximize configurational entropy and avoid phase separation. We previously explored non-equimolar cationic rocksalt structure Mg–Co–Ni–Cu–Zn–O HEOs using cluster-plus-glue-atom model. In this paper, the mixing entropy, enthalpy and Gibbs free energy of constructed superclusters were numerically calculated and compared with the correlated crystal structure based on recent studies. It indicated the Gibbs free energy rather than mixing entropy agrees well with the phase stability of HEOs. Mg 28 Co 17 Ni 19 Cu 16 Zn 16 O 96 shows the optimal phase stability which is related to the lowest Gibbs free energy, reflecting a regular octahedral environment preferred by the cation composition in the system. Enthalpy and entropy are among important design criteria in determining the phase stability of HEOs but the function of enthalpy is obviously higher than that of entropy. This study provides a comprehensive way to access HEOs which is undoubtedly very important for the development of other non-equimolar cationic high entropy materials such as carbides, silicides, borides or nitrides. [ABSTRACT FROM AUTHOR]

Higher manganese silicides (denoted as MnSiγ ) are a prominent class of intermetallic compound for thermoelectric applications that crystallizes into a Nowotny Chimney Ladder (NCL) phase and constitutes a higher concentration of silicon with odd stoichiometry, typically represented by an irrational number. In this work, the genesis of Si odd stoichiometry and secondary phase relations in silicon-rich and silicon-deficient MnSix is presented to clarify the significance of labile (i.e., easily alterable) Si-subsystem in inheriting the modulated lattice structure with characteristic anharmonicity. The transport properties show an interrelation to the presence of a secondary phase, which is driven by the odd stoichiometry, where the thermoelectric figure of merit (zT) is found to be optimal for MnSi1.74. The structural characterization of rapidly solidified melt-spun ribbons and spark plasma sintered bulk specimens reveal a characteristic presence of MnSi and Si as secondary phases in Si-deficient (x ≈ 1.5) and Si-excess (x ≈ 2) compositions of nominal MnSix, respectively, that coexists with the major MnSiγ based NCL phase. This study provides the fundamental basis of phase evolution and the relevance of odd stoichiometry in silicon-rich manganese silicides which exhibit fascinating phonon dynamics in optimal MnSi1.74 stoichiometry. [ABSTRACT FROM AUTHOR]

To study the formation of silicides, dislocation-free ingots of single-crystalline silicon with a diameter of 65÷110 mm, grown by the Czochralski method, were used. When studying such silicon samples using electron microscopy, small-angle scattering of CO2 laser radiation, three types of defects were identified: swirl defects, impurity micro inclusions and impurity clouds. It has been shown that silicide inclusions with sizes of 8-20 μm are formed in the near-surface layer of doped silicon, and they decrease linearly deeper into the crystal. The electrical parameters of semiconductor chromium silicide were determined: resistivity 1800 μOhm·cm, thermopower coefficient 180 μV/k, Hall constant 1.2·10-2 cm3/Kl, hole concentration 6·1019 cm-3, charge carrier mobility 18.6 cm2/V·s, band gap (0.29±0.02) еV. [ABSTRACT FROM AUTHOR]

The temperature dependences of the thermoelectromotive force of chromium mono and disilicides in the temperature range 200℃÷+600℃ have been studied. For chromium disilicide, the dependence of the thermopower coefficient (α) on temperature (T) has three sections. Chromium monosilicide is characterized by a smooth increase in thermopower with increasing temperatures up to 200℃, and then its constancy. It was revealed that silicides rich in chromium atoms have lower thermopower values than silicides rich in silicon. The maximum thermo-EMF values of 110 μV/K and 190 μV/K were observed for chromium mono- and disilicides, respectively. It was revealed that for chromium silicides the dependence of the dimensionless parameter Q = Z∙T on temperature is linear. The possibility of predicting the technology of synthesis of semiconductor material with optimal thermoelectric properties using the dependence of thermopower on conductivity and the parameter Q on temperature is shown. [ABSTRACT FROM AUTHOR]

The oxidation products (MoO3 and V2O5) have low melting points and tend to sublimate at high temperatures despite that MoSi2 and VSi2 may possess good self-lubricating properties. To copewith this challenge, a high-entropy transition metal disilicide was designed in this work in which transition metal elements that could form high melting point oxides were deliberately added. The highentropy (Ti0.2V0.2Nb0.2Mo0.2W0.2)Si2 (HE-MSi2) with hexagonal structure was successfully prepared by SPS using Ti, V, Nb, Mo, W, and Si powders as the initial materials in thiswork. TheHE-MSi2 presents a high hardness (11.8±0.4GPa) and elastic modulus (387.2 ± 46.8 GPa). In particular, its hardness is higher than that of the corresponding disilicides. Noteworthy, HE-MSi2 demonstrated superior wear resistance when compared to Mo-Si-based ceramics (such as MoSi2, Mo5 Si3, and Mo5 SiB2), high-entropy carbides (such as (MoTaWVTi)C, (HfMoNbTaTi)C, and (TiVNbMoW)4.375, and traditional single-phase ceramics (including Sialon, Si3N4, Al2O3, SiC, and ZrO2). Meanwhile, at a high temperature of 600°C, the friction coefficient and wear rate were reduced to 0.64 ± 0.05 and (1.88±0.15)x106 mm³/N•m, respectively. The preferential oxidation of different elements of the HE-MSi2 was validated through systematical characterization of composition evolution, which was dominantly impacted by high temperature and friction induction. [ABSTRACT FROM AUTHOR]

This study introduces Sn-substituted higher manganese silicides (MnSi1.75, HMS) synthesized via an arc-melting process followed by spark plasma sintering (SPS). The influences of Sn concentrations on the thermoelectric performance of Mn(Si1−xSnx)1.75 (x = 0, 0.001, 0.005, 0.01, 0.015) are systematically investigated. Our findings reveal that metallic Sn precipitates within the Mn(Si1−xSnx)1.75 matrix at x ≥ 0.005, with a determined solubility limit of approximately x = 0.001. In addition, substituting Si with Sn effectively reduces the lattice thermal conductivity of HMS by introducing point defect scattering. In contrast to the undoped HMS, the lattice thermal conductivity decreases to a minimum value of 2.0 W/mK at 750 K for the Mn(Si0.999Sn0.001)1.75 sample, marking a substantial 47.4% reduction. Consequently, a figure of merit (ZT) value of ~0.31 is attained at 750 K. This considerable enhancement in ZT is primarily attributed to the suppressed lattice thermal conductivity resulting from Sn substitution. [ABSTRACT FROM AUTHOR]

The effects of Fe 2 O 3 addition on the electrical resistivity, thermal conductivity, and microstructure formation of SiC processed under Ar, N 2 , and N 2 + 5% H 2 sintering atmospheres were investigated. The use of N 2 + 5% H 2 resulted in the lowest electrical resistivity, improved thermal conductivity and enhanced flexural strength of SiC as compared to Ar and N 2. The use of 10 wt% Fe 2 O 3 resulted in an electrical resistivity of 3.8 × 10−1 Ω cm, a thermal conductivity of 20 W/m.K, and a flexural strength of 40 MPa with 33% porosity of samples sintered at 1250 °C under N 2 + 5% H 2. The in-situ formation of a network-like structure of iron silicide (Fe 3 Si) at contact points of SiC yielded a conductive path and reduced the electrical resistivity, while the formation of Si 3 N 4 improved the mechanical property. Although, all sintering atmospheres resulted in the formation of electrically conductive Fe 3 Si, but the use of N 2 + 5% H 2 produced samples with highest Si 3 N 4 content, lowest amount of oxide phase (SiO 2 and Si 2 N 2 O), and additionally densified the microstructure. [ABSTRACT FROM AUTHOR]

The growing demand for composite materials capable of enduring prolonged loads in high-temperature and aggressive environments presents pressing challenges for materials scientists. Ceramic materials composed of silicon carbide largely possess high mechanical strength at a relatively low density, even at elevated temperatures. However, they are inherently brittle in nature, leading to concerns about their ability to fracture. The primary objective of this study was to develop a novel technique for fabricating layered composite materials by incorporating SiC-based ceramics, refractory metals, and their silicides as integral constituents. These layered composites were produced through the liquid-phase siliconization method applied to metal–carbon blanks. Analysis of the microstructure of the resultant materials revealed that when a metal element interacts with molten silicon, it leads to the formation of a layer of metal silicide on the metal's surface. Furthermore, three-point bending tests exhibited an enhancement in the bending strength of the layered composite in comparison to the base silicon carbide ceramics. Additionally, the samples demonstrated a quasi-plastic nature during the process of destruction. [ABSTRACT FROM AUTHOR]

The silicides ScT2Si2 (T = Ru, Rh, Os) were synthesized by arc-melting of the elements and subsequent annealing in sealed silica ampoules. They crystallize with the rarely observed HfFe2Si2 type structure, space group Pbcm. The structures of ScRu2Si2 (a = 761.64(4), b = 730.70(6), c = 521.07(6) pm, wR = 0.0314, 633 F2 values, 31 variables) and ScOs2Si2 (a = 771.10(8), b = 736.68(7), c = 521.88(5) pm, wR = 0.0479, 623 F2 values, 31 variables) were refined from single crystal X-ray diffractometer data. The refinements showed small degrees of Ru/Si respectively Os/Si mixing on one 4c site, leading to the refined compositions ScRu1.96(1)Si2.04(1) and ScOs1.91(1)Si2.09(1). The monomeric building units in both structures are two slightly distorted, crystallographically independent RuSi5 respectively OsSi5 square pyramids, which are condensed via common edges. The resulting densely packed [Ru2Si2] and [Os2Si2] networks leave voids for the scandium atoms with coordination number 18: Sc@Si8Ru8Sc2 and Sc@Si8Os8Sc2. Temperature dependent magnetic susceptibility measurements of ScRu2Si2 and ScOs2Si2 indicate Pauli paramagnetism. Solid-state 29Si and 45Sc static and MAS NMR spectroscopy reveal significant Knight shifts and a strong influence of the T/Si mixing on the experimental NMR line shapes. A larger overall 29Si magnetic shift for ScRu2Si2 compared to ScOs2Si2, although with a negative sign for one of the 29Si resonances, suggests stronger paramagnetic effects for ScRu2Si2, in agreement with the magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

In this study, the influences of thermal exposure on the microstructure and creep resistance of matrix alloy and (TiB+TiC+Y 2 O 3)/α-Ti composites were systematically studied. The results indicate that long-term thermal exposure leads to β-Ti dissolution, as well as the precipitation of a large number of S1 type silicides and α 2 particles. The high temperature and internal stress by thermal exposure promote β-Ti→α-Ti phase transition. In order to reduce the total energy, nanoscale {10 1 ̅ 1} transformation twins were formed at the α/β interfaces. The introduction of precipitates and nano twins leads to a significant improvement in the creep resistance after thermal exposure. The creep life can be increased by up to 108 %, while the steady-state creep rate can be reduced by an order of magnitude. After creep, there was no significant increase in the size of precipitated silicides and α 2 particles. The rod-shaped S1 type silicide has a better pinning strengthening effect on dislocations than spherical S2 type silicide. Nano twins improve the stability of the α/β interfaces during creep. Some twins were coarsened after creep by merging mechanism. Twins and reinforcements provide nucleation sites for sub-grains during the creep process. • The characteristics of α 2 phases, silicides and nano twins after thermal exposure were investigated. • The reasons for the enhanced creep properties by thermal exposure were analyzed. • The response of silicides and nano twins to creep deformation were analyzed by TEM and HRTEM. • Dynamic recrystallization behavior based on DDRX and CDRX process were discussed. [ABSTRACT FROM AUTHOR]

Understanding the structure and its relations with the transport properties is important for designing a good thermoelectric (TE) material. In this work, we investigate the relationship between those properties of the low-cost and eco-friendly materials, β-Fe 1- x Mn x Si 2 (0≤ x ≤0.10), prepared by direct arc melting and heat treatment process. The metallic phases (tetragonal α-Fe 2 Si 5 and cubic ε-FeSi) are transformed into the semiconductor phase (orthorhombic β-FeSi 2) through heat treatment. The amount of β-FeSi 2 significantly decreases at x ≥ 0.09. Mn atoms act as an acceptor and improve the carrier density (n H of holes) but decrease the mobility (μ H). By substituting Mn to β-FeSi 2 , the Seebeck coefficient (S) is more uniform at high temperatures and the electrical resistivity (ρ) effectively decreases, leading to an improvement in the power factor. The thermal conductivity (κ) slightly increases with Mn doping. However, with increasing Mn content, the formation of secondary phases increases, resulting in the reduction of solid solution of Mn in β-phase; therefore, the electrical transport deteriorates. As a result, the optimum doping level for improving TE performance is obtained at x = 0.05 sample, verifying with crystal structure analysis that the optimum doping level is in the range of 0 ≤ x ≤ 0.08 because the amount of semiconducting β-FeSi 2 drastically drops at x ≥ 0.09. Our study reveals that by judging the variation of the crystal structures, we could achieve the optimum doping level for improving TE transport properties. [Display omitted] • Structural relations with transport properties of Mn-doped β-FeSi2 are established. • Metallic structures (ε-FeSi and α-Fe2Si5) increase with Mn doping. • The formation of the metallic phase decreases the solubility of Mn in β-FeSi2. • The optimum Mn doping for enhancing the transport properties ranges from 5% to 8%. [ABSTRACT FROM AUTHOR]

• Vanadium disilicide grown on silicon with a specific crystal orientation is strained. • Due to this strain, the islands become elongated as they grow beyond a critical size. • Competing strain relaxation and edge formation energy can explain this transition. We investigated the growth and shape of vanadium silicide clusters on Si(111) using scanning tunneling microscopy, atomic force microscopy and scanning electron microscopy. The deposition of 8 monolayers of vanadium on Si(111) and subsequent annealing at 1200 K leads to the formation of large elongated VSi 2 clusters. This is in marked contrast to the deposition of submonolayer amounts of V where the VSi 2 islands have a compact shape. The shape transition can be explained by a competition between edge formation and strain relaxation energy terms. The VSi 2 clusters, which are aligned along the three high symmetry directions of the Si(111) surface and surrounded by a denuded zone, form a two-dimensional network. [ABSTRACT FROM AUTHOR]

• Design of experiment methodology is used to evaluate the formation of TiSi 2. • Arsenic doping dosage, Ti thickness and RTP temperature were studied. • Ti thickness and RTP-2 temperature dominate the formation of C54-TiSi 2. • The DoE results suggest an optimum condition for yielding C54-TiSi 2. • The process yields C54-TiSi 2 on a 0.25 μm polysilicon gate. A low-resistivity titanium silicide (TiSi 2) is crucial as a gate and source/drain material in microelectronic device fabrication, offering notable properties to enhance device performance. This study aims to experimentally determine the optimum process parameters, including arsenic doping dosage, titanium thickness, and two-step rapid thermal process (RTP) temperature, for the sheet resistance of titanium self-aligned silicide process using a design of experiment methodology. The results demonstrate that both the thickness of the titanium and the temperature of the RTP play crucial roles in determining the sheet resistance of TiSi 2. Statistical analysis reveals that increasing the titanium thickness or the temperature of the first-step RTP (RTP-1) could reduce the sheet resistance. Additionally, an optimal second-step RTP (RTP-2) temperature is critical to yield low-resistivity TiSi 2 by completely converting C49- to C54-phase. The optimum process conditions for obtaining low sheet resistance are a titanium thickness of 32–35 nm, RTP-1 temperature of 720–750 °C for 75 s, and RTP-2 temperature of 860 °C for 20 s. Moreover, surface amorphization of the polysilicon by arsenic ion implantation before the deposition of Ti/TiN films also plays a crucial role in the formation of C54-TiSi 2. The lowest sheet resistance achieved was 3.91 Ω/sq with an arsenic dosage of 1 × 1014 cm−2. The optimum condition was adopted for forming a submicron polysilicon gate, providing a promising approach for designing the process parameters for titanium self-aligned silicide formation to achieve low resistance in nanoscale electronic devices. [ABSTRACT FROM AUTHOR]

In this work, the structural, electronic, mechanical, elastic anisotropy, thermodynamic, and optical properties of TM 5 Si 3 C silicides have been examined using first-principles calculations. All studied silicides fulfill the structural stability criteria. Computed mechanical properties reveal the ductile nature of Mo 5 Si 3 C, Nb 5 Si 3 C, and W 5 Si 3 C silicides, while Ta 5 Si 3 C silicide is brittle in character. Elastic anisotropy plots, including 2D and 3D, show highly anisotropic behaviour. The ascertained electronic and dielectric properties substantiate the conductive nature of all these silicides. All silicides in the visible region have an average reflectivity of 46 %, making them ideal for coatings to reduce solar heating. Debye temperature, melting point, thermal conductivity, and Gr u ¨ neisen constant has also been investigated in current work. Thermodynamic properties have been computed at different pressure and temperature values including bulk modulus (B), volume (V), thermal expansion coefficient (α), Debye temperature (θ D), and lattice heat capacity (C v). The probed results of TM 5 Si 3 C ternary silicides demonstrate their viability for applications at elevated temperatures and as well as solar reflectors. Our findings may provide a gateway for exploring new ternary silicides and can act as an efficient, cost-effective guide for experimentalists. [Display omitted] • The mechanical properties result reflects that Ta 5 Si 3 C silicide is the stiffest and strongest shear deformation resistance. • Elastic anisotropy plots, including 2D and 3D, show highly anisotropic behavior of TM 5 Si 3 C silicides. • Nb 5 Si 3 C silicide has higher Debye temperature (544 K) than other examined silicides. • W 5 Si 3 C reveals the highest melting point (2404.95 K), while Nb 5 Si 3 C reflects the lowest melting point (2005.35 K). • All ternary silicides display maximum reflectivity in visible region. [ABSTRACT FROM AUTHOR]

A titanium matrix composite reinforced by TiB, TiC and Y 2 O 3 was prepared by induction skull melting. The creep behavior of the composite was tested at the temperature range from 600 °C to 700 °C in short time to investigate the deformation mechanism and microstructure involution. The as-cast composite shows a typical basket-weave microstructure. At the stress of 150 MPa, the stress exponents of the composite are 3.48 at 600 °C and 5.33 at 700 °C, corresponding to the deformation mechanism mainly controlled by solute-dragging and dislocation climbing respectively. Reinforcements added hinder dislocations movement effectively, which improves the creep resistance of the composite. As the creep temperature rises, the solubility of β-Ti increases, accompanied by the precipitation of silicides with different morphologies. Silicides play a role in pinning dislocations and hindering interface from migration. The dislocation movement and rearrangement during creep lead to the formation of sub-grains. • The short-time creep behavior and microstructure evolution of (TiB + TiC+Y 2 O 3)/α-Ti composite were studied. • The characteristics of reinforcements and their interaction with silicides were discussed. • The morphologies of silicides at different temperatures were investigated. • The creep deformation mechanisms were analyzed by creep exponent and dislocation movement. [ABSTRACT FROM AUTHOR]

In this study, Cu–6Ni-1.5Si- x Al (x = 0 and 0.15 wt%) alloys are manufactured as billet materials by casting and their metallurgical and physical properties are characterized. Aluminum modified alloy is obtained also by a powder metallurgical (PM) route and its structural properties are determined to be compared with the cast materials. The findings indicate that (i) solidified alloys have distributed nickel silicides (27.01 %) embedded in α-Cu(Ni,Si) solid solution, (ii) the addition of aluminum increases the amount of silicides (29.09 %) in the solidified matrix and reduces both the grain size and the secondary dendrite arm spacing, (iii) although PM alloy has similar microstructural features as cast alloys, it exhibits the highest hardness (159 HV 1) due to both finer grain structure and better distribution of silicides, (iv) both impurity and porosity have a determining effect on the electrical conductivity (27–32 % IACS, International Annealed Copper Standard) values of the alloys. • Aluminum modified Corson alloy is produced by casting and PM. • Aluminum addition provides a grain refinement and increases the amount of nickel silicides in cast alloy. • PM alloy has higher hardness due to finer grain structure and well distributed silicides compared to cast alloys. • The electrical conductivities of both Corson alloys are higher than that of Cu–2Be (wt.%) alloy. [ABSTRACT FROM AUTHOR]

The hydrogen absorption behavior of ▪ was examined using a Sieverts apparatus. Experimental results revealed the formation of a hydride phase with a stoichiometry reaching ▪ at pressures up to 250 kPa and temperatures below 300 °C. By employing Van 't Hoff analysis, the enthalpy and entropy of formation for the newly formed hydride phase were measured as -19.73 k J ⋅ m o l − 1 and -251.18 J ⋅ m o l − 1 ⋅ T − 1 , respectively. Rietveld refinement showcased an expansion in lattice parameters a and c, resulting in an overall increase in unit cell volume of up to 8%; volume expansion can induce structural failures within the material. [ABSTRACT FROM AUTHOR]

To ameliorate the potential of a promising solar cell material BaSi 2, the effects of substituting Ba with Ca atoms on the crystal structure and band gap E g of BaSi 2 , were investigated both experimentally and computationally. The solid-solution limit of the Ca atoms in BaSi 2 was approximately 2.3 at.%. Single-crystal X-ray diffraction analysis of Ba 1− x Ca x Si 2 (0.025 ≤ x ≤ 0.072) revealed that the unit cell volume decreases with Ca content x , and the Ba atoms at the A1 crystallographic site are preferentially substituted by Ca atoms. Diffuse reflectance measurements indicated that E g decreases with x (1.24 eV at x = 0 and 1.17 eV at x = 0.07). The density functional theory calculations demonstrate that the experimentally observed decrease in E g by Ca substitution can be explained qualitatively by the combination of the substitution of Ca atoms in the unit cell volume of BaSi 2 and the volume reduction. Lattice parameters normalized with respect to those of BaSi 2 and band gaps of Ba 1− x Ca x Si 2 as functions of Ca content x [Display omitted] • Solid solution limit of Ca atoms in BaSi 2 is approximately 2.3 at.%. • Lattice parameters decrease with Ca content. • Ba atoms at the A1 crystallographic site are preferentially substituted by Ca atoms. • Band gap decreases with Ca content. • Volume reduction due to Ca substitution is a main reason for decrease of band gap. [ABSTRACT FROM AUTHOR]

The influence of Zr (3 at%) addition on non-isothermal and isothermal oxidation behaviour of the Nb-19Si-5Mo-20Ti (base alloy) has been investigated. During heating in a thermogravimetric analyser to 1300 °C in air, the mass-gain begins at ∼600 °C, and shows a more gradual rise as well as a lower peak value for the Zr-containing alloy compared to the base alloy. Furthermore, the Zr-containing alloy exhibits superior oxidation resistance in isothermal test for 24 h at 1100 °C, but not at 900 °C and 1200 °C, probably due to the differences in oxide scale growth kinetics and defect density. The oxidation products have been identified as Nb 2 O 5 , SiO 2 , TiO 2 , MoO 2 , TiNb 2 O 7 , Ti 2 Nb 10 O 29 for both the alloys, with ZrO 2 being additionally observed in the Zr-containing alloy. Analysis of the isothermal oxidation kinetics suggests an initial stage of interface-reaction controlled rapid mass increase followed by parabolic behaviour, where oxygen diffusion through the oxide scale is apparently rate-controlling. Slow down to parabolic kinetics is ascribed to the formation of a SiO 2 -rich compact oxide scale. The oxide scale becomes protective due to reduced oxygen anion diffusivity in Nb 2 O 5 having Mo, Ti and Zr as substitutional solute, along with the formation of ZrO 2 and TiO 2 with Pilling-Bedworth ratio less than 2. • A comparative study of non-isothermal and isothermal oxidation behavior of Zr added arc melted hypereutectic alloy (Nb-19Si-5Mo-20Ti or Nb-19Si-5Mo-20Ti-3Zr) compositions. • Non-isothermal oxidation has been done in TGA from ambient temperature to 1300 °C, whereas that of isothermal oxidation has been carried out at 900–1200 °C. • The mechanisms involved in the role of microstructural modifications due to Zr addition on the oxidation kinetics and mechanisms have been discussed. [ABSTRACT FROM AUTHOR]

In this work, an (α + β) TRIPLEX heat treatment process was designed, as well as its impact on the microstructures and high–temperature mechanical properties of 2.5 vol% (TiB + TiC)/Ti–6Al–4Sn–7Zr–1Nb–1Mo–1W–0.2Si (wt.%) was carefully investigated. The results show that the microstructures of heat–treated TMCs consist of the primary α phase (α p) and the transformed β (β t) with a large number of nano–scale secondary α phases (α s). The TRIPLEX heat treatment encourages the effect of structural heredity, causing the residual α p lamellae to develop adequately and even mature into lamellae clusters with the same orientation, which induces a visible strengthening of the variant selection for the α phase. After the TRIPLEX heat treatment, the increase in content and size of silicides is mainly due to the process providing favorable sites and sufficient time for nucleation and growth. The longitudinal axes of some silicides exhibit an approximate 40° angle or parallel arrangement with the β/α p interfaces, which means that the silicides will grow preferentially along a specific orientation to minimize the strain energy. The (α + β) TRIPLEX heat treatment significantly increases the high–temperature strength of the TMCs with no appreciable elongation loss (as–cast TMCs: UTS = 487.6 MPa, EL = 17.4%; HT–4#: UTS = 558.1 MPa, EL = 11.5%). The strength improvement of HT–4 # is mainly related to the combined effects of α p content reduction, α s precipitation, obstruction of dislocations by the β t /α p interface, hetero–deformation strengthening, silicides precipitation strengthening, and α 2 dispersion strengthening. [ABSTRACT FROM AUTHOR]

To improve the mechanical properties of the as-rolled composite under large rolling deformation, the effect of solid solution and aging on the microstructural characteristics and mechanical properties of the as-rolled TiB/(TA15-Si) composite was detailedly investigated. The solid solution temperatures of 1050 °C in the β-phase field and different aging temperatures of 550–750 °C were chosen to regulate the evolution of matrix and silicides. After solid solution treatment, the matrix transformed from elongated and kinkled lamella into acicular martensite microstructure. And the silicides completely redissolved into matrix and a uniform diffusion of Si atom was presented. Meanwhile, the aging temperature can obviously affect the evolution of martensite and silicides. As aging temperature increased, the martensite gradually decomposed into acicular α+β lamella (at 650–700 °C) and abnormal growth of α phase appeared (at 750 °C), which dominated the decreasing trend of microhardness and high-temperature strength. Besides, the silicides gradually precipitated along the prior β phase and TiB whiskers (at 600 °C) as well as α/β phase boundaries (at 650 °C). Eventually, 600 °C and 700 °C strengths of the as-rolled composite can be obviously improved by 39.7 % and 84.6 % after solid solution and aging processes. And the composite aged at 600 °C can obtain the highest 600 °C strength of 992 MPa, which is mainly attributed to martensite, precipitation of silicides and weak α 2 phase. [ABSTRACT FROM AUTHOR]

A melt spinning technique followed by spark plasma sintering technique was used to synthesize nanostructured SrSi 2 alloys with high homogeneity and density (>99 %). The impact of the wheel speed on the microstructure of the ribbons was investigated and shows the presence of nanostructures. After sintering, typical grain size between ∼140 and ∼400 nm was obtained. We show that they permit to decrease strongly the lattice thermal conductivity. The ZT values of these melt-spun alloys are about two times higher than in our bulk material. We finally show that this short step process could be of strong interest for further development. [Display omitted] • Pure α-SrSi 2 is obtained after melt spinning. • Nanostructuring of α-SrSi 2 is maintained after spark plasma sintering. • Lattice thermal conductivity is reduced by nanostructuring. • A maximum value of ZT = 0.12 is obtained for p-type α-SrSi 2 at room temperature. [ABSTRACT FROM AUTHOR]