Close Lattice Parameters Research Articles

Microstructure, mechanical properties, and energetic characteristics of novel peritectic W x NbTiZr medium entropy alloys

Novel W x NbTiZr medium entropy alloys (MEAs) with tungsten concentrations of 15–25 at.% were produced using arc vacuum melting. The microstructure formation, mechanical behaviours and energetic characteristics were studied. Peritectic reaction occurs in these alloys, resulting in BCC1 and BCC2 phases with close lattice parameters, along with unique pearl chain structures. The average grain sizes of these alloys are less than 10 μm. W0.75NbTiZr alloy exhibited the most significant grain refinement, resulting in a remarkable combination of strength and ductility. When subjected to high-speed impact, the W x NbTiZr projectiles reacted with air and release high amounts of energy. These W x NbTiZr MEAs exhibit high density, exceptional mechanical properties, and significant energy release, showcasing their immense potential as high-strength energetic structural materials

Twirling and Spontaneous Symmetry Breaking of Domain Wall Networks in Lattice-Reconstructed Heterostructures of Two-Dimensional Materials.

Lattice relaxation in twistronic bilayers with close lattice parameters and almost perfect crystallographic alignment of the layers results in the transformation of the moiré pattern into a sequence of preferential stacking domains and domain wall networks. Here, we show that reconstructed moiré superlattices of the perfectly aligned heterobilayers of same chalcogen transition metal dichalcogenides have broken-symmetry structures featuring twisted nodes ("twirls") of domain wall networks. The analysis of twist-angle dependence of strain characteristics for the broken-symmetry structures shows that the formation of twirl reduces the amount of hydrostatic strain around the nodes, potentially weakening their influence on the band edge energies of electrons and holes.

Comprehensive clustering-based topology optimization for connectable multi-scale additive manufacturing structures

This paper develops a multi-scale topology optimization method that realizes optimized structural stiffness design while achieves inter-connectivity among the heterogeneous unit cells. Specifically, about the technical details, lattice structure topology optimization (LSTO) is conducted by optimizing the parameter field of the specially-designed multi-variable lattices, through which the optimized lattice parameters reflect the density and stress states of the associated macro-element. Then, the macro-elements with close lattice parameters are gathered into clusters, providing the initial guess for the next-step freeform optimization. Finally, multiscale topology optimization (MTO) through the inverse homogenization approach is performed to further design the unit cell structures. The unit cell structures for each cluster are forced to be identical to save homogenization-related computational resources and the interconnectivity is ensured due to the optimized and perfectly connected initial guess from LSTO. Using the proposed method, three classical numerical examples are studied that prove the effects of improved mechanical performance, ensured micro-structure inter-connectivity, and the affordable computing scale. Finally, mechanical tests are conducted to verify the design performance benefits of the proposed method.

Discovery of superconductivity in AlB2-type hexagonal YGa2

A crystalline sample YGa2 with the AlB2-type hexagonal structure has been synthesized using the self-flux method. We measured electrical resistivity and specific heat down to 0.4 K and in fields up to 200 mT. The obtained data reveal type-II superconductivity. Unusual behaviour of the temperature dependence of upper critical field H c2(T c) was attributed to the crystal twinning of two phases possessing close lattice parameters. We determined thermodynamic parameters in the superconducting and normal states of YGa2. DFT calculations indicated a large change in the Fermi velocity of carriers nearby cylinder-like structured Fermi surface along the Γ − A line.

A MnS/FeS2 heterostructure with a high degree of lattice matching anchored into carbon skeleton for ultra-stable sodium-ion storage

Taking their similarities in crystal structures and close lattice parameters into consideration, cubic pyrite FeS2 and MnS were used to construct a heterostructure for achieving synchronous improvements in specific capacity and rate performance.

Improvement of superconducting properties by high mixing entropy at blocking layers in BiS2-based superconductor REO0.5F0.5BiS2

To investigate the interlayer interaction in the recently synthesized high-entropy-alloy-type (HEA-type) REO0.5F0.5BiS2 superconductors (RE: rare earth), we have systematically synthesized two sets of samples with close lattice parameters (close to those of PrO0.5F0.5BiS2 or CeO0.5F0.5BiS2) but having different mixing entropy (ΔSmix) for the RE site. The crystal structure was investigated using synchrotron X-ray diffraction and Rietveld refinement. For the examined samples having different ΔSmix, the increase in ΔSmix does not largely affect the bond lengths and the bond angle of the BiS2 conducting layer but clearly suppresses the in-plane disorder at the in-plane S1 site, which is the parameter essential for the emergence of bulk superconductivity in the REO0.5F0.5BiS2 system. Bulk nature of superconductivity is improved by the increase in ΔSmix for the present samples. The results of this work clearly show that the increase in mixing entropy at the blocking layer can positively affect the emergence of bulk superconductivity by modifying the local structure of the conducting layer. This is the evidence of the interaction between the high entropy states of the blocking layers and the physical properties of the conducting layers.

HSE hybrid functional calculation of band gap deformation potential in MgGeN2

The MgGeN2 has been proposed as an alternative wide band gap semiconductor of III-N due to its flexibility in electronic property engineering. In this work, we calculated the relative deformation potential of band gap (ag ) in MgGeN2 comparing with those in the well-known binary semiconductors such as GaN and ZnO which possess very close lattice parameters of MgGeN2. The calculations were performed by using the density functional theory (DFT) with Heyd-Scuseria-Ernzerhof hybrid functional (HSE) approach. As the results, the ag of MgGeN2 is predicted as -5.37 eV, which is between those of GaN (-7.45 eV) and ZnO (-2.67). This ag is useful for advanced study in band alignment, which is crucial quantity in all optoelectronic devices using semiconductor heterostructures.

QUASITERNARY SYSTEM PbS–PbSе–Tl4PbSe3

Binary and complex chalcogenides of p-elements are perspective objects as a functional materials in the optics and thermoelectric technologies. To the investigation of the phisico-chemical interaction between them its devoted a considerable amount of work. That's why the study of new systems based on the known binary and ternary chalcogenides are actual.The initial compounds of the quasiternary PbS–PbSе–Tl4PbSe3 system had close lattice parameters (for PbS and PbSe compounds), similar structural motives ([PbS6(Se6)] octahedrons). Combination of structural similarity with high functional parameters determine the practicality of the investigation of the phase equilibria in the PbS–PbSе–Tl4PbSe3 system.The aim of the work is the study of the physico-chemical interaction system PbS–PbSе–Tl4PbSe3 determination of the coordinates of invariant points and monovariant lines courses, the homogeneity regions of the initial binary and ternary phases.Using the differential thermal (DTA) and X-ray diffraction (XRD) analyzes the pre-synthesized compounds Tl2Se, PbS, PbSе, Tl4PbSe3 were identified. Established that the obtained compounds are individual phases.Based on the results of the DTA, XRD and microstructural analysis (MSA) the physico-chemical interaction in the quasiternary system PbS–PbSе–Tl4PbSe3 were investigated. Established that in quasiternary system PbS–PbSе–Tl4PbSe3 at 573K exist two regions of solid solution based on Tl4PbSe3 and PbSхSe1-х (х=0–1) phases and one region of their co-crystallization. The widest range of homogeneity has a solid solution PbSхSe1-х (х=0–1) based on the initial binary lead chalcogenides. The PbSхSe1-х (х=0–1) solid solution occupies all section PbS–PbSe and extends to 10 mol. % into the system PbS–PbSе–Tl4PbSe3. The solid solution based on Tl4PbSe3 occupies the egde of the PbS–PbSе–Tl4PbSe3 concentration triangle. The width of the solid solution based on Tl4PbSe3 does not exceed 2 mol.% along the PbS–Tl4PbSe3 section and 7 mol.% in the PbSе–Tl4PbSe3.Based on the temperatures of the primary crystallization of alloys the projection of liquidus surface has been studied and built. Established that the fields of primary crystallization of Tl4PbSe3 and PbSхSe1-х (х=0–1) phases are divided by the line of monovariant eutectic equlibria e2–e1 (800–793K)

Preparation and characterization of (CuInTe2)1-x(TaTe)x solid solutions (0

Polycrystalline samples of the (CuInTe2)1-x(TaTe)x alloys system were prepared by the melt and anneal technique in the composition range 0 < x < 1. Products were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Differential Thermal Analysis (DTA) and SQUID techniques. From XRD and SEM, it was found that the solubility of TaTe in CuInTe2 is around 10%; however, samples up to x = 2/3 are composed by a mean tetragonal CuInTe2-like phase with traces of Ta2Te3. Samples with x > 2/3 show diffraction patterns with several phases with poor crystallization. In addition, the tetragonal CuInTe2-like phase shows spinodal decomposition i.e. there are two phases, one Ta-rich and the other Ta-poor, with the same crystal structure and very close lattice parameters. SEM measurements also show up to six different phases, although they do not produce observed diffraction line in powder XRD patterns.DC magnetic susceptibility measurements as a function of temperature using the ZFC-FC protocol were performed in samples with x ≤ 2/3. With the exception of x = 2/3, all samples show a similar behavior in the ZFC and FC curves which are typical of a system with a distribution of magnetic cluster sizes. Sample x = 2/3 shows ferromagnetic behavior with Tc = 50 K. For sample x = 1/4, measurements of the magnetization as a function of the applied magnetic field and temperature were performed. From the analysis of the curves it was found that the clusters contain 105 Ta-atoms and a coercitive field of 0.22 kOe at T = 5 K.

Interfaces in arc evaporated Al-Cr-N/Al-Cr-O multilayers and their impact on hardness

The impact of interfaces on mechanical properties of arc evaporated ~1.2–2-μm-thin multilayers—composed of alternating AlxCr1-xN and (AlxCr1-x)2O3 layers with either 12, 25, or 50 bilayers and each with either distinct, blurred, or hybrid interfaces—is investigated by detailed X-ray diffraction, TEM, and nanoindentation studies.All multilayers are single-phase cubic structured but the individual nitride and oxide layers can only be detected by XRD for the coatings composed of 12 bilayers, hence with bilayer periods λ of at least 170nm. Especially these multilayers (with the largest bilayer periods) show a significant dependence of their hardness on the interface-type, which decreases from 19 to 16 to 14GPa when composed of distinct, hybrid, or blurred interfaces, respectively. Multilayers composed of 25 or 50 bilayers exhibit overlapping XRD peaks of their nitride and oxide layers, due to the rather close lattice parameters of 4.08 and 4.00Å for cubic AlxCr1-xN and (AlxCr1-x)2O3, respectively. These multilayers with bilayer periods below 40nm, hence with a significantly higher interface fraction than those composed of only 12 bilayers, do not show a dependence of their hardness (~22.5GPa) on the interface types investigated. These studies suggest that for mechanical properties of oxide/nitride multilayers, the interface fraction is more important than their thickness—within the investigated conditions.

Magnetic and Structural Properties of the Nanostructured Cu50Ni50 Powders

Nanocrystalline Cu50Ni50 alloy powder was prepared by the mechanical alloying process in high-energy planetary ball mill P7 under an argon atmosphere. Structural, microstructural, morphological, and magnetic properties were followed by X-ray diffraction, scanning electron microscopy coupled with EDX analysis, and vibrating sample magnetometry. The mixing of Cu and Ni powders at the atomic level leads to the formation, after 30 h of milling, of two fcc NiCu structures having crystallite sizes of about 15.6 and 65.9 nm and close lattice parameters of about 3.5783 and 3.5794 A that would correspond to Ni 41.8Cu 58.1 (40.75 %) and Ni 40.6Cu 59.4 (59.25 %) compositions, respectively. Magnetic measurements reveal that the obtained powders are typical soft magnetic materials. According to the Mr/Ms ratio, the grains are either pseudo-single domain or multidomain.

Crystallographic analysis of the martensitic transformation in medium-carbon steel with packet martensite

Based on X-ray diffraction studies of the martensite texture in a single martensite packet, exact orientation relationships between the orientations of martensite crystallites and the original austenite single crystal in medium-carbon steel 37KhN3A have been determined to be as follows: (011)α||(1; 0.990; 1.009)γ to an accuracy of \( \pm 0.15^\circ ,{\left[ {01\overline 1 } \right]_\alpha }||{\left[ {1;1.163; - 2.133} \right]_\gamma }\) to an accuracy of ±0.15°. It has been shown that the orientation relationships proved to be almost the same as in the Fe–31% Ni alloy with a twinned martensite with close lattice parameters. Therefore, the conclusion has been drawn that the mechanism of the lattice deformation upon the martensitic transformation is the same in both alloys. It is described as follows. The lattice deformation occurs by shear on the (111) plane in the \({\left[ {11\overline 2 } \right]_{_\gamma }}\) direction and is accompanied by an additional change in the dimensions in the mutually perpendicular directions \({\left[ {11\overline 2 } \right]_{_\gamma }},\left[ {111} \right],\;and{\left[ {1\overline 1 0} \right]_{_\gamma }}\). The invariantlattice deformation is implemented by slip in martensite on the planes of the (112)α type in the direction \({\left[ {\overline 1 \overline 1 1} \right]_\alpha }\). One of the 24 crystallographically equivalent variants of the transformation mechanism has been considered. Apart from this type of deformation, an additional deformation of martensite is possible that does not change its orientation. It has been shown that the orientation of the martensite crystallite calculated via the phenomenological theory of the martensitic transformations (PTMT) differs by approximately 1° from the experimentally determined orientation. This refers to both the lath and twinned martensite. In the twinned martensite, the invariant plane obtained in the PTMT calculations and the habit plane coincide. In lath martensite of 37KhN3A steel, the invariant plane of the martensite crystal obtained in PTMT calculations deviates by ~25° from the orientation of the surface of the martensite plate (habit plane), which is close to the (111)γ plane. An explanation of this phenomenon is given.

Structure of some CoCrFeNi and CoCrFeNiPd multicomponent HEA alloys by diffraction techniques

The structure of CoCrFeyNi (y = 0, 0.8 and 1.2) and CoCrFeNi-Pdx (x = 0.0, 0.5, 0.8, 1.0, 1.2 and 1.5) High Entropy Alloys has been investigated by neutron and standard X-ray as well as by high-energy X-ray diffraction techniques. The alloys were produced by arc melting and afterwards heat treated under several different conditions. It has been concluded that the CoCrFeNi alloy in as-cast condition is, contrary to what is claimed in the literature, not single-phase but consists of at least two different phases, both of fcc type. The difference in lattice constant between the two phases is close to 0.001 Å. Diffraction patterns measured by X-ray and neutron diffraction have shown that the structure of the alloy is not affected by 3 h heat treatment up to 1100 °C. Changing the amount of Fe has no drastic effect on alloy structure. The Pd-containing alloys have also all been found not to be single-phase but to consist of at least four different phases, all being of fcc type. The lattice constants for all phases increase with Pd content. The relative amounts of the different phases depend on Pd concentration. Furthermore, heat treatments of 3 h duration at different temperatures have a significant effect on the alloy phase composition. It is suggested that HEAs should be considered as multicomponent alloys presenting “simple” diffraction patterns, e.g. consisting of one or several lattices of fcc, hcp or bcc type with very close lattice parameters.

The Temperature Effect on Properties of Fe-Co-Ni Nanostructured System

&lt;p&gt;The influence of heating process (up to 200, 400 and 600 °C) on the phase transformation of non-equilibrium biphase Fe-Co-Ni systems was studied. The system was not changed at 200 °C, it remained nanostructured, and there were no phase transformations. At higher temperatures phase transformation BCC- into FCC-phase (high-temperature phase modification) was observed. The degree of phase transformation depended on the system composition. At 400–600 °C there was coarsening of the crystallites. In addition, there was the phenomenon of system oxidizing attended by iron outflow from phase; as a result, the lattice parameters were decreased. According to the measurements of the lattice parameters at coolingdown, parameters dependences on temperature and coefficients of thermal expansion were obtained. Changing of the system composition (due to metal oxidation) had low impact on the coefficients. The phases with different compositions and close lattice parameters had different coefficients of expansion. It was supposed that the expansion coefficients dependence from the composition was not additive. Magnetic characteristics of the samples were measured. It was found that heating changed it essentially. The main reasons of it was coarsening of grains (crystallites) and changes of the phase composition. The dependence of the magnetic properties of systems on phase composition and size of the crystallites (particles), as well as changes occurring under the temperature effect were required a more detailed study.&lt;/p&gt;

Microstructure and Properties of Aluminum-Containing Refractory High-Entropy Alloys

A new metallurgical strategy, high-entropy alloying (HEA), was used to explore new composition and phase spaces in the development of new refractory alloys with reduced densities and improved properties. Combining Mo, Ta, and Hf with “low-density” refractory elements (Nb, V, and Zr) and with Ti and Al produced six new refractory HEAs with densities ranging from 6.9 g/cm3 to 9.1 g/cm3. Three alloys have single-phase disordered body-centered cubic (bcc) crystal structures and three other alloys contain two bcc nanophases with very close lattice parameters. The alloys have high hardness, in the range from H v = 4.0 GPa to 5.8 GPa, and compression yield strength, σ 0.2 = 1280 MPa to 2035 MPa, depending on the composition. Some of these refractory HEAs show considerably improved high temperature strengths relative to advanced Ni-based superalloys. Compressive ductility of all the alloys is limited at room temperature, but it improves significantly at 800°C and 1000°C.

Investigation of Photoinduced Electrical Properties in the Heterojunction TiO&lt;sub&gt;2&lt;/sub&gt;/SnO&lt;sub&gt;2&lt;/sub&gt;

TiO2/SnO2 thin films heterostructures are grown by the sol-gel-dip-coating technique. It was found that the crystalline structure of TiO2 depends on the annealing temperature and the substrate type. TiO2 films deposited on glass substrate, submitted to thermal annealing until 550°C, present anatase structure, whereas films deposited on quartz substrate transform to rutile structure when thermally annealed at 1100°C. When structured as rutile, this oxide semiconductor has very close lattice parameters to those of SnO2, making easier the heterostructure assembling. Electrical properties of TiO2/SnO2 heterostructure were evaluated as function of temperature and excitation with different light sources. The temperature dependence of conductivity is dominated by a deep level with energy coincident with the second ionization level of oxygen vacancies in SnO2, suggesting the dominant role of the most external layer material (SnO2) to the electrical transport properties. The fourth harmonic of a Nd:YAG laser line (4.65eV) seems to excite the most external layer whereas a InGaN LED (2.75eV) seems to excite electrons from the ground state of a quantized interfacial channel as well as intrabandgap states of the TiO2 layer.

Preparation of TiO2/SnO2 thin films by sol-gel method and periodic B3LYP simulations.

Titanium dioxide (TiO2) thin films are grown by the sol-gel dip-coating technique, in conjunction with SnO2 in the form of a heterostructure. It was found that the crystalline structure of the most internal layer (TiO2) depends on the thermal annealing temperature and the substrate type. Films deposited on glass substrate submitted to thermal annealing until 550 °C present anatase structure, whereas films deposited on quartz substrate transform to rutile structure at much higher temperatures, close to 1000 °C, unlike powder samples where the phase transition takes place at about 780 °C. When structured as rutile, the oxide semiconductors TiO2/SnO2 have very close lattice parameters, making the heterostructure assembling easier. The SnO2 and TiO2 have their electronic properties evaluated by first-principles calculations by means of DFT/B3LYP. Taking into account the calculated band structure diagram of these materials, the TiO2/SnO2 heterostructure is qualitatively investigated and proposed to increase the detection efficiency as gas sensors. This efficiency can be further improved by doping the SnO2 layer with Sb atoms. This assembly may be also useful in photoelectrocatalysis processes.

Effect of aluminum on the microstructure and properties of two refractory high-entropy alloys

The microstructure, phase composition and mechanical properties of the AlMo0.5NbTa0.5TiZr and Al0.4Hf0.6NbTaTiZr high-entropy alloys are reported. The AlMo0.5NbTa0.5TiZr alloy consists of two body-centered cubic (bcc) phases with very close lattice parameters, a1=326.8pm and a2=332.4pm. One phase was enriched with Mo, Nb and Ta and another phase was enriched with Al and Zr. The phases formed nano-lamellae modulated structure inside equiaxed grains. The alloy had a density of ρ=7.40gcm−3 and Vickers hardness Hv=5.8GPa. Its yield strength was 2000MPa at 298K and 745MPa at 1273K. The Al0.4Hf0.6NbTaTiZr had a single-phase bcc structure, with the lattice parameter a=336.7pm. This alloy had a density ρ=9.05gcm−3, Vickers microhardness Hv=4.9GPa, and its yield strength at 298K and 1273K was 1841MPa and 298MPa, respectively. The properties of these Al-containing alloys were compared with the properties of the parent CrMo0.5NbTa0.5TiZr and HfNbTaTiZr alloys and the beneficial effects from the Al additions on the microstructure and properties were outlined. A thermodynamic calculation of the solidification and equilibrium phase diagrams was conducted for these alloys and the calculated results were compared with the experimental data.

Influence of the Bulk Growth Direction on TiO&lt;sub&gt;2&lt;/sub&gt; and SnO&lt;sub&gt;2&lt;/sub&gt; Surface Energies

TiO2 and SnO2 have the (P42/mnm) rutile structure with close lattice parameters and are extensively used in technological applications due to catalytic and optical properties. These properties can dependend on the surface directions and surface energy. It is of interest to estimate which directions are appropriate or energetically more favorable. Mathematical expressions often used in the literature to estimate the surface energy in oxides are based on a direct relationship between surface and bulk energies. However, for other workers the solid growth direction is represented only in the surface energy term (Esurf), whereas the bulk energy factor (Ebulk) has no influence of the solid growth direction. The latter term (Ebulk) is important for surface growth direction of a solid because both surface and bulk can grow in the same direction. This objective of our work is to investigate the influence of the bulk energy term (Ebulk), traditionally used in the literature, as well as the supercell energy term (Esupercell) representing the influence of the bulk growth direction on the surface energy of the solid.

The Precipitation and Strengthening Mechanism of Cu-Ni-Si-Co Alloy

The precipitates, mechanical properties and strengthening effect of Cu-Ni-Si,Cu-Ni-Si-Co0.8 and Cu-Ni-Si-Co1.9 alloys are investigated. It is concluded from the TEM and XRD analysis that the strengthening of Cu-Ni-Si-Co alloy is mainly attributed to precipitates of both Ni2Si and Co2Si phases, with the same structures and very close lattice parameters. The addition of 1.9 wt% Co barely affects the precipitation process of Ni2Si or Co2Si, and may not be beneficial for enhancing the strength. The strengthening of Cu-Ni-Si-Co alloy is determined by the Orowan mechanism, and a critical precipitate radii rc about 1.5 nm corresponding to the peak strength is obtained through the theoretical analysis. It can be deduced that the peak strength of aged Cu-Ni-Si-Co alloy is obtained with the microstructures containing metastable phase and Ni2Si (or Co2Si) precipitates.