Showing papers on "Solid solution published in 2018"
TL;DR: It was found that the lattice parameter mismatch of the component monocarbides is a key factor for predicting single phase solid solution formation, revealing a vast new compositional space for the exploration of new UHTCs.
Abstract: Bulk equiatomic (Hf-Ta-Zr-Ti)C and (Hf-Ta-Zr-Nb)C high entropy Ultra-High Temperature Ceramic (UHTC) carbide compositions were fabricated by ball milling and Spark Plasma Sintering (SPS). It was found that the lattice parameter mismatch of the component monocarbides is a key factor for predicting single phase solid solution formation. The processing route was further optimised for the (Hf-Ta-Zr-Nb)C composition to produce a high purity, single phase, homogeneous, bulk high entropy material (99% density); revealing a vast new compositional space for the exploration of new UHTCs. One sample was observed to chemically decompose; indicating the presence of a miscibility gap. While this suggests the system is not thermodynamically stable to room temperature, it does reveal further potential for the development of new in situ formed UHTC nanocomposites. The optimised material was subjected to nanoindentation testing and directly compared to the constituent mono/binary carbides, revealing a significantly enhanced hardness (36.1 ± 1.6 GPa,) compared to the hardest monocarbide (HfC, 31.5 ± 1.3 GPa) and the binary (Hf-Ta)C (32.9 ± 1.8 GPa).
440 citations
TL;DR: It is shown that a nanostructured phase at lattice defects in CoCrNi causes its extraordinary properties, while it is magnetically frustrated and suppressed in CrMnFeCoNi.
Abstract: CrCoNi alloy exhibits a remarkable combination of strength and plastic deformation, even superior to the CrMnFeCoNi high-entropy alloy. We connect the magnetic and mechanical properties of CrCoNi, via a magnetically tunable phase transformation. While both alloys crystallize as single-phase face-centered-cubic (fcc) solid solutions, we find a distinctly lower-energy phase in CrCoNi alloy with a hexagonal close-packed (hcp) structure. Comparing the magnetic configurations of CrCoNi with those of other equiatomic ternary derivatives of CrMnFeCoNi confirms that magnetically frustrated Mn eliminates the fcc-hcp energy difference. This highlights the unique combination of chemistry and magnetic properties in CrCoNi, leading to a fcc-hcp phase transformation that occurs only in this alloy, and is triggered by dislocation slip and interaction with internal boundaries. This phase transformation sets CrCoNi apart from the parent quinary, and its other equiatomic ternary derivatives, and provides a new way for increasing strength without compromising plastic deformation.
259 citations
TL;DR: In this article, an equi-atomic high-entropy carbide powder was synthesized using spark plasma sintering (SPS), and its phase evolution, microstructure, composition and oxidation behaviour were investigated in detail.
248 citations
TL;DR: In this paper, the phase constitution and microstructure of laser-cladded FeNiCoAlCu high-entropy alloy coating were analyzed by XRD, SEM, EPMA and TEM.
205 citations
TL;DR: In this article, the corrosion and electrochemical behavior of carefully prepared ultra-lightweight magnesium-lithium (Mg-Li) alloys were investigated and compared, and the alloy compositions studied were selected to provide the ability to compare unique microstructures and crystal structures, which arise from specific alloying additions of Li.
156 citations
TL;DR: It was found that the large activation barrier for the transition from the tetragonal/orthorhombic to the monoclinic phase, which is the stable phase at room temperature, suppresses the phase transition, and thus, plays a critical role in the emergence of ferroelectricity.
Abstract: Hf1-xZrxO2 (x ∼ 0.5-0.7) has been the leading candidate of ferroelectric materials with a fluorite crystal structure showing highly promising compatibility with complementary metal oxide semiconductor devices. Despite the notable improvement in device performance and processing techniques, the origin of its ferroelectric crystalline phase (space group: Pca21) formation has not been clearly elucidated. Several recent experimental and theoretical studies evidently showed that the interface and grain boundary energies of the higher symmetry phases (orthorhombic and tetragonal) contribute to the stabilization of the metastable non-centrosymmetric orthorhombic phase or tetragonal phase. However, there was a clear quantitative discrepancy between the theoretical expectation and experiment results, suggesting that the thermodynamic model may not provide the full explanation. This work, therefore, focuses on the phase transition kinetics during the cooling step after the crystallization annealing. It was found that the large activation barrier for the transition from the tetragonal/orthorhombic to the monoclinic phase, which is the stable phase at room temperature, suppresses the phase transition, and thus, plays a critical role in the emergence of ferroelectricity.
138 citations
30 May 2018
TL;DR: In this article, the authors demonstrate how to etch a laminated (Nb2/3Sc1/3)2AlC MAX phase (solid solution) of both the Sc and Al atoms results in a 2D Nb1.33C material (MXene) with a large number of vacancies and vacancy clusters.
Abstract: Introducing point defects in two-dimensional (2D) materials can alter or enhance their properties. Here, we demonstrate how etching a laminated (Nb2/3Sc1/3)2AlC MAX phase (solid solution) of both the Sc and Al atoms results in a 2D Nb1.33C material (MXene) with a large number of vacancies and vacancy clusters. This method is applicable to any quaternary, or higher, MAX phase, wherein one of the transition metals is more reactive than the other and could be of vital importance in applications such as catalysis and energy storage. We also report, for the first time, on the existence of solid solution (Nb2/3Sc1/3)3AlC2 and (Nb2/3Sc1/3)4AlC3 phases.
122 citations
TL;DR: In this paper, two phases, solid solution and Laves phase, are identified in the alloys and two phases are transformed from hypoeutective to hypereutectic solidification by increasing Ta content.
117 citations
TL;DR: The w-LEDs component constructed by coupling the UV-LED chip with red/green/blue phosphors demonstrate an excellent correlated color temperature (CCT) of 3404 K, as well as color rendering index (CRI) of 86.8.
Abstract: Non-rare-earth Mn4+-doped double-perovskite (Ba1–xSrx)2YSbO6:Mn4+ red-emitting phosphors with adjustable photoluminescence are fabricated via traditional high-temperature sintering reaction. The structural evolution, variation of Mn4+ local environment, luminescent properties, and thermal quenching are studied systematically. With elevation of Sr2+ substituting content, the major diffraction peak moves up to a higher angle gradually. Impressively, with increasing the substitution of Ba2+ with Sr2+ cation from 0 to 100%, the emission band shifts to short-wavelength in a systematic way resulting from the higher transition energy from excited states to ground states. Besides, this blue-shift appearance can be illuminated adequately using the crystal field strength. The thermal quenching of the obtained solid solution is dramatically affected by the composition, with the PL intensity increasing 16% at 423 K going from x = 0 to 1.0. The w-LEDs component constructed by coupling the UV-LED chip with red/green/bl...
115 citations
TL;DR: It is shown that incorporating merely several atomic percent of Fe solutes into Al enables the formation of nanotwinned columnar grains with high-density 9R phase in Al(Fe) solid solutions.
Abstract: Light-weight aluminum (Al) alloys have widespread applications. However, most Al alloys have inherently low mechanical strength. Nanotwins can induce high strength and ductility in metallic materials. Yet, introducing high-density growth twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it is shown that incorporating merely several atomic percent of Fe solutes into Al enables the formation of nanotwinned (nt) columnar grains with high-density 9R phase in Al(Fe) solid solutions. The nt Al-Fe alloy coatings reach a maximum hardness of ≈5.5 GPa, one of the strongest binary Al alloys ever created. In situ uniaxial compressions show that the nt Al-Fe alloys populated with 9R phase have flow stress exceeding 1.5 GPa, comparable to high-strength steels. Molecular dynamics simulations reveal that high strength and hardening ability of Al-Fe alloys arise mainly from the high-density 9R phase and nanoscale grain sizes.
111 citations
TL;DR: In this article, the surface oxidation properties of Cr-Mn-Fe-Co-Ni high entropy alloy (HEA) at high temperatures (900 °C, 1000C, 1100°C/24h) in the 21%O2 and 79%N2 atmosphere were examined.
TL;DR: In this paper, an equiatomic quinary AlCoCrFeNi high entropy alloy (HEA) has been synthesized by mechanical alloying, and the analysis of in-situ heating X-ray diffraction patterns at various temperatures extends support to the diffusive nature of the phase transformation.
TL;DR: In this article, the evolution of microstructure and fundamental mechanical properties with Mo concentration in the arc-melted (TiZrNbTa)100-xMox (0,≤※x ≤ 20) high-entropy alloys (HEAs) are investigated.
TL;DR: In this article, entropy-stabilized oxides, in the system (Mg, Co, Ni, Cu, Zn)O, were produced by co-precipitation and hydrothermal synthesis.
Abstract: Entropy-stabilized oxides represent a novel family of advanced ceramic materials with attractive functional properties. In this work, entropy-stabilized oxides, in the system (Mg, Co, Ni, Cu, Zn)O, were produced by co-precipitation and hydrothermal synthesis. Although TG/DTA and XRD analyses of as-synthetized powders point out complex thermal evolution, in both cases the desired single-phase rock salt solid solution was obtained after a proper thermal treatment. The dilatometric analysis points out the excellent sinterability of the obtained powders, which were successfully consolidated for the first time reaching nearly full density (~ 97%) at relatively low temperature (1050 °C).
TL;DR: It was found that there are multiple crystal defects of Bi5+ , Bi(3-x)+ , and oxygen vacancies in the BiOClx I1-x samples.
Abstract: BiOClx I1-x solid solutions with different band gaps were synthesized by adjusting the initial Cl to I molar ratios through a chemical precipitation method at room temperature. The structures, morphologies and optical properties of the samples were characterized by XRD, XPS, Raman, SEM, TEM and UV/Vis, respectively. The photocatalytic experiments showed that the BiOCl0.9 I0.1 sample totally decomposed a large concentration of 50 mg L-1 aqueous Rhodamine B (RhB) solution within 12 minutes under visible light irradiation (λ>420 nm), which is 11 times higher than that of pure BiOI. Furthermore, the electron band structure and density of states of BiOCl, BiOI and BiOClx I1-x have been investigated using the DFT (density functional theory) calculation method and electrochemical methods. It was found that there are multiple crystal defects of Bi5+ , Bi(3-x)+ , and oxygen vacancies in the BiOClx I1-x samples. The results for Mott-Schottky plots and valence-band XPS spectra showed the position of conduction band (CB) for BiOCl0.9 I0.1 was up-shifted, which is favourable to the redox capacity for the photocatalysts. It could be elucidated that the synergistic effects of multiple crystal defects and unique band structure are critical to improving solar driven photocatalytic activity. This work provides a new highlight toward the construction of high property photocatalysts by tuning the crystal defect and band structure in a simple and efficient way.
TL;DR: The phase purity of the BaFe12-xTixO19 (x = 0.5, 1, 2) solid solution was verified by X-ray diffraction as mentioned in this paper.
TL;DR: In this article, the impact of lattice distortion on solid solution strengthening in a series of body-centered-cubic (bcc) Al-containing, refractory high entropy alloys (HEAs) from the Nb-Mo-Cr-Ti-Al system was analyzed.
Abstract: We present an experimental approach for revealing the impact of lattice distortion on solid solution strengthening in a series of body-centered-cubic (bcc) Al-containing, refractory high entropy alloys (HEAs) from the Nb-Mo-Cr-Ti-Al system. By systematically varying the Nb and Cr content, a wide range of atomic size difference as a common measure for the lattice distortion was obtained. Single-phase, bcc solid solutions were achieved by arc melting and homogenization as well as verified by means of scanning electron microscopy and X-ray diffraction. The atomic radii of the alloying elements for determination of atomic size difference were recalculated on the basis of the mean atomic radii in and the chemical compositions of the solid solutions. Microhardness (μH) at room temperature correlates well with the deduced atomic size difference. Nevertheless, the mechanisms of microscopic slip lead to pronounced temperature dependence of mechanical strength. In order to account for this particular feature, we present a combined approach, using μH, nanoindentation, and compression tests. The athermal proportion to the yield stress of the investigated equimolar alloys is revealed. These parameters support the universality of this aforementioned correlation. Hence, the pertinence of lattice distortion for solid solution strengthening in bcc HEAs is proven.
TL;DR: In this article, a series of NiO catalysts doped by Li+ cations have been synthesized and probed by using CO oxidation as a model reaction, and it has been revealed that the Li-cations preferentially replace the lattice Ni2+cations instead of directly refilling the Ni 2+ vacancies in the cubic NiO lattice.
Abstract: To investigate the Li+ doping effect on the structure and reactivity of NiO, a series of NiO catalysts doped by Li+ cations have been synthesized and probed by using CO oxidation as a model reaction. With a combination of experimental methods and DFT calculations, it has been revealed that the Li+ cations preferentially replace the lattice Ni2+ cations instead of directly refilling the Ni2+ vacancies in the cubic NiO lattice to form a solid solution structure below the lattice capacity. For samples possessing a pure solid solution phase, the Ni3+ cation amount increases with the increasing of lattice Li+ cation content, hence inducing the formation of larger quantities of surface mobile oxygen species. In addition, the surface reducibility and the CO adsorption and activation ability can be enhanced, accompanying the easier formation of surface oxygen vacancies and the extraction of surface active oxygen. Therefore, the intrinsic CO oxidation activity can be remarkably enhanced. In contrast, by the additi...
TL;DR: Temperature stable ceramic was obtained for x = 0.516: εr ∼ 46.11, Q × f ∼ 27 031 GHz, and τf ∼ -1.51 ppm/°C, which is promising for microwave applications.
Abstract: Structure and microwave properties of xZn0.5Ti0.5NbO4-(1 - x)Zn0.15Nb0.3Ti0.55O2 ceramics in the range of x = 0.0-1.0 were investigated. Rietveld refinement analysis and Raman spectra show that rutile- and orthorhombic-type solid solutions formed at 0-0.2 and 0.65-1, a composite at 0.2-0.64. In the solid solution regions, chemical bonds are enlarged. In this case, the Zn/Ti/Nb-O1 bond covalency and bond susceptibility are reduced, and lattice energy and thermal expansion coefficient increase along with x increases, which is mainly responsible for the development of microwave dielectric properties. Furthermore, far-infrared spectra and a classical oscillator model were used to discuss the intrinsic dielectric properties in detail. Temperature stable ceramic was obtained for x = 0.516: er ∼ 46.11, Q × f ∼ 27 031 GHz, and τf ∼ -1.51 ppm/°C, which is promising for microwave applications.
TL;DR: In this article, the magnetic properties of BaFe 11.9 Me 0.1 O 19 (Me = In 3 + and Ga 3 + ; x = 1.1 − 1.2 ) solid solutions have been investigated by time-of-flight neutron diffraction method.
TL;DR: This device is also better than sodium-ion batteries of FeS2- xSe x//Na3V2(PO4)3 and Sodium-ion capacitors of metal oxides//AC, particularly at high rates.
Abstract: Transition-metal sulfides/selenides are explored as advanced electrode materials for nonaqueous sodium-ion capacitors, using FeS2–xSex as an example. A solid solution of S/Se in FeS2–xSex allows it to combine the high capacity of FeS2 and the good diffusion kinetics of FeSe2 together, thereby exhibiting excellent cycle stability (∼220 mA h g–1 after 6000 cycles at 2 A g–1) and superior rate capability (∼210 mA h g–1 at 40 A g–1) within 0.8–3.0 V. These results are much better than those of FeS2 and FeSe2, confirming the advantages of S/Se solid solution, as supported by EIS spectra, DFT calculations, and electronic conductivity. As FeS2–xSex is paired with the activated carbon (AC) as Na-ion capacitors, this device is also better than sodium-ion batteries of FeS2–xSex//Na3V2(PO4)3 and sodium-ion capacitors of metal oxides//AC, particularly at high rates. These results open a new door for the applications of sulfides/selenides in another device of electrochemical energy storage.
TL;DR: The results showed that the Irx Cu1-x alloys had a face-centered-cubic structure; charge transfer from Cu to Ir occurred in the alloy nanoparticles, as the core-level Ir 4f peaks shifted to lower energy region with the increase in Cu content.
Abstract: For the first time, we synthesize solid-solution alloy nanoparticles of Ir and Cu with a size of ca. 2 nm, despite Ir and Cu being immiscible in the bulk up to their melting over the whole composition range. We performed a systematic characterization on the nature of the Irx Cu1-x solid-solution alloys using powder X-ray diffraction, scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results showed that the Irx Cu1-x alloys had a face-centered-cubic structure; charge transfer from Cu to Ir occurred in the alloy nanoparticles, as the core-level Ir 4f peaks shifted to lower energy region with the increase in Cu content. Furthermore, we observed that the alloying of Ir with Cu enhanced both the electrocatalytic oxygen evolution and oxygen reduction reactions. The enhanced activities could be attributed to the electronic interaction between Ir and Cu arising from the alloying effect at atomic-level.
TL;DR: By precisely tuning the reduction speed of the metal precursors, this work selectively control the crystal structure of alloy nanoparticles, and is able to selectively synthesize fcc and hcp AuRu3 Alloy nanoparticles at ambient conditions.
Abstract: Binary solid-solution alloys generally adopt one of three principal crystal lattices—body-centred cubic (bcc), hexagonal close-packed (hcp) or face-centred cubic (fcc) structures—in which the structure is dominated by constituent elements and compositions. Therefore, it is a significant challenge to selectively control the crystal structure in alloys with a certain composition. Here, we propose an approach for the selective control of the crystal structure in solid-solution alloys by using a chemical reduction method. By precisely tuning the reduction speed of the metal precursors, we selectively control the crystal structure of alloy nanoparticles, and are able to selectively synthesize fcc and hcp AuRu3 alloy nanoparticles at ambient conditions. This approach enables us to design alloy nanomaterials with the desired crystal structures to create innovative chemical and physical properties. The crystal structure of a solid-solution alloy is generally determined by its elemental composition, limiting synthetic control over the alloy’s properties. Here, the authors are able to selectively control the crystal structure of Au–Ru alloy nanoparticles by rationally tuning the reduction speed of the metal precursors.
TL;DR: In this article, a series of emission-tunable Ba3−xSrxSc4O9:yBi3+,zEu3+ (x = 0−3.0, y = 0-0.15, z = 0 −0.30) solid solution phosphors were synthesized via a high-temperature solid-state route.
Abstract: Controllable luminescence tuning can modify and improve the luminescence performances of phosphor materials and thus promote their application in white light emitting diodes (W-LEDs). Usually, crystal field modulation by constructing solid solutions based on diverse composition substitutions and energy transfers are effective strategies for adjusting the luminescence properties of phosphors. Herein, we report a series of novel emission-tunable Ba3−xSrxSc4O9:yBi3+,zEu3+ (x = 0–3.0, y = 0–0.15, z = 0–0.30) solid solution phosphors synthesized via a high-temperature solid-state route. The XRD patterns and Rietveld refinements were utilized to confirm the phase purity and analyze the structural variation. Cation substitution-dependent color-tunable evolution as a function of Sr content in Bi3+-doped Ba3−xSrxSc4O9 was observed and investigated in detail. The regular emission red-shift located in the blue-green region with the increase of Sr content was attributed to the combined effect of the crystal field splitting. Due to the suitable optical band gap (5.50 eV), Bi3+ ions realized a highly efficient doping in the Sr3Sc4O9 matrix. The as-prepared Sr3Sc4O9:Bi3+ samples were efficiently excited by UV light, and the photoluminescence properties presented obvious preferential-occupation selected excitation phenomenon where the emission peaks had remarkable red-shifts along with increasing the excitation wavelength. In addition, luminescence tuning from green to orange was achieved by designing the energy transfer from Bi3+ to Eu3+ ions in the as-prepared Sr2.97−zSc4O9:0.03Bi3+,zEu3+ samples and the corresponding mechanism was proposed. Moreover, the thermal stabilities of the studied phosphors were revealed. According to the distortion calculation of the Ba/Sr crystallographic occupation, the thermal stability is related to the lattice rigidity, which would become much stronger with the reduction of distortion. These results illustrate that the as-prepared Ba3−xSrxSc4O9:Bi3+,Eu3+ phosphors can be potential candidates for color-tunable phosphors applied in UV-pumped W-LEDs.
TL;DR: An equiatomic AlCoCrFeNiMn hexanary high entropy alloy (HEA) was successfully synthesized by mechanical alloying as mentioned in this paper, which exhibits chemical homogeneity with an average particle size of less than 3μm.
TL;DR: A tube-shaped Mn-Ni-Ti solid solution for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) through a facile self-templated urea-homogeneous precipitation method was presented in this paper.
Abstract: We present a tube-shaped Mn-Ni-Ti solid solution for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) through a facile self-templated urea-homogeneous precipitation method, which leads to the fine dispersion of the MnO x and NiO x active species in the TiO 2 lattice. The ratio of Mn/Ni/Ti is an important factor to affect the crystallinity of Mn-Ni-Ti solid sulotion, and the catalyst with a Mn/Ni/Ti ratio of 2/3/5 (Mn2-Ni3) exhibits the significant structure distortion. The abundant surface defects induce more generation of Mn 4+ species, surface adsorbed oxygen and Lewis acid sites, and acclerate the adsorption and activation of NO molecules. The appropriate Mn/Ni ratio inhibits the competitive adsorption of NH 3 with NO, and facilitates the Langmuir-Hinshelwood (L-H) mechanism to form N 2 , which acts as a much more rapid pathway in comparison to the parallel one following Eley-Rideal (E-R) mechanism. The readily occurence of L-H mechanism significantly improves the SCR performance of catalyst.
TL;DR: In this article, Mn4+-activated Ca1−xYxAl12−xMgxO19 (x = 0-0.50) solid solutions were prepared using a conventional high-temperature solid-state reaction.
Abstract: Herein, Mn4+-activated Ca1−xYxAl12−xMgxO19 (x = 0–0.50) solid solutions were prepared using a conventional high-temperature solid-state reaction. Crystal structure transformation via chemical co-substitution of Y3+/Mg2+ for Ca2+/Al3+ was investigated in detail. The optical properties of Ca1−xYxAl12−xMgxO19 (x = 0–0.50) have been reported for the first time using a combination of techniques including structural refinement and luminescence measurements. Co-doping of Mg and Y cations within the CaAl12O19 host in a controlled manner resulted in the as-prepared samples with red/far-red ratio-tunable luminescence properties. The emission bands well-matched with the absorption band of phytochrome. Interestingly, enhanced Mn4+ luminescence can be obtained upon the addition of Mg2+ and Y3+. Unexpectedly, the quantum yields exhibit a slight change when x is in the range from 0.05 to 0.40; this indicates that these solid solutions have significant potential as lighting systems for plant growth.
TL;DR: The mechanism of how Mo, Nb, Ta, Ti, and Zr affect the HfMoNbTaTiZr alloys was established after comparing the properties of these alloys.
Abstract: Nowadays refractory high-entropy alloys (RHEAs) are regarded as great candidates for the replacement of superalloys at high temperature. To design a RHEA, one must understand the pros and cons of every refractory element. However, the elemental effect on mechanical properties remains unclear. In this study, the subtraction method was applied on equiatomic HfMoNbTaTiZr alloys to discover the role of each element, and, thus, HfMoNbTaTiZr, HfNbTaTiZr, HfMoTaTiZr, HfMoNbTiZr, HfMoNbTaZr, and HfMoNbTaTi were fabricated and analyzed. The microstructure and mechanical properties of each alloy at the as-cast state were examined. The solid solution phase formation rule and the solution strengthening effect are also discussed. Finally, the mechanism of how Mo, Nb, Ta, Ti, and Zr affect the HfMoNbTaTiZr alloys was established after comparing the properties of these alloys.
TL;DR: In this article, the production and characterization of a high-entropy alloy in the refractory Zr-Nb-Ti-V-Hf system is described.
TL;DR: In this paper, the effects of M atomic species mixing on the structural, elastic, electronic, and thermodynamic properties of newly synthesized MAX phase (Zr1-xTix)2AlC (0,≤※x ≤ 1) solid solutions have been studied by means of density functional theory (DFT) based first principles calculations.