Facile Tailoring of Surface Terminations of MXenes by Doping Nb Element: Toward Extraordinary Pseudocapacitance Performance

MXenes show promising potential in supercapacitors due to their unique two-dimensional (2D) structure and abundant surface functional groups. However, most studies about MXenes have focused on tailoring surface structures by alternating synthesis methods or post-etch treatments, and little is known about the inherent relationship between surface groups and M elements. Herein, we propose a simple and novel strategy to adjust the surface structure of few-layered MXene flakes by adding a small amount of Nb element. Because of the strong affinity between Nb and O elements, the as-received V_1.8Nb_0.2CT_x and Ti_2.7Nb_0.3C₂T_x MXenes have much fewer -F functional groups and a higher O content than V₂CT_x and Ti₃C₂T_x MXenes, respectively. Thus, both V_1.8Nb_0.2CT_x and Ti_2.7Nb_0.3C₂T_x MXenes show enhanced pseudocapacitance performance. Especially, V_1.8Nb_0.2CT_x delivers an ultrahigh volumetric capacitance of 1698 F/cm³ at a scan rate of 2 mV/s. Moreover, benefiting from the high activity of MAX precursors obtained through a fast self-propagating high-temperature synthesis, the etching time to produce V-based MXenes is much shorter than that in previous reports. Therefore, the results presented here are applicable to the surface engineering and rational design of 2D MXene materials and develop them into promising, cost-effective electrode materials for supercapacitors or other energy-storage equipment.

Enhanced Solid-State Fluorescence of Flavin Derivatives by Incorporation in the Metal-Organic Frameworks MIL-53(Al) and MOF-5

The flavin derivatives 10-methyl-isoalloxazine (MIA) and 6-fluoro-10-methyl-isoalloxazine (6F-MIA) were incorporated in two alternative metal-organic frameworks, (MOFs) MIL-53(Al) and MOF-5. We used a post-synthetic, diffusion-based incorporation into microcrystalline MIL-53 powders with one-dimensional (1D) pores and an in-situ approach during the synthesis of MOF-5 with its 3D channel network. The maximum amount of flavin dye incorporation is 3.9 wt% for MIA@MIL-53(Al) and 1.5 wt% for 6F-MIA@MIL-53(Al), 0.85 wt% for MIA@MOF-5 and 5.2 wt% for 6F-MIA@MOF-5. For the high incorporation yields the probability to have more than one dye molecule in a pore volume is significant. As compared to the flavins in solution, the fluorescence spectrum of these flavin@MOF composites is broadened at the bathocromic side especially for MIA. Time-resolved spectroscopy showed that multi-exponential fluorescence lifetimes were needed to describe the decays. The fluorescence-weighted lifetime of flavin@MOF of 4 ± 1 ns also corresponds to those in solution but is significantly prolonged compared to the solid flavin dyes with less than 1 ns, thereby confirming the concept of "solid solutions" for dye@MOF composites. The fluorescence quantum yield (Φ_F) of the flavin@MOF composites is about half of the solution but is significantly higher compared to the solid flavin dyes. Both the fluorescence lifetime and quantum yield of flavin@MOF decrease with the flavin loading in MIL-53 due to the formation of various J-aggregates. Theoretical calculations using plane-wave and QM/MM methods are in good correspondence with the experimental results and explain the electronic structures as well as the photophysical properties of crystalline MIA and the flavin@MOF composites. In the solid flavins, π-stacking interactions of the molecules lead to a charge transfer state with low oscillator strength resulting in aggregation-caused quenching (ACQ) with low lifetimes and quantum yields. In the MOF pores, single flavin molecules represent a major population and the computed MIA@MOF structures do not find π-stacking interactions with the pore walls but only weak van-der-Waals contacts which reasons the enhanced fluorescence lifetime and quantum yield of the flavins in the composites compared to their neat solid state. To analyze the orientation of flavins in MOFs, we measured fluorescence anisotropy images of single flavin@MOF-5 crystals and a static ensemble flavin@MIL53 microcrystals, respectively. Based on image information, anisotropy distributions and overall curve of the time-resolved anisotropy curves combined with theoretical calculations, we can prove that all fluorescent flavins species have a defined and rather homogeneous orientation in the MOF framework. In MIL-53, the transition dipole moments of flavins are orientated along the 1D channel axis, whereas in MOF-5 we resolved an average orientation that is tilted with respect to the cubic crystal lattice. Notably, the more hydrophobic 6F-MIA exhibits a higher degree order than MIA. The flexible MOF MIL-53(Al) was optimized essentially to the experimental large-pore form in the guest-free state with QuantumEspresso (QE) and with MIA molecules in the pores the structure contracted to close to the experimental narrow-pore form which was also confirmed by PXRD. In summary, the incorporation of flavins in MOFs yields solid-state materials with enhanced rigidity, stabilized conformation, defined orientation and reduced aggregations of the flavins, leading to increased fluorescence lifetime and quantum yield as controllable photo-luminescent and photo-physical properties.

Microstructures and Enhanced Mechanical Properties of (Zr, Ti)(C, N)-Based Nanocomposites Fabricated by Reactive Hot-Pressing at Low Temperature

Dense and enhanced mechanical properties (Zr, Ti)(C, N)-based composites were fabricated using ZrC, TiC_0.5N_0.5, and Si powders as the raw powders by reactive hot-pressing at 1500-1700 °C. At the low sintering temperature, both (Zr, Ti)(C, N) and (Ti, Zr)(C, N) solid solutions were formed in the composites by adjusting the ratio of ZrC to TiC_0.5N_0.5. During the sintering process, the Si added at a rate of 5 mol% reacted with ZrC and TiC_0.5N_0.5 to generate SiC. With the increase in Si addition, it was found that the residual β-ZrSi was formed, which greatly reduced the flexural strength of composites but improved their toughness. The reaction and solid-solution-driven inter-diffusion processes enhanced mass transfer and promote densification. The solid solution strengthening and grain refinement improved the mechanical properties. The ZrC-47.5 mol% TiC_0.5N_0.5-5 mol% Si (raw powder) composite possessed excellent comprehensive performance. Its flexural strength, Vickers hardness, and fracture toughness were 508 ± 33 MPa, 24.5 ± 0.7 GPa, and 3.8 ± 0.1 MPa·m^1/2, respectively. These reached or exceeded the performance of most (Zr, Ti)(C, N) ceramics reported in previous studies. The lattice distortion, abundant grain boundaries, and fine-grained microstructure may make it possible for the material to be resistant to radiation.

A mixed phosphine sulfide/selenide structure as an instructional example for how to evaluate the quality of a model

This paper compares variations on a structure model derived from an X-ray diffraction data set from a solid solution of chalcogenide derivatives of cis-1,2-bis-(di-phenyl-phosphan-yl)ethyl-ene, namely, 1,2-(ethene-1,2-di-yl)bis-(di-phenyl-phoshpine sulfide/selenide), C₂₆H₂₂P₂S_1.13Se_0.87. A sequence of processes are presented to ascertain the composition of the crystal, along with strategies for which aspects of the model to inspect to ensure a chemically and crystallographically realistic structure. Criteria include mis-matches between F _obs ² and F _calc ², plots of |F _obs| vs |F _calc|, residual electron density, checkCIF alerts, pitfalls of the OMIT command used to suppress ill-fitting data, comparative size of displacement ellipsoids, and critical inspection of inter-atomic distances. Since the structure is quite small, solves easily, and presents a number of readily expressible refinement concepts, we feel that it would make a straightforward and concise instructional piece for students learning how to determine if their model provides the best fit for the data and show students how to critically assess their structures.

Effect of Si on the Oxidation Behaviors of Ti3 Al1-x Six C2 at 1000 °C

In this work, Ti₃ Al_1-x Si_x C₂ (x=0, 0.2, 0.4, and 0.6) with Al/Si solid solution structure are synthesized, and the effects of Si on their oxidation behaviors at 1000 °C are evaluated. The addition of Si not only contributes to the formation of Ti₅ Si₃ impurity but also affects the composition of the oxide scale. Particularly, the incorporation of Si in the TiO₂ lattice is demonstrated, which alters the formation energy of the (110) plane in TiO₂ , thus leading to the preferential growth of Si-doped TiO₂ to dendritic congeries. Moreover, the Si addition is believed to affect mass transportation during the oxidation process, which accelerates the formation of a continuous Al₂ O₃ layer in the oxide scale. With an optimized Si content, the oxidation of Ti₃ Al_1-x Si_x C₂ is restrained. However, with excess Si content, the continuity of the resulting Al₂ O₃ layer is destroyed, thus the oxidation rate rises again.

Macro- and Microstructure of In Situ Composites Prepared by Friction Stir Processing of AA5056 Admixed with Copper Powders

This paper is devoted to using multi-pass friction stir processing (FSP) for admixing 1.5 to 30 vol.% copper powders into an AA5056 matrix for the in situ fabrication of a composite alloy reinforced by Al-Cu intermetallic compounds (IMC). Macrostructurally inhomogeneous stir zones have been obtained after the first FSP passes, the homogeneity of which was improved with the following FSP passes. As a result of stirring the plasticized AA5056, the initial copper particle agglomerates were compacted into large copper particles, which were then simultaneously saturated by aluminum. Microstructural investigations showed that various phases such as α-Al(Cu), α-Cu(Al) solid solutions, Cu₃Al and CuAl IMCs, as well as both S and S'-Al₂CuMg precipitates have been detected in the AA5056/Cu stir zone, depending upon the concentration of copper and the number of FSP passes. The number of IMCs increased with the number of FSP passes, enhancing microhardness by 50-55%. The effect of multipass FSP on tensile strength, yield stress and strain-to-fracture was analyzed.

The Local and Electronic Structure Study of LuxGd1-xVO4 (0 ≤ x ≤ 1) Solid Solution Nanocrystals

Rare-earth-doped mixed crystals have demonstrated tunable optical properties, and it is of great importance to study the structural characteristics of the mixed-crystal hosts. Herein, Lu_xGd_1-xVO₄ (0 ≤ x ≤ 1) solid solution nanocrystals were synthesized by a modified sol-gel method, with a pure crystalline phase and element composition. The X-ray diffraction (XRD) and Rietveld refinement results showed that Lu_xGd_1-xVO₄ nanocrystals are continuous solid solutions with a tetragonal zircon phase (space group I4₁/amd) and the lattice parameters strictly follow Vegard's law. The detailed local structures were studied by extended X-ray absorption fine structure (EXAFS) spectra, which revealed that the average bond length of Gd-O fluctuates and decreases, while the average bond length of Lu-O gradually decreases with the increase in Lu content. Furthermore, the binding energy differences of core levels indicate that the covalent V-O bond is relatively stable, while the ionicity of the Lu-O bond decreases with the increasing x value, and the ionicity of the Gd-O bond fluctuates with small amplitude. The valence band structures were further confirmed by the first-principles calculations, indicating that the valence band is contributed to by the O 2p nonbonding state, localized Gd 4f and Lu 4f states, and the hybridized states between the bonding O 2p and V 3d. The binding energies of the Lu core and the valence levels tend to decrease gradually with the increase in Lu content. This work provides insight into the structural features of mixed-crystal hosts, which have been developed in recent years to improve laser performance by providing different positions for active ions to obtain inhomogeneous broadening spectra.

Homogeneous Nanoparticles of Multimetallic Phosphides via Precursor Tuning: Ternary and Quaternary M2P Phases (M = Fe, Co, Ni)

Transition metal phosphides (TMPs) are a highly investigated class of nanomaterials due to their unique magnetic and catalytic properties. Although robust and reproducible synthetic routes to narrow polydispersity monometallic phosphide nanoparticles (M₂P; M = Fe, Co, Ni) have been established, the preparation of multimetallic nanoparticle phases (M_2-x M' _x P; M, M' = Fe, Co, Ni) remains a significant challenge. Colloidal syntheses employ zero-valent metal carbonyl or multivalent acetylacetonate salt precursors in combination with trioctylphosphine as the source of phosphorus, oleylamine as the reducing agent, and additional solvents such as octadecene or octyl ether as "noncoordinating" cosolvents. Understanding how these different metal precursors behave in identical reaction environments is critical to assessing the role the relative reactivity of the metal precursor plays in synthesizing complex, homogeneous multimetallic TMP phases. In this study, phosphorus incorporation as a function of temperature and time was evaluated to probe how the relative rate of phosphidation of organometallic carbonyl and acetylacetonate salt precursors influences the homogeneous formation of bimetallic phosphide phases (M_2-x M' _x P; M, M' = Fe, Co, Ni). From the relative rate of phosphidation studies, we found that where reactivity with TOP for the various metal precursors differs significantly, prealloying steps are necessary to isolate the desired bimetallic phosphide phase. These insights were then translated to establish streamlined synthetic protocols for the formation of new trimetallic Fe_2-x-y Ni _x Co _y P phases.

Mesoporous crystalline Ti1-xSnxO2 (0 < x < 1) solid solution for a high-performance photocatalyst under visible light irradiation

We report a facile and effective inorganic polycondensation combined with aerosol-spray strategy towards high-performance photocatalyst by fabricating mesoporous Ti_1-xSn_xO₂ (0 < x < 1) solid solution. Such Ti_1-xSn_xO₂ nanocrystals with high Sn-doped contents are self-assembled into mesoporous spheres can effectively promote visible-light harvest and high quantum yield, leading a longer lifetime of the photoelectron-hole pairs and less recombination. Such the photocatalysts enhanced photocatalytic activity for the degradation of Rhodamine B (RhB). The representative Ti_0.9Sn_0.1O₂ and Ti_0.8Sn_0.2O₂ compounds reach an optimum degradation of ≈50% and 70%, respectively, after 120 min irradiation under visible irradiation. The mesoporous Ti_1-xSn_xO₂ solid solution could inhibit the recombination of electron-hole pairs, which promote reaction thermodynamics and kinetics for RhB degradation.

Origin of Ferroelectricity in BiFeO3-Based Solid Solutions

We investigate the origin of ferroelectricity in the BiFeO₃-LaFeO₃ system in rhombohedral R3c and tetragonal P4mm symmetries by ab initio density functional theory calculations and compare their electronic features with paraelectric orthorhombic Pnma symmetry. We show that a coherent accommodation of stereo-active lone pair electrons of Bi is the detrimental factor of ferroelectricity. A Bloch function arising from an indirect Bi_6p-Fe_3d hybridization mediated through O_2p is the primary origin of spontaneous polarization (P_s) in the rhombohedral system. In the orthorhombic system, a similar Bloch function was found, whereas a staggered accommodation of stereo-active lone pair electrons of Bi exclusively results in paraelectricity. A giant P_s reported in the tetragonal system originates from an orbital hybridization of Bi_6p and O_2p, where Fe-3d plays a minor role. The P_s in the rhombohedral system decreases with increasing La content, while that in the tetragonal system displays a discontinuous drop at a certain La content. We discuss the electronic factors affecting the P_s evolutions with La content.

Efficient Photocatalytic Hydrogen Production over NiS-Modified Cadmium and Manganese Sulfide Solid Solutions

In this work, new photocatalysts based on Cd_1-xMn_xS sulfide solid solutions were synthesized by varying the fraction of MnS (x = 0.4, 0.6, and 0.8) and the hydrothermal treatment temperature (T = 100, 120, 140, and 160 °C). The active samples were modified with Pt and NiS co-catalysts. Characterization was performed using various methods, including XRD, XPS, HR TEM, and UV-vis spectroscopy. The photocatalytic activity was tested in hydrogen evolution from aqueous solutions of Na₂S/Na₂SO₃ and glucose under visible light (425 nm). When studying the process of hydrogen evolution using an equimolar mixture of Na₂S/Na₂SO₃ as a sacrificial agent, the photocatalysts Cd_0.5Mn_0.5S/Mn(OH)₂ (T = 120 °C) and Cd_0.4Mn_0.6S (T = 160 °C) demonstrated the highest activity among the non-modified solid solutions. The deposition of NiS co-catalyst led to a significant increase in activity. The best activity in the case of the modified samples was shown by 0.5 wt.% NiS/Cd_0.5Mn_0.5S (T = 120 °C) at the extraordinary level of 34.2 mmol g^-1 h^-1 (AQE 14.4%) for the Na₂S/Na₂SO₃ solution and 4.6 mmol g^-1 h^-1 (AQE 2.9%) for the glucose solution. The nickel-containing samples possessed a high stability in solutions of both sodium sulfide/sulfite and glucose. Thus, nickel sulfide is considered an alternative to depositing precious metals, which is attractive from an economic point of view. It worth noting that the process of photocatalytic hydrogen evolution from sugar solutions by adding samples based on Cd_1-xMn_xS has not been studied before.

Phytosterols and γ-Oryzanol as Cholesterol Solid Phase Modifiers during Digestion

Literature reports that ingestion of phytosterols and γ-oryzanol contributes to cholesterol lowering. Despite in vivo observations, thermodynamic phase equilibria could explain phenomena occurring during digestion leading to such effects. To advance the observations made by previous literature, this study was aimed at describing the complete solid-liquid phase equilibrium diagrams of cholesterol + phytosterol and γ-oryzanol systems by DSC, evaluating them by powder X-ray, microscopy, and thermodynamic modeling. Additionally, this study evaluated the phenomena observed by an in vitro digestibility method. Results confirmed the formation of solid solution in the cholesterol + phytosterols system at any concentration and that cholesterol + γ-oryzanol mixtures formed stable liquid crystalline phases with a significant melting temperature depression. The in vitro protocol supported the idea that the same phenomena can occur during digestion in which mechanochemical forces were probably the mechanisms promoting cholesterol solid phase changes in the presence of such phytocompounds. In this case, these changes could alter cholesterol solubility and possibly its absorption in the gastrointestinal lumen.

Enhanced Mechanical Properties of Yellow ZrN Ceramic with Addition of Solid Solution of TiN

As a superhard ceramic with a yellow color and excellent electrical conductivity, ZrN has potential applications in the field of decoration, but it is limited by its poor mechanical properties. In this work, the mechanical properties of ZrN ceramic were improved by forming a (Zr, Ti)N solid solution via spark plasma sintering of a ZrN and TiN powder mixture. The influences of the amount of TiN additive on the sinterability, microstructure, color, and mechanical properties of ZrN ceramic were investigated. X-ray diffraction analysis, energy-dispersive spectroscopy, and microstructural images indicated that Ti atoms dissolved into a ZrN lattice, and a (Zr, Ti)N solid solution was formed during the sintering process. When the content of TiN was 10 vol%, the obtained (Zr, Ti)N composite exhibited the best comprehensive mechanical properties; the Vickers hardness, flexural strength, and fracture toughness were 15.17 GPa, 520 MPa, and 6.03 MPa·m^1/2, respectively. The color coordinates and color temperature diagram revealed the addition of TiN hardly impacted the color performance of the ZrN ceramic.

Synthesis of Metal Chalcogenide Semiconductors by Thermal Decomposition of Organosulfur and Organoselenium Compounds

Metal chalcogenides - because of their excellent optical and electrical properties - are important semiconductor materials for optical devices, such as solar cells, sensors, and photocatalysts. The challenges associated with metal chalcogenides are the complexity of the conventional synthesis methods and the stringent synthesis conditions. In this study, the synthesis conditions were simplified in a solvent-free synthesis method using cadmium precursor, thiourea and selenium to synthesize metal chalcogenides, such as CdS and CdSe, which have particularly suitable band gaps for the optical devices. CdS_x Se_1-x solid solution was successfully synthesized under molten thiourea as the reactive reaction medium at relatively low temperatures, even at 180 °C, with residual melamine derivatives in the solid phase. The luminescence properties of CdS_x Se_1-x and the products in the gas and solid phases were investigated. Optimization of the synthesis conditions for solid solutions of CdS_x Se_1-x and the role of organic compounds in the formation of metal chalcogenides are discussed.

Structural Characterization of Phosphorous Slag Regarding Occurrence State of Phosphorus in Dicalcium Silicate

Phosphorous slag is a solid waste generated in the process of yellow phosphorus production. In order to deeply understand the structural and cementitious characteristics of phosphorous slag, comprehensive characterizations, including X-ray fluorescence spectrometry, X-ray diffraction, thermogravimetry, Fourier transform infrared spectrometry, Raman, scanning electron microscope, and inductively coupled plasma mass spectrometry were adopted to investigate the composition, thermal stability, microstructure, and cementitious activity of phosphorous slag. In addition, scanning electron microscope with energy dispersive X-ray spectroscopy, electron microprobe analysis, and solid-state nuclear magnetic resonance techniques were used to analyze the occurrence state of P in phosphorous slag. The results show that phosphorous slag is mostly vitreous with good thermal stability. Its chemical composition mainly comprises 43.85 wt % CaO, 35.87 wt % SiO_2, and 5.57 wt % Al₂O₃, which is similar to that of blast furnace slag, but it presents lower cementitious activity than blast furnace slag. P is uniformly distributed in the phosphorous slag with P₂O₅ content of 3.75 wt %. The distribution pattern of P is extremely similar to that of Si. P is mainly existing in orthophosphate of 3CaO·P₂O₅, which forms solid solution with dicalcium silicate (2CaO·SiO₂). This work specifically clarifies the occurrence state of P in dicalcium silicate within the phosphorous slag. It is theoretically helpful to solve the retarding problem of phosphorous slag in cement and concrete.

Bright UV-C Phosphors with Excellent Thermal Stability-Y1-xScxPO4 Solid Solutions

The structural and luminescence properties of undoped Y_1-xSc_xPO₄ solid solutions have been studied. An intense thermally stable emission with fast decay (τ_1/e ~ 10^-7 s) and a band position varying from 5.21 to 5.94 eV depending on the Sc/Y ratio is detected and ascribed to the 2p O-3d Sc self-trapped excitons. The quantum yield of the UV-C emission, also depending on the Sc/Y ratio, reaches 34% for the solid solution with x = 0.5 at 300 K. It is shown by a combined analysis of theoretical and experimental data that the formation of Sc clusters occurs in the solid solutions studied. The clusters facilitate the creation of energy wells at the conduction band bottom, which enables deep localization of electronic excitations and the creation of luminescence centers characterized by high quantum yield and thermal stability of the UV-C emission.

Cu2+-Ion-Substitution-Driven Microstructure and Microwave Dielectric Properties of Mg1-xCuxAl2O4 Ceramics

In this work, Cu-substituted MgAl₂O₄ ceramics were prepared via solid-state reaction. The crystal structure, cation distribution, and microwave dielectric properties of Mg_1-xCu_xAl₂O₄ ceramics were investigated. Cu²⁺ entered the MgAl₂O₄ lattice and formed a spinel structure. The substitution of Cu²⁺ ions for Mg²⁺ ions contributed to Al³⁺ ions preferential occupation of the octahedron and changed the degree of inversion. The quality factor (Qf) value, which is correlated with the degree of inversion, increased to a maximum value at x = 0.04 and then decreased. Ionic polarizability and relative density affected the dielectric constant (ε_r) value. The temperature coefficient of the resonant frequency (τ_f) value, which was dominated by the total bond energy, generally shifted to the positive direction. Satisfactory microwave dielectric properties were achieved in x = 0.04 and sintered at 1550 °C: ε_r = 8.28, Qf = 72,800 GHz, and τ_f = -59 ppm/°C. The Mg_1-xCu_xAl₂O₄ solid solution, possessing good performance, has potential for application in the field of modern telecommunication technology.

The Reaction Behavior of 2CaO·SiO2 with CaO-SiO2-FeO-P2O5 Slag

It is important to clarify the reaction behavior of 2CaO·SiO₂ (C₂S) during hot metal dephosphorization. In this study, C₂S was prepared and added to steel slag to investigate the reaction of C₂S particles with CaO-SiO₂-FeO-P₂O₅ slag at 1723 K. The diffusion coefficient of phosphorus in C₂S was calculated. In addition, the influence of the addition of BaO to C₂S was discussed. The results show that the diffusion coefficient of phosphorus in C₂S is 9.23 × 10^-14 m²·s^-1. The Ca in C₂S can be replaced by Ba. Small particles in the solid solution were easily generated from the C₂S body by the addition of BaO, which is beneficial for improving the phosphorus partition between the C₂S solid phase and the liquid phase of the slag.

Activated Sintering of Cr2O3-Based Composites by Hot Pressing

The paper presents and discusses questions on structure formation during the sintering process of Cr₂O₃-based composites using the hot pressing method, when a chemical reaction between the components takes place. The task was difficult because Cr₂O₃ decomposes when sintered at temperatures above 1300 °C. The proposed novel method allowed for interaction between aluminum and chromia, thus avoiding the decomposition of the latter. Here, ultrafine aluminum powder played the role of the active agent forming a liquid phase and reacting with Cr₂O₃. The appearance of the solid solutions of (Cr,Al)₂O₃ with different stoichiometry of Cr and Al depended on the aluminum content in the initial mixture. The solid solution significantly strengthened boundaries between composite phases, resulting in the composite material of high fracture toughness between 5 and 7 MPa m^½ and bending strength of ca. 500 MPa. The best mechanical properties exhibited the cermet with 22 wt.% of the restored chromium.

Effects of Nb Additions and Heat Treatments on the Microstructure, Hardness and Wear Resistance of CuNiCrSiCoTiNbx High-Entropy Alloys

In this research, a set of CuNiCrSiCoTi (H-0Nb), CuNiCrSiCoTiNb_0.5 (H-0.5Nb) and CuNiCrSiCoTiNb₁ (H-1Nb) high-entropy alloys (HEAs) were melted in a vacuum induction furnace. The effects of Nb additions on the microstructure, hardness, and wear behavior of these HEAs (compared with a CuBe commercial alloy) in the as-cast (AC) condition, and after solution (SHT) and aging (AT) heat treatments, were investigated using X-ray diffraction, optical microscopy, and electron microscopy. A ball-on-disc configuration tribometer was used to study wear behavior. XRD and SEM results showed that an increase in Nb additions and modification by heat treatment (HT) favored the formation of BCC and FCC crystal structures (CS), dendritic regions, and the precipitation of phases that promoted microstructure refinement during solidification. Increases in hardness of HEA systems were recorded after heat treatment and Nb additions. Maximum hardness values were recorded for the H-1Nb alloy with measured increases from 107.53 HRB (AC) to 112.98 HRB, and from 1104 HV to 1230 HV (aged for 60 min). However, the increase in hardness caused by Nb additions did not contribute to wear resistance response. This can be attributed to a high distribution of precipitated phases rich in high-hardness NiSiTi and CrSi. Finally, the H-0Nb alloy exhibited the best wear resistance behavior in the aged condition of 30 min, with a material loss of 0.92 mm³.

Internal Sulphate Attack in Masonry Mortars with Thaumasite Formation

The present paper focuses on the study of mortar samples where expansions with thaumasite formation occur as a consequence of sulphate attack. The samples correspond to a masonry mortar used in a rural construction located in the Spanish province of Toledo made of cement with limestone filler addition CEM II/AL. Composition and microstructure of the mortars have been analysed by means of scanning electron microscopy (SEM) using secondary and backscattered electrons (BSE) and X-ray diffraction (XRD). The results show that aggregates are contaminated with gypsum, which is the source of the sulphates for the internal attack. It seems that thaumasite is formed through an ettringite transformation where aluminium atoms are replaced with silicon atoms by means of a solid solution. The study highlights that thaumasite can be formed in warm weather through an internal sulphate attack due to gypsum contamination of aggregates.

Tuning the Band Gap in the Halide Perovskite CsPbBr3 through Sr Substitution

The ability to continuously tune the band gap of a semiconductor allows its optical properties to be precisely tailored for specific applications. We demonstrate that the band gap of the halide perovskite CsPbBr₃ can be continuously widened through homovalent substitution of Sr²⁺ for Pb²⁺ using solid-state synthesis, creating a material with the formula CsPb_1-xSr_xBr₃ (0 ≤ x ≤ 1). Sr²⁺ and Pb²⁺ form a solid solution in CsPb_1-xSr_xBr₃. Pure CsPbBr₃ has a band gap of 2.29(2) eV, which increases to 2.64(3) eV for CsPb_0.25Sr_0.75Br₃. The increase in band gap is clearly visible in the color change of the materials and is also confirmed by a shift in the photoluminescence. Density-functional theory calculations support the hypothesis that Sr incorporation widens the band gap without introducing mid-gap defect states. These results demonstrate that homovalent B-site alloying can be a viable method to tune the band gap of simple halide perovskites for absorptive and emissive applications such as color-tunable light-emitting diodes, tandem solar cells, and photodetectors.

The Influence of SiO2 + SiC + Al (H2PO4)3 Coating on Mechanical and Dielectric Properties for SiCf/MWCNTS/AlPO4 Composites

SiC fiber-reinforcedAlPO₄ matrix (SiC_f/MWCNTs/AlPO₄) composites were fabricated using a hot laminating process with multi-walled carbon nanotubes (MWCNTs) as the absorber. A coating prepared from SiO₂ + SiC + Al (H₂PO₄)₃ was applied to the surface of the SiC_f/MWCNTs/AlPO₄ composites prior to an anti-oxidation test at 1273 K in air for 40 h. The anti-oxidation effect was verified by a three-point bending test, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and a dielectric property test. Anti-oxidation mechanism investigations revealed that the coating effectiveness could be attributed to three substances, i.e., SiO₂, SiP₂O_7, and SiO₂ +AlPO₄ solid solution from the reactions of SiC + O₂→SiO₂ + CO, SiO₂ + P₂O₅→SiP₂O₇ and SiO₂ +AlPO₄→solid solution, respectively.

Remarkable similarity of molecular packing in crystals of racemic and enantiopure 2-phenylpropionamide: Z' = 4 structures, molecular disorder, and the formation of a partial solid solution

Substituted acetamides (many of which are chiral) are known to be pharmacologically active. 2-Phenylpropionamide (2PPA) is one of the simplest chiral α-substituted acetamides and thus is of interest as a model compound in the growth and design of pharmaceutical crystals. In this study, the crystal structures of racemic and enantiopure forms of 2PPA were determined for the first time using single crystal X-ray diffraction at 100 K. The relationship between the signs of optical rotation and the absolute configurations is (+)-(S)-2PPA and (-)-(R)-2PPA. Four symmetrically independent molecules with different conformations are observed in crystals of both racemic and enantiopure forms. Remarkably, all forms adopt very similar supramolecular structures, H-bonded corrugated layers, that can be described using a R 2 2 ( 8 ) R 6 4 ( 16 ) graph set. The outer surfaces of these layers are built of nonpolar phenyl groups, and their inner structures are composed of H-bonded amide groups. The presence of these layers determines the thin plate shape of 2PPA crystals. Spectroscopically, the racemic and enantiopure forms substantially differ only in the low-frequency Raman region. X-ray diffraction data suggest that the racemic form of 2PPA is a partial solid solution made possible by statistical occupancy of molecular positions by (R)- and (S)-enantiomers.

Synthesis of a New Ferroelectric Relaxor Based on a Combination of Antiferroelectric and Paraelectric Systems

Relaxor ferroelectric-based energy storage systems are promising candidates for advanced applications as a result of their fast speed and high energy storage density. In the research field of ferroelectrics and relaxor ferroelectrics, the concept of solid solution is widely adopted to modify the overall properties and acquire superior performance. However, the combination between antiferroelectric and paraelectric materials was less studied and discussed. In this study, paraelectric barium hafnate (BaHfO₃) and antiferroelectric lead hafnate (PbHfO₃) are selected to demonstrate such a combination. A paraelectric to relaxor ferroelectric, to ferroelectric, and to antiferroelectric transition is observed by varying the composition x in the (Ba_1-xPb_x)HfO₃ solid solution from 0 to 100%. It is noteworthy that ferroelectric phases can be realized without primal ferroelectric material. This study creates an original solid solution system with a rich spectrum of competing phases and demonstrates an approach to design relaxor ferroelectrics for energy storage applications and beyond.