Good Phase Stability Research Articles

Surface Matrix-Mediated Cation Exchange of Perovskite Quantum Dots for Efficient Solar Cells.

Cesium-formamidinium lead triiodide perovskite quantum dot (CsxFA1-xPbI3 PQD) is very promising for photovoltaic applications due to its good phase stability and outstanding optoelectronic properties. However, achieving the CsxFA1-xPbI3 PQDs with tunable compositions and robust surface matrix remains a challenge. Here, the surface matrix-mediated cation exchange of PQDs is proposed, in which a bi-functional molecule, tetrafluoroborate methylammonium (FABF4), is applied for the cation exchange and stabilizing surface matrix of PQDs. The results reveal that the FA+ of FABF4 molecules could exchange the Cs+ of CsPbI3 PQDs forming alloy CsxFA1-xPbI3 PQDs, allowing to tune the spectroscopies of PQDs. Meanwhile, the BF4- of FABF4 molecules can effectively stabilize the surface lattice and substantially diminish the surface vacancies of PQDs, improving the phase stability and optoelectronic properties of PQDs. Consequently, CsxFA1-xPbI3 PQD solar cells deliver an efficiency of up to 17.49%, which is the highest value of CsxFA1-xPbI3 PQD solar cells. This work provided important design principles for the composition and surface matrix regulation of PQDs for high-performance solar cells or other optoelectronic devices.

Surface Matrix‐Mediated Cation Exchange of Perovskite Quantum Dots for Efficient Solar Cells

Cesium‐formamidinium lead triiodide perovskite quantum dot (CsxFA1‐xPbI3 PQD) is very promising for photovoltaic applications due to its good phase stability and outstanding optoelectronic properties. However, achieving the CsxFA1‐xPbI3 PQDs with tunable compositions and robust surface matrix remains a challenge. Here, the surface matrix‐mediated cation exchange of PQDs is proposed, in which a bi‐functional molecule, tetrafluoroborate methylammonium (FABF4), is applied for the cation exchange and stabilizing surface matrix of PQDs. The results reveal that the FA+ of FABF4 molecules could exchange the Cs+ of CsPbI3 PQDs forming alloy CsxFA1‐xPbI3 PQDs, allowing to tune the spectroscopies of PQDs. Meanwhile, the BF4‐ of FABF4 molecules can effectively stabilize the surface lattice and substantially diminish the surface vacancies of PQDs, improving the phase stability and optoelectronic properties of PQDs. Consequently, CsxFA1‐xPbI3 PQD solar cells deliver an efficiency of up to 17.49%, which is the highest value of CsxFA1‐xPbI3 PQD solar cells. This work provided important design principles for the composition and surface matrix regulation of PQDs for high‐performance solar cells or other optoelectronic devices.

A high‐entropy (Er0.25Y0.25Ho0.25Yb0.25)2Si2O7 ceramic with good thermal properties and water‐vapor corrosion resistance

AbstractA high‐entropy rare‐earth disilicate (Er0.25Y0.25Ho0.25Yb0.25)2Si2O7 (hereinafter referred to as (EYHY)2Si2O7) ceramic was synthesized by a heat treatment process combined with spark plasma sintering. According to the experimental results, (EYHY)2Si2O7 presents good phase stability and low thermal conductivity ([1.48–2.35] W∙m−1∙K−1) from room temperature to 1200°C. Its coefficient of thermal expansion is (3.89–5.32) × 10−6 K−1 from 200 to 1400°C, similar to SiC‐based materials ([4.5–5.5] × 10−6 K−1). Due to the multiple doping effects, (EYHY)2Si2O7 exhibits outstanding corrosion resistance performance in water‐vapor corrosion tests. Its weight loss is 1.79 mg/cm2 after corrosion at 1600°C for 30 h in the presence of 50% H2O‐50% O2, which is lower than the corresponding four single components Re2Si2O7 (Er2Si2O7, Y2Si2O7, Ho2Si2O7, and Yb2Si2O7) under the same conditions. Therefore, high‐entropy (EYHY)2Si2O7 ceramics are regarded as potential environmental barrier coatings materials for SiC ceramic matrix composites.

Multi-objective optimisation and verification of creep-resistant Ni-base superalloy for electron-beam powder-bed-fusion

This paper reports the use of integrated computational alloy design, coupled with a rapid printability screening method, to downselect from a total of 70000 datasets in design space to five candidates in the first step, and then from five to one in the second step. The new Ni-base superalloy with compositions of Ni-5.03Al-2.69Co-5.63Cr-0.04Hf-1.91Mo-2.36Re-3.32Ta-0.57Ti-8.46W-0.05C-0.019B exhibits an optimal balance of density (8.82 g/cm2), printability (freezing range of 107 °C), thermal stability (γ′-volume fraction of 50.7% at 980 °C and low Md‾ value) and creep (rupture time of 612 h at 980 °C/120 MPa). The micro-hardness varies mildly from 417.2 ± 18.5 to 434.7 ± 14.6 HV, suggesting good phase stability. This is substantiated by microstructure observations, which revealed the absence of a topologically close-packed phase. Machine-learning tools of the artificial neural network (ANN), random forest, and support vector regression, respectively, were used to predict creep rupture time. The ANN algorithm achieves the highest accuracy in predicting creep life. By recognising the “black box” nature of the ANN, interpretability analysis was conducted using the local interpretable model-agnostic method. The analysis supports that the ANN model truly learned meaningful functional relationships, and thus is judged as reliable. Feature correlation evaluation outcome emphasises the importance of incorporating microstructure-related input features.

Effects of CeO2 doping on the mechanical, infrared radiative, and thermophysical properties of Pr2Zr2O7 ceramics for potential thermal protective coatings

A series of Ce4+-doped Pr2Zr2O7 ceramics were produced using a solid reaction method to utilize novel ceramic materials as potential candidates for thermally protective coatings. The effects of Ce4+ doping on the phase composition and mechanical, infrared radiative, and thermophysical properties were studied in detail. The results indicated the good phase stability and sintering resistance of the Pr2(Zr1−xCex)2O7 ceramics. Moreover, Ce4+-doped Pr2Zr2O7 bulk materials exhibited higher infrared emissivity (0.904) at wavelengths of 3–5 μm and 1000 °C for Pr2(Zr0.5Ce0.5)2O7) owing to the introduction of impurity energy levels. Pr2(Zr0.7Ce0.3)2O7 exhibited an appropriate average coefficient of thermal expansion of 12.4 × 10−6 K−1 and a low thermal conductivity of 1.14 W m−1 K−1 at 1000 °C, owing to the reduction of lattice energy and the presence of more oxygen vacancies and substitution atoms.

A single-phase Nb25Ti35V5Zr35 refractory high-entropy alloy with excellent strength-ductility synergy

Refractory high entropy alloys (RHEAs) are promising candidates for high-temperature structural materials due to their excellent high-temperature performance. However, the room-temperature brittleness of most alloys results in poor plastic formability, thereby limiting their engineering applications. In this study, Nb25Ti35V5Zr35 alloy with cold-rollability was developed, and its phase stability, tensile mechanical properties, elastic properties, strengthening mechanism, and deformation mechanism were investigated by combining experiments, CALPHAD, DFT and molecular statics (MS) methods. The results demonstrate that Nb25Ti35V5Zr35 alloy possesses good phase stability, with both the as-cast and annealed states maintaining a single-phase BCC structure without undergoing phase transformation. The tensile yield strength of the alloy reaches its peak at 1152 MPa in the cold-rolled condition, while its annealed state exhibits an optimal balance of strength and plasticity, with a yield strength of 836 MPa and an elongation of 22.45 %, respectively. Solid solution strengthening is the primary source of its high strength, with V and Zr playing key roles in this strengthening mechanism. Dislocation slip plays a dominant role in plastic deformation. Additionally, compared to traditional BCC alloys, the significance of edge dislocations in the deformation process is notably enhanced, with the {112} plane serving as the preferred slip plane for dislocations. DFT results indicate that the alloy exhibits significant anisotropy in both Young's modulus and shear modulus. This work contributes to understanding the material properties of the Nb25Ti35V5Zr35 alloy and provides a reference for the design of new ductile RHEAs.

Microstructure and high-temperature phase stability of Co-precipitation (Mg0.2Al0.2Ce0.2Y0.2Zr0.2)O1.6 high entropy ceramics powders

(Mg0.2Al0.2Ce0.2Y0.2Zr0.2)O1.6 high entropy ceramics powders have been prepared by co-precipitation method with two calcination temperatures (1000 °C and 1200 °C). The microstructure, phase composition and phase stability after repeated calcination at 1400 °C with various times of the powders have been investigated. The powder calcined at 1200 °C has the better crystallinity and the stronger diffraction peak of t-ZrO2 phase at room temperature. The existence of Ce4+ and Y3+ with large radius in the ZrO2 lattice can enhance the tetragonality of the powders. The Mg2+ and Al3+ with small radii can exist in the lattice gap of ZrO2 or replace the position of Zr4+, causing lattice contraction, offsetting the lattice expansion which caused by Ce4+ and Y3+, and reducing the negative effects induced by the large ion doping. Thus, (Mg0.2Al0.2Ce0.2Y0.2Zr0.2)O1.6 has a good phase stability after repeated calcination at 1400 °C for 80h.

Synthesis, Characterization, and Analysis of Probenecid and Pyridine Compound Salts

This study aimed to address the issue of the low solubility in the model drug probenecid (PRO) and its impact on bioavailability. Two salts of probenecid (PRO), 4-aminopyridine (4AMP), and 4-dimethylaminopyridine (4DAP) were synthesized and characterized by PXRD, DSC, TGA, FTIR, and SEM. The crystal structures of the two salts were determined by SCXRD, demonstrating that the two salts exhibited different hydrogen bond networks, stacking modes, and molecular conformations of PRO. The solubility of PRO and its salts in a phosphate-buffered solution (pH = 6.8) at 37 °C was determined, the results showed that the solubility of PRO salts increased to 142.83 and 7.75 times of the raw drug, respectively. Accelerated stability experiments (40 °C, 75% RH) showed that the salts had good phase stability over 8 weeks. Subsequently, Hirshfeld surface (HS), atom in molecules (AIM), and independent gradient model (IGM) were employed for the assessment of intermolecular interactions. The analyses of salt-forming sites and principles were conducted using molecular electrostatic potential surfaces (MEPs) and pKa rules. The lattice energy (EL) and hydration-free energy (EHF) of PRO and its salts were calculated, and the relationships between these parameters and melting points and the solubility changes were analyzed.

Phenylethylammonium bromide-assisted solution-phase ligand exchange in CsPbBr3 quantum dot solar cells

CsPbBr3 quantum dots (QDs) have excellent optical properties and good phase stability, but the long-chain ligands on their surfaces affect the charge transfer between QDs. Here, we propose a simple ligand exchange strategy: solution-phase ligand exchange. By adding an acetone solution of phenylethylammonium bromide to the purification process of CsPbBr3 QDs, the long-chain ligands were effectively replaced and the electric coupling between QDs was improved. As a result, the power conversion efficiency of the solar cell was increased from 1.95% to 2.83%. Meanwhile, the stability of the devices was significantly improved in the unencapsulated case.

Effects of Y doping on phase structure, mechanical properties and sintering behavior of (Yb1-xYx)2SiO5 environmental barrier coating materials

Yb2SiO5 is one of the most widely studied environmental barrier coating materials due to its excellent high-temperature phase stability and resistance to water oxygen corrosion. In this paper, a series of (Yb1-xYx)2SiO5 (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were fabricated by high-temperature solid state sintering at 1550 °C. The effects of Y doping concentration on phase composition, mechanical properties, thermal conductivity and high-temperature sintering behavior of Yb2SiO5 ceramics were investigated in detail. The results show that all the (Yb1-xYx)2SiO5 ceramic specimens are composed of single X2-Yb2SiO5 phase with relative high compactness. The introduction of Y gives rise to the reduction of the thermal conductivity of Yb2SiO5 and the value of cell parameters and volume of (Yb1-xYx)2SiO5 is proportional to the Y3+ doping concentration. Among the five (Yb1-xYx)2SiO5 ceramics, (Yb0.9Y0.1)2SiO5 possesses the lowest brittleness index and its average fracture toughness is 2.85 MPa m1/2, which is about 10 % higher than pure Yb2SiO5. In addition, (Yb0.9Y0.1)2SiO5 has good high temperature phase stability from room temperature to 1450 °C and the grain size of (Yb0.9Y0.1)2SiO5 is basically unchanged after sintering at 1400 °C for 100 h. We believe that (Yb0.9Y0.1)2SiO5 is one of the most promising candidate materials for environmental barrier coatings.

Stable preparation of defective fluorite structure high entropy (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2Zr2O7 ceramic powders by molten salt synthesis

Rare earth zirconate ceramic has been considered as one of the potential thermal barrier coating materials to replace 6–8% YSZ material (6–8% yttrium oxide stabilized zirconia), because of its low thermal conductivity and good high temperature phase stability. However, there is a problem that the coefficient of thermal expansion does not match the matrix. In this paper, rare earth high entropy zirconate ceramic powder with defective fluorite structure was prepared by molten salt synthesis(MSS). The results show that the reaction temperature and the ratio of reactants to molten salt will affect the synthesis effects. With the action of the high entropy effect, the synthesized ceramic powder has low thermal conductivity, improved thermal expansion coefficient and high infrared reflectivity.

Serrated flow stress in the CoCrFeNi multi-principal element alloys with different grain sizes and added Re

Multi-principal element alloys have attracted extensive attention as a new alloy design concept. In particular, the CoCrFeNi alloys with low stacking fault energy have excellent tensile plasticity and fracture toughness at both low and room temperature, and good phase stability at high temperatures, considered a new type of structural material with great potential. Multi-principal element alloys exhibit plastic instability termed serrated flow, at certain strain rates and temperature ranges. The serrated flow stress is usually closely related to dynamic strain aging, which reflects dislocation and barrier processes and impacts the mechanical properties of alloys. In the present study, CoCrFeNi alloys were selected as the research object, and the impact of grain size and the addition of Re elements on the serrated flow stress behavior was investigated. The results showed that in the tensile tests at 600 °C, the serrated flow stress behavior occurred in the fine-grain specimen only at a lower strain rate. The tensile curves of the coarse-grain specimen at different strain rates all show serration. Overall, the serrated type changes with the decreasing grain size, the increasing strain rate, and the addition of Re element, all of which result in a decrease in the magnitude and number of serrations and a weakening of the serrated behavior.

High-temperature oxidation and diffusion studies on selected Al–Cr–Fe–Ni high-entropy alloys for potential application in thermal barrier coatings

In this work, the properties of two high-entropy alloys (HEAs) Al25Cr20Fe20Ni35 and Al20Cr20Fe20Ni40 (at.%) were compared for potential application as bond coats in thermal barrier coatings (TBCs). For this reason, both their oxidation resistance under isothermal and thermal shock conditions, as well as diffusion phenomena occurring at the substrate-HEA diffusion couple interface, were investigated. It was determined that both alloys demonstrate good phase stability and oxidation resistance during prolonged exposure to air atmosphere at 1000°C. In the initial 100 h period, selective aluminum oxidation is responsible for the protective scale growth on both materials under both isothermal and thermal shock conditions. However, only the Al20Cr20Fe20Ni40 high entropy alloy maintains a single Al2O3 layer for over 1000 h of oxidation with cyclic temperature changes. On the other hand, diffusion studies indicate that mainly iron and chromium travel between the ferritic steel substrate and the HEAs. Aluminum diffusion is seemingly limited by the unexpected formation of a thin aluminum nitride layer at the interface between the materials. From all these results it can be concluded that the Al20Cr20Fe20Ni40 alloy shows more promise for application in TBCs based on high entropy materials than Al25Cr20Fe20Ni35.

Study on Microstructure and High Temperature Stability of WTaVTiZrx Refractory High Entropy Alloy Prepared by Laser Cladding.

The extremely harsh environment of the high temperature plasma imposes strict requirements on the construction materials of the first wall in a fusion reactor. In this work, a refractory alloy system, WTaVTiZrx, with low activation and high entropy, was theoretically designed based on semi-empirical formula and produced using a laser cladding method. The effects of Zr proportions on the metallographic microstructure, phase composition, and alloy chemistry of a high-entropy alloy cladding layer were investigated using a metallographic microscope, XRD (X-ray diffraction), SEM (scanning electron microscope), and EDS (energy dispersive spectrometer), respectively. The high-entropy alloys have a single-phase BCC structure, and the cladding layers exhibit a typical dendritic microstructure feature. The evolution of microstructure and mechanical properties of the high-entropy alloys, with respect to annealing temperature, was studied to reveal the performance stability of the alloy at a high temperature. The microstructure of the annealed samples at 900 °C for 5-10 h did not show significant changes compared to the as-cast samples, and the microhardness increased to 988.52 HV, which was higher than that of the as-cast samples (725.08 HV). When annealed at 1100 °C for 5 h, the microstructure remained unchanged, and the microhardness increased. However, after annealing for 10 h, black substances appeared in the microstructure, and the microhardness decreased, but it was still higher than the matrix. When annealed at 1200 °C for 5-10 h, the microhardness did not increase significantly compared to the as-cast samples, and after annealing for 10 h, the microhardness was even lower than that of the as-cast samples. The phase of the high entropy alloy did not change significantly after high-temperature annealing, indicating good phase stability at high temperatures. After annealing for 10 h, the microhardness was lower than that of the as-cast samples. The phase of the high entropy alloy remained unchanged after high-temperature annealing, demonstrating good phase stability at high temperatures.

Microwave photonic I/Q mixer for wideband frequency downconversion with serial electro-optical modulations.

In this paper, we propose a serial electro-optical (EO)-modulation-based microwave photonic in-phase and quadrature (I/Q) mixer and investigate its performance for wideband frequency downconversion. The proposed I/Q mixer uses two EO modulators and a programmable optical processor in a serially cascaded structure, which ensures good phase stability and flexibility to achieve high-performance broadband frequency downconversion. A proof-of-concept experiment is carried out in which the frequency downconversion of the RF signals in the range from 10 to 40 GHz is demonstrated with an average image rejection ratio of 38.66 dB. The spurious-free dynamic range (SFDR) measured at around 15 GHz is 86 dBc·Hz2/3. Based on this microwave photonic I/Q mixer, a broadband radar receiver is established and de-chirping of linearly frequency modulated (LFM) radar echoes with an instantaneous bandwidth of 8 GHz (10-18 GHz) is achieved. The results verify its feasibility for high-performance I/Q mixing in practical applications.

Potential thermal barrier coating material: High entropy ceramic (Ca0.5Sr0.5)(5RE)2O4 with enhanced thermophysical properties

Single-phase high entropy ceramic (Ca0.5Sr0.5)(5RE)2O4 (RE = Y, Sm, Gd, Dy, Yb) (CSHO) with anti-spinel structure was synthesized via solid-state reaction method. The CSHO has good high-temperature phase stability at 1600 °C for 10–50 h. In addition, the CSHO ceramics exhibit much lower thermal conductivity and higher thermal expansion coefficient than that of SrY2O4, towing to the intensified phonon-point defect scattering and the enhanced anharmonic vibrations of the lattice. The thermal conductivity of CSHO is 1.48–1.81 W∙m−1 K−1 (25–1500 °C), and the thermal expansion coefficient is 11.5–12.0 × 10−6 K−1 (1000–1500 °C). The obtained results suggest that CSHO has the potential to become the next-generation thermal barrier coating materials.

Design and Waveguide Measurement of 2-Bit Reconfigurable Amplification Metasurface Cell

This letter presents a novel 2-bit amplification metasurface cell (APMC) for nonreciprocal reflection of linearly polarized EM waves into high-intensity orthogonal waves. The 2-bit APMC consists of four parts, a reconfigurable receiving patch, a reconfigurable phase shifter, a power amplifier circuit, and a reradiating patch. By tuning the bias voltage of the p-i-n diodes mounted on the receiving patch and the phase shifter, the APMC could manipulate reflected waves with four discrete phase states. A power amplifier is placed between the receiving patch and the phase shifter to increase the energy intensity of the reflected wave. In addition, an orthomode transducer (OMT) waveguide is designed and fabricated for measurement of the performance of the 2-bit APMC. From the measurement results, the maximum phase variation of the APMC is less than 25.5°, and the saturation reflected power is 27dBm, indicating good phase stability and high energy transfer capability. The proposed APMC could be used as a metasurface unit cell to provide arbitrary microwave beams for wireless power transmission.

Effect of Ti on microstructure and mechanical properties of Al0.8Nb0.5TixV2Zr0.5 refractory complex concentrated alloys

In this study, lightweight Al0.8Nb0.5TixV2Zr0.5 refractory complex concentrated alloys with different Ti contents (x = 0.4, 0.8, 1.2, and 1.6) are fabricated via vacuum arc melting. The effects of Ti on microstructurale evolution, density, and mechanical properties at room and elevated temperatures are investigated. The Al0.8Nb0.5TixV2Zr0.5 alloys are composed of a BCC solid solution matrix and a C14-Laves (hexagonal) phase, and the volume fraction of the BCC phase increases as the Ti content increases from 63.48% to 90.97%. The density decreases from 5.70 to 5.42 g/cm3, whereas the hardness first increases and then decreases in the range of 625.2 to 669.5 HV. The results of compression test at different temperatures show that the yield strength and deformability of the Al0.8Nb0.5TixV2Zr0.5 alloys first increases and then decreases, and that the alloys show good phase stability when the Ti content is 1.2. The compressive yield strength of Ti1.2 alloy is 1848 MPa at room temperature, 1507 MPa at 673 K, and 1068 MPa at 1073 K. The increase in yield strength is due to various strengthening mechanisms caused by the addition of Ti, including the solid-solution strengthening effect caused by severe lattice distortion, the decrease in the valence electron concentration, and the grain boundary strengthening effect caused by grain size reduction. The present study is an example of a systematic investigation into the effects of elements on the structure and properties of refractory complex concentrated alloys through alloy design, which is expected to facilitate the design of lightweight refractories and their compositions.

Sintering resistance and phase stability of (Y0.2La0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 for ultra-high temperature thermal barrier coatings

High-temperature stability, including sintering resistance and phase stability, is critical for thermal barrier coatings (TBCs) applied at ultra-high temperature over 1500 °C. In this work, we reported a high-entropy rare-earth zirconate (Y02La0.2Nd0.2Sm0.2Eu0.2)2Zr2O7 (YLNSE) synthesized by solid-state reaction method. X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive spectrometer (EDS) mapping results confirmed that YLNSE formed a single-phase pyrochlore structure with uniform rare earth elements distribution. YLNSE maintained more uniform microstructure, higher porosity retention, lower grain growth rate and better thermomechanical properties during sintering at 1500 °C, as the results of the ordered crystal structure and sluggish diffusion effect, indicating a better sintering resistance than conventional TBC material yttria-stabilized zirconia (YSZ). In addition, YLNSE also demonstrated high coefficient of thermal expansion (CTE, 11.04 × 10-6K-1, 25–1500 °C) and low thermal conductivity (1.95 W m-1 K-1, 1500 °C), as well as good phase stability at 1500 °C. In view of the excellent high-temperature stability of YLNSE, it is a promising candidate for ultra-high temperature TBCs.

Long-Term Stability of Perovskite-Based Fuel Electrode Material Sr2Fe2-XMoxO6-δ – GDC for Enhanced High-Temperature Steam and CO2 Electrolysis

Severe performance loss of state-of-the-art Ni-cermet fuel electrodes has been observed due to Ni particle agglomeration and Ni migration away from the triple-phase boundary at the active electrode layer. Investigation of Ni-free perovskite Sr2Fe2-xMoxO6-δ (SFM)–30 wt% Ce0.8Gd0.2O2-δ (GDC) as fuel electrode material showed good redox stability in oxidizing and reducing atmospheres. These characteristics meet exactly the targeted requirements for new solid oxide electrolyzer materials. A comparison of SFM and SFM-GDC fuel electrodes showed similar performance for H2O, CO2, and co-electrolysis between 750 °C and 900 °C. Long-term degradation measurements and post-test SEM-EDX analysis clarified that SFM-GDC exhibits good phase stability in comparison to pure SFM fuel electrodes. The composite fuel electrode Sr2Fe1.1Mo1.0O6-δ–30 wt% Ce0.8Gd0.2O2-δ (SFM15-GDC) reached polarization resistances (RP) in the same range as Sr2Fe1.0Mo1.0O6-δ with around 127 mΩ∙cm² and 137 mΩ∙cm at 900 °C in steam electrolysis.