Electronegativity Difference Research Articles

Structural stability and the low-lying singlet and triplet states of BN-n-acenes, n=1-7.

The chemical stability and the low-lying singlet and triplet excited states of BN-n-acenes (n=1-7) were studied using single reference and multireference methodologies. From the calculations, descriptors such as the singlet-triplet splitting, the natural orbital (NO) occupations and aromaticity indexes are used to provide structural and energetic analysis. The boron and nitrogen atoms form an isoelectronic pair of two carbon atoms, which was used for the complete substitution of these units in the acene series. The structural analysis confirms the effects originated from the insertion of a uniform pattern of electronegativity difference within the molecular systems. The covalent bonds tend to be strongly polarized which does not happen in the case of a carbon-only framework. This effect leads to a charge transfer between neighbor atoms resulting in a more strengthened structure, keeping the aromaticity roughly constant along the chain. The singlet-triplet splitting also agrees with this stability trend, maintaining a consistent gap value for all molecules. The BN-n-acenes molecules possess a ground state with monoconfigurational character indicating their electronic stability. The low-lying singlet excited states have charge transfer character, which proceeds from nitrogen to boron.

MIL-101(FeII3,Mn) with dual-reaction center as Fenton-like catalyst for highly efficient peroxide activation and phenol degradation

Metal organic frameworks are important Fenton-like materials in environment remediation. Nevertheless, the slow Fe(III)/Fe(II) cycling and low H2O2 utilization limit their application. In this study, we develop the ferrous bimetallic MIL-101(FeII3, Mn), which significantly enhanced catalytic performance (5.8 and 31.4-fold higher phenol removal rate and apparent rate constant, respectively) compared with the original MIL-101(Fe). The mechanisms are fully investigated by XPS, EPR and DFT. The Fe2+ substitution affords the mixed-valences of Fe(III)/Fe(II) in the frameworks, which serve as stronger sites for H2O2 activation. Mn in MIL-101(FeII3, Mn) can also function as another reaction center to activate H2O2. Catalysts could coordinate with the π–electrons of pollutants, resulting in the electron transfer from pollutants to MIL-101(FeII3, Mn). Moreover, electrons around Mn atoms tends to transfer to the region of Fe atoms owing to the electronegativity difference, inducing to strengthen the electron-rich Fe micro-region. Therefore, H2O2 was primarily adsorbed onto electron-rich regions where it would be efficiently reduced to •OH, contributing to a higher H2O2 utilization (81.2 %). This study opens new insight into design of Fe-based MOFs as highly efficient Fenton-like catalysts in wastewater treatment.

Application of Fundamental Chemical Principles for Solvation Effects: A Unified Perspective for Interaction Patterns in Solution.

We demonstrate the utility of basic chemical principles like the "|Δμ| big is good" (DMB) rule for the study of solvation interactions between distinct solutes such as ions and solvents. The corresponding approach allows us to define relevant criteria for maximum solvation energies of ion pairs in different solvents in terms of electronegativities and chemical hardnesses. Our findings reveal that the DMB principle culminates into the strong and weak acids and bases concept as recently derived for specific ion effects in various solvents. The further application of the DMB approach highlights a similar condition for the chemical hardnesses with a reminiscence to the hard/soft acids and bases principle. Comparable conclusions can also be drawn with regard to the change of the solvent. We show that favorable solvent interactions are mainly driven by low chemical hardnesses as well as high electronegativity differences between the ions and the solvent. Our findings highlight that solvation interactions are governed by basic chemical principles, which demonstrates the close similarity between solvation mechanisms and chemical reactions.

Superstrong Chemical Bonding of Noble Gases with Oxidoboron (BO+) and Sulfidoboron (BS+).

Inspired by the overwhelming exploration of noble gas-boron (Ng-B) bond containing chemical compounds, the stability of the Ng bound BY+ and AlY+ (Y = O and S) has been investigated by using various ab initio based quantum chemical methods. Ng atoms are found to form exceptionally strong bonds with BO+ species in the predicted NgBO+ (Ng = He-Rn) complexes with remarkably high Ng-B dissociation energies ranging from 138.0 to 462.2 kJ mol-1 for the He-Rn series. It is the highest ever Ng-B binding energy in conjunction with the smallest Ng-B bond length for any of the cationic species involving a Ng-B bond as reported until today. More importantly, the calculated Ng-B bond lengths have been found to be much lower than the respective covalent limits in both NgBO+ and NgBS+ ions. The electronegativity difference between O and S atoms has been reflected nicely in the Ng-B and Ng-Al binding energies, which are found to be 91.9-346.5, 9.6-169.2, and 6.8-142.1 kJ mol-1 in NgBS+, NgAlO+, and NgAlS+, respectively. The strong covalent bonding between Ng and B/Al atoms in the predicted chemical systems has also been supported by the natural bonding orbital (NBO) and electron density based atoms-in-molecule (AIM) analysis. In addition, the energy decomposition analysis (EDA) in combination with the natural bond orbital for chemical valence (NOCV) indicates that the orbital interaction term is the prime contributor to the total attraction energy in the Ng-B and Ng-Al bonds. Furthermore, Ng-B and Ng-Al bonding can be assessed using the donor-acceptor model where the σ-electron donation that takes place from Ng (HOMO) → XY+ (LUMO) (X = B and Al; Y = O and S) is the major contributor to the orbital interaction energy. All the computational results along with the very recent experimental observation of ArOH+ and NgMX (Ng = Ar-Xe; M = Cu, Ag, Au; X = F, Cl) clearly indicate that it might be possible to synthesize and characterize these superstrong complexes, NgXY+ (Ng = He-Rn; X = B and Al; Y = O and S), under suitable experimental technique(s).

Investigation of near-room and high-temperature thermoelectric properties of (Bi0.98In0.02)2Se2.7Te0.3/Bi2Te3 composite system

Polycrystalline composite samples of (Bi0.98In0.02)2Se2.7Te0.3/Bi2Te3 with different concentrations of Bi2Te3 such as 5%,10%,15% and 20% were prepared by the solid-state reaction technique. The X-Ray diffraction analysis has shown the hexagonal composite crystal structure with space group of Roverline{3 }m. Field emission scanning electronic microscope shows secondary particles on the surface of the samples. All the samples have shown the usual semi-conducting behaviour throughout the temperature range. It is observed that bismuth has been co-ordinated with 6 selenium atoms in (Bi0.98In0,02)2Se2.7Te0.3 compound and it has enormous selenium vacancies. The electrical resistivity represents the noteworthy result of the grain boundaries leading to the higher content of scattering centres in the polycrystalline composite samples. It is found that the electronegativity differences of In and Te, In and Se are less than Bi and Se, Bi and Te is the reason for the decrease in Seebeck coefficient in the compound containing 15% and 20% of Bi2Te3.

A Conceptual Strategy toward High-Reliability Metal-Thermoplastic Hybrid Structures Based on a Covalent-Bonding Mechanism.

Metal-thermoplastic hybrid structures have proven their effectiveness to achieve lightweight design concepts in both primary and secondary structural components of advanced aircraft. However, the drastic differences in physical and chemical properties between metal and thermoplastic make it challenging to fabricate high-reliability hybrid structures. Here, a simple and universal strategy to obtain strong hybrid structures thermoplastics is reported by regulating the bonding behavior at metal/thermoplastic interfaces. To achieve such, we first researched and uncovered the bonding mechanism at metal/thermoplastic interfaces by experimental methods and density functional theory (DFT) calculations. The results suggest that the interfacial covalency, which is formed due to the interfacial reaction between high-electronegativity elements of thermoplastics and metallic elements at metal surfaces, dominates the interfacial bonding interaction of metal-thermoplastic hybrid structures. The differences in electronegativity and atomic size between bonding atoms influence the covalent-bond strength and finally control the interfacial reliability of hybrid structures. Based on our covalent-bonding mechanism, the carboxyl functional group (COOH) is specifically grafted on polyetheretherketone (PEEK) by plasma polymerization to increase the density and strength of interfacial covalency and thus fabricate high-reliability hybrid structures between PEEK and A6061-T6 aluminum alloy. Current work provides an in-depth understanding of the bonding mechanism at metal-thermoplastics interfaces, which opens a fascinating direction toward high-reliability metal-thermoplastic hybrid structures.

Charge Transport Across Dynamic Covalent Chemical Bridges.

Relationships between chemical structure and conductivity in ordered polymers (OPs) are difficult to probe using bulk samples. We propose that conductance measurements of appropriate molecular-scale models can reveal trends in electronic coupling(s) between repeat units that may help inform OP design. Here, we apply the scanning tunneling microscope-based break-junction (STM-BJ) method to study transport through single-molecules comprising OP-relevant imine, imidazole, diazaborole, and boronate ester dynamic covalent chemical bridges. Notably, solution-stable boron-based compounds dissociate in situ unless measured under a rigorously inert glovebox atmosphere. We find that junction conductance negatively correlates with the electronegativity difference between bridge atoms, and corroborative first-principles calculations further reveal a different nodal structure in the transmission eigenchannels of boronate ester junctions. This work reaffirms expectations that highly polarized bridge motifs represent poor choices for the construction of OPs with high through-bond conductivity and underscores the utility of glovebox STM-BJ instrumentation for studies of air-sensitive materials.

Active Asymmetric Electron-Transfer Effect on the Enhanced Piezoelectricity in MoTO (T = S, Se, or Te) Monolayers and Bilayers.

Development of piezoelectric materials is limited partly due to the incompleteness of internal mechanism and the lack of vertical piezoelectricity. Herein, we theoretically identify the stable MoTO (T = S, Se, or Te) monolayers and bilayers. When two elements are given but another element can be changed, the larger the electronegativity difference ratio Rratio is, the stronger the piezoelectricity will be. Vertical piezoelectric coefficient d33 of the MoTeO bilayer reaches 38.907 pm/V, which is 12 times larger than that of the bulk GaN. The "active asymmetric electron-transfer" strategy mainly contributes to the spontaneous remarkable piezoelectricity of MoTO. Importantly, we proposed the new method for calculating the piezoelectric coefficients of two-dimensional (2D) materials, which corresponds to the fact that 2D materials have a certain thickness. This study not only provides novel extraordinary candidates for energy conversion and touch-sensor nanodevices but also promotes a deeper understanding of piezoelectricity of 2D materials.

Improving the Stability of the Nickel Phosphide HER Catalyst Using Metal Additives in Acidic Media

Energy and the environment are key issues for the development of sustainable society. Renewable energies such as wind, solar, tidal, and biomass energy are clean and it can replace fossil fuels. However, since renewable energy is produced intermittently according to region, time, and season, it also requires the systems for conversion, storage, and transport of surplus energy. In response to this need, hydrogen has received much attention as an energy carrier due to its high gravimetric energy density and long-term storage possibility. The hydrogen production through water splitting is a promising strategy to convert excess electrical energy generated from renewable energy into high-density energy source in the form of hydrogen gas (H2). Moreover, the produced hydrogen can be used as electrical energy via the fuel cells with high energy conversion efficiency and zero pollution. However, in this technology, the problematic point is the high price of hydrogen production, and it is mostly due to low efficiency and kinetics of water splitting=To overcome this problem, it is essential to develop a high-performance catalyst for water splitting. Among the various candidates of the catalytic materials, the Pt-based catalyst has the best performance especially in the hydrogen evolution reaction (HER), but it is needed to be substituted into non-noble metal based ones due to a cost problem.In particular, transition metal phosphides (TMPs) such as Ni-P are receiving much attention due to its remarkable catalytic performance approaching that of Pt-based one. [1]. Specifically, in Ni-P, the electrons are transferred from Ni to P due to the difference in electronegativity, so that the energy of the HER intermediate can be controlled to have the optimal activity. Moreover, the binding site of Ni-P acts as a new active site, increasing the performance more. Nevertheless, the major issue to be solved for commercialization of Ni-P is the low stability due to the dissolution of Ni, especially in acidic media where its corrosion potential is lower than HER. Specially, the Ni dissolution is most severe in the isolated Ni phases, which is relatively unbounded with P [2].In this context, we suggest a stability enhancement method of NiP by adopting the metallic stabilizer. Specifically, We prepared NiP-Cu by substituting Cu into the isolated Ni sites (Fig. 1a). We believed that the higher reduction potential of Cu might increase the overall corrosion resistance of the NiP-based material. As a result (Fig1. c), the corrosion potential of NiP-Cu was measured to be -333 mV, which is 12 mV higher than the pristine Ni-P. Also, in the accelerated degradation test (ADT) including potential sweep, the NiP-Cu showed three times lower degradation rate (3 mV/h)than NiP (12 mV/h), as shown in Fig1c-d.

Effect of Oxide Thickness by Metallic Residue during Radical Oxidation Using Vertical Batch-Type Furnace Equipment on 300-Mm-Diameter Silicon Substrates

Metallic residues have a detrimental effects on device performance as well as retard gate oxide growth rate to induce unintended thinner oxide layer. In this study, we found that oxide thickness could be subjective to metallic residues on the edge of silicon substrate. Hydrogen-assisted radical oxidation was investigated using vertical batch-type furnace equipment for a 300-mm wafer fab. Radical oxidation has been used to improve gate oxide quality overcoming the disadvantages of conventional wet or dry thermal oxidation for some applications. Since the radical oxidation method reduces dangling bonds and defects in the oxide layer due to activated oxygen radicals, a high-quality oxide film can be formed. It also helps improve reliability due to reduced dependence on the silicon crystal direction of oxidation, enabling uniform membrane deposition of stress-focused corner rounding oxidation. In addition, it has excellent throughput as it is possible to process up to 100 wafers simultaneously. This study has shown that as the number of wafers with metallic residues in the dummy pattern on the edge due to the wafer edge exposure (WEE) difference for each photo step increases in the same batch for radical oxidation, the median thickness has decreased. When the silicon wafer with the metallic residue was included within the same batch of the furnace equipment, the thickness of the oxide layer was reduced by 1.8% compared to when the metallic residue-free silicon wafer was included. The radical oxygen have a tendency to react to tungsten rather than silicon, which reduces the O2 value required to form SiO2 and lowers the thickness, which is due to the difference in electronegativity between silicon and tungsten, 1.9 and 2.36 respectively. The study is expected to improve gate oxide quality by controlling metal residues on the wafer edge or backside during the fab process.

(Invited, Digital Presentation) Low Voltage Operation of CMOS Inverter Based on WSe2 n/p FETs

Transition metal dichalcogenides (TMDC) have remarkable properties for the next generation of electronic devices [1]. A complementary metal-oxide-semiconductor (CMOS) inverter consisting of pairs of p-type and n-type field-effect transistor (FET) is a fundamental building block in modern digital electronics [2]. Therefore, realization of both p-type and n-type FETs based on semiconducting TMDC is of particular importance. Among various semiconducting TMDC, tungsten diselenide (WSe2) is a promising candidate for constructing a CMOS inverter because of its high mobility, symmetric electron and hole effective mass and ambipolar transport [3]. These prominent features of WSe2 motivates the fabrication and characterization of a CMOS inverter. One of the significant challenges is to develop a high-gain CMOS inverter for operation at a low power supply voltage (Vdd) for future low power digital electronics. Previous studies on a WSe2 CMOS inverter were limited to operation with a low gain of 3 or a high Vdd of more than 1 V under conditions of relatively low gate capacitance and degraded interfacial properties [3-5]. This study addressed these issues by developing a doping technique and gate stack technology to demonstrate the high-gain with low-Vdd operation of a WSe2 CMOS inverter [6]. The focus is on the doping technique of both electrons and holes to a WSe2 layer by simple spin-coating. Of particular interest in this study is the impact of gate stack technology on the CMOS inverter characteristics in low-Vdd operation. In this study, a hybrid self-assembled monolayer (SAM)/aluminum oxide (AlOx) gate dielectric is applied to a WSe2 CMOS inverter for high-gain low-Vdd operation since superior interfacial properties with high gate capacitance have been reported in molybdenum disulfide (MoS2) FETs.For p-type WSe2 FETs, the fluoropolymer CYTOP (AGC, CTX-809A) was applied since polarization in CYTOP due to the difference in electronegativity between C–F bonds generates holes in WSe2. On the other hand, poly(vinyl alcohol) (PVA) was utilized for n-type WSe2 FETs because positive charges in PVA accumulates electrons in WSe2. The resin solutions of both CYTOP and PVA were purchased from a commercial supplier. A heavily doped p-type silicon substrate (p+-Si) was thermally oxidized to form a 60 nm thick silicon dioxide (SiO2) layer for the global back-gate architecture. Palladium (Pd) and gold (Au) as the source and drain contacts for p-type and n-type WSe2 FETs were fabricated by the lift-off process, respectively. An aluminum (Al) gate was prepared and a hybrid SAM/AlOx gate dielectric was formed by oxygen (O2) plasma and an immersion process. After that, mechanically exfoliated WSe2 was transferred with a poly(dimethylsiloxane) (PDMS) stamp. Finally, CYTOP and PVA were deposited by spin-coating for p-type and n-type WSe2 FETs, respectively.Figures 1 (a) and (b) show the Id–Vg characteristics of fabricated FETs. For the p-type WSe2 FET, a small SS of 78 mV/dec and an on/off ratio of about 106 order were observed. On the other hand, the Id–Vg characteristics of the n-type WSe2 FET were degraded compared with those of the p-type WSe2 FET because of the Schottky contacts.Figures 2 (a) and (b) show the transfer characteristics and gain as a function of Vdd in CMOS inverter. The gain of the CMOS inverter increased to as high as 9 at Vdd of 0.5 V.Figure 3 shows the benchmark of this study. Our proposed concepts enabled the operation with high gain at a low Vdd as low as 0.5 V for the WSe2 CMOS inverter, which had not been realized in previous studies. The dangling-bond-free and ultrathin SAM/AlOx gate dielectric has an important role in the low-Vdd operation of the WSe2 CMOS inverter. This study opens up interesting directions for the research and development of TMDC-based devices and circuits.

Effect of H2 for Growing Germanium–Lead Alloys By Magnetron Sputtering Epitaxy

Si and Ge are indirect bandgap materials, and their low light emission efficiency limits the development of silicon-based optoelectronics. Studies have shown that the introduction of Pb into Ge can make the Γ valley decrease faster than the L valley, and GePb alloys can be transformed into direct bandgap materials, thereby realizing high-efficiency luminescence of silicon-based materials. Since Pb atoms have a larger core and can provide a greater electronegativity difference for Ge, GePb alloys can be transformed into direct bandgap materials with only about 3.4% Pb. In addition, the maximum optical gain of GePb alloys is much higher than that of GeSn alloys, as revealed by first principal calculations. Therefore, the epitaxial investigation of GePb alloys is of great significance for Si photonics. In this work, Ge1- x Pb x (1.2% < x < 2.4%) alloys were grown by magnetron sputtering epitaxy using H2 and Ar mixture. The effects of different proportions of H2 and Ar on the growth of GePb were studied in detail. High crystal quality Ge0.984Pb0.016 alloys without Pb surface segregation were successfully fabricated. The results show that the increase of H2/Ar ratio contributes to the increase of Pb composition in GePb alloys. Figure 1

The regulation of resistivity for SiHfBCN thin films prepared by magnetron sputtering method

SiHfBCN ceramic is a kind of potential thin film electrode material applied in high temperature sensors. The ability to tune the resistivity is of primary importance for its further applications. Therefore, in this paper, the SiHfBCN film was prepared using magnetron sputtering method. The regulation means of resistivity were investigated through analyzing the relationship between microstructure and resistivity. The result shows that the resistivity of amorphous SiHfBCN film is mainly related to the overall electronegativity difference and contents of insulating chemical bonds. The resistivity of SiHfBCN films can be controlled over a broad range by changing their composition. In addition, the behavior of annealed SiHfBCN indicates a stable structure. • The SiHfBCN film, a potential high temperature electrode material, was prepared by magnetron sputtering method. • The relationship between resistivity and microstructure of SiHfBCN film was established to explain its conductive behavior. • The resistivity of SiHfBCN film is related to the “insulating” chemical bonds and overall electronegativity difference.

Electronic, structural, and optical properties of Cs2SnGeX6 (X = I, Br, Cl) and mixed halides for solar cell applications

The mixed metal-halide perovskites of the form ABX3, (where, A is the organic or inorganic cation, B is the metal cation, and X is the halide anion) have a wide range of tunable structural and electronic properties leading to intense research over the past decade. This study reports the density functional theory calculations on the sn-Ge based perovskite Cs2SnGeX6 (where, X = I, Br, Cl), for determining the most stable structural configuration and the corresponding electronic properties based on GGA (Generalized Gradient Approximation) functional. In addition, two mixed halide variants like Cs2SnGeI3Br3 and Cs2SnGeBr3Cl3 are also simulated. The structures show a broadly tunable bandgap of 0.46 to 1.45 eV by the substitution of various halides in the mixed sn-Ge-based perovskite. The halide perovskites show ambipolar transport behavior with long diffusion lengths. The charge density and electronegativity difference analysis show the predominant ionic nature between the Cesium and halogen atoms and the covalent nature of bonding between the Tin/Germanium and halogen atoms. In the mixed halides, an asymmetric charge distribution is visualized for the first time, which is resulting due to the disproportionate bond strength caused by the difference in the electronegativities of I-Br and Br-Cl. This helps in the manifestation of stereochemically-active lone-pair electrons in Sn and Ge which lead to large variations in the Sn(Ge)-halogen bond lengths and enable the high mobility of the charge carriers. The major optical absorption is due to the transition between the hybridized Sn/Ge(s)-X(p) states to Sn/Ge(p) states. The long charge carrier diffusion lengths and significant covalent bonding interactions can enable in improving the efficiency and structural stability of these materials, making them suitable for solar cell applications.

Tailoring of thermal expansion and phase transition temperature of ZrW2O8 with phosphorus and enhancement of negative thermal expansion of ZrW1.5P0.5O7.75

ZrW2O8 is a typical isotropic negative thermal expansion material with cubic structure. However, quenching preparation, pressure phase transition and metastable structure influence its practical applications. Adopting P to part-substitute W for ZrW2−x P x O8–0.5x has decreased the sintering temperature and avoided the quenching process. When x = 0.1, ZrW1.9P0.1O7.95 with a stable cubic structure can be obtained at 1150 °C. The thermal expansion coefficient is tailored with the P content, and phase transition temperature is lowered. When x = 0.5, thermal expansion coefficient attains −13.6 × 10−6 °C−1, ZrW1.5P0.5O7.75 exhibits enhance negative thermal expansion property. The difference of electronegativity leads to the decrease of phase transition temperature with the increase of P content. The different radii of ions lead to new structure of materials when P substitutes more. The results suggest that the P atom plays the stabilization role in the crystal structure of ZrW2−x P x O8–0.5x .

A DFT study of the adsorption of F atoms on germanene nanoribbons

In the paper, we investigate the structure and electronic properties of the pristine germanene nanoribbon and four adsorption configurations of 1F and 2F on the substrate of germanene nanoribbon. We obtained the parameters of the most stable structures of pristine germanene nanoribbon and four adsorption configurations. The band structure and the density of state and the part density of state for each element were also obtained. Findings show the adsorption configuration of 1F-GeNR.bridge has no band structure, while other configurations are semimetals with band gap from 0.175eV to 0.67eV; both four adsorption configurations are chemisorption and non-magnetic. The charge distribution of all configurations also was investigated; it showed that there is a charge shift from Ge atoms towards F atoms due to their electronegativity difference.

Segregation mediated design of single-phase refractory medium and high entropy intermetallic compounds with complete suppression of pest oxidation

Refractory intermetallic compounds are potential candidates for high-temperature applications owing to their high thermal stability and excellent softening resistance. However, they suffer from the pest oxidation phenomenon at low temperatures, which highly restricts their applications. Here, after determining the stable segregated phases in complex mixtures of refractory elements, two novel refractory intermetallic compounds with complex compositions are engineered, (Ti1/5Zr1/5Nb1/5Hf1/5Ta1/5)Al3 and (Mo1/3W1/3Ta1/3)Si2. These two single-phase materials exhibit excellent oxidation resistance with complete suppression of pest phenomenon in the as-cast state. Exploring the underlying oxidation resistance mechanisms, it is found that the synergistic effect of high entropy lattice sites and the ability of Si and Al elements to develop a dense protecting layer are the main reasons for the complete elimination of the pest oxidation. Besides, we introduce and verify a sublattice electronegativity difference criterion as a new indicator for forming single-phase high and medium entropy materials. The approach to engineering single-phase entropy-stabilized intermetallic compounds reported here can be used to develop additional medium- and high-entropy intermetallic compounds with tailorable properties.

Insights on phase formation from thermodynamic calculations and machine learning of 2436 experimentally measured high entropy alloys

Both CALPHAD (CALculation of PHAse Diagrams) and machine learning (ML) approaches were employed to analyze the phase formation in 2436 experimentally measured high entropy alloy (HEA) compositions consisting of various quinary mixtures of Al, Co, Cr, Cu, Fe, Mn, and Ni. CALPHAD was found to have good capabilities in predicting the BCC/B2 and FCC phase formation for the 1761 solid-solution-only compositions, excluding HEAs containing an amorphous phase (AM) or/and intermetallic compound (IM). Phase selection rules were examined systematically using several parameters and it was revealed that valence electron concentration (VEC)< 6.87 and VEC> 9.16 are the conditions for the formation of single-phase BCC/B2 and FCC, respectively; and CALPHAD could predict this with essentially 100% accuracy. Both CALPHAD predictions and experimental observations show that more BCC/B2 alloys are formed over FCC alloys as the atomic size difference between the elements increases. Four ML algorithms, decision tree (DT), k-nearest neighbor (KNN), support vector machine (SVM), and artificial neural network (ANN), were employed to study the phase selection rules for two different datasets, one consisting of 1761 solid-solution (SS) HEAs without AM and/or IM phases, and the other set consisting of all the 2436 HEA compositions. Cross validation (CV) was performed to optimize the ML models and the CV accuracies are found to be 90.4%, 94.1%, 93.8%, 89.7% for DT, KNN, SVM, and ANN respectively in predicting the formation of BCC/B2, BCC/B2 + FCC, and FCC; and 92.9%, 96.3%, 96.9%, 92.3% for DT, KNN, SVM, and ANN respectively in predicting SS, AM, SS + AM, and IM phases. Sixty-six experimental bulk alloys with SS structures are predicted with the trained ANN model, and the accuracy reaches 80.3%. VEC was found to be most important parameter in phase prediction for BCC/B2, BCC/B2 + FCC, and FCC phases. Electronegativity difference and FCC-BCC-index (FBI) are the two dominating features in determining the formation of SS, AM, SS + AM, and IM. A separation line ΔHmix=29×VEC−247 was found in the ΔHmix-vs-VEC plot to predict the formation of single-phase BCC/B2 or FCC with a 96.2% accuracy (ΔHmix = mixing enthalpy). These insights will be very valuable for designing HEAs with targeted crystal structures.

Extraordinary thermoelectric performance, thermal stability and mechanical properties of n-type Mg3Sb1.5Bi0.5 through multi-dopants at interstitial site

Mg3Sb2-based thermoelectric materials have attracted much interest since the discovery of their excellent n-type thermoelectric performance with excess Mg content and proper dopant. Herein, we proposed a doping diagram for Mg3Sb2-based material in a binary parameters space of electronegativity difference and atomic radius difference of extrinsic elements with Mg atom. Based on this doping diagram, we designed a multiple interstitial doped TMx:Mg3Sb1.5Bi0.5 (TM = CrMnFeCoCu) material, and achieved a high dimensionless figure of merit value of 0.76 at room temperature and 1.83 at 500 °C, respectively. The multiple interstitial dopants significantly suppress the formation of Mg vacancy, which is of great importance in protecting the electrical transport channel and improving the thermal stability. Besides, the mechanical properties are also enhanced due to the random distribution of elements in the matrix, impeding the migration of dislocations. Our work verifies the benefits of maximized sub-lattice disordering through the multi-elements doping strategy in the Mg3Sb1.5Bi0.5 material.

Effect of Surface Charge on the Fabrication of Hierarchical Mn-Based Prussian Blue Analogue for Capacitive Desalination.

Multiple and hierarchical manganese (Mn)-based Prussian blue analogues obtained on different substrates are successfully prepared using a universal, facile, and simple strategy. Different functional groups and surface charge distributions on carbon cloth have significant effects on the morphologies and nanostructures of Mn-based Prussian blue analogues, thereby indirectly affecting their physicochemical properties. Combined with the advantages of the modified carbon cloth and the nanostructured Mn-based Prussian blue analogues, the composite with negative surface charge formed by the electronegativity differences shows good electrochemical properties, leading to improvement in charge efficiency during capacitive desalination. An asymmetric device fabricated with Mn-based Prussian blue analogue-modified F-doped carbon cloth as the cathode and acid-treated carbon cloth as the anode presents the highest salt adsorption capacity of 10.92 mg g–1 with a charge efficiency of 82.28% and the lowest energy consumption of 0.45 kW h m–3 at 1 V due to the main influencing factor from the negative surface charge leading to co-ion expulsion boosting the capacitive deionization performance. We provide insights for further exploration of the relationship between second-phase materials and carbon cloth, while offering some guidance for the design and preparation of electrodes for desalination and beyond.