Average Electronegativity Difference Research Articles

Designing high-entropy rare-earth zirconates with tunable thermophysical properties for thermal barrier coatings

The development of rare-earth zirconates with tunable thermal expansion coefficient (TEC) and thermal conductivity is of great importance in the area of thermal barrier coatings. In general, TEC can be tailored by the average electronegativity difference, and the thermal conductivity can be customized by the atomic mass difference and/or ionic radius. Based on this thermophysical properties design principle, a series of high-entropy rare-earth zirconate ceramics were synthesized and characterized, and the obtained results indicate that: (1) the TEC is negatively correlated with the average electronegativity difference of cation and anion concerning its corresponding compound; (2) the thermal conductivity is negatively correlated with the atomic mass difference and ionic radius difference concerning its corresponding compound; (3) the synthesized ceramics have excellent high-temperature long-term thermal phase stability, larger TEC (RT-1500 °C, 10.20 ~ 10.39 × 10-6 K-1), lower thermal conductivity (1500 °C, 1.17 ~ 1.37 W·m-1·K-1), and higher fracture toughness (1.61 ~ 1.69 MPa·m1/2) compared with lanthanum zirconate. The tailorable design principle involved in this work sheds new insights for designing alternative ceramics with pre-assigned thermophysical properties for the next-generation thermal barrier coatings.

Principal element design of garnets to access structure stability and excellent microwave dielectric properties

AbstractGuided by the tolerance factor and average electronegativity difference, two stable garnets with compositions Ca3BTiGe3O12 (B = Mg, Zn) were designed, synthesized followed by structural, and dielectric characterization. The phase purity and structural characteristics were analyzed using X‐ray, Rietveld refinement, and microstructural analysis through scanning electron microscopy. A cubic structure with an Ia‐3d space group was confirmed for synthesized compositions. A combination of microwave dielectric properties for both garnets suggested that Ca3MgTiGe3O12 ceramic possessed a much higher quality factor (Q × f) ∼ 84 000 ± 3000 GHz coupled by a higher dielectric constant (εr) ∼ 12.97 ± 0.03, and a smaller temperature coefficient of resonance frequency (τf) ∼ −29.4 ± 1.5 ppm/°C compared to its Zn counterpart (Q × f ∼ 45 000 ± 2000 GHz, εr ∼ 12.84 ± 0.03, and τf ∼ −33.19 ± 1.6 ppm/°C). Such differences in dielectric performances were further explored utilizing packing fraction, ion polarizability, bond valence, Raman, and infrared spectrum to understand structure–property relationship.

Optimization of Ti-Zr-Cr-Fe alloys for 45 MPa metal hydride hydrogen compressors using orthogonal analysis

A series of (Ti1-xZrx)yCr2-zFez (x=0.1, 0.2, 0.3; y=1, 1.05, 1.1; z=0.9, 1, 1.1) alloys has been designed by orthogonal experiments for a three-stage metal hydride hydrogen compressor. XRD results show that such alloys exist as a single C14 Laves phase, and SEM with energy-dispersive spectroscopy reveals a uniform distribution of the elements. The effects of substitution of Ti by Zr, of Cr by Fe, and over-stoichiometry on the hydrogen storage properties of the Ti-Zr-Cr-Fe alloys have been investigated by orthogonal analysis. With increasing Zr content and 2A/B ratio (1, 1.05, 1.1), the cell volume and enthalpy gradually increase, while the plateau pressure and hysteresis decrease. With increasing Fe content, the cell volume and enthalpy decrease, while the plateau pressure, plateau slope, and hysteresis all dramatically increase. The (Ti0.85Zr0.15)yCr2-zFez (y=1, 1.05, 1.1; z=0.9, 1, 1.1) alloys show the largest average hydrogen storage capacity at 1.73 wt%. Besides, a simple model is proposed to predict enthalpy, which is based on the unit cell volume and average electronegativity difference with hydrogen. Finally, the (Ti0.85Zr0.15)1.05Cr1.1Fe0.9 alloy has been selected for a three-stage metal hydride hydrogen compressor. Its maximum and usable storage capacities were evaluated as 1.75 wt% and 1.40 wt%, respectively, with a dissociation plateau pressure derived from the van’t Hoff equation of 45.5 MPa at 90 °C.

Realizing room temperature double hysteresis loops in antiferroelectric NaNbO3 based ceramics

Lead-free antiferroelectric (AFE) materials have seen a surge of research activity in environmentally friendly energy storage technologies. Recently, considerable work has been done to improve the stability of AFE in NaNbO3 (NN) ceramics, but it remains a grand challenge to obtain typical AFE characteristic double P-E loops in NN ceramics at ambient conditions. In a preliminary estimate of tolerance factor versus average electronegativity difference, we reported the stable AFE phase in 0.95NaNbO3-0.05BiMg2/3Ta1/3O3 sample. The orthorhombic Q to P phase transition was verified by XRD and TEM. Then, the remarkable double P-E loops were obtained in 0.95NaNbO3-0.05BiMg2/3Ta1/3O3 ceramics. Furthermore, a phenomenological model was proposed to explain the P-E relationships and our results. Compared with other reported compounds, the TP-R decreased more obviously from 350 °C to 200 °C. Superior temperature stability (variations of maximum current, current density, and power density within 15% over 30–140 °C) and field induced phase transition were also confirmed by the pulse charge testing. Our work develops a new road for achieving room-temperature double P-E loops in NN ceramics by BiM1M2O3 (M1 might be Mg, Zn, etc; M2 might be Nb, Ta, etc) additives.

Fast and Accurate Machine Learning Strategy for Calculating Partial Atomic Charges in Metal-Organic Frameworks.

Computational high-throughput screening using molecular simulations is a powerful tool for identifying top-performing metal-organic frameworks (MOFs) for gas storage and separation applications. Accurate partial atomic charges are often required to model the electrostatic interactions between the MOF and the adsorbate, especially when the adsorption involves molecules with dipole or quadrupole moments such as water and CO2. Although ab initio methods can be used to calculate accurate partial atomic charges, these methods are impractical for screening large material databases because of the high computational cost. We developed a random forest machine learning model to predict the partial atomic charges in MOFs using a small yet meaningful set of features that represent both the elemental properties and the local environment of each atom. The model was trained and tested on a collection of about 320 000 density-derived electrostatic and chemical (DDEC) atomic charges calculated on a subset of the Computation-Ready Experimental Metal-Organic Framework (CoRE MOF-2019) database and separately on charge model 5 (CM5) charges. The model predicts accurate atomic charges for MOFs at a fraction of the computational cost of periodic density functional theory (DFT) and is found to be transferable to other porous molecular crystals and zeolites. A strong correlation is observed between the partial atomic charge and the average electronegativity difference between the central atom and its bonded neighbors.

Thermophysical performances of (Sm1-xLux)3TaO7 (x = 0, 0.1, 0.3 and 0.5) ceramics

To optimize thermophysical performances, Sm3TaO7 was doped with Lu3+ and pressureless sintered at 1600 ?C. It was shown that Sm3+ is partly substituted by Lu3+ cations and the (Sm1-xLux)3TaO7 ceramics with a single pyrochlore structure are obtained.With increasing x value from 0 to 0.5, the band gap increases gradually from 4.677 to 4.880 eV. Owing to the enhanced phonon scattering caused by Lu3+ doping, the thermal conductivities at 800 ?C of the prepared samples are in the range of 0.95-1.44W?K?1?m?1. It was also confirmed that the phase transition is restrained effectively by substituting Sm3+ with Lu3+. Due to the reduction of crystal lattice energy and average electro-negativity difference, the thermal expansion coefficient (TEC) is heightened with increasing Lu content. TEC achieves the highest value (10.45 ? 10?6 K?1 at 1200 ?C) at the equal molar ratio between Sm3+ and Lu3+ cations (i.e. x = 0.5), which is much higher than those of 7YSZ and Sm2Zr2O7 ceramics.

The role of electronegativity in the thermoelectric performance of GeTe–I–V–VI2 solid solutions

The influence of the average electronegativity difference between the alloying atom and host atom on alloy scattering potential and thus carrier mobility is studied.

Realizing high low-electric-field energy storage performance in AgNbO3 ceramics by introducing relaxor behaviour

Both sustainable development in environment and safety of high-power systems require to develop a novel lead-free dielectric capacitor with high energy density (Wrec) at low applied electric field. In this work, a remarkably high Wrec of 2.9 J/cm3 accompanying with energy storage efficiency of 56% was achieved in Ag0.9Sr0.05NbO3 ceramic at a low applied electric field of 190 kV/cm, by improving anti-ferroelectricity and introducing relaxor behaviour. The improved anti-ferroelectric stability was attributed to the decreased tolerance factor and average electronegativity difference, while the relaxor behaviour was associated with the increased disordered local structure by Sr-doping. Moreover, the Ag0.9Sr0.05NbO3 ceramics also exhibited outstanding temperature stability in energy density with small variation less than 5% over 20–140 °C. The results indicate that the Ag0.9Sr0.05NbO3 ceramic is a promising candidate for low-electric-field driving capacitors.

Antiferroelectricity in new silver niobate lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01)

The critical need for clean energy has led to the development of lead-free electroceramics. However, lead-free antiferroelectrics seldom have been reported because of the difficulties in materials fabrication and their low electrical performance. In this work, we successfully synthesized lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01) using the solid state reaction method in flowing oxygen (O2) atmosphere. Calcium zirconate (CaZrO3) dopant effectively stabilized the antiferroelectricity of silver niobate (AgNbO3) by dramatically decreasing the tolerance factor t. Additionally, we identified an orthorhombic Pbcm structure similar to that of pure AgNbO3. With the introduction of CaZrO3, phase transition temperatures M1–M2, M2–M3 and the freezing temperature Tf decreased. The shift of the M1–M2 phase transition temperature and Tf was the result of the restriction of the M1 phase due to CaZrO3 substitution. The compositions of x < 0.001 displayed a double hysteresis loop with a raised critical field EF. However, when the doping concentration exceeded 0.002, the double hysteresis loop with a higher polarization could not be obtained until the breakdown strength of EB exceeded 200 kV/cm because of the tremendously enhanced free energy barrier between the virgin antiferroelectric state and the field-induced ferroelectric state. We also evaluated the polarization hysteresis loops are also evaluated at temperatures up to 100 °C for the compositions x = 0.00–0.005. With an elevated temperature, at which the free energy barrier was reduced, the double hysteresis loop was obtained at a lower electric field when compared with that at room temperature for the compositions x = 0.004 and 0.005. These results demonstrated that by adjusting the tolerance factor t and average electronegativity difference X, the antiferroelectricity could be predicted in AgNbO3-based lead-free solid solution systems, thus providing a new strategy for designing a new class of antiferroelectric materials.

Effect of BiYbO3 Addition with a Small Tolerance Factor on Ferroelectricity and TC in PbZrO3 Ceramics

Perovskite (Pb(1–3x/2)Bix)(Zr(1–3x/4)Ybx)O3 (PZ-BY) ceramics, where x = 0.01–0.10, were synthesized by conventional solid state reaction. The effect of BiYbO3 on crystal structure, phase transitions and electrical properties was studied as a function of composition. The X-ray diffraction (XRD) result indicated that the perovskite structure with orthorhombic symmetry was a major phase for all samples. The pyrochlore phase, identified as Yb0.2Zr0.8O1.9, coexists in PZ-BY ceramics. The influence of instability and a small tolerance factor (t) and the average electronegativity difference () of pure BY on phase formation of PZ-BY ceramic has been discussed. Furthermore, it was found that adding small tolerance factor BiYbO3 compound can stabilize the antiferroelectric (AFE) phase of PZ solid solutions and decreasing t of solid solution can enhance Curie temperature of PZ.

Phase transition behavior of Ba(Mg1/3Nb2/3)O3 modified PbZrO3 solid solution

Different compositions of (1 − x)PbZrO3–xBa(Mg1/3Nb2/3)O3 (PZ–BMN) system, with x = 0.00–0.50, were synthesized using the columbite precursor method. The effects of BMN content on phase transition, electrical and thermal properties of PbZrO3 ceramic were investigated. The composition range and stability of the ferroelectric phase in perovskite PZ–BMN system can be improved by optimizing BMN substitution. Phase transition behavior of various solid solutions of PZ compositions can be predicted by a phase diagram established from the average electronegativity difference versus tolerance factor of the end members.

Prediction of good glass formers in the Al-Ni-La and Al-Ni-Gd systems using topological instability and electronegativity

A new criterion has been recently proposed combining the topological instability (λ criterion) and the average electronegativity difference (Δe) among the elements of an alloy to predict and select new glass-forming compositions. In the present work, this criterion (λ.Δe) is applied to the Al-Ni-La and Al-Ni-Gd ternary systems and its predictability is validated using literature data for both systems and additionally, using own experimental data for the Al-La-Ni system. The compositions with a high λ.Δe value found in each ternary system exhibit a very good correlation with the glass-forming ability of different alloys as indicated by their supercooled liquid regions (ΔTx) and their critical casting thicknesses. In the case of the Al-La-Ni system, the alloy with the largest λ.Δe value, La56Al26.5Ni17.5, exhibits the highest glass-forming ability verified for this system. Therefore, the combined λ.Δe criterion is a simple and efficient tool to select new glass-forming compositions in Al-Ni-RE systems.

Dielectric and pyroelectric studies of Li-modified rare-earth dysprosium-doped barium strontium sodium niobate ceramics

This paper highlights the dielectric, pyroelectric, and resistivity studies of Ba1.45Sr2.4Dy0.1LixNa2−xNb10O30 (x = 0 ≤ x ≤ 1.0) tungsten–bronze-structured ceramics. X-ray diffraction studies indicated single orthorhombic (mm2) phase supported by tolerance factor and average electronegativity difference. The lattice parameters, unit cell volume, axial ratio, and densities are calculated from XRD studies. The experimental densities obtained are about 95% to that of theoretical values. It is found that the unit cell volume enhanced up to Li0.8. The effect of Li modification and Dy doping on eRT, $$ \varepsilon_{{{\text{T}}_{\text{c}} }}, $$ and Tc in BSNN system are discussed. D.C. resistivity studies indicated the positive temperature coefficient of resistivity (PTCR) response in these compositions.

Alkali-lithium modification on rare-earth-neodymium-doped barium strontium sodium niobate ceramics for dielectric and pyroelectric properties

The influence of alkali-Li + modification on rare-earth Nd 3+-doped BSNN tungsten bronze system and its effect on phase formation, dielectric and pyroelectric properties is reported. The structure of Ba 1.45Sr 2.4Nd 0.1Li x Na 2− x Nb 10O 30 ceramics is comprehensively studied in the range of x = 0.0 ≤ x ≤ 1.0. X-ray diffraction studies indicated single orthorhombic ( mm2) phase supported by tolerance factor and average electronegativity difference of BSNLNN compositions. The average particle size was maximum (406 Å) at Li 0.6. The dielectric properties are maximum ( ɛ RT = 649 and ε T c = 1254 ) at 1 kHz for Li 0.6. The values of T c for Li-modified and Nd-doped BSNN varied from 190 °C to 202 °C. The ρ max value in the order of 10 10 Ω cm which is three orders of magnitude larger when compared with the ρ RT. The value of ρ max is 1.05 × 10 10 Ω cm observed at x = 0.2 of BSNLNN ceramics.

Topological instability, average electronegativity difference and glass forming ability of amorphous alloys

In this paper, we report the remarkable agreement of the glass forming ability of binary alloys with a new criterion that combines the topological instability parameter ( λ) and the average electronegativity difference among the elements of an alloy, assuming both exert a synergetic effect. The best glass forming compositions for Zr–Cu and Ti–Ni systems are well predicted by this new approach. Although the new criterion needs further refinement, it is concluded that the proposed approach is a promising and simple tool to guide and reduce the tedious and labour intensive work to find good glass former compositions in metallic systems.

Dielectric and pyroelectric properties of monovalent-lithium modified trivalent-samarium doped barium strontium sodium niobate tungsten bronze structured ceramics

The dielectric and pyroelectric properties of trivalent-samarium doped barium strontium sodium niobate tungsten bronze structured ceramics are further modified with monovalent-Lithium. Ba1.6−(3/2)ySr2.4SmyLixNa(2−x)Nb10O30 was studied for y = 0.1 and x in the range of 0 ≤ x ≤ 1. The BSSLNN ceramics can be indexed by typical orthorhombic structure and these orthorhombic (mm2) peaks are assigned to standard file No. C73-1214. Tolerance factor and average electronegativity difference has been determined for BSSLNN ceramics. Pyroelectric and DC resistivity properties of BSSLNN ceramics are reported. x = 1 composition was found to be optimum among the series for possible pyroelectric applications.

Topological instability and electronegativity effects on the glass-forming ability of metallic alloys

The glass-forming ability (GFA) of metallic alloys is associated with a topological instability criterion combined with a new parameter based on the average electronegativity difference of an element and its surrounding neighbours. In this model, we assume that during solidification the glassy phase competes directly with the supersaturated solid solution having the lowest topological instability factor for a given composition. This criterion is combined with the average electronegativity difference among the elements in the alloy, which reflects the strength of the liquid. The GFA is successfully correlated with this combined criterion in several binary glass-forming systems.

Effect of rare-earth donor Ce3+ doping at A-site of PLSZNT on dielectric and piezoelectric properties

Dielectric and piezoelectric properties of [Pb0.976La0.014−xCexSr0.01][Zr0.57Ti0.43](0.9975−((0.014−x)/4)−(x/4))Nb0.002O3 (PLCSZNT) ceramic compositions for 0⩽x⩽1mol% were investigated. The XRD analysis showed the presence of single rhombohedral phase. Grain size and density increased until 0.6mol% Ce and further Ce concentration inhibited the grain growth. The stability of rhombohedral phase has been supported by tolerance factor and average electronegativity difference. The room temperature dielectric response (εRT) increased up to 0.6mol% combined with a significantly reduced dielectric loss (Tanδ) and low Curie temperature (Tc). The higher piezoelectric properties associated with low Ce concentration are attributed to rhombohedral phase. The optimum dielectric and piezoelectric properties were found in 0.6mol% Ce composition which could be suitable for possible piezoelectric applications.

Calculation and prediction for the hydriding properties of LaNi5−M alloys

Abstract The enthalpy of formation and hydrogen content for hydrides of LaNi 5− x M x (M stands for Mn, Fe, Co, Ni, Al, Ga, Ge and Si) alloys have been investigated by the stepwise regression method and atomic parameters. The models used for quantitative prediction of the enthalpy of formation and hydrogen content are presented. The main factors affecting hydrogen content and the enthalpy of formation are given. It is demonstrated that the plateau pressure can be expressed as a semi-empirical model, which consists of the atomic size parameter and the average electronegativity difference as well as the average of the outer electron number of alloys. It is found that the amount of absorbed hydrogen of LaNi 5− x M x alloys is controlled by electronegativity difference, atomic size, electron concentration and charge-radii ratio.

Nuclear Quadrupole Coupling Constants and Charge Distributions in Ionic Crystals of the α-NaFeO2 Type

The 23Na nuclear quadrupole coupling constant is determined for 10 compounds of the α-NaFeO2 type, namely, NaInO2, NaInS2, NaInSe2, NaCrO2, NaCrS2, NaCrSe2, NaTiO2, NaTlO2, NaScO2, and NaAlO2. The electric field gradient is calculated on the basis of a point-charge model, and charge distributions are obtained for the complex ions. The charges on the metal ions appear to correlate with the average electronegativity difference between the metal and chalcogen.