Electronic Contribution Research Articles

About the Impact of Defect Phases on the Thermoelectric Properties of Cr3S4–xSex

Phase relations in Cr3S4 and the substituted system Cr3S4–x Se x are studied to determine the influence of chemical substitutions on the thermoelectric properties. In addition to the expected equilibrium phase crystallizing in the monoclinic space group I2/m, some samples exhibit a defect phase with Cr2S3‐like structure. The defect phase can be observed in a few samples prior to sintering, with the majority being phase‐pure Cr3S4. The defect phase can, however, be introduced in phase‐pure samples through in situ heating. It can be proven that the defect phase has an influence on the thermoelectric properties, by lowering the electrical and thermal conductivity, while increasing the Seebeck coefficient. Substitution in the anion lattice of Cr3S4 with Se lowers the thermal conductivity. The improvement is mainly achieved through a reduction of the electronic contribution to the thermal conductivity, leading to total values as low as 1.6 Wm−1 K−1 for the substituted system in comparison to the pristine material 2.3 Wm−1 K−1.

The thermal and mechanical properties of Li-based Half Heusler alloys LiAlZ(Z = Si, Ge) using Quasi-Harmonic Approach

Using the Density Functional Density (DFT) method coupled with a Quasi-Harmonic Approximation (QHA), we studied the structural stability and thermal properties of Li-based Half Heusler alloys LiAlZ (Z= Si and Ge). The obtained results show that type I for both compounds is the most stable of all the examined structural phase types i (i = I, II, III) and have semiconductor behavior with narrow indirect band gaps. The study of the elastic constants and phonon curves confirmed that these compounds are mechanically and dynamically stable. The obtained results of total free energy are considered while estimating the thermal properties as the lattice parameters, volume thermal expansion, heat capacity, electronic and entropy in the range of temperature from 0 K to 1000 K. The thermal properties show that half Heuslers LiAlZ are thermodynamically stable, and the vibrational contribution is dominant compared to configurational and electronic contributions in the heat capacity and entropy. In contrast, the vibrational contribution is very small to the configurational and electronic free energy contributions.

Excellent Structural Stability-Driven Cyclability in P2-Type Ti-Based Cathode for Na-Ion Batteries

In the current study, we have synthesized Ti-based P2-type Na0.7Ni0.2Cu0.1Ti0.65O2 (NNCT) through the sol–gel route and characterized it for its structural, electrical, and electrochemical properties. The analysis of X-ray diffraction (XRD) data confirmed the existence of a single P2 phase for the sample calcined at 950 °C with suppressed Na-ion vacancy ordering. Impedance studies and chronoamperometric data revealed that NNCT exhibited a poor conductivity of ∼1.37 × 10–7 S cm–1 at room temperature, with the electronic conductivity contribution to the total electrical conduction being only 0.4%. The sample exhibited specific capacities of 83, 54, and 42 mA h g–1 at discharge rates of 0.1C, 0.5C, and 1C, respectively, with remarkable cyclic stability of 96% capacity retention after 700 cycles at 0.5C which makes NNCT an attractive cathode for Na-ion batteries in stationary storage applications. The ex situ XRD analysis confirmed that NNCT maintains a single P2 phase during cycling between 2.0 and 4.2 V. NNCT also exhibited moisture stability, thus enabling the use of a cost-effective water-based slurry for cathode layer fabrication.

Small, Electron-Donating Substituents Give CO2 Activation by Permethylpentalene Zirconium Amido Complexes the Upper Hand: A DFT Study of Distortion and Interaction

An insight into factors controlling CO2 activation is necessary to develop molecular systems that utilize CO2 as a chemical feedstock. Two permethylpentalene zirconium cyclopentadienyl (mono)amido complexes, Pn*ZrCp(NR2), were previously assessed for CO2 activation, and a strong dependence on the amido substituent was observed. The R = Me analogue reacted rapidly and quantitatively at room temperature to form the carbamato complex, while the R = Ph species was inert. Here, we investigate the origin of this reactivity difference using DFT and the distortion-interaction model to characterize steric and electronic contributions to the activation barrier. We find that the barrier for CO2 insertion with R = Me (19.1 kcal/mol) is lower than with R = Ph (36.6 kcal/mol), explaining the inertness of the Ph-substituted analogue. The distortion energy trend follows the steric bulk of the amido substituents, and the bulkier Ph-substituted complex has a consistently higher distortion energy along its potential energy surface than that of the Me-substituted complex. The interaction energy trend follows the electronics, and a more electron-donating Me-substituted complex shows a consistently lower interaction energy. The balance of these effects at the corresponding TS gives a reduced activation barrier. Small, electron-donating substituents therefore facilitate CO2 activation in these complexes.

First-principles theory of electrochemical capacitance

The differential capacitance comprises the most relevant thermodynamic information about an electrochemical system. Classical approaches to describe electrochemical capacitance have difficulties to combine the treatment of the ionic contribution of the electrolyte with the electronic contribution of the electrode. Moreover, different approaches are typically required for the description of the double-layer capacitance, on the one hand, and the pseudocapacitive contribution due to adsorption or intercalation of reactive species, on the other. In the present work, a new approach to describe electrochemical capacitance from first principles is developed. The treatment of a general electrochemical system at the level of multicomponent density-functional theory (MCDFT) yields an exact analytical expression for the total capacitance of the system, which corresponds to a formal series-circuit partitioning into “quantum” capacitance contributions of the density of states of electrons and ions, the (mean-field) electrostatic capacitance, as well as capacitance contributions of exchange and correlation among all active species. It is shown that the classical expression of the double-layer capacitance involving the interfacial Galvani potential is obtained in the limit of extended electrode and electrolyte regions. Importantly, the present formalism also describes systems with confined electrode and electrolyte phases, where the definition of the (classical) inner potentials of the electrode and electrolyte domains becomes problematic. Moreover, the new approach unifies the treatment of double-layer capacitance and pseudocapacitance resulting from reactive processes.

High-Temperature Thermodynamics of Uranium from Ab Initio Modeling

We present high-temperature thermodynamic properties for uranium in its γ phase (γ-U) from first-principles, relativistic, and anharmonic theory. The results are compared to CALPHAD modeling. The ab initio electronic structure is obtained from density-functional theory (DFT) that includes spin–orbit coupling and an added self-consistent orbital-polarization (OP) mechanism for more accurate treatment of magnetism. The first-principles method is coupled to a lattice dynamics scheme that is used to model anharmonic lattice vibrations, namely, Self-Consistent Ab Initio Lattice Dynamics (SCAILD). The methodology can be summarized in the acronym DFT + OP + SCAILD. Upon thermal expansion, γ-U develops non-negligible magnetic moments that are included for the first time in thermodynamic theory. The all-electron DFT approach is shown to model γ-U better than the commonly used pseudopotential method. In addition to CALPHAD, DFT + OP + SCAILD thermodynamic properties are compared with other ab initio and semiempirical modeling and experiments. Our first-principles approach produces Gibbs free energy that is essentially identical to CALPHAD. The DFT + OP + SCAILD heat capacity is close to CALPHAD and most experimental data and is predicted to have a significant thermal dependence due to the electronic contribution.

Enhancing the Photocatalytic Activity of TiO2 for the Degradation of Congo Red Dye by Adjusting the Ultrasonication Regime Applied in Its Synthesis Procedure

Recently, the ultrasound-assisted sol-gel synthesis procedure of mesoporous titania (TiO2) photocatalysts caught the researcher’s attention, due to the physicochemical properties enhancement of the resulting titania nanomaterials. Thus, by varying different synthesis parameters particular characteristics could be obtained. In the present study, the ultrasound pulse on/off ratio has been considered and the effect of the envisaged parameter on the textural, morphological, and optical features of titania nanomaterial has been investigated. Therefore, X-ray Diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR), N2-sorption measurements, SEM imaging, and UV-Vis Diffuse Reflectance spectroscopy (UVDR) have been used. And further, the photocatalytic activity of the prepared TiO2 materials was evaluated by the features developed about the applied ultrasound pulse on/off ratio as 1/1, 2/1, 3/1, 4/1, 1/3 and 2/2. It was found that the ultrasound pulse on/off ratio considered in the synthesis procedure of titania leads to TiO2 materials with different textural (SBET = 98–156 m2/g), morphological, and optical (Eg = 3.1–3.2 eV) characteristics. For this reason, TiO2 nanomaterials prepared were found to exhibit suitable features for photocatalytic applications. Thus, the TiO2 4.1 sample prepared at 4/1 ultrasound pulse on/off ratio revealed the highest photodegradation efficiency of Congo Red dye (98.28%) as the results of photocatalytic tests show. More than that, a possible reaction mechanism of the CR photodegradation process through the contribution of reactive oxygen species (·HO, ·O2−), holes (h+), and electrons (e−) of developed titania photocatalyst was proposed.

Topological contribution to magnetism in the Kane-Mele model: An explicit wave-function approach

In our previous publication [Ozaki and Ogata, Phys. Rev. Res. 3, 013058 (2021)], the quantization of the orbital-Zeeman (OZ) cross term in the magnetic susceptibility, or the cross term of spin Zeeman and orbital effect, was shown for the Kane-Mele model using the expansion around the Dirac points. In the present study, we accurately evaluate the orbital, spin-Zeeman, and OZ cross term of the Kane-Mele model using a recently developed formulation. This method uses the explicit real-space Bloch wave functions and enables us to accurately evaluate each contribution taking into account an infinite number of high-energy bands and core electron contribution at arbitrary chemical potential. We find that the effect beyond the previous formulations does not change the quantization of the OZ cross term. We also study the OZ cross term in the metalic case, and the sum rule of the OZ cross term with respect to the chemical potential is found. The possibility of experimental detection of the quantization is also discussed.

Examining Silver Deposition Pathways onto Gold Nanorods with Liquid-Phase Transmission Electron Microscopy

Liquid-phase transmission electron microscopy (LP-TEM) enables one to directly visualize the formation of plasmonic nanoparticles and their postsynthetic modification, but the relative contributions of plasmonic hot electrons and radiolysis to metal precursor reduction remain unclear. Here we show silver deposition onto plasmonic gold nanorods (AuNRs) during LP-TEM is dominated by water radiolysis-induced chemical reduction. Silver was observed with LP-TEM to form bipyramidal shells at higher surfactant coverage and tip-preferential lobes at lower surfactant coverage. Ex situ silver photodeposition formed nanometer-thick shells on AuNRs with preferential deposition in inter-rod gaps, while chemical reduction deposited silver at AuNR tips at low surfactant coverage and formed pyramidal shells at higher surfactant coverage, consistent with LP-TEM. Silver deposition locations during LP-TEM were inconsistent with simulated near-field enhancement and hot electron generation hot spots. Collectively, the results indicate chemical reduction dominated during LP-TEM, indicating observation of plasmonic hot electron-induced photoreduction will necessitate suppression of radiolysis.

Penetrative Superplumes in the Mantle of Large Super‐Earth Planets: A Possible Mechanism for Active Tectonics in the Massive Super‐Earths

AbstractRecent theoretical studies suggest that the physical and rheological mantle properties in massive rocky planets fall outside conventional behaviors inferred for mantle properties at the Earth's mantle pressures. The vacancy diffusion occurring at low pressures is assumed to be followed by interstitial diffusion above ∼0.1 TPa resulting in viscosity reduction at higher pressures. In addition, the dissociation transition of MgSiO3 post‐perovskite (pPv) into new phases of minerals at 0.9 and 2.1 TPa, both with large negative Clapeyron slopes, has further impact(s) on the style of circulation in the mantle of super‐Earth planets. Further, the electronic contribution of conductivity increases exponentially with temperature at temperatures ∼5000 K and higher. We employ 3D‐controlled volume spherical convection models to explore the style of mantle circulation in large rocky super‐Earth planets with different core temperatures. Our numerical models resembling a GJ 876 d size super‐Earth reveal that due to the buffering influence of the pPv‐dissociation transition at ∼0.9 TPa, for deep mantle viscosities lower than ∼1022 Pa.s a small‐scale convective layer may develop at the top of the core‐mantle boundary (CMB). Penetrative superplumes originating from deep mantle‐layered regions can maintain the heat flux from the CMB required for the planet's geodynamo, and can survive for billions of years reaching shallow depths of the mantle without significant lateral migration. The strength of the focused penetrative superplumes that can potentially sustain surface volcanism and plate tectonics is enhanced with increasing CMB temperature, but diminished by higher rates of internal heating.

Electron transfer routes in nitrate-pentavalent vanadium co-contaminated system of oligotrophic microbiology niche

Microbial techniques have been extensively used for the remediation of nitrate and V(V) co-contaminations, but the mechanisms of electron and substances transport and metabolism of co-contaminations under oligotrophic niche have been largely overlooked. This study quantified the electron transfer and consumption, substance transfer, and metabolic pathways in the nitrate and V(V) co-contamination system under oligotrophic condition to explore the underlying mechanisms by characterizing the products and elucidating conventional cognitive pathways. This study compared the composition of the precipitates under the conditions of sufficient and insufficient carbon sources using energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and discovered the re-oxidation process of the already reduced V(IV). Electronic evidence for the re-oxidation process of V(IV) was also provided by electron transfer and quantitative analysis. Besides, this study found that the electron contribution ratio of NO3−-N → NO2−-N and V(V) → V(IV) reduction was 40.2:1. In addition, based on the functional prediction of PICRUSt 2, it was found that the utilization of intracellular reserve carbon source and enzymes in the transport chain were enhanced in oligotrophic microbiology niche. These results provide new insights into the stability of co-contamination reduction in oligotrophic microbiology niche and demonstrate a new mobilization pathway for V(V) in oligotrophic systems.

Microstructural evolution and phase stability in semi-Heusler NiMnSb and vanadium added equi-atomic NiMnSbV alloys

Phase and microstructure evolution in semi-Heusler NiMnSb and vanadium added quaternary equi-atomic NiMnSbV alloys has been studied in the as solidified state. In the as solidified NiMnSb alloy, cubic semi-Heusler phase and in the as solidified NiMnSbV alloy, Frank-Kasper type cubic SbV3 phase along with the cubic semi-Heusler NiMnSb phase are observed. Nucleation and growth of SbV3 phase takes place in the alloy through solute rejection mechanism, and at the interface of SbV3 and NiMnSb semi-Heusler phase, lamellar structure is observed. While SbV3 phase is stable upto 700 °C, the semi-Heusler NiMnSb phase is not stable beyond 400 °C and it transforms to hexagonal (Ni/Mn)Sb phase. Line defects are observed in the NiMnSb semi-Heusler phase. However, extensive twin like defects are observed in the cubic SbV3 phase. In the SbV3 phase edge sharing 12-fold coordinated icosahedral clusters and 14-fold coordinated clusters are present. Atomic size difference of Sb and V indicates that the clusters are distorted, which might be the viable cause behind the formation of such kind of compound deformation twins. The phase formation and stability in these two alloys has been studied through Miedema’s model. It is observed that apart from atomic size difference, enthalpy of mixing; the ternary and higher order self-interactions, electronic contribution to enthalpy also play an important role. Systematic substitution in the lattice of semi-Heusler NiMnSb phase based on enthalpy of mixing and atomic radius may not be the design strategy for development of semi-Heusler NiMnSb based single phase multicomponent/high entropy alloys.

Role of donors in triggering second order non-linear optical properties of non-fullerene FCO-2FR1 based derivatives: A theoretical perspective

The organic compounds are known as an emerging class in the field of nonlinear optical (NLO) materials. In this paper, D–π–A configured oxygen containing organic chromophores (FD2-FD6) were designed by incorporating various donors in the chemical structure of FCO-2FR1. This work is also inspired by the feasibility of FCO-2FR1 as an efficient solar cell. Theoretical approach involving DFT functional i.e., B3LYP/6-311G(d,p) was utilized to achieve useful information regarding their electronic, structural, chemical and photonic properties. The structural modifications revealed significant electronic contribution in designing HOMOs and LUMOs for the derivatives with lowered energy gaps. The lowest HOMO-LUMO band gap obtained was 1.223 eV for FD2 compound in comparison to the reference molecule (FCO-2FR1) i.e., 2.053 eV. Moreover, the DFT findings revealed that the end-capped substituents play a key role in enhancing the NLO response of these push-pull chromophores. The UV–Vis spectra of tailored molecules revealed larger λmax values than the reference compound. Furthermore, strong intramolecular interactions showed the highest stabilization energy (28.40 kcal mol-1) for FD2 in the natural bond orbitals (NBOs) transitions, combined with the least binding energy (-0.432 eV). Successfully, the NLO results were favorable for the same chromophore (FD2) which showed the highest value for dipole moment (μtot = 20.049 D) and first hyper-polarizability (βtot = 11.22 × 10-27 esu). Similarly, the largest value for linear polarizability ⟨α⟩ was obtained as 2.936 × 10-22 esu for FD3 compound. Overall, the designed compounds were calculated with greater NLO values as compared to FCO-2FR1. The current study may provoke the researchers towards designing of highly efficient NLO materials via using the suitable organic linking species.

Microscopic origin of the abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals: An extended ab initio study

As a promising next-generation material for superconducting radiofrequency cavities, superconducting Nb3Sn, once developed for fabricating a high-field magnet, has attracted tremendous research interest due to the significant potential for both compact and large scale accelerator applications. However, the intrinsic physical origin, especially at atomic and electronic scale, of the abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals is still controversial and not fully understood yet. Through an extended atomic and electronic modelling of electronic structure evolution arising from the perturbation of lattice strain and temperature, we proposed an analytical model for depicting the abnormal temperature-dependent elastic constants and transition resistivities of superconducting Nb3Sn. The extended ab initio modeling takes into account the interaction of the d electrons with the strain, the strain-modulated electronic structure evolution and the accompanied variations in the density of states at the Fermi level, and the competition between the lattice contribution and the electron contribution in governing the abnormal elastic response along with the superconducting transition of Nb3Sn. The model predictions of the elastic constants and the superconducting phase transition resistivities of single crystal and polycrystalline Nb3Sn qualitatively agree with the experimental observations. The extended ab initio studies indicate the abnormal changes in the elastic properties and the transition resistivity response characteristics are intrinsically correlated, the contribution arising from the d-band electrons determines the cross-scale abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals.

Phonon Dominated Thermal Transport in Metallic Niobium Diselenide from First Principles Calculations.

Niobium diselenide (NbSe2) is a layered transition metal dichalcogenide material which possesses unique electrical and superconducting properties for future nanodevices. While the superconducting, electrical, and bulk thermal transport properties of NbSe2 have been widely studied, the in-plane thermal transport property of NbSe2, which is important for potential thermoelectric applications, has not been thoroughly investigated. In this report, we study the lattice in-plane thermal transport of 2D NbSe2 by solving the phonon Boltzmann transport equation with the help of the first principles calculation. The thermal conductivity obtained at room temperature is 12.3 W/mK. A detailed analysis shows that the transverse acoustic phonon dominates the lattice thermal transport, and an anomalously small portion of electron contribution to the total thermal conductivity is observed for this metallic phase. The results agree well with experimental measurements and provide detailed mode-by-mode thermal conductivity contribution from different phonon modes. This study can provide useful information for integrating NbSe2 in nanodevices where both electrical and thermal properties are critical, showing great potential for integrating monolayer NbSe2 to thermoelectric devices.

Fast electron contribution in electronic stopping for p-He and p-Ar collisions

Our study has shown that in collisions p-He and p-Ar with energies above 50 keV fast electrons carry away as kinetic energy up to 70 % of energy released during particle stopping. Ignoring the fast electron contribution makes impossible bringing independently measured cross sections of elementary processes of ionization, excitation, stripping and charge exchange into compliance with measured cross sections of electronic stopping. Fast electron emission in collisions of energetic ions with solids may induce extra radiation effects (create additional vacancies and defects in solid).Mean kinetic energies of ejected electrons We obtained from the analysis of cross section ratio agree well with directly measured energy spectra of the emitted electrons. The dynamic ionization theory implies the We proportionality to initial velocity v. In the considered cases, such a dependence takes place at the velocities below 2 a.u. At higher velocities, the observed dependence is successfully described in the framework of the Born approximation.

Electronic and phononic absorption contributions to near-infrared reflectance of Mg1−xCoxAl2O4, Zn1−xCoxFe2O4 and CrxSbxTi1–2xO2 pigments

Mg1−xCoxAl2O4, Zn1−xCoxFe2O4 and CrxSbxTi1–2xO2 pigment series with varying chemical constitution were prepared and structurally confirmed. Valence band maximum extracted from photoemission spectrum and Raman signal area obtained from Raman spectrum were used as representative of electronic and phononic absorption, respectively. Mg1−xCoxAl2O4, Zn1−xCoxFe2O4 exhibit a trivial cooperative behavior of electronic and phononic absorption to the near-infrared reflectance. Nevertheless, CrxSbxTi1–2xO2 established a nontrivial phononic absorption behavior. At low doping regime in CrxSbxTi1–2xO2, electronic absorption dominates the controlling of near-infrared reflectance. Conversely, at high doping regime, the shrinking of phononic absorption play a dominance role to the reflectance. The nontrivial scenario could lead to the understanding of underlying reflective mechanism associated with effects from electronic structure and lattice properties. The results would pave the way for the improvement of solar reflective pigment with compromise of color tuning.

Механизм ионизации пучковой плазмы, генерируемой электронным пучком в среднем вакууме

We present the results of the measurements of the ionic composition of plasma generated by an accelerated electron beam at medium vacuum (fore-vacuum) pressures. Calculations of the contribution of plasma electrons and beam electrons to the mechanism of ionization are presented. Comparison of the calculated with the experimental data led us to the conclusion about the dominating contribution of beam electrons and to the ionization process.

Ionization mechanism of beam plasma generated by an electron beam in medium vacuum

We present the results of the measurements of the ionic composition of plasma generated by an accelerated electron beam at medium vacuum (fore-vacuum) pressures. Calculations of the contribution of plasma electrons and beam electrons to the mechanism of ionization are presented. Comparison of the calculated with the experimental data led us to the conclusion about the dominating contribution of beam electrons and to the ionization process. Keywords: beam plasma, fore-vacuum, electron beam, plasma-cathode electron source.

Quantitative analysis of steric effects on the regioselectivity of the Larock heteroannulation reaction.

Alkylphenylacetylene derivatives were synthesized and used as reactants in the Larock heteroannulation reaction to investigate the steric influence on regioselectivity. Large alkyl groups preferentially yielded 2-alkyl-3-phenylindole products, while smaller alkyl groups provided 3-alkyl-2-phenylindole as major products. The logarithm of regioisomeric product ratios exhibited good correlations with various steric parameters. Notably, the Charton values provided the best correlation when excluding the cyclopropyl group. In addition, the Boltzmann-weighted Sterimol parameter (wSterimol) was utilized to generate a good predictive model, indicating the B1 wSterimol as the significant regiochemical determining parameter with no obvious deviation for the cyclopropyl group. Relative atomic distances within the DFT-optimized transition state structures revealed good correlations with the logarithm of regioisomeric ratios. Furthermore, the cyclopropyl adsorption complex indicated electronic contribution, explaining the peculiar behavior of this substituent in the experimental observation.