Change In Chemical Potential Research Articles

Effect of QCD Phase Transition on Axion Properties for Two Flavors of NJL Model

The effect of chiral phase transition on the properties of the axion in the Nambu-Jona-Lasinio two-flavor model was studied at finite temperature. We tend to study and analyze the changes of thermodynamic potential, and note that the changes of temperature, coupling parameters and quark chemical potential have great influence on thermodynamic potential. Then the variations of axion mass, self-coupling and quark condensation are given by numerical calculation.

Influence of functional groups in chemical reactivity and optoelectronic properties of novel glycidyl nitrate copolymers (GNCOP): a DFT study.

Nowadays, propulsion materials are receiving increased attention as an important component in electric motors. So, awareness of their chemical reactivity and geometric and electronic structures can help to make materials with higher quality and efficiency. In this study, we have proposed novel glycidyl nitrate copolymers (GNCOPs) and meta-substituted derivatives as propulsion materials. Based on density functional theory (DFT) method, chemical reactivity indices have been calculated for predicting their behavior in burning process. Adding functional groups changes reactivity of the GNCOP compound, especially, in the -CN functional group, chemical potential, chemical hardness, and electrophilicity change -0.374, +0.007, and +1.342eV, respectively. In addition, these compounds have dual properties in interaction with oxygen molecule. Optoelectronic study in time-dependent DFT framework shows that there are three peaks with significant excitations. In conclusion, adding functional group into the GNCOPs can introduce new materials with high energetic properties.

Quantum capacitance properties of the holes in planar germanium

Quantum capacitance of two-dimensional (2D) systems contains useful physical information. Here, we report a high sensitivity quantum capacitance measurement with an improved radio frequency superheterodyne bridge technique for probing the electronic characteristic of Ge/SiGe 2D hole gas (2DHG) at low temperatures and under a perpendicular magnetic field B⊥. At low fields, a rapid decrease in quantum capacitance following B⊥−3 dependence is observed, indicating an abrupt change in chemical potential near the gate boundary at high frequencies; at high fields, a series of capacitance oscillations are observed due to the Landau quantization and Zeeman splitting of the Ge/SiGe 2DHG, where gate-dependent effective g factor under B⊥ is extracted. These results represent implementation of the high-precision capacitance measurement for exploring the physical properties of Ge/SiGe 2DHG.

Reconfigurable graphene-gold-based microstrip patch antenna: RHCP to LHCP

In the designed study, a reconfigurable graphene-gold-based microstrip patch antenna is proposed. Designed antenna has the ability to access a variety of right hand circular polarization, and left hand circular polarization polarizations by switching the positions of its slots. The central frequency of the antenna is adjusted to 0.92 THz according to the conditions. The main approach of the article is based on the principle that if the position of the slot is rotated 90°, the polarization will be switched from right hand circular polarization to left hand circular polarization. In the design outputs of S11 below −10 dB for the range of 0.8 THz through 1.1 THz is observed, which is desirable. Incidentally, the axial ratio is less than 3 dB in the direction of the antenna axis according to the simulation outputs. Important parameters of the antenna such as efficiency, directivity radiation pattern, matching, E-field distribution, H-field distribution, current density distribution, polar radiation pattern, 3D radiation pattern, and S11 sweep based on chemical potential changes (frequency reconfigurable) in the desired frequency domain are analysed. While for the range of 0.6 THz to 1.4 THz, the results obtained from the point of view of matching and polarization are good conditions. The chemical potential in the designs is 0.6.

Quantum oscillations of Kondo screening phases in strong magnetic fields

We generalize the iterative diagonalization procedure adopted in method of numerical renormalization group to analyze the Kondo effect in strong magnetic fields, where the density of states for itinerary electrons at the chemical potential varies discontinuously as the magnetic field changes. We first examine phases of many-body ground states in the presence of single impurity. By investigating change of $z$-component of total spin, $\Delta S_z$, and spin-spin correlation between the impurity and conduction electrons, we find that there are three states competing for the ground state when Zeeman splitting is present. One of the states is doublet in which the impurity spin is unscreened. The other two states are Kondo screening states with $\Delta S_z=1/2$ and $\Delta S_z=1$, in which the impurity spin is partially screened and completely screened respectively. For Kondo systems with two-impurities in strong magnetic fields, we find that the interplay between the Kondo screening effect, RKKY interaction, and quantum oscillations due to Landau levels determines the ground state of the system. Combination of these three factors results in different screening scenarios for different phases in which spins of two impurities can form spin-0 or spin-1 states, while impurity spins in these phases can be either screened, partially screened, or unscreened by conduction electrons. The emergence of the ground state from these competing states oscillates with the change of magnetic field, chemical potential or inter-impurity distance. This leads to quantum oscillations in magnetization and conductivity. In particular, we find extra peak structures in longitudinal conductivity that reflect changes of Kondo screening phases and are important features to be observed in experiments. Our results provide a complete characterization of phases for Kondo effect in strong magnetic fields.

Solubility of Methane in Water: Some Useful Results for Hydrate Nucleation.

In this paper, the solubility of methane in water along the 400 bar isobar is determined by computer simulations using the TIP4P/Ice force field for water and a simple LJ model for methane. In particular, the solubility of methane in water when in contact with the gas phase and the solubility of methane in water when in contact with the hydrate has been determined. The solubility of methane in a gas-liquid system decreases as temperature increases. The solubility of methane in a hydrate-liquid system increases with temperature. The two curves intersect at a certain temperature that determines the triple point T3 at a certain pressure. We also determined T3 by the three-phase direct coexistence method. The results of both methods agree, and we suggest 295(2) K as the value of T3 for this system. We also analyzed the impact of curvature on the solubility of methane in water. We found that the presence of curvature increases the solubility in both the gas-liquid and hydrate-liquid systems. The change in chemical potential for the formation of hydrate is evaluated along the isobar using two different thermodynamic routes, obtaining good agreement between them. It is shown that the driving force for hydrate nucleation under experimental conditions is higher than that for the formation of pure ice when compared at the same supercooling. We also show that supersaturation (i.e., concentrations above those of the planar interface) increases the driving force for nucleation dramatically. The effect of bubbles can be equivalent to that of an additional supercooling of about 20 K. Having highly supersaturated homogeneous solutions makes possible the spontaneous formation of the hydrate at temperatures as high as 285 K (i.e., 10K below T3). The crucial role of the concentration of methane for hydrate formation is clearly revealed. Nucleation of the hydrate can be either impossible or easy and fast depending on the concentration of methane which seems to play the leading role in the understanding of the kinetics of hydrate formation.

(Invited) Understanding and Mitigating Chemo-Mechanical Degradation in Solid Oxide Cells

Solid-state electrochemical cells may undergo significant chemical potential changes in the electrolyte region near the electrodes, depending on operating conditions. Lithium dendrite growth, which may eventually induce mechanical stresses and short circuit in all-solid-state batteries (SSBs) in the charging process, is one of the well-known examples representing chemo-mechanical failure in solid-state electrochemical cells [1, 2]. A similar phenomenon has been observed in solid oxide cells (SOCs) operated in electrolysis mode and also in fuel cell mode with a negative voltage [3, 4]. Contrary to lithium precipitation in SSBs, high partial pressure of oxygen is developed in SOCs, resulting in electrode/electrolyte delamination. In the present study, we investigated the mechanism of delamination growth in SOCs with respect to operating conditions, based on which we determined a critical factor correlated to mechanical failure. This study provides basic understanding and critical insights into the chemo-mechanical failure mechanism of SOCs with respect to operating conditions.

Chiral effects in classical spinning gas

We consider a statistical mechanics of rotating ideal gas consisting of classical non-relativistic spinning particles. The microscopic structure elements of the system are massive point particles with a nonzero proper angular momentum. The norm of proper angular momentum is determined by spin. The direction of proper angular momentum changes continuously. Applying the Gibbs canonical formalism for the rotating system, we construct the one-particle distribution function, generalising the usual Maxwell–Boltzmann distribution, and the partition function of the system. The model demonstrates a set of chiral effects caused by interaction of spin and macroscopic rotation, including the change of entropy, heat capacity, chemical potential and angular momentum.

Realization of Multifunctional Metamaterial Structure Based on the Combination of Vanadium Dioxide and Graphene.

Combining tunable properties and various functionalities into a single metamaterial structure has become a novel research hotspot and can be used to tackle great challenges. The multifunctional metamaterial structure that combines absorption, linear-to-circular (LTC) polarization conversion, filtering and switching functions into a single metamaterial device was designed and investigated in this study. The switching of different functions can be achieved based on the phase transition of vanadium dioxide (VO2) and change of graphene chemical potential. When VO2 is in a metal state, the multi-frequency absorption and LTC polarization conversion can be achieved with different chemical potentials. When VO2 is in the insulator state and the polarization angle of incident wave is 45°, the device can be used to select or isolate the incident waves with different polarization states in the frequency region of 1.2–1.8 THz. Furthermore, when the chemical potentials are 0.05 eV and 1.2 eV, the corresponding transmissions of the TE-polarized wave demonstrate the opposite results, realizing the switching functions in the frequency region of 0.88–1.34 THz. In the frequency region above 2 THz, the multi-frequency rejection filter can be achieved. The designed switchable multifunctional metamaterial device can be widely implemented in radar monitoring and communication systems.

Effects of polysaccharides' molecular structure on membrane fouling and the related mechanisms.

Fouling behaviors of polysaccharides vary with their structure, while the mechanisms underlying this phenomenon remain unexplored. This work was carried out to explore the thermodynamic fouling mechanisms of polysaccharides with different structure. Carrageenan and xanthan gum were selected as the model polysaccharides with structure of straight and branch chains, respectively. Batch filtration experiments showed that xanthan gum solution corresponded to a more rapid flux decline trend, and specific filtration resistance (SFR) of xanthan gum (2.32 × 1015 m-1 kg-1) was over 10 times than that of carrageenan (2.21 × 1014 m-1 kg-1). It was found that, xanthan gum possessed a more disordered structure and a rather higher viscosity (15.03 mPa·s V.S. 1.98 mPa·s for carrageenan). Calculation of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed higher adhesion energy of xanthan gum (-42.82 my m-2 V.S. -23.26 mJ m-2 for carrageenan). Scanning electron microscopy (SEM) analyses showed that xanthan gum gel layer had a more homogenous structure and rigid polymer backbone, indicating better mixing with water to form a gel. As verified by heating experiments, such a structure tended to contain more bound water. According to this information, Flory-Huggins lattice theory was introduced to build a bridge between polymeric structure and SFR. It was revealed that branch structure corresponded to higher chemical potential change during gel layer formation, and higher ability to carry bound water, resulting in higher filtration resistance during filtration process. This work revealed the fundamental thermodynamic mechanism of membrane fouling caused by polysaccharides with different structure, deepening understanding of membrane fouling.

Molecular interactions from the density functional theory for chemical reactivity: Interaction chemical potential, hardness, and reactivity principles.

In the first paper of this series, the authors derived an expression for the interaction energy between two reagents in terms of the chemical reactivity indicators that can be derived from density functional perturbation theory. While negative interaction energies can explain reactivity, reactivity is often more simply explained using the “|dμ| big is good” rule or the maximum hardness principle. Expressions for the change in chemical potential (μ) and hardness when two reagents interact are derived. A partial justification for the maximum hardness principle is that the terms that appear in the interaction energy expression often reappear in the expression for the interaction hardness, but with opposite sign.

The differential conductance tunnel spectroscopy in an analytical solvable two-terminal Majorana device

In this paper, we investigate the non-Markovian quantum transport dynamics of a two-terminal Majorana device that is made of an asymmetric topological superconducting chain coupled to two leads. This asymmetric superconducting chain is analytically solvable and can be realized by a hybrid system of semiconductor nanowire coupled to superconductors or by 1D transverse-field Ising chains. In such asymmetric superconducting chains, by the change of chemical potential, its ground state undergoes a topological quantum phase transition from the topological Majorana bound state to the trivial Andreev bound state while the ground state energy remains zero. We solve the exact transient transport current and the corresponding differential conductance. The results show that the presence or absence of the interference between the left and right Majorana zero modes plays an important role on the topological phase transition of conductance. It causes the edge-localized topologically trivial states to be insulated with zero conductance, while the nonlocally distributed topologically nontrivial states always have a quantized conductance 2e 2/h. This dramatic change associated with topological phase transition in the zero-mode differential conductance at zero bias is independent of the structure of leads and the coupling strength. We also examine the finite size effect of the superconducting chain and the coherence effect between zero mode and non-zero energy modes in the differential conductance of this two-terminal Majorana device.

Gibbsian interpretation of Langmuir, Freundlich and Temkin isotherms for adsorption in solution

ABSTRACT Adsorption is a physicochemical phenomenon important in both natural and engineering processes. In the research and practice of adsorption equilibrium, a long-standing challenge is how to reconcile the classical models proposed by Gibbs, Langmuir, Freundlich, and Temkin for interpreting experimentally obtained adsorption isotherms. Here, we show that the Langmuir, Freundlich, and Temkin isotherms can be derived from the Gibbs equation under different conditions for the change of surface energy (a.k.a. surface tension) by adsorption. When the change of surface energy is predominantly controlled by the change of chemical potential with negligible contribution from the change of internal energy and entropy, the Gibbs equation can be integrated to give the Langmuir isotherm. When changes of internal energy and entropy are no longer negligible, the integration of the Gibbs equation gives the Freundlich and Temkin equations, according to a change of surface energy either independent or linearly dependent on the adsorption capacity. These results indicate that the classical models share the common mechanism of phase equilibrium described by the Gibbsian thermodynamics, thereby providing novel insights for their application.

Active Fano resonance switch using dual-layer graphene in an embedded dielectric metasurface.

We propose an active optical Fano switch (OFS) based on an embedded dielectric metasurface (EDM) including dual-layer graphene (DLG). An EDM is a dielectric grating overlapped by two cladding layers, and it excites a Fano resonance. DLG is positioned inside the upper cladding layer to maximize light-graphene interaction. Thus, with a small change of the chemical potential (µc) of graphene, a resonance wavelength is tuned to switch the OFS on and off. First, a red-parity asymmetric Fano resonance is realized, and a sharp asymmetric lineshape is achieved by controlling the structural parameters of the EDM and the interaction between the Fano resonance and additional weak Fabry-Perot interference for efficient switching. The distance of a peak-to-dip wavelength (Δλp-d) and the change of chemical potential (Δµc) for switching is analyzed by varying the duty cycle (DC) and grating thickness (tg) of the EDM. Furthermore, switching contrast as a figure of merit (FoM) is analyzed. With DC of 0.5 and tg of 70 nm, the OFS requires Δλp-d of 7.3 nm and Δµc of 0.25 eV. The FoM of 0.97 is achieved. By adjusting the two parameters, the switching condition is tuned. In the case of a blue parity, the effect of the two parameters exhibits a similar trend to that of the red parity. The FoM, however, is lower due to the reversed parity.

Impact of ultrathin coating layer on lithium-ion intercalation into particles for lithium-ion batteries

Ultrathin film coatings on battery materials via atomic layer deposition (ALD) have been demonstrated as an efficient technology for battery performance enhancement. However, the fundamental understanding on lithium intercalation into active materials through the interface between the coating and active materials is unclear, which makes it difficult to optimize ALD coating strategies. Further, like most active materials, a coating layer can undergo volume change during the intercalation process, which can produce detrimental structural changes and mechanical failure of the layer. In this work, first-principles calculations are conducted to reveal the behavior of a coating layer on an active material particle by focusing on the intercalation energy variation, lithium-ion transport, electron chemical potential change, and structural changes of the coating layer. The analysis comprehensively explains an experimental observation that a CeO2 coating on LiMn2O4 particles exhibits better performance in capacity and cycling than an Al2O3 coating on the same particles. The fundamental knowledge imparted from this work provides an important understanding about the beneficial role of ALD coatings in lithium-ion battery performance and capacity retention.

Dissolution and remobilization of NAPL in surfactant-enhanced aquifer remediation from microscopic scale simulations

In this paper, the dissolution and mobilization of non-aqueous phase liquid (NAPL) blobs in the Surfactant-Enhanced Aquifer Remediation (SEAR) process were upscaled using dynamic pore network modeling (PNM) of three-dimensional and unstructured networks. We considered corner flow and micro-flow mechanisms including snap-off and piston-like movement for two-phase flow. Moreover, NAPL entrapment and remobilization were evaluated using force analysis to develop the capillary desaturation curve (CDC) and predict the onset of remobilization. The corner diffusion mechanism was also applied in the modeling of interphase mass transfer to represent NAPL dissolution as the dominant mass transfer process. In addition, the effect of pore-scale heterogeneity on mass transfer rate coefficient and recovered residual NAPL was considered in the simulations. Sodium dodecyl sulfate (SDS) and Triton X-100 were used as the surfactant for the SEAR process. The results indicate that although surfactants enhance NAPL recovery during two-phase flow, surfactant-enhanced remediation of residual NAPL through dissolution is highly dependent on surfactant type. When SDS ─as a surfactant with high critical micelle concentration (CMC) and low micelle partition coefficient (Km)─ was injected into a NAPL contaminated site, the mass transfer rate coefficient decreased (due to considerable changes in interface chemical potentials) which leads to a significant reduction in NAPL recovery after the end of two-phase flow. In contrast, Triton X-100 (with low CMC and high Km) improved NAPL recovery, by enhancing solubility at surfactant concentrations greater than CMC which overcompensates the interphase mass transfer reduction.

Selectivity in Yttrium Manganese Oxide Synthesis via Local Chemical Potentials in Hyperdimensional Phase Space.

In sharp contrast to molecular synthesis, materials synthesis is generally presumed to lack selectivity. The few known methods of designing selectivity in solid-state reactions have limited scope, such as topotactic reactions or strain stabilization. This contribution describes a general approach for searching large chemical spaces to identify selective reactions. This novel approach explains the ability of a nominally "innocent" Na2CO3 precursor to enable the metathesis synthesis of single-phase Y2Mn2O7: an outcome that was previously only accomplished at extreme pressures and which cannot be achieved with closely related precursors of Li2CO3 and K2CO3 under identical conditions. By calculating the required change in chemical potential across all possible reactant-product interfaces in an expanded chemical space including Y, Mn, O, alkali metals, and halogens, using thermodynamic parameters obtained from density functional theory calculations, we identify reactions that minimize the thermodynamic competition from intermediates. In this manner, only the Na-based intermediates minimize the distance in the hyperdimensional chemical potential space to Y2Mn2O7, thus providing selective access to a phase which was previously thought to be metastable. Experimental evidence validating this mechanism for pathway-dependent selectivity is provided by intermediates identified from in situ synchrotron-based crystallographic analysis. This approach of calculating chemical potential distances in hyperdimensional compositional spaces provides a general method for designing selective solid-state syntheses that will be useful for gaining access to metastable phases and for identifying reaction pathways that can reduce the synthesis temperature, and cost, of technological materials.

SrTiO3 based high temperature solid oxide solar cells: Photovoltages, photocurrents and mechanistic insight

High temperature solid oxide solar cells based on SrTiO3 (STO) are investigated. Schottky contacts between STO and different materials, including La1-xSrxCrO3, La0.8Sr0.2MnO3, La0.6Sr0.4CoO3 and metals like Au and Pt are illuminated by UV light with a wavelength of 365 nm at 350 °C in air and the resulting voltages and currents are measured. With certain material combinations, e.g. LaCrO3/STO or Au/STO heterojunctions, high photovoltages of more than 1.0 V are obtained. Current measurements reveal changes in the bulk STO due to stoichiometry polarization, leading to a self-enhancement effect of the photovoltaic cell. Mechanistic insight in the processes under UV light is gained by electrochemical impedance spectroscopy, especially regarding the space charge region at the heterojunction and bulk changes due to stoichiometry polarization. In addition to the electronic effects upon illumination, also photo-ionic effects of oxygen transport caused by chemical potential changes were observed.

Phase Coexistence and Structural Dynamics of Redox Metal Catalysts Revealed by Operando TEM.

Metal catalysts play an important role in industrial redox reactions. Although extensively studied, the state of these catalysts under operating conditions is largely unknown, and assignments of active sites remain speculative. Herein, an operando transmission electron microscopy study is presented, which interrelates the structural dynamics of redox metal catalysts to their activity. Using hydrogen oxidation on copper as an elementary redox reaction, it is revealed how the interaction between metal and the surrounding gas phase induces complex structural transformations and drives the system from a thermodynamic equilibrium toward a state controlled by the chemical dynamics. Direct imaging combined with the simultaneous detection of catalytic activity provides unparalleled structure-activity insights that identify distinct mechanisms for water formation and reveal the means by which the system self-adjusts to changes of the gas-phase chemical potential. Density functional theory calculations show that surface phase transitions are driven by chemical dynamics even when the system is far from a thermodynamic phase boundary. In a bottom-up approach, the dynamic behavior observed here for an elementary reaction is finally extended to more relevant redox reactions and other metal catalysts, which underlines the importance of chemical dynamics for the formation and constant re-generation of transient active sites during catalysis.

Topological classification of nodal-line semimetals in square-net materials

Fermi surface topology and Berry phase of square-net-layered materials with P4/nmm space group were classified based on the first-principles analysis of Berry phases in each materials. The variation of electron-hole (e-h) asymmetry, driven by the third-nearest-neighbor hoppings of pnictogen ${p}_{x,y}$ orbitals in square-net, is essential to yield various topological Fermi surfaces. The change of chemical potential too yields various topological Fermi surfaces. By determining e-h asymmetry and chemical potential of the reported square-net-layered materials, we construct the phase diagram of the Fermi surface topologies. In addition, we adopt interlayer interaction and investigate three-dimensional Fermi surface. We classify the three-dimensional Fermi surface topologies based on the phase diagram, and our classification reproduces the quantum oscillation and spectroscopy results for various square-net compounds.