Chemical Potential Conditions Research Articles

Propagation of rayleigh waves in transversely isotropic generalized thermoelastic diffusion

This paper is devoted to the study of propagation of Rayleigh waves in a homogeneous, transversely isotropic, thermoelastic diffusive half-space that is subjected to stress-free, thermally insulated/isothermal, and chemical potential boundary conditions in the context of the generalized theory of thermoelastic diffusion. The Lord and Shulman theory, where thermal and thermomechanical relaxation as well as diffusion relaxation are governed by two different time constants, is selected. Secular equations for surface wave propagation in the considered media are derived. The amplitudes of surface displacements, temperature change, and concentration are computed. The paths of the surface particles are determined. Transverse isotropy and diffusion effects on the phase velocity, group velocity, and attenuation coefficient are presented graphically.

Electronic properties of graphene nanoribbons embedded in boron nitride sheets

Using first principles calculations, we investigate the stabilities and electronic properties of graphene nanoribbons which are embedded in boron nitride (BN) sheets. We find that carbon atoms doped in BN sheets have stable hexagonal configurations and can form one-dimensional nanoribbons under suitable chemical potential conditions. All the armchair graphene nanoribbons embedded in BN sheets are semiconductors. While for the zigzag ones, the wide nanoribbons become half-metals.

Propagation of Rayleigh waves on free surface of transversely isotropic generalized thermoelastic diffusion

The present paper is devoted to the study of Rayleigh wave propagation in a homogeneous, transversely isotropic, thermoelastic diffusive half-space, subject to stress free, thermally insulated/isothermal, and chemical potential boundary conditions in the context of the generalized thermoelastic diffusion theory. The Green-Lindsay(GL) theory is used in the study. In this theory, thermodiffusion and thermodiffusion mechanical relaxations are governed by four different time constants. Secular equations for surface wave propagation in the considered media are derived. Anisotropy and diffusion effects on the phase velocity, attenuation coefficient are graphically presented in order to present the analytical results and make comparison. Some special cases of frequency equations are derived from the present investigation.

Rayleigh waves in transversely isotropic thermoelastic diffusive half-space

The present investigation is devoted to the study of the propagation of Rayleigh waves in a homogeneous, transversely isotropic, thermoelastic diffusive half-space subjected to stress-free, thermally insulated and (or) isothermal, and chemical potential boundary conditions, in the context of the theory of coupled thermoelastic diffusion. Secular equations for surface-wave propagation in the media being considered are derived. The surface-particle paths during the motion are found to be elliptical, but degenerate into straight lines in case where there is no phase difference between the horizontal and vertical components of the surface displacements. The phase velocity; attenuation coefficient; specific loss of energy; and the amplitudes of surface displacements, temperature change, and concentration are computed numerically and presented graphically to depict the anisotropy and diffusion effects. Some special cases of frequency equations are also deduced from the present investigation. PACS Nos.: 62.20.–x, 62.20.D–, 62.20.de, 62.20.dj, 62.20.dq, 62.30.+d, 66.10.C–, 66.10.cd, 66.10.cg, 66.30.–h

Unified properties of a weakly interacting Fermi gas in a weak magnetic field

When the orbital motion and the spin motion of particles were considered simultaneously, the thermodynamic potential function of a weakly interacting Fermi gas in a weak magnetic field was derived using the thermodynamics method. Based on the derived expression, the analytical expressions of energy, heat capacity, chemical potential, susceptibility and stability conditions of the system were given, and the effects of the interparticle interactions as well as the magnetic field on the properties of the system were analyzed. It was shown that the magnetic field always causes energy and stability to decrease, while the chemical potential of the system to increase. The repulsive (attractive) interactions always increase (decrease) energy and stability, but decrease (increase) the chemical potential and paramagnetism. The repulsive (attractive) interactions decrease (increase) heat capacity of the system at high temperatures but increase (decrease) it at low temperatures.

Effect of rotation on Rayleigh waves in an isotropic generalized thermoelastic diffusive half-space

The present investigation is a study of the effect of rotation on the characteristics of Rayleigh waves propagation in a homogeneous, isotropic, thermoelastic diffusive half-space in the framework of different theories of thermoelastic diffusion, including the Coriolis and Centrifugal forces. The medium is subjected to stress-free, thermally insulated/isothermal and chemical potential boundary conditions and is rotating about an axis perpendicular to its plane. Secular equations of surface wave propagation in the considered media are derived. The phase velocities and attenuation coefficients of surface wave propagation have been computed by using the irreducible case of Cardano's method, with the help of DeMoivre's theorem known from the secular equations. The amplitudes of surface displacements, temperature change, concentration and the specific loss of energy are computed numerically. Rotation effect on the phase velocity, attenuation coefficient, amplitudes of surface wave propagation and specific loss of energy are presented graphically in order to illustrate and compare the analytically obtained results. Some special cases of frequency equation are also deduced from the present investigation.

Electrochemical impedance spectroscopy of mixed conductors under a chemical potential gradient: a case study of Pt|SDC|BSCF

The AC impedance response of mixed ionic and electronic conductors (MIECs) exposed to a chemical potential gradient is derived from first principles. In such a system, the chemical potential gradient induces a gradient in the carrier concentration. For the particular system considered, 15% samarium doped ceria (SDC15) with Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-delta) (BSCF) and Pt electrodes, the oxygen vacancy concentration is a constant under the experimental conditions and it is the electron concentration that varies. The resulting equations are mapped to an equivalent circuit that bears some resemblance to recently discussed equivalent circuit models for MIECs under uniform chemical potential conditions, but differs in that active elements, specifically, voltage-controlled current sources, occur. It is shown that from a combination of open circuit voltage measurements and AC impedance spectroscopy, it is possible to use this model to determine the oxygen partial pressure drop that occurs between the gas phase in the electrode chambers and the electrode|electrolyte interface, as well as the interfacial polarization resistance. As discussed in detail, this resistance corresponds to the slope of the interfacial polarization curve. Measurements were carried out at temperatures between 550 and 650 degrees C and oxygen partial pressure at the Pt anode ranging from 10(-29) to 10(-24) atm (attained using H(2)/H(2)O/Ar mixtures), while the cathode was exposed to either synthetic air or neat oxygen. The oxygen partial pressure drop at the anode was typically about five orders of magnitude, whereas that at the cathode was about 0.1 atm for measurements using air. Accordingly, the poor activity of the anode is responsible for a loss in open circuit voltage of about 0.22 V, whereas the cathode is responsible for only about 0.01 V, reflecting the high activity of BSCF for oxygen electro-reduction. The interfacial polarization resistance at the anode displayed dependences on oxygen partial pressure and on temperature that mimic those of the electronic resistivity of SDC15. This behavior is consistent with hydrogen electro-oxidation occurring directly on the ceria surface and electron migration being the rate-limiting step. However, the equivalent resistance implied by the oxygen partial pressure drop across the anode displayed slightly different behavior, possibly indicative of a more complex reaction pathway.

Native point defects in yttria and relevance to its use as a high-dielectric-constant gate oxide material: First-principles study

Yttria $({\mathrm{Y}}_{2}{\mathrm{O}}_{3})$ has become a promising gate oxide material to replace silicon dioxide in metal-oxide-semiconductor devices. Using a first-principles approach the electronic structure, defect structure, and formation energy of native point defects in ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ are studied. Vacancies, interstitials, and antisites in their relevant charge states are considered. We find that within the band gap of ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ oxygen vacancies, oxygen interstitials, yttrium vacancies, and yttrium interstitials can be stable depending on the Fermi level and external chemical potentials. When the Fermi level is constrained to be within the band gap of silicon, oxygen vacancies are the dominant defect type under low oxygen chemical potential condition. A higher oxygen chemical potential leads to oxygen interstitials and ultimately yttrium vacancies.

Theoretical study of cation-related point defects inZnGeP2

First-principles calculations are presented for the ${V}_{\mathrm{Zn}}$ and ${V}_{\mathrm{Ge}}$ cation vacancies and the ${\mathrm{Zn}}_{\mathrm{Ge}}$ and ${\mathrm{Ge}}_{\mathrm{Zn}}$ antisites in ${\mathrm{ZnGeP}}_{2}$, using full-potential linearized muffin-tin orbital method supercell calculations in the local-density approximation to density-functional theory. Under Zn-poor conditions, the lowest Gibbs energy defects are found to be the ${\mathrm{Ge}}_{\mathrm{Zn}}$ and ${V}_{\mathrm{Zn}}$ defects, leading to a compensated $p$-type material in agreement with experimental evidence. The occupation energy levels of the defects are determined and compared with available experimental information. As expected, the ${\mathrm{Ge}}_{\mathrm{Zn}}$ is found to be a donor while the other three are acceptors. Good agreement is obtained with optical quenching and activation of electron paramagnetic resonance signal studies if a direct transfer of electrons from ${\mathrm{V}}_{\mathrm{Zn}}^{2\ensuremath{-}}$ to ${\mathrm{Ge}}_{\mathrm{Zn}}^{2+}$ is assumed rather than a process via the conduction band. This suggests a close association of the dominant acceptors and donors. This is further confirmed by showing that the formation of complexes consisting of two ${V}_{\mathrm{Zn}}^{\ensuremath{-}}$ with a single ${\mathrm{Ge}}_{\mathrm{Zn}}^{2+}$ antisite are favorable in energy. The ${V}_{\mathrm{Ge}}$ on the other hand is found to have high energy of formation under any chemical potential conditions and is found to be unstable toward formation of a ${V}_{\mathrm{Zn}}$ and ${\mathrm{Zn}}_{\mathrm{Ge}}$ pair. Structural relaxation of all defects is performed but no symmetry breaking distortions are found. As a result, the defect wave functions of the unpaired electron in the ${V}_{\mathrm{Zn}}^{\ensuremath{-}}$ is found to be spread equally over the four neighboring P atoms, in disagreement with electron nuclear double resonance data which indicate primary localization on a pair of P atoms. Several possible origins for this discrepancy are discussed.

Effectiveness of BaZrO3 buffer layer in SmBa2Cu3Oy epitaxial growth on MgO substrate: A first-principles study

The atomic structure and energies of SmBa2Cu3O6(Sm123)/BaZrO3(BZO) and Sm123/MgO interfaces have been investigated using first-principles calculations. The interfacial energies were evaluated for various atomic configurations under relevant conditions of the chemical potentials. For the Sm123/BZO, an interface composed of a BaO layer is found to be energetically favorable, irrespective of the chemical potentials. This is much lower in energy than the Sm123/MgO interfaces where the preferable configuration even varies with the chemical potential conditions. The stability of the Sm123/BZO interface is attributed to the local atomic arrangement and chemical composition common to Sm123 and BZO, and such an atomic structure is confirmed by high-resolution transmission electron microscopy. The results suggest that the insertion of a BZO buffer layer facilitates the epitaxial growth of Sm123 films on MgO substrates because of the energetically favorable film/buffer layer interface.

Development of an intelligent design tool for non-stoichiometric compound devices: an example

In this paper, we discuss the idea of intelligent design of thin film CIGS solar cell, and we focus on the methodology of material design. We first introduce the calculation of the neutral defect concentrations of non-stoichiometric CuInSe 2, CuGaSe 2 and ZnO under specific atomic chemical potential conditions, and predict the formation of the order defect compound using the concept of minimization of total free energy, which includes the configurational entropy. This calculation is the main procedure in the material design and the key to the device design and process design. We then calculate the carrier concentrations using multi-level defect statistics and mobilities of these materials of different constitutions. The functions of the intelligent design tool are demonstrated.

Preliminary steps toward industrialization of Cu-III-VI 2 thin-film solar cells: development of an intelligent design tool for non-stoichiometric photovoltaic materials

In this paper, we introduce the idea of intelligent design of thin film CIGS solar cell, and we focus on the methodology of material design. We first describe in detail the calculation of the neutral defect concentrations of non-stoichiometric CuInSe 2, CuGaSe 2 and ZnO under specific atomic chemical potential conditions ( μ x=0, x=Cu,In/Ga,Zn), and this calculation is the main procedure in the intelligent design and the key to the device design and process design. We then calculate the carrier concentrations and the electrical properties of these materials of different atomic constitutions. The main functions of this CAD tool are demonstrated.

Currents, chemical potential and boundary conditions in lattice QCD

A connection between the operator fermionic currents Jˆ and corresponding ‘Grassmannian’ currents J in the functional integral formalism is studied. The QCD action with non-zero chemical potential μ is derived. A connection between the fermionic Fock space and boundary conditions along the forth direction is discussed.

Electronic Structure of Native Point Defects in Zngep2

ABSTRACTFirst-principles calculations are presented for various native point defects in ZnGeP2 us-ing a full-potential linearized muffin-tin orbital method in the local density approximation to density functional theory. Under Zn-poor conditions, the lowest Gibbs energy defects are found to be the Gezn antisite and Vzn. The Vae is found to have high energy of formation under any chemical potential conditions and is unstable towards formation of a Vzn and ZnGe pair. It is shown that the V−Zn cannot account for the ALI EPR spectrum commonly associated with this vacancy and an alternative model consisting of a Vzn – GeZn – Vzn is tentatively proposed.

Experimental setup for rapid crystallization using favoured chemical potential and hydrodynamic conditions

The rapid crystallization of KH2PO4 (KDP) from solution is demonstrated at a rate up to ≈ 7.5 mm/day along [100] and 22 mm/day along [001] in a crystallizer of 5 l capacity, using accelerated crucible rotation technique (ACRT) and simulated platform geometry for controlling the hydrodynamic conditions. On an experimental basis we have grown the crystals up to 40 · 43 · 66 mm3 size in about 3 days. Comparative analysis of the main structural and optical properties of crystals grown by conventional and rapid crystallization technique, is discussed.

Surface structures of GaAs passivated by chalcogen atoms

When a GaAs(001) surface with Se adsorbates was flash-heated under a low chemical potential condition, a 2 × 3 RHEED pattern, previously reported as an intermediate structure, remained even after the sample was cooled. The atomic structure observed by STM is in good agreement with the dimer model proposed to explain the chalcogen-passivated GaAs(001) surfaces. Se dimers were found to be buckled, but the 2 × -periodicity was maintained in the [ 1 10] direction, unlike the previously observed 4 × -structure forming the dimer row pairs. Some other structures, the axes of which are in directions different from [110], were also observed on the Se/GaAs(001) surface. The S-passivation effect was studied by measuring current-voltage properties for the S/GaAs(001) surface.

The distribution of partial melt in a granitic system: The application of liquid phase sintering theory

Two series of experiments, four crystallization and four partial melting, were performed at 1000°C and 10 kilobars in the quartz-alkali feldspar-granitic melt system in order to determine the equilibrium melt distribution and textural adjustment processes. The melt distribution in both types of experiments was characterized by melt residing at grain edge intersections and in a few large pools scattered throughout the sample. Wetting angle measurements from both sets of experiments gave values of 44, 49, and 59 degrees for the feldspar/feldspar, feldspar/quartz, and quartz/quartz wetting angles, respectively. Interparticle welding, a process consistent with the measured wetting angles, resulted in the formation of a skeleton of solid grains with very few unattached grains in any sample. Analysis of wetting angle distributions indicates that the longest duration experiments closely approached textural equilibrium and that the distributions of observed wetting angles from both sets of experiments were nearly identical. Measurement of quartz grain sizes from the 2, 4, 7, and 14-day crystallization experiments revealed: 1. 1) a probable cube root of time dependence for the quartz growth rate; 2. 2) a decrease in the number of quartz grains per square micron with increasing time; 3. 3) a normalized distribution of grain sizes that appeared stationary in time. These results were shown to be consistent with the processes observed during the liquid phase sintering of ceramic materials and suggest that identical processes may occur in natural partially-molten systems. Finally, it was shown that interfacial energy considerations lead to a model of interparticle welding (clustering) in which it is discovered that there is an equilibrium melt fraction stable along grain edges of a partially-molten crystalline aggregate. This melt fraction may be greater, equal to, or less than the equilibrium fraction of melt dictated by the pressure, temperature, and chemical potential conditions. If the interfacial energy-derived equilibrium melt fraciton is less than the P-T-u equilibrium derived melt fraction, then segregation of the melt in excess of the interfacial energy-derived equilibrium melt fraction may be expected to result in the formation of melt pools.