Baric Dependences Research Articles

Исследование массотранспортных потерь структурно-модифицированных электродов воздушно-водородных топливных элементов методом вольт-амперной характеристики

The article discusses platinum-carbon electrodes with mixed conductivity as part of membrane-electrode assemblies of fuel cells containing structural-modifying additives with structural elements of various types: carbon nanotubes with elongated structural elements and graphene-like materials with almost two-dimensional planes. Based on the data on the limiting current density obtained in potentiodynamic and potentiostatic modes, the mass transport losses of molecular oxygen transfer in these electrodes are investigated. Using different measurement conditions, the baric dependences of the current density were constructed, the limiting factors and mechanisms of oxygen transfer in the studied structures and the role of the introduced modifiers were clarified.

Study of properties of fcc-Au-Fe alloys in macro- and nano-crystalline states under various P-T-conditions

The parameters of the paired interatomic potential of Mie–Lennard-Jones for a disordered fcc-Au-Fe substitution alloy were determined by the “average atom” analytical method. Based on these parameters, the concentration dependencies of lattice properties for the macro-crystal of this alloy are calculated. Calculations of 20 properties of macrocrystals fcc-Au, fcc-Fe and fcc-Au0.5Fe0.5 have shown good agreement with experimental data., The state equation P(v, T; N) and baric dependences of both lattice and surface properties of the fcc-Au0.5Fe0.5 alloy are calculated, using the RP-model of the nanocrystal. Calculations were performed at temperatures T = 100, 300 and 500 K for both a macrocrystal (N = ∞) and a cubic nanocrystal with N = 306 atoms. It is shown that with an isothermal-isobaric (P = 0) decrease in the size of a nanocrystal, its Debye temperature, elastic modulus, and specific surface energy decrease, while its specific volume, thermal expansion coefficient, specific heat capacity, and Poisson's ratio increase. At low temperatures in a certain pressure region, the specific surface energy increases with an isothermal-isobaric decrease in the number of atoms in the nanocrystal. As the temperature increases, this pressure region disappears.

Study of Properties of Gold–Iron Alloy in the Macro- and Nanocrystalline States under Different P–T Conditions

Parameters of the Mie–Lennard-Jones pair interatomic potential for a disordered substitutional fcc-Au–Fe alloy are determined. The concentration dependences of the lattice properties of a macrocrystal of this alloy are calculated based on these parameters. The results of calculating twenty properties of fcc-Au, fcc-Fe, and fcc-Au0.5Fe0.5 macrocrystals showed good consistency with the experimental data. The equation of state P(ν, T; N) and baric dependences of both the lattice and surface properties of the fcc-Au0.5Fe0.5 alloy are calculated using the RP nanocrystal model. The calculations have been performed at temperatures T = 100, 300, and 500 K for both the macrocrystal (N = ∞) and the cubic nanocrystal consisting of N = 306 atoms. It is shown that, during isothermal–isobaric (P = 0) decrease in the nanocrystal size, its Debye temperature, elastic modulus, and specific surface energy decrease, while its specific volume, coefficient of thermal expansion, specific heat, and Poisson ratio increase. At low temperatures, the specific surface energy increases in a certain range of pressures with an isothermal–isobaric decrease in the number of atoms in the nanocrystal. This range of pressures disappears with an increase in temperature.

Change of baric dependencies of thermophysical properties under variation of the size and shape of niobium nanocrystal

The changes caused by decreasing size of the niobium nanocrystal in both the equation of state and the thermophysical properties are calculated using unified formalism based on the Mie-Lenard-Jones pair interatomic interaction potential and the RP-model of the nanocrystal. The pressure dependencies of the thermophysical properties were calculated along the 300 K and 3000 K isotherms. The change in the melting temperature and its pressure derivative was studied with decreasing size and deformation of the shape of the niobium nanocrystal.

Изучение свойств сплава золото-железо в макро- и нанокристаллических состояниях в различных P-T-условиях

For a disordered fcc-Au-Fe substitution alloy, the parameters of the Mie–Lennard-Jones pairwise interatomic potential are determined. Based on these parameters, the concentration dependencies of lattice properties for the macrocrystal of this alloy are calculated. Calculations of 20 properties of macrocrystals fcc-Au, fcc-Fe and fcc-Au0.5Fe0.5 are showed good agreement with experimental data. Using the RP-model of the nanocrystal, the state equation P(v, T; N) and baric dependences of both lattice and surface properties of the fcc-Au0.5Fe0.5 alloy are calculated. Calculations were performed at temperatures T = 100, 300 and 500 K for both a macrocrystal (N = Macro) and a cubic nanocrystal with N = 306 atoms. It is shown that with an isothermal-isobaric (P = 0) decrease in the size of a nanocrystal, its the Debye temperature, elastic modulus, and specific surface energy decrease, while its the specific volume, thermal expansion coefficient, specific heat capacity, and Poisson's ratio increase. At low temperatures in a certain pressure region, the specific surface energy increases at an isothermal-isobaric decrease in the number of atoms in the nanocrystal. As the temperature increases, this pressure region disappears.

High pressure effect on the crystal structure of the BaTiO3

Crystal structure of [Formula: see text] compound was studied using Atomistix Tool Kit software program at high pressure. It is defined that in this combination, tetragonal–cubic phase transition occurs under high pressure [Formula: see text] GPa. The character of this phase transition is explained in respect of baric dependence of spontaneous strain. Birch–Murnaghan equation is solved, compression ratio is determined. Results gained by theoretical calculations are compared with experimental values.

Baric and dimensional changes of niobium properties

We have calculated the baric dependencies of thermophysical properties and melting temperature as well as the thermal equation of state for niobium based on the pair interatomic Mi-Lenard-Jones potential and the crystal Einstein model for niobium (Nb). Baric dependencies computations made along two isotherms 300 K and 3000 K are in good agreement with the experimental data for niobium. We have obtained the charts of pressure dependencies for the following properties: Debye temperature, the first, second and third Gruneisen parameters, isothermal compression modulus, isochoric and isobaric heat capacity, volumetric coefficient of thermal expansion and the melting temperature. The article investigates size dependencies of both specified properties and the melting temperature of niobium using an RP-model of nanocrystal.

On the Characteristic Features of the Impurity Energy Spectrum in Arsenides

The impurity energy spectrum of undoped n-type GaAs, InAs, CdSnAs2, CdGeAs2, and CdTe, ZnO bulk crystals is studied based on a quantitative analysis of the baric and temperature dependences of the kinetic coefficients. It is found that the deep-level donor center corresponds to the intrinsic vacancy defect in the anion sublattice in the above-listed semiconductors. The conclusion on the nature of the donor center, i.e., the vacancy in the anion sublattice, is based on the fact that, in contrast to shallow impurity centers which trace the intrinsic band under uniform pressure, to which they are genetically related, the energy of deep impurity centers with respect to absolute vacuum remains constant under isotropic compression of the lattice. Therefore, it seems favorable to study the evolution of the carrier energy spectrum in semiconductors under uniform-pressure conditions. The energy-level positions with respect to the conduction-band edge and pressure coefficients of the energy gaps between them and the corresponding conduction-band bottom are determined. The shift of the energy level of the deep donor center to the conduction-band depth with decreasing band gap is observed.

Change in baric properties with decreasing size of germanium nanocrystal

The equation of state P(v/vo) and the baric dependences of both the lattice and the surface properties for germanium macro- and nanocrystals were calculated using the Mie-Lennard-Jones pairwise interatomic potential and the RP-model of a nanocrystal. It is shown that at a certain value of the relative volume (v/vo)0, the isothermal dependences P(v/vo) for the macro- intersect with those for the nanocrystal. At the intersection point (at (v/vo)0), the surface pressure becomes zero. The value (v/vo)0 decreases both with an isomorphic-isomeric rise in temperature, and with an isomorphically-isothermal decrease in the number of atoms in a nanocrystal, or with an isomeric-isothermal deviation of the shape of the nanocrystal from the energy-optimal shape (a cube for the RP-model). Based on the equation of state obtained, the change in 23 properties of Ge was studied both at an isochoric (v/vo = 1) and at an isobaric (P = 0) decrease in the number of atoms in a nanocrystal at temperatures of 100, 300, and 1000 K.

Pressure-Induced Changes in Parameters of the Indicatrix of Lithium Sodium Sulfate Crystals

Spectral, temperature, and baric dependences of birefringence Δni of LiNaSO4 (LSS) crystals have been studied. It is established that dispersion Δn(λ) is anomalous. It is shown that uniaxial compression leads to changes in Δnі with different magnitudes and signs. The dispersion effect of changes in Δnі decreases under stress $$\sigma \, \bot \, z$$ and increases in the opposite case (σ || z). Pressure-induced changes in the refractive index are estimated; it is established that the refractive indices of an LSS crystal increase under uniaxial compression, which may be related to compression of the crystal and change in its interatomic bond nature.

Изменение термодинамических свойств при уменьшении размера нанокристалла германия в различных Р-Г-условиях

The equation of state P ( v / v o ) and the baric dependences of both the lattice and the surface properties for macro- and nano- crystals germanium were calculated by means of the method with using the Mie-Lennard-Jones pairwise interatomic potential and by of the RP-model of a nanocrystal. It is shown that at a certain value of the relative volume ( v / v o ) 0 , the isothermal dependences P ( v / v o ) for the macro- and nano-crystal intersect. At the intersection point (at ( v / v o ) 0 ), the surface pressure becomes zero. The value ( v / v o ) 0 decreases both with an isomorphic-isomeric rise in temperature, and with an isomorphically-isothermal decrease in the number of atoms in a nanocrystal, or with an isomeric-isothermal deviation of the shape of the nanocrystal from the energy-optimal shape (for the RP-model it is a cube). Based on the obtained equation of state, the change in 23 properties of germanium was studied both at an isochoric ( v / v o = 1) and at an isobaric ( P = 0) decrease in the number of atoms in a nanocrystal at temperatures of 100, 300, and 1000 K. It is shown that at an isobaric ( P = 0) decrease in size, the specific volume of the germanium nanocrystal increases the more, the higher the temperature of the nanocrystal.

Equation of state and properties of Nb at high temperature and pressure

Baric dependencies of the thermalphysic properties and melting temperature, as well as the thermal equation of state for niobium were obtained based on the pair interatomic Mie-Lenard-Jones potential and the crystal Einstein model. Calculations of niobium thermalphysic properties pressure dependencies made along two isotherms 300 K and 3000K are in good agreement with the experimental data. The charts of the pressure dependencies for the following properties were obtained: the Debye temperature, the first, the second and the third Grüneisen parameters, isothermal bulk modulus, isochoric and isobaric heat capacity, volumetric coefficient of thermal expansion and the melting temperature.

Variation of the 13C Diamond Properties under Isothermal Compression

The parameters of atomic interaction pair potential for 13C diamond have been determined from experimental data on the ratio of Raman frequencies for isotopically different diamonds. Based on these parameters, an equation of state and baric dependences of 13C diamond lattice properties at 300 K have been calculated. Specifically, the Debye temperature; the first, second, and third Gruneisen parameters; elastic modulus; thermal expansion coefficient; heat capacity; surface energy; and pressure derivatives of these parameters along a 300 K isotherm have been determined. The results have been compared with available data for diamond having a natural isotopic composition, i.e., for 12.01C.

Changes of the Thermodynamic Properties at Isochoric and Isobaric Decrease of the Silicon Nanocrystal Size

Equation of state P(ν/νo) and the baric dependences of the lattice and surface properties of silicon macro- and nanocrystals have been calculated using the method of calculation of crystal properties from the pair Mie–Lennard-Jones interatomic potential and the RP-model of nanocrystal. The isothermal dependences of P(ν/νo) for the macro- and the nanocrystal are shown to be intersected at a certain value of relative volume (ν/νo)0. The surface pressure becomes zero at the intersection point (at (ν/νo)0). The value of (ν/νo)0 decreases upon isomorphic–isomeric increase in temperature and also at isomorphic–isothermic decrease in the number of atoms N in the nanocrystal, or at isomeric–isothermic deviation of the nanocrystal shape from the most energetically optimal shape (in the RP-model, this shape is a cube). The obtained equation of state is used to study the changes of the silicon properties at isochoric (ν/νo = 1) and also isobaric (P = 0) decrease in N at temperatures 300 and 1000 K.

Lattice Dynamics and Baric Behavior of Phonons in the Hg2Br2 Model Ferroelastics

Raman spectra of Hg2Br2 model improper ferroelastic crystals have been investigated in a wide range of high hydrostatic pressures. Baric dependences of the phonon frequencies have been obtained; of greatest interest are the observed soft mode originating from the slowest TA1 acoustic branch at the Brillouin zone boundary (X point) of the tetragonal phase and the anomalous behavior of this mode. In the ferroelastic phase spectra, the ignition of the second acoustic TA2 from the same point has also been detected and its baric behavior has been studied. Under sufficiently high pressures, splitting of doubly degenerate phonons with the Eg symmetry has been observed and explained. The parameters of the Gruneisen constants have been determined from the baric dependences of the phonon frequencies and discussed.

Об особенностях примесного энергетического спектра арсенидов

The impurity energy spectrum of non-doped bulk crystals of n-type GaAs, InAs, CdSnAs2, CdGeAs2 and CdTe, ZnO is investigated basing on the findings from the quantitative analysis of baric and temperature dependences of kinetic coefficients. It`s found that in the above-listed semiconductors the deep level donor center corresponds to the intrinsic defect of vacancy in the anion sublattice. The energy level positions relative to conduction band edge and the pressure coefficients of energy gaps between them and corresponded conduction band bottom are determined. The shift of deep donor center energy levels towards the depth of the conduction band is observed with a decrease in the forbidden band width in above-listed semiconductors.

Динамика решеток и барическое поведение фононов в модельных сегнетоэластиках Hg-=SUB=-2-=/SUB=-Br-=SUB=-2-=/SUB=-

AbstractRaman spectra of Hg_2Br_2 model improper ferroelastic crystals have been investigated in a wide range of high hydrostatic pressures. Baric dependences of the phonon frequencies have been obtained; of greatest interest are the observed soft mode originating from the slowest TA _1 acoustic branch at the Brillouin zone boundary ( X point) of the tetragonal phase and the anomalous behavior of this mode. In the ferroelastic phase spectra, the ignition of the second acoustic TA _2 from the same point has also been detected and its baric behavior has been studied. Under sufficiently high pressures, splitting of doubly degenerate phonons with the E _ g symmetry has been observed and explained. The parameters of the Grüneisen constants have been determined from the baric dependences of the phonon frequencies and discussed.

Изменение термодинамических свойств при изохорическом и изобарическом уменьшении размера нанокристалла кремния

AbstractEquation of state P (ν/ν_o) and the baric dependences of the lattice and surface properties of silicon macro- and nanocrystals have been calculated using the method of calculation of crystal properties from the pair Mie–Lennard-Jones interatomic potential and the RP-model of nanocrystal. The isothermal dependences of P (ν/ν_o) for the macro- and the nanocrystal are shown to be intersected at a certain value of relative volume (ν/ν_o)_0. The surface pressure becomes zero at the intersection point (at (ν/ν_o)_0). The value of (ν/ν_o)_0 decreases upon isomorphic–isomeric increase in temperature and also at isomorphic–isothermic decrease in the number of atoms N in the nanocrystal, or at isomeric–isothermic deviation of the nanocrystal shape from the most energetically optimal shape (in the RP-model, this shape is a cube). The obtained equation of state is used to study the changes of the silicon properties at isochoric (ν/ν_o = 1) and also isobaric ( P = 0) decrease in N at temperatures 300 and 1000 K.

Изменение свойств алмаза из -=SUP=-13-=/SUP=-C при изотермическом сжатии

AbstractThe parameters of atomic interaction pair potential for ^13C diamond have been determined from experimental data on the ratio of Raman frequencies for isotopically different diamonds. Based on these parameters, an equation of state and baric dependences of ^13C diamond lattice properties at 300 K have been calculated. Specifically, the Debye temperature; the first, second, and third Grüneisen parameters; elastic modulus; thermal expansion coefficient; heat capacity; surface energy; and pressure derivatives of these parameters along a 300 K isotherm have been determined. The results have been compared with available data for diamond having a natural isotopic composition, i.e., for ^12.01C.

The Changes in the Thermodynamic Properties of a Germanium Nanocrystal with a Decrease in Its Size under Various P–T-Conditions

The equation of state P(v/vo) and the baric dependences of both the lattice and surface properties of germanium macro- and nanocrystals have been determined on the basis of the Mie–Lennard–Jones pairwise interatomic potential and the RP-model of a nanocrystal. It has been shown that the isothermal dependences P(v/vo) of macro- and nanocrystals intersect each other at a certain value of the relative volume (v/vo)0. The surface pressure becomes zero at the intersection point (at (v/vo)0). The relative volume (v/vo)0 decreases with both an isomorphic–isomeric increase in the temperature and an isomorphic–isothermic decrease in the number of atoms in a nanocrystal or upon the isomeric–isothermic deviation of a nanocrystal from its energetically optimal shape (a cube for the RP-model). Based on the derived equation of state, the changes in 23 properties of germanium with both an isochoric (v/vo = 1) and isobaric (P = 0) decrease in the number of atoms in a nanocrystal at temperatures of 100, 300, and 1000 K have been studied. It has been shown that the higher the temperature of a nanocrystal is, the greater the increase is in the specific volume of a germanium nanocrystal under an isobaric (P = 0) decrease in its size.