Electron Phonon Interaction Coefficient Research Articles

Evolution of the Continuous-Atomistic Method for the Simulation of Processes of the Interaction between Heavy Ions and Metals

The evolution of the continuous-atomistic approach to the simulation of processes of the interaction between high-energy heavy ions and metals is presented in this paper. The continuous-atomistic model is described by two different classes of equations, namely, thermal-conductivity equations with a source in the thermal-spike model and equations of motion of material points irradiated with a beam in a model of molecular dynamics. A software package is developed for simulation within the framework of the continuous-atomistic model. The results of simulation of the processes of metal-target irradiation with high-energy heavy ions depending on the parameters of the source function and the electron–phonon interaction coefficient are obtained.

Scroll-like Alloyed CdSxSe1–x Nanoplatelets: Facile Synthesis and Detailed Analysis of Tunable Optical Properties

Scroll-like colloidal quasi-two-dimensional CdSxSe1–x nanoplatelets (NPLs) with a thickness of five monolayers and average lateral dimensions of 100 nm over the whole composition range (0 ≤ x ≤ 1) were synthesized by using a mixture of chalcogenide precursors. According to X-ray diffraction and X-ray energy dispersive spectroscopy mapping in a scanning transmission electron microscope, as-synthesized NPLs are solid solutions with a uniform elemental distribution in each individual nanoplatelet. A change in composition leads to the continuous shift and gradual broadening of exciton absorption and photoluminescence (PL) lines in the visible blue and near-ultraviolet light range. Detailed analysis of optical properties, including temperature-dependent PL spectroscopy, revealed the nonmonotonic behavior of several optical parameters (average phonon temperature, electron–phonon interaction coefficient, and Stokes shift) starting from a sulfur content of ∼40% in alloyed NPLs. This behavior may be attributed to ...

Grain size effects on the transport properties of Li3V2(PO4)3 glass–ceramic nanocomposites for lithium cathode batteries

The effect of grain size on the structural and transport properties of glass–ceramic nanocomposites consisting of Li3V2(PO4)3 crystals were investigated by differential scanning calorimeter, X-ray diffraction (XRD), transmission electron micrograph (TEM), density (d) and dc conductivity. XRD patterns exhibit the formation of Li3V2(PO4)3 with monoclinic structure. It was shown by XRD and TEM studies that by appropriate heat-treatment glasses can be turned into glass–ceramic nanocomposites consisting of crystallites smaller than 56 nm embedded in the glassy matrix. Density was found to increase with increasing grain size while the molar volume decreases. The dc conductivity measured in high temperature range increased with decreasing of the grain size while the activation energy decreased. The calculated dc conductivity at 400 K for the present glass was 5.77 × 10−7 S/cm, while in its glass–ceramic nanocomposites was in the range of 1.712 × 10−5–2.10 × 10−6 S/cm. On the other hand, the calculated activation energy for the present glass was 0.542 eV, while in its glass–ceramic nanocomposites was in the range of 0.165–0.468 eV. The increase in electrical conductivity in the glass–ceramic nanocomposite annealed at 450 °C for 4 h compared to that annealed at 450 °C for 2, 8, 24 h can be attributed to the decrease in grain boundary scattering due to the reduction in grain size. The conduction was confirmed to obey non-adiabatic small polaron hopping. The electron–phonon interaction coefficient (γ p) was calculated and found to be in the range of 5.09–16.64.

Kapitza resistance between electron and phonon gases in the 1D case

This study addresses the exact behavior of electrons and phonons in semi-infinite 1D systems with due allowance for the local interaction between them. The spectral functions of electrons and phonons in such a system have been derived and analyzed in an analytical form. The paper considers, in particular, the problems involved in the hardening and softening of phonon modes and renormalization of the electron–phonon interaction constant. The results obtained have been employed in calculation of the thermal resistance constant at the boundary separating the electron from the phonon systems and in an analysis of its dependence on the renormalized electron–phonon interaction constant. All the results were obtained in the adiabatic limit for several cases of special significance, such as a half-filled and an empty conduction band at temperatures both higher and lower than the characteristic phonon frequencies. Significantly, the problem was treated exactly for an arbitrary electron–phonon interaction constant, in both the weak and the strong limits. It has been demonstrated that thermal resistance decreases with increasing electron–phonon interaction coefficient and/or temperature; at large values of these parameters, thermal resistance at the boundary no longer depends on these quantities.

Dynamical stability and phase transition of ZrC under pressure

A comprehensive first principles study of structural, elastic, electronic, and phonon properties of zirconium carbide (ZrC) is reported within the density functional theory scheme. The aim is to primarily focus on the vibrational properties of this transition metal carbide to understand the mechanism of phase transition. The ground state properties such as lattice constant, elastic constants, bulk modulus, shear modulus, electronic band structure, and phonon dispersion curves (PDC) of ZrC in rock-salt (RS) and high-pressure CsCl structures are determined. The pressure-dependent PDCs are also reported in NaCl phase. The phonon modes become softer and finally attain imaginary frequency with the increase of pressure. The lattice degree of freedom is used to explain the phase transition. Static calculations predict the RS to CsCl phase transition to occur at 308 GPa at 0 K. Dynamical calculations lower this pressure by about 40 GPa. The phonon density of states, electron–phonon interaction coefficient, and Eliashberg's function are also presented. The calculated electron–phonon coupling constant λ and superconducting transition temperature agree reasonably well with the available experimental data.

Analyses of the thermal shifts of spectral lines in Nd3+-doped LiYF4 laser crystal

The red-shift of spectral line E-1(R-1 -> Y-2) and blue-shift of line E-2(R-1 -> X-5) with temperature in Nd3+-doped LiYF4 laser crystal are studied by considering both the static contribution due to lattice thermal expansion and vibrational contribution due to electron-phonon interaction. The study is based on the analyses of pressure and temperature dependences of these spectral lines. It is found that for both lines, the static and vibrational contributions result in the blue- and red-shift, respectively. So, the observed red-shift of line E-1 and blue-shift of line E-2 are due respectively to the static contribution being smaller and larger than the vibrational one. Also, we infer that the thermal shifts of lines E-3(R-1 -> Y-5) and E-4(R-2 -> Y-5) are very small because both contributions may be approximately canceled. When both the contributions are contained, whether the red-shift or blue-shift of a spectral line can be fitted with the almost same theoretical expression as that by including only the vibrational contribution used in red-shift in the previous papers if we change the expression concerning electron-phonon interaction coefficient.

Effect of sulfur addition on the transport properties of semiconducting iron phosphate glasses

Transport properties and redox state of iron in glasses with compositions × S– (40 Fe 2O 3 – 60 P 2O 5)(mol%), where x = 0, 2,4,6 and 8 (mass%), were studied. The overall features of the XRD curves confirm the amorphous nature of the present glasses. Sulfur acted as a reducing agent for redox reaction during glass synthesis and affected the conductivity. Mössbauer spectral analyses revealed that the Fe 2+ ratio increases with increasing sulfur content. The high temperature above θ/2 ( θ D Debye temperature) dependence of conductivity could be qualitatively explained by the small polaron hopping model. The physical parameters obtained from the best fits of this model are found reasonable and consistent with the glass compositions. The conduction is confirmed to be due to adiabatic small polaron hopping of electrons between iron ions. The electron–phonon interaction coefficient γ p was large (21.42–26.26). The estimated hopping mobility was low, 1.12 × 10 −9–24.83 × 10 −9 cm 2 V −1 s −1 and increased with increasing S(mass%) content. Moreover, the low temperature (below θ/2) conductivity could not be explained either by Mott’s or greaves variable – range hopping model giving rise to unusually large values of the density of states at the Fermi level compared to those of transition metal oxide glasses. The conductivity of the present glasses was primarily determined by hopping carrier mobility.

A nonlinear thermal spike model for pyrolytic graphite under irradiation with 86Kr and 209Bi high-energy heavy ions

The temperature dependences of the specific heat capacity and thermal conductivity are introduced for a highly oriented pyrolytic graphite; i.e., the nonlinear model of a thermal spike is considered and a comparative analysis of the obtained results and those for the linear model of a thermal spike is performed. The temperature effects observed in the highly oriented pyrolytic graphite with a change in the electron-phonon interaction coefficient g are investigated in detail. It is shown that, under irradiation of the highly oriented pyrolytic graphite by bismuth ions with an energy of 710 MeV, the temperature on the surface of the target within the framework of the nonlinear model can exceed the sublimation temperature, whereas the temperature on the surface of the target under irradiation by krypton ions with an energy of 253 MeV does not exceed the sublimation temperature. The characteristic range of variations in the electron-phonon interaction coefficient g is evaluated. For values of g in this range, the thermal spike model explains the experimental data on the presence of structures in the form of hillocks with craters at their centers on the surface of the highly oriented pyrolytic graphite exposed to irradiation by 209Bi ions and on the absence of such structures in the case of irradiation by 86Kr ions.

Application of the thermal spike model for explanation of variations of surface structure of highly oriented pyrolytic graphite under bombardment by 86Kr and 209Bi fast ions with high ionization energy loss

Temperature effects in the highly oriented pyrolytic graphite (HOPG) under bombardment by 86Kr (253 MeV) and 209Bi (710 MeV) heavy ions are studied in the framework of a three-dimensional thermal spike model. It is shown that the surface temperature of an HOPG target under bombardment by bismuth ions can exceed the sublimation temperature at particular values of the electron-phonon interaction coefficient. At the same time, the temperature at the target surface during bombardment of HOPG by krypton ions does not exceed the sublimation temperature over a wide range of variations in the electron-phonon interaction belongs. The calculations allow the explanation of the observed changes in the surface structure of HOPG single crystal under bombardment by 209Bi and 86Kr ions.

Electrical transport studies in alkali iron phosphate glasses

The electrical properties of xFe2O3−(100 −x) Na2P2O5 glasses with x = 0, 6, 12, 18 and 24 mol% have been studied in the temperature range from 323 to 573 K. The dc conductivity was found to decrease as the iron content increases while the activation energy increases with increasing iron content in the glasses. In the high—temperature regime above θD/2 (θD is the Debye temperature), the Mott model of small polaron hopping (SPH) between nearest neighbors is consistent with the conductivity data. The electron—phonon interaction coefficient γP was very large (66.74–97.60). The electrical conduction of the glasses was confirmed to be non-adiabatic small polaron hopping. The physical parameters obtained by fitting the experimental results to these models are consistent with glass compositions.

D.c. conductivity of V2O5–MnO–TeO2 glasses

Semiconductive oxide glasses in the system V2O5–MnO–TeO2 were prepared, and the mechanism of d.c. conduction was studied. The Seebeck coefficient measurements at temperatures from 375–475 K indicated the glasses to be n-type semiconducting. The d.c. conductivity ranged from 5×10−5 to 1.9×10−6 S cm−1 at 405 K for V2O5=60 mol% and MnO=0–20 mol%, and decreased with increasing MnO content. The conduction was confirmed to obey the adiabatic small polaron hopping model, and was due to mainly hopping between V-ions in the glasses. The polaron band width J was estimated to be J=0.10–0.20 eV. The electron–phonon interaction coefficient γp was very large (21–26). The hopping mobility evaluated as 2.3×10−7–2.7×10−6 cm2 V−1 s−1 increased with increasing V2O5 content. The estimated carrier concentration was the order of 1019 cm−3. The principal factor determining conductivity was the polaron hopping mobility in these glasses. © 1998 Chapman & Hall