Showing papers on "Debye published in 2018"

Rationalizing phonon dispersion for lattice thermal conductivity of solids

Abstract: Lattice thermal conductivity (κL) is one of the most fundamental properties of solids. The acoustic-elastic-wave assumption, proposed by Debye (Debye P. Ann Phys 1912; 344: 789-839), has led to linear phonon dispersion being the most common approximation for understanding phonon transport over the past century. Such an assumption does not take into account the effect of a periodic boundary condition on the phonon dispersion, originating from the nature of periodicity on atomic arrangements. Driven by modern demands on the thermal functionality of materials, with κL ranging from ultra-low to ultra-high, any deviation from the Debye approximation in real materials becomes more and more significant. This work takes into account the periodic boundary condition, and therefore rationalizes the phonon dispersion to be more realistic. This significantly improves the precision for quickly predicting κL without any fitting parameters, as demonstrated in hundreds of materials, and offers a theoretical basis rationalizing κL to be lower than the minimum currently accepted based on the Debye dispersion. This work paves the way for designing solids with expected κL and particularly inspires the advancement of low-κL materials for thermal energy applications.

Spectroscopy and Dipole Moment of the Molecule C13h20beli2sesi Via Quantum Chemistry Using Ab Initio, Hartree-Fock Method in the Base Set CC-PVTZ and 6-311G** (3df, 3pd)

Abstract: The work characterizes the electric dipole moment and the infrared spectrum of the molecule C13H20BeLi2SeSi. Calculations obtained in the ab initio RHF (Restrict Hartree-Fock) method, on the set of basis used indicate that the simulated molecule C13H20BeLi2SeSi features the structure polar-apolar-polar predominant. The set of basis used that have are CC-pVTZ and 6-311G** (3df, 3pd). In the CC-pVTZ base set, the charge density in relation to 6-311G** (3df, 3pd) is 50% lower. The length of the molecule C13H20BeLi2SeSi is of 15.799A. The magnitude of the electric dipole moment |p| total obtained was p = 4.9771 Debye and p = 4.7936 Debye, perpendicular to the main axis of the molecule, for sets basis CC-pVTZ and 6-311**(3df,3pd), respectively. The infrared spectra for absorbance and transmittance and their wavenumber (cm-1) were obtained in the set of bases used. The infrared spectrum for Standard CC-pVTZ shows peaks in transmittance with Intensity (I), at wavenumber 1,125.44 cm-1, 1,940.70 cm-1, 2,094.82 cm-1, 2,178.43 cm-1, 2,613.99 cm-1 and transmittance 433.399 km/mol, 399.425 km/mol, 361.825 km/mol, 378.993 km/mol, 433.774 km/mol, respectively. While the infrared spectrum for Standard 6-311G**(3df, 3pd), shows peaks in transmittance, at wavelengths 1,114.83 cm-1, 1,936.81 cm-1, 2,081.49 cm-1, 2,163.23 cm-1, 2,595.24 cm-1 and transmittance 434.556 km/mol, 394.430 km/mol, 345.287 km/mol, 375.381 km/mol, 409.232 km/mol, respectively. It presents “fingerprint” between the intervals (680 cm-1 and 1,500 cm-1) and (3,250 cm-1 and 3,500 cm-1). The dipole moments CC-pTZV are 3.69% bigger than 6-311G** (3df, 3pd). As the bio-inorganic molecule C13H20BeLi2SeSi is the basis for a new creation of a bio-membrane, later calculations that challenge the current concepts of biomembrane should advance to such a purpose.

Spectroscopy and Dipole Moment of the Molecule C 13 H 20 BeLi 2 SeSi via Quantum Chemistry Using Ab initio , Hartree-Fock Method in the Base Set CC-pVTZ and 6-311G** (3df, 3pd)

Abstract: The work characterizes the electric dipole moment and the infrared spectrum of the molecule C13H20BeLi2SeSi. Calculations obtained in the ab initio RHF (Restrict Hartree-Fock) method, on the set of basis used indicate that the simulated molecule C13H20BeLi2SeSi features the structure polar-apolar-polar predominant. The set of basis used that have are CC-pVTZ and 6-311G** (3df, 3pd). In the CC-pVTZ base set, the charge density in relation to 6-311G** (3df, 3pd) is 50% lower. The length of the molecule C13H20BeLi2SeSi is of 15.799A. The magnitude of the electric dipole moment | | total obtained was p = 4.9771 Debye and p = 4.7936 Debye, perpendicular to the main axis of the molecule, for sets basis CC-pVTZ and 6-311**(3df, 3pd), respectively. The infrared spectra for absorbance and transmittance and their wavenumber (cm-1) were obtained in the set of bases used. The infrared spectrum for Standard CC-pVTZ shows peaks in transmittance with Intensity (I), at wavenumber 1,125.44 cm-1, 1,940.70 cm-1, 2,094.82 cm-1, 2,178.43 cm-1, 2,613.99 cm-1 and transmittance 433.399 km/mol, 399.425 km/mol, 361.825 km/mol, 378.993 km/mol, 433.774 km/mol, respectively. While the infrared spectrum for Standard 6-311G**(3df, 3pd), shows peaks in transmittance, at wavelengths 1,114.83 cm-1, 1,936.81 cm-1, 2,081.49 cm-1, 2,163.23 cm-1, 2,595.24 cm-1 and transmittance 434.556 km/mol, 394.430 km/mol, 345.287 km/mol, 375.381 km/mol, 409.232 km/mol, respectively. It presents “fingerprint” between the intervals (680 cm-1 and 1,500 cm-1) and (3,250 cm-1 and 3,500 cm-1). The dipole moments CC-pTZV are 3.69% bigger than 6-311G** (3df, 3pd). As the bio-inorganic molecule C13H20BeLi2SeSi is the basis for a new creation of a bio-membrane, later calculations that challenge the current concepts of biomembrane should advance to such a purpose.

Nonperturbative finite-temperature Yang-Mills theory

Abstract: We present non-perturbative correlation functions in Landau-gauge Yang-Mills theory at finite temperature. The results are obtained from the functional renormalisation group within a self-consistent approximation scheme. In particular, we compute the magnetic and electric components of the gluon propagator, and the three- and four-gluon vertices. We also show the ghost propagator and the ghost-gluon vertex at finite temperature. Our results for the propagators are confronted with lattice simulations and our Debye mass is compared to hard thermal loop perturbation theory.

Nature of the Debye-Process in Monohydroxy Alcohols: 5-Methyl-2-Hexanol Investigated by Depolarized Light Scattering and Dielectric Spectroscopy.

Abstract: The slow Debye-like relaxation in the dielectric spectra of monohydroxy alcohols is a matter of long-standing debate. In the present Letter, we probe reorientational dynamics of 5-methyl-2-hexanol with dielectric spectroscopy and depolarized dynamic light scattering (DDLS) in the supercooled regime. While in a previous study of a primary alcohol no indication of the Debye peak in the DDLS spectra was found, we now for the first time report clear evidence of a Debye contribution in a monoalcohol in DDLS. A quantitative comparison between the dielectric and DDLS manifestation of the Debye peak reveals that while the dielectric Debye process represents fluctuations in the end-to-end vector dipole moment of the transient chains, its occurrence in DDLS shows a more local signature and is related to residual correlations that occur due to a slight anisotropy of the $\ensuremath{\alpha}$ relaxation caused by the chain formation.

Intensity of gluon bremsstrahlung in a finite plasma

Abstract: The intensity of single gluon bremsstrahlung in a QCD plasma is evaluated with a Monte Carlo which solves the transport equation for a generic interaction with the medium. In particular, the calculation is performed for a Debye screened potential and compared to the well-known Gaussian/Fokker-Planck results. The full calculation including the first and last gluons shows a qualitatively different behavior from the Baier-Dokshitzer-Mueller-Peigne-Schiff result for any finite medium length. It is shown that the emission intensity is underestimated for the Gaussian approximation, compared to the Debye screened potential. This change cannot be accounted for by a redefinition of the Gaussian parameter ($\stackrel{^}{q}$).

Modified Poisson--Nernst--Planck Model with Accurate Coulomb Correlation in Variable Media

Abstract: We derive a set of modified Poisson--Nernst--Planck (PNP) equations for ion transport from the variation of the free energy functional which includes the many-body Coulomb correlation in media of variable dielectric coefficient. The correlation effects are considered through the Debye charging process in which the self energy of an ion is governed by the generalized Debye--Huckel equation. We develop the asymptotic expansions of the self energy taking the ion radius as the small parameter such that the multiscale model can be solved efficiently by numerical methods. It is shown that the variations of the energy functional give the self-energy-modified PNP equations which satisfy a proper weak formulation. We present numerical results from different asymptotic expansions with a semi-implicit conservative numerical method and investigate the effect of the Coulomb correlation.

Transient dynamics of electric double-layer capacitors: Exact expressions within the Debye-Falkenhagen approximation.

Abstract: We revisit a classical problem of theoretical electrochemistry: the response of an electric double-layer capacitor (EDLC) subject to a small, suddenly applied external potential. We solve the Debye-Falkenhagen equation to obtain exact expressions for key EDLC quantities: the ionic charge density, the ionic current density, and the electric field. In contrast to earlier works, our results are not restricted to the long-time asymptotics of those quantities. The solutions take the form of infinite sums whose successive terms all decay exponentially with increasingly short relaxation times. Importantly, this set of relaxation times is the same among all aforementioned EDLC quantities; this property is demanded on physical grounds but not generally achieved within approximation schemes. The scaling of the largest relaxation timescale τ_{1}, that determines the long-time decay, is in accordance with earlier results: Depending on the Debye length, λ_{D}, and the electrode separation, 2L, it amounts to τ_{1}≃λ_{D}L/D for L≫λ_{D} and τ_{1}≃4L^{2}/(π^{2}D) for L≪λ_{D}, respectively (with D being the ionic diffusivity).

Excited State Dipole Moments in Solution: Comparison between State-Specific and Linear-Response TD-DFT Values.

Abstract: We compare different response schemes for coupling continuum solvation models to time-dependent density functional theory (TD-DFT) for the determination of solvent effects on the excited state dipole moments of solvated molecules In particular, linear-response (LR) and state-specific (SS) formalisms are compared Using 20 low-lying electronic excitations, displaying both localized and charge-transfer character, this study highlights the importance of applying a SS model not only for the calculation of energies, as previously reported ( J Chem Theory Comput, 2015, 11, 5782, DOI: 101021/acsjctc5b00679), but also for the prediction of excited state properties Generally, when a range-separated exchange–correlation functional is used, both LR and SS schemes provide very similar dipole moments for local transitions, whereas differences of a few Debye units with respect to LR values are observed for CT transitions The delicate interplay between the response scheme and the exchange–correlation functional

Relativistic effects on the energy levels and radiative properties of He-like ions immersed in Debye plasmas

Abstract: Systematic investigations are performed for the energy levels and radiative properties for selected He-like C4+, Ne8+, Ar16+, and Kr34+ ions embedded in weakly coupled plasmas. For the conditions in which the Coulomb coupling parameter is small, the standard Debye model is adopted to describe the plasma screening effects. Within the relativistic framework, the modified version of the Flexible Atomic Code computations is carried out by considering a Debye-Huckel potential, in which the plasma screening is taken into account for both the electron-nucleus and electron-electron (e-e) interactions. An independent calculation for various Debye lengths is also presented using the multiconfiguration Dirac-Fock method for comparison purposes. For the nonrelativistic treatment, the analytical solution of the Schrodinger equation with the Debye screened potential is proposed. The variation method is developed with Slater wave function as a trial wave function that contains the variational parameters. An exact analytical expression of relativistic corrections such as the mass-velocity correction, the one/two-body Darwin correction, the spin-spin contact interaction correction, and the orbit-orbit interaction correction is derived. Differences among our three kinds of calculated energy levels and transition properties are analyzed in terms of the nuclear charge and/or the Debye length. Systematic trend is observed for all the properties under study with respect to increased screening. The influence of relativistic effects is also investigated in detail and found to play an important role in these systems. Our results are compared with available results from other theoretical calculations and the experimental values in the literature, and a good agreement is achieved. This work should be useful for astrophysical applications where such plasma environments exist.Systematic investigations are performed for the energy levels and radiative properties for selected He-like C4+, Ne8+, Ar16+, and Kr34+ ions embedded in weakly coupled plasmas. For the conditions in which the Coulomb coupling parameter is small, the standard Debye model is adopted to describe the plasma screening effects. Within the relativistic framework, the modified version of the Flexible Atomic Code computations is carried out by considering a Debye-Huckel potential, in which the plasma screening is taken into account for both the electron-nucleus and electron-electron (e-e) interactions. An independent calculation for various Debye lengths is also presented using the multiconfiguration Dirac-Fock method for comparison purposes. For the nonrelativistic treatment, the analytical solution of the Schrodinger equation with the Debye screened potential is proposed. The variation method is developed with Slater wave function as a trial wave function that contains the variational parameters. An exact analyt...

Electronic structure, magnetic, mechanical and thermo-physical behavior of double perovskite Ba 2 MgOsO 6

Abstract: The electronic structure, the magnetic, elasto-mechanical and thermodynamic belongings of cubic double oxide perovskites Ba2MgOsO6 have been successfully investigated within the full potential linearized augmented plane wave method (FP-LAPW), based upon the density functional theory (DFT). The structural examination reveals ferromagnetic stability and the spin polarized electronic band structure and density of states display half-metallic nature of the compound. The calculated magnetic moment was found to have an integer value of 2μ_B. From the knowledge of obtained elastic constants mechanical properties like Young’s modulus (E), shear modulus (G), Poisson ratio ( $ u$ ) and the anisotropic factor have been predicted. The calculated B/G and Cauchy pressure ( $ C_{12}-C_{44}$ ) both portray the ductile nature of the compound. For a complete understanding of the thermo-physical behavior of vital parameters like heat capacity, thermal expansion, Gruneisen parameter and Debye temperature were predicted using quasi harmonic Debye approximation.

Proximity force approximation and specular reflection: Application of the WKB limit of Mie scattering to the Casimir effect

Abstract: The electromagnetic Casimir interaction between two spheres is studied within the scattering approach using the plane-wave basis. It is demonstrated that the proximity force approximation (PFA) corresponds to the specular-reflection limit of Mie scattering. Using the leading-order semiclassical WKB approximation for the direct reflection term in the Debye expansion for the scattering amplitudes, we prove that PFA provides the correct leading-order term in the small-distance limit for arbitrary materials and temperatures in the sphere-sphere and the plane-sphere geometry. Our derivation implies that only a small section around the points of closest approach between the interacting spherical surfaces contributes in the PFA regime. The corresponding characteristic length scale is estimated from the width of the Gaussian integrand obtained within the saddle-point approximation. At low temperatures, the area relevant for the thermal corrections is much larger than the area contributing to the zero-temperature result.

From electrodiffusion theory to the electrohydrodynamics of leaky dielectrics through the weak electrolyte limit

Abstract: The Taylor–Melcher (TM) model is the standard model for describing the dynamics of poorly conducting leaky dielectric fluids under an electric field. The TM model treats the fluids as ohmic conductors, without modelling the underlying ion dynamics. On the other hand, electrodiffusion models, which have been successful in describing electrokinetic phenomena, incorporate ionic concentration dynamics. Mathematical reconciliation of the electrodiffusion picture and the TM model has been a major issue for electrohydrodynamic theory. Here, we derive the TM model from an electrodiffusion model in which we explicitly model the electrochemistry of ion dissociation. We introduce salt dissociation reaction terms in the bulk electrodiffusion equations and take the limit in which the salt dissociation is weak; the assumption of weak dissociation corresponds to the fact that the TM model describes poor conductors. Together with the assumption that the Debye length is small, we derive the TM model with or without the surface charge convection term depending upon the scaling of relevant dimensionless parameters. An important quantity that emerges is the Galvani potential (GP), the jump in voltage across the liquid–liquid interface between the two leaky dielectric media; the GP arises as a natural consequence of the interfacial boundary conditions for the ionic concentrations, and is absent under certain parametric conditions. When the GP is absent, we recover the TM model. Our analysis also reveals the structure of the Debye layer at the liquid–liquid interface, which suggests how interfacial singularities may arise under strong imposed electric fields. In the presence of a non-zero GP, our model predicts that the liquid droplet will drift under an imposed electric field, the velocity of which is computed explicitly to leading order.

Dispersion coefficient in an electro-osmotic flow of a viscoelastic fluid through a microchannel with a slowly varying wall zeta potential

Abstract: The dispersion coefficient of a passive solute in a steady-state pure electro-osmotic flow (EOF) of a viscoelastic liquid, whose rheological behaviour follows the simplified Phan-Thien–Tanner (sPTT) model, along a parallel flat plate microchannel, is studied. The walls of the microchannel are assumed to have modulated and low potentials, which vary slowly in the axial direction in a sinusoidal manner. The flow field required to obtain the dispersion coefficient was solved using the lubrication approximation theory (LAT). The solution of the electric potential is based on the Debye–Huckel approximation for a symmetric electrolyte. The viscoelasticity of the fluid is observed to notably amplify the axial distribution of the effective dispersion coefficients due to the variation in the potentials of the walls. The problem was formulated for two cases: when the Debye layer thickness (EDL) was on the order of unity (thick EDL) and in the limit where the thickness of the EDL was very small compared with the height of the microchannel (thin EDL limit). Due to the coupling between the nonlinear governing equations and the sPTT fluid model, they were replaced by their approximate linearized forms and solved in the limit of using the regular perturbation technique. Here is the amplitude of the sinusoidal function of the potentials. Additionally, the numerical solution of the simplified governing equations was also obtained for and compared with the approximate solution, showing excellent agreement for . Note that the dispersion coefficient primarily depends on the Deborah number, on the ratio of the half-height of the microchannel to the Debye length, and on the assumed variation in the potentials of the walls.

Terahertz radiation and second-harmonic generation from a single-component polar organic ferroelectric crystal

Abstract: A rare single-component polar organic crystal with a distinctive four-fold screw axis is grown from a new dipole molecule, namely 4-(4-(methylthio)phenyl)-2,6-di(1H-pyrazol-1-yl)pyridine (UOH1). The polar molecular ordering is facilitated by a moderate molecular dipole moment (1.42 Debye) and supramolecular (S⋯H–C and N⋯H–C type hydrogen bonding and π–π stacking) interactions. Remarkably, a UOH1 crystal exhibits a ferroelectric hysteresis loop at room temperature without any discontinuity in temperature-dependent dielectric measurements. Additional advantages of this non-centrosymmetric UOH1 crystal are its high second-order nonlinear susceptibility, superior phase matching conditions and low THz absorption. As a result, UOH1 produces both second harmonic and terahertz (THz) waves with ample energy conversion efficiency. These combinations of properties demonstrate the direct technological usefulness of the UOH1 crystal as a non-linear optical and electro-optical material operating at ambient temperature.

Protein Sensing Beyond the Debye Length Using Graphene Field-Effect Transistors

Abstract: Sensing biomolecules in electrolytes of high ionic strength has been a difficult challenge for field-effect transistor-based sensors. Here, we present a graphene-based transistor sensor that is capable of detection of antibodies against protein p53 in electrolytes of physiological ionic strength without dilution. As these molecules are much larger than the Debye screening length at physiological ionic strengths, this paper proves the concept of detection beyond the Debye length. The measured signal associated with the expected specific binding of the antibodies to p53 is concluded to result from resistance changes at the graphene-electrolyte interface, since a sensor responding to resistance changes rather than charge variations is not limited by Debye screening. The conclusion with changes in interface resistance as the underlying phenomena that lead to the observed signal is validated by impedance spectroscopy, which indeed shows an increase of the total impedance in proportion to the amounts of bound antibodies. This finding opens up a new route for electrical detection of large-size and even neutral biomolecules for biomedical detection applications with miniaturized sensors.

Basic microscopic plasma physics from N -body mechanics

Abstract: Computing is not understanding. This is exemplified by the multiple and discordant interpretations of Landau damping still present after seventy years. For long deemed impossible, the mechanical N-body description of this damping, not only enables its rigorous and simple calculation, but makes unequivocal and intuitive its interpretation as the synchronization of almost resonant passing particles. This synchronization justifies mechanically why a single formula applies to both Landau growth and damping. As to the electrostatic potential, the phase mixing of many beam modes produces Landau damping, but it is unexpectedly essential for Landau growth too. Moreover, collisions play an essential role in collisionless plasmas. In particular, Debye shielding results from a cooperative dynamical self-organization process, where " collisional " deflections due to a given electron diminish the apparent number of charges about it. The finite value of exponentiation rates due to collisions is crucial for the equivalent of the van Kampen phase mixing to occur in the N-body system. The N-body approach incorporates spontaneous emission naturally, whose compound effect with Landau damping drives a thermalization of Langmuir waves. O'Neil's damping with trapping typical of initially large enough Langmuir waves results from a phase transition. As to collisional transport, there is a smooth connection between impact parameters where the two-body Rutherford picture is correct, and those where a collective description is mandatory. The N-body approach reveals two important features of the Vlasovian limit: it is singular and it corresponds to a renormalized description of the actual N-body dynamics.

Comparison of focusing of short pulses in the Debye approximation

Abstract: We have examined different types of pulses and features of their frequency spectra. Calculations have shown that a significant distinction between the pulses only takes place at a very short pulse duration (shorter than the oscillation period). In this case, the Gaussian pulse becomes nonphysical and one needs to use other types of pulses, for example, the Poisson pulse. We performed comparative modeling of focusing of short pulses by an aplanatic lens for different polarization states and vortex singularity orders in the Debye approximation. We have shown that the polarization state and the presence of vortex phase singularity essentially affect the distribution in the focal area for a subcycle Poisson pulse.

Spontaneous Interfacial Dipole Orientation Effect of Acetic Acid Solubilized PFN.

Abstract: Poly[(9,9-dioctyl-2,7-fluorene)-alt-(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)] (PFN) is a very important interfacial modifier in organic photovoltaic and organic light-emitting diodes to improve device performance, where their molecular dipole has been regarded to play a key role. In this work, we have reported a spontaneous interfacial dipole orientation effect in acetic acid dissolved PFN, which is strongly related to the interfacial dipole and the corresponding device performance. In direct spin-coating, the interfacial dipole is 1.08 Debye with interfacial contact angle 84.8°, whereas after self-assembly of 10 min, the interfacial dipole is balanced at 4.21 Debye, with the interfacial contact angle decreasing to 76.8°. Without strong interaction with the substrate, the energy of upward amine groups is much lower than that of downward ones in theoretical simulation, which would be the driving force of this spontaneous process. The preferred conformations of PFN molecules on hydroxylated subs...

Nonlinear Effects on Electrophoresis of a Soft Particle and Sustained Solute Release

Abstract: A numerical study is made on the electrophoresis of a core-shell soft particle based on the first principle of electrophoresis. The soft particle consists of a charged rigid core coated with a polymer shell. Numerical computations for the electrophoretic velocity are obtained and compared with the existing analytical solution. The analytical solutions, based on the Boltzmann distribution of ions and the Debye–Huckel approximation, are valid for lower range of charge density, weak applied electric field and thin double layer. Discrepancy from the existing analytical solution is found when the Debye layer extends beyond the porous shell. This discrepancy becomes larger for higher values of the rigid core surface potential, fixed charge density of the soft shell and stronger imposed electric field. The double-layer polarization is found to have a strong impact when the shell thickness is lower than the Debye length. The electrophoretic velocity is found to vary nonlinearly with the imposed electric field when the imposed field strength is large enough to create a potential drop across the particle bigger than the thermal potential. We have also analyzed the mechanism of sustained solute release from the soft particle. Our results show that the rate of solute release is large compared to a pure diffusion dominated process.

Temperature Rise and SAR Distribution at Wide Range of Frequencies in a Human Head due to an Antenna Radiation

Abstract: Temperature rise and specific absorption rate distribution in a human head due to electromagnetic energy produced by an adjacent antenna are evaluated. An algorithm proposed in this paper provides these distributions at multiple frequencies using a single simulation. The head tissue parameters are used from the available three-term Debye coefficients obtained by the experimental data from 500 MHz to 20 GHz. The proposed algorithm is developed by integrating the Debye model of human head tissues parameters into the finite-difference time-domain method by using the auxiliary differential equation approach along with the use of bioheat equation for specific absorption rate and temperature computations.

Determination of Debye temperatures and Lamb-Mössbauer factors for LnFeO3 orthoferrite perovskites (Ln = La, Nd, Sm, Eu, Gd).

Abstract: Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO3 (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through X-ray diffraction and X-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO3 compounds. 57Fe Mossbauer spectroscopy was performed over a temperature range of 10 K to 293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θD) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental Centre Shift (CS) and theoretical Isomer Shift (IS), by allowing the Debye temperature and Isomer Shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mossbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, Ag(3) and Ag(5) from La to GdFeO3 corresponding to octahedral rotations and tilts in the [010] and [101] planes respectively.

Stretch tuning of the Debye ring for 2D photonic crystals on a dielectric elastomer membrane

Abstract: The tunable diffracted pattern (Debye ring) of the well-ordered close-packed 2D photonic crystal (PC) is achieved via large deformation of the dielectric elastomer (DE) membrane for the first time. Two deformation models are proposed, the in-plane deformation driven by voltage and the out-of-plane deformation actuated by pressure. Both experimental and theoretical analyses are conducted to explore the tunability of the DE stretch on the Debye ring of the 2D PC, by voltage and pressure. An excellent agreement is found between the experimental and analytical results. This study shows that tuning the size of the Debye ring by voltage driven in-plane deformation is easy to operate and space-saving. However, it needs a high voltage and the adjustable range is relatively small. On the other hand, the pneumatic tuning by out-of-plane deformation has a widely adjustable range compared with the electric one and the pressure needed is only hundreds to less than two thousand pascal, which is energy-saving. This work may pave the way for the design of various smart sensors and soft displays with the combination of PCs and DEs.

Hund's rule in the (1s2s)1,3S states of the two-electron Debye atom

Abstract: We present an investigation of the (1s2s)1,3S excited states of the two-electron atom immersed in a plasma modeled by the Debye or screened Coulomb potential. Three variants of the Debye atom are considered. The validity of Hund's multiplicity rule is confirmed, and the contribution of the interparticle repulsion energy to the singlet-triplet splitting is examined. The feature that this system shares with the unscreened two-electron atom as well as with the confined two-electron atom and the two-electron quantum dot is that the triplet wave function is contracted relative to that of the singlet. This feature affects both the behavior of the 2s-electron ionization energies and the relative magnitudes of the interparticle repulsion energies in the singlet vs. the triplet. Debye screening of the one-body attraction effectively reduces the nuclear charge, enhancing the reversal of the relative magnitudes of the triplet vs. singlet interparticle repulsion energies. Debye screening of the interparticle repulsion acts in an opposite way.We present an investigation of the (1s2s)1,3S excited states of the two-electron atom immersed in a plasma modeled by the Debye or screened Coulomb potential. Three variants of the Debye atom are considered. The validity of Hund's multiplicity rule is confirmed, and the contribution of the interparticle repulsion energy to the singlet-triplet splitting is examined. The feature that this system shares with the unscreened two-electron atom as well as with the confined two-electron atom and the two-electron quantum dot is that the triplet wave function is contracted relative to that of the singlet. This feature affects both the behavior of the 2s-electron ionization energies and the relative magnitudes of the interparticle repulsion energies in the singlet vs. the triplet. Debye screening of the one-body attraction effectively reduces the nuclear charge, enhancing the reversal of the relative magnitudes of the triplet vs. singlet interparticle repulsion energies. Debye screening of the interparticle repulsio...