Decrease In Interatomic Distance Research Articles

Synthesized polymeric nanocomposites with enhanced optical and electrical properties based on gold nanoparticles for optoelectronic applications

In the present work, gold nanoparticles (Au-NPs) were synthesized in two ways: plant extract and laser ablation techniques. Then, Au-NPs were added to (PVP/PVA/CMC) blend (TB) to produce novel nanocomposites using the solution casting technique. X-ray diffraction analysis, Ultraviolet and visible spectroscopy, and transmission electron microscopy provided conclusive evidence for preparing Au-NPs through the above methods. The optical, structural, and dielectric properties of the prepared samples were prudently investigated and confirmed their semicrystalline nature. TEM study concluded that Au-NPs are more uniformly distributed in the TB/AuNPs-biosynthesized (TBAu-B) matrix than in the TB/Au-NPs prepared by laser ablation (TBAu-L) matrix. The decrease in interatomic distances increases the refractive index with an enhancement in optical properties. The change in loss tangent provided a deeper discernment into the relaxation dynamics that arose inside the current films. The electric modulus formalism verified the non-Debye behavior of charge carriers inside the TB-based nanocomposite samples. It also demonstrated a remarkable capacitive feature of the nanocomposite films. The dielectric characteristics of the TBAu-B nanocomposite sample have improved, where AC electrical conductivity reached 1.58 × 10−3 S/cm. Because of this favorable enhancement, the TBAu-B nanocomposite has the potential to be utilized in optoelectronic applications such as sensors.

Synchrotron x-ray total scattering and modeling study of high-pressure-induced inhomogeneous atom reconfiguration in an equiatomic Zr50Cu50 metallic glassy alloy

We studied in situ the local atomic structure evolution of an equiatomic ${\mathrm{Zr}}_{50}{\mathrm{Cu}}_{50}$ metallic glassy alloy under high pressure compression inside a diamond anvil cell using synchrotron x-ray total scattering. The empirical potential structure refinement method was used to reconstruct the three-dimensional atomic models at each pressure step, and to analyze the spatially averaged local atomic structure configurations. The interatomic distances of different atomic pairs are reduced at different rates with increasing pressure and the Cu-Cu pairs exhibit the highest percentage reduction. Between ambient pressure and 36.85 GPa, the atomic separation of the Cu-Cu pairs is reduced by \ensuremath{\sim}12% compared to \ensuremath{\sim}5% for Zr-Zr and Zr-Cu pairs. Such disproportional decrease in interatomic distance results in inhomogeneous atom reconfiguration in the short atomic range. With the increase of pressure, the Zr atoms move preferentially towards the Zr-Zr pairs, while the Cu atoms move preferentially towards the Cu-Cu pairs, creating inhomogeneous atom reconfiguration with positive short-range order coefficients of 0.0309 and 0.0464 for Zr-Zr and Cu-Cu respectively, but a negative value of \ensuremath{-}0.0464 for Zr-Cu pairs. Voronoi tessellation method was also used to study the evolution of the short-range atom packing versus pressure, elucidating the cause for the bimodal distribution of the bond angle distributions. The research sheds light on understanding of the atomic reconfiguration of equiatomic alloys under high pressure.

Discriminating High-Pressure Water Phases Using Rare-Event Determined Ionic Dynamical Properties* *Supported by the National Basic Research Program of China under Grant Nos. 2016YFA0300900 and 2017YFA0205003, the National Science Foundation of China under Grant Nos. 11774003, 11634001, 11934003, and 11774072. D. Pan also acknowledges the support from Hong Kong Research Grands Council (Nos. ECS-26305017 and GRF-16307618), the Alfred R. Sloan Foundation

Recent discoveries of dynamic ice VII and superionic ice highlight the importance of ionic diffusions in discriminating high-pressure (P) water phases. The rare event nature and the chemical bond breaking associated with these diffusions, however, make extensive simulations of these processes unpractical to ab initio and inappropriate for force field based methods. Using a first-principles neural network potential, we performed a theoretical study of water at 5–70 GPa and 300–3000 K. Long-time dynamics of protons and oxygens were found indispensable in discriminating several subtle states of water, characterized by proton’s and oxygen ion’s diffusion coefficients and the distribution of proton’s displacements. Within dynamic ice VII, two types of proton transfer mechanisms, i.e., translational and rotational transfers, were identified to discriminate this region further into dynamic ice VII T and dynamic ice VII R. The triple point between ice VII, superionic ice (SI), and liquid exists because the loosening of the bcc oxygen skeleton is prevented by the decrease of interatomic distances at high P’s. The melting of ice VII above ∼40 GPa can be understood as a process of two individual steps: the melting of protons and the retarded melting of oxygens, responsible for the forming of SI. The boundary of the dynamic ice VII and SI lies on the continuation line ice VII’s melting curve at low P’s. Based on these, a detailed phase diagram is given, which may shed light on studies of water under P’s in a wide range of interdisciplinary sciences.

Superheating of free-standing nanometals under pressure

A simple and new analytical model is proposed to explore the pressure effect on melting temperature for free-standing nanoparticles, based on the Lindemann's formula of melting and the size-dependent Grüneisen parameter. The Grüneisen parameter is a valuable quantity which can be used to set the limitations on the pressure and temperature dependence of thermal properties. The present study reveals that the Grüneisen parameter decreases with the decrement in particle size due to variation in specific heat and lattice constant. On the other hand, melting temperature shows a superheating phenomenon with an increment in pressure for an individual size of free-standing nanoparticles. Due to compression the interatomic distance decreases and there is comparatively more interaction within the atoms of nanoparticles under pressure. Compactness of nanomaterial and reduction in surface vibrations due to external pressure create favourable conditions for superheating. This model is applied to Al (37 nm), Pb (6.7 nm) and Bi (50 nm) nanometals over a range of pressure up to 1 GPa. The consistency of the calculated results with the available experimental data of melting for the above-said materials as core in a particle/matrix system by induced pressure supports the validity of the proposed model.

Insight into an atomic arrangement of [KNbO3]0.9 – [BaNi0.5Nb0.5O3]0.1 powder formed at various calcination temperatures by X-ray absorption spectroscopy

Lead-free [KNbO3]0.9 – [BaNi0.5Nb0.5O3]0.1 (KBNNO) perovskite powders are synthesized by the solid-state combustion technique. Phase identification and the crystal structure change at various calcination temperatures Tcal are carried out by X-ray diffraction (XRD) technique. Local structure distortion is studied by X-ray absorption spectroscopy (XAS) for revealing X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XRD result shows that the structure of KBNNO changes from pseudo-cubic to weakly tetragonal structure when the calcination temperature increases. The extracted parameters from Nb L3-edge and K K-edge XANES signals show that the KBNNO structure formed at high Tcal (≥750°C) has an orthorhombic structure. In addition, the fitted EXAFS spectra indicate a decrease of interatomic distances for three shells when Tcal increases. The obtained structural distortion difference from XRD and XAS can be explained by the fact that XRD signal is from all atoms in the unit cell, while XAS can specifically probe the local structure of specific atoms in the unit cell.

Blue-emitting Eu2+-activated LaOX (X = Cl, Br, and I) materials: crystal field effect.

Novel blue-emitting LaOBr:Eu(2+) and LaOI:Eu(2+) phosphors have been successfully synthesized and compared to LaOCl:Eu(2+). The emission spectra of LaOX:Eu(2+) (X = Cl, Br, and I) show that the peak maxima change somewhat to the red-shift region; 425 nm for LaOCl:Eu(2+), 427 nm for LaOBr:Eu(2+), and 431 nm for LaOI:Eu(2+), which is quite opposite to one based on spectrochemical series (I(-) < Br(-) < Cl(-)). From diffuse reflectance spectra, the band gap energies for LaOCl, LaOBr, and LaOI host lattice are estimated as 5.53 eV (44,594 cm(-1)), 5.35 eV (43,142 cm(-1)), and 4.82 eV (38,868 cm(-1)), respectively, using the Kubelka-Munk function. For LaOX host lattices, the band gap energies are gradually decreased going from Cl to I as the order of energy levels of np orbitals is Cl 3p < Br 4p < I 5p. A quantum wave function calculation from crystal field theory (CFT) indicates the same tendency with experimental data in the LaOX:Eu(2+) (X = Cl, Br, and I) phosphor materials. With considerations of the radial wave function shape, crystral structure differences and electronegativities among phosphor materials, the splitting energies of 5d orbitals are calculaed; ΔECl = 14,597 cm(-1), ΔEBr = 14,864 cm(-1), ΔEI = 15,001 cm(-1) for LaOX:Eu(2+) (X = Cl, Br, and I). It is noteworthy that the crystal field strength decreases when the interatomic distance decreases, which is probably dependent on the ionic radius of halide ions in the series of LaOX:Eu(2+) phosphor materials.

Rovibrational energy and spectroscopic constant calculations of CH4⋯CH4, CH4⋯H2O, CH4⋯CHF3, and H2O⋯CHF3 dimers.

In this work, we performed a thorough investigation of potential energy curves, rovibrational spectra, and spectroscopic constants for dimers whose interactions are mediated by hydrogen bonds and other hydrogen interactions. Particularly, we deal with CH4⋯CH4, CH4⋯H2O, CH4⋯CHF3, and H2O⋯CHF 3 dimers by employing accurate electronic energy calculations with two different basis sets at the MP2 level of theory. Following this, the discrete variable representation method was applied to solve the nuclear Schrödinger equation, thus obtaining spectroscopic constants and rovibrational spectra. The harmonic constant, ω e , presents a direct relation to the strength of dimer interactions. As a general rule, it was found that a decrease of interatomic distances is followed by the increase of D e for all dimers. This behavior suggests that the interaction of CH4⋯CH4 is the weakest among all dimers, followed by CH4⋯CHF3, CH4⋯H2O and the strongest interaction given by the H2O⋯CHF 3 dimer.

Plasmon resonances and plasmon‐induced charge transport in linear atomic chains

In linear hydrogen atomic chains, plasmon resonances and plasmon‐induced charge transport are studied by time‐dependent density functional theory. For the large linear chain, it is a general phenomenon that, in the longitudinal excitation, there are high‐energy resonances and a large low‐energy resonance. The energy of the large low‐energy resonance conforms to the results calculated by the classical Drude model. In order to explain the formation mechanism of the high‐energy resonances, we present a simple harmonic oscillator model. This model may reasonably account for the relationship between low‐energy and high‐energy resonances, and has a certain degree of universality. As the interatomic distance decreases, the current shows a gradual transition from insulator to metal. The current enhancement mainly depends on the local field enhancement associated with plasmon excitation, and the enhanced electron delocalization effect as a result of the decrease of the interatomic distance. © 2013 Wiley Periodicals, Inc.

Systematic study of photoluminescence upon band gap excitation in perovskite-type titanates R1/2Na 1/2TiO 3:Pr ( R=La, Gd, Lu, and Y)

Pr 3+-doped perovskites R 1/2Na 1/2TiO 3:Pr ( R=La, Gd, Lu, and Y) were synthesized, and their structures, optical absorption and luminescent properties were investigated, and the relationship between structures and optical properties are discussed. Optical band gap of R 1/2Na 1/2TiO 3 increases in the order R=La, Gd, Y, and Lu, which is primarily due to a decrease in band width accompanied by a decrease in Ti–O–Ti bond angle. Intense red emission assigned to f– f transition of Pr 3+ from the excited 1D 2 level to the ground 3H 4 state upon the band gap photo-excitation (UV) was observed for all compounds. The wavelength of emission peaks was red-shifted in the order R=La, Gd, Y, and Lu, which originates from the increase in crystal field splitting of Pr 3+. This is attributed to the decrease in inter-atomic distances of Pr–O together with the inter-atomic distances ( R, Na)-O, i.e., increase in covalency between Pr and O. The results indicate that the luminescent properties in R 1/2Na 1/2TiO 3:Pr are governed by the relative energy level between the ground and excited state of 4 f 2 for Pr 3+, and the conduction and valence band, which is primarily dependent on the structure, e.g., the tilt of TiO 6 octahedra and the Pr-Ti inter-atomic distance and the site symmetry of Pr ion.

M�ssbauer Study of Fe7Se8?xSx

Effects of interatomic separation on superexchange interactions, interatomic binding, and spin-rotation transition in Fe7Se8—xSx have been studied by Mossbauer spectroscopy and X-ray diffraction. The crystal structure is found to be “3c” hexagonal superstructure of the NiAs structure, and lattice constants A and C decrease linearly with increasing sulphur concentration. As interatomic distance decreases, Debye temperature, Ne�el temperature, and magnetic hyperfine field increase monotonically. When the number of sulfur ions replacing selenium ions increases from 1 to 7, the interatomic distance decreases by 4.4%, and Debye temperature, Neel temperature, and magnetic hyperfine field at 15 K increase by 12%, 10%, and 6%, respectively. While the spin rotation near 130 K persists for Fe7Se7S, it disappears in Fe7Se8—xSx (x ≥ 2). The iron ions at all three sites are found to be in a highly covalent ferrous state.

High-pressure effects in SiAsTe amorphous chalcogenide glasses fabricated under microgravity environment

The effect of high pressure on electrical properties has been investigated for two sets of Si 9As 14Te 21 ternary chalcogenide amorphous semiconductor samples, fabricated either in a microgravity environment (rocket or spacelab) or under the gravity environment of earth. The primary effect of pressure is a decrease in interatomic distances; the compression gives rise to changes in electronic structure and a transition from semiconductor to metal. For pressures up to 3 GPa, the decrease of the resistivity of space-made materials is not significant compared with the terrestrially-made materials, whereas for higher pressures the change in resistivity of both kinds of material is similar in shape and extends for the same orders of magnitude.

Mössbauer study of Ni x(Cu 0.5Fe 0.5) 1− xCr 2S 4

Ni x (Cu 0.5Fe 0.5) 1− x Cr 2S 4 has been studied by Mössbauer spectroscopy and X-ray diffraction. The crystal is found to have a cubic spinel structure and the lattice constant decreases with increasing Ni concentration. The iron ions are in ferric states and occupy the tetrahedral sites. When the nickel concentration at the tetrahedral sites increases from 10 to 30%, magnetic hyperfine field and Néel temperature are found to decrease by 2 and 9%, respectively. As the interatomic distance decreases by 0.4%, Debye temperature increases rapidly by 37%.

Hyperfine Interaction, Chemical Bonding, and Isotope Effect in ZnH, CdH, and HgH Molecules

ESR spectra of ZnH, CdH, HgH, and HgD molecules in their ground Σ+2 states were measured while trapped in solid argon matrices at 4°K. g tensors and hyperfine structure (hfs) constants for interaction with H, D, 111,113Cd, and 199,201Hg nuclei were observed. Coefficients of approximate LCAO wavefunctions are derived from these magnetic parameters and correlated with chemical bonding trends in the series and with the limiting united-atom model. Replacing H by D in HgH causes an increase of spin density on Hg and a decrease in g∇. This is shown to be largely due to the small decrease in interatomic distance and is discussed relative to other spectroscopic observations.

An optimized LCAO method for crystals

A modification is proposed to the linear combination of atomic orbitals (LCAO) method for calculating electronic wave functions in crystals. Instead of using fixed atomic orbitals, atomic orbitals characterized by an internal parameter, such as scaling factor are used. This is optimized by applying a variational principle for Wannier functions, using as a trial function a localized orbital constructed from the atomic orbitals by a symmetric orthogonalization procedure. In this way, both the accuracy and range of applicability of the LCAO method for crystals are greatly increased. As shown for the example of the one-dimensional Mathieu problem, the optimum atomic orbital tends to expand as the interatomic distance decreases, and the optimized LCAO orbital tends to expand as the interatomic distance decreases, and the optimized LCAO method describes accurately the change in the energy bands and wave functions as the lattice parameter decreases and the electron states change from tight-binding to free-electron like. The application of the method to crystals containing defects and to amorphous materials is discussed.

ヒドロキソ第一鉄錯体の酸化におよぼす酸化速度およびCu&lt;SUP&gt;2+&lt;/SUP&gt;，PO&lt;SUB&gt;4&lt;/SUB&gt;&lt;SUP&gt;3&amp;minus;&lt;/SUP&gt;イオンの影響

The effect of oxidation rate and addition of Cu2+ or PO43− ion on the oxidation of Fe(II) hydroxo-complexes in aqueous solutions were investigated by means of measurements of the infrared and Mössbauer’s spectra and the X-ray diffraction of oxidation products.The results obtained are summarized as follows:(1) The rapid oxidation of Fe(II) hydroxo-complexes in solutions with the addition of H2O2 resulted in the formation of δ-FeOOH. The oxyhydroxide was obtained also by removing water from the Fe(II) complexes and leaving them in air to be oxidized.(2) The size of δ-FeOOH crystallite formed by the oxidation of Fe(OH)2 with H2O2 is determined by the size of particle of the starting compound. The broad absorption band at 450 cm−1 shifted to 480 cm−1 with the increase in crystallite size. The shift of the absorption band probably corresponds to the increase in force constant of vibration, which may result from the increase of crystallite size, i.e. the decrease in interatomic distance.(3) Green Rust I was converted to Fe3O4 by the slow oxidation in solution.(4) In the presence of Cu2+ or PO43− ion, freshly precipitated Fe(II) hydroxo-complexes were oxidized to amorphous δ-FeOOH with air in solutions. This transformation is considered to be caused by the catalytic effect of Cu2+ or PO43− ion in the oxidation of the Fe(II) complexes.

The lattice expansion of iron

The lattice spacings of high-purity iron have been measured accurately between 20 and 1502°C. The results, together with previous low-temperature data, give data between the absolute zero and the melting-point (1534°C). The thermal expansion of the lattice and of bulk metal are in good agreement over the temperature range for which the latter has been studied accurately. At the A 2 point, there is no discontinuity in the lattice spacing. In contrast to the work of some previous investigators, we have found no observ­able difference between the coefficients of expansion of the lattice immediately above and below the A 2 point, and the results suggest that the forces responsible for ferromagnetism do not affect the interatomic distances by more than 1 part in 10000. At the A 3 point, the α → γ transformation is accompanied by an increase in the interatomic distance which, when expressed as a percentage change, is slightly less than the decrease in interatomic distance during the γ → δ change at the A 4 point. The change in bond length calculated by the Pauling equation for the change (f. c. c.⇌b. c. c.) lies between the observed values for the A 3 and A 4 points, and the accuracy of the equation is confirmed.

The valencies of the transition elements in the metallic state

The melting-points, interatomic distances and compressibilities of the transition elements are reviewed, and are shown not to be in complete agreement with the valency scheme proposed by Pauling. In all three Long Periods on passing from Groups I A to IV A there is a steady rise in melting-point, and decrease in interatomic distance and compressibility, and for these elements Pauling’s view of a metallic valency equal to the Group number is correct. In the First Long Period there is comparatively little increase in melting-point on passing from Ti to V and Cr, in contrast to the behaviour of the corresponding elements in the later Periods where the melting-points rise steeply to a maximum in Group VI. This suggests that in Groups V A and VI A the metallic valency is less for the elements of the First Long Period than in the later Periods, and this agrees with the general inorganic chemistry of the elements. The same principle is shown to hold for the elements of Groups VII A and VIII, and a new scheme of metallic valencies is suggested which appears attractive in several ways.