EPR investigations on γ-irradiated 4-hydroxyacetophenone single crystals: an NLO material

The single crystals of 4-hydroxyacetophenone (4HAP) were grown by the solution growth technique and characterized by X-ray diffraction, UV–VIS, FT-IR, and FT-Raman techniques. TGA–DTA analyses have also been carried out. Electron paramagnetic resonance spectra of γ-irradiated 4HAP were recorded and the spin Hamiltonian parameters were evaluated.     

Experimental and theoretical study on the β-FeOOH nanorods: growth and conversion

This study presents an experimental and theoretical study on the growth of monodispersed akaganéite (β-FeOOH) nanorods with tunable aspect ratios (longitudinal to transversal) under mild conditions (80 °C, aqueous solution). The synthesis of β-FeOOH nanorods is highly influenced by the presence of salt ions, and thus, the effect of various anions (e.g., NO₃ ⁻, SO₄ ²⁻, F⁻, Cl⁻, and Br⁻) were investigated on the microstructure, morphology, and size of the nanoparticles. It was found that these anions could interact strongly or weakly with the FeO₆ octahedral unit in the ferric oxyhydroxides, hence greatly affect the morphology, crystallization, and structure of the iron oxide/oxyhydroxide nanoparticles under the reported conditions. Moreover, these nanorods could be converted into magnetite (Fe₃O₄) through the reduction of hydrazine, which provides a new template approach to prepare magnetite nanorods with shape and size control at ambient conditions. The microstructure, composition, and structural transformation of the as-synthesized nanoparticles were characterized by various techniques, such as transmission electron microscopy (TEM and HRTEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The possible formation and growth mechanism of akaganéite nanorods were discussed. Finally, the influence of anions on the β-FeOOH(100), (110), and (001) surfaces was further understood by theoretical simulations (e.g., molecular dynamics method).     

Electrical and thermoluminescence properties of γ-irradiated La2CuO4 crystals

Abstract

Measurements of the electrical properties of unirradiated as well as γ-irradiated La₂CuO₄ crystals were carried out at different temperatures in the frequency range of 0.1-100 kHz. Thermoluminescence (TL) studies were also performed on such crystals in the temperature range of 300-600K. The conductivity of the unirradiated La₂CuO₄ crystals were found to obey the power law frequency dependence at each measured temperature below the transition temperature (T_c = 450K). The activation energies for conduction and dielectric relaxation time have been calculated. The TL response and the dc resistance were found to increase with γ-irradiation dose up to 9-10 kGy. The results showed that the ferroelastic domain walls of La₂CuO₄ crystal as well as its TL traps are sensitive to γ-raditaion. This material can be used in radiation measurements in the range 225 Gy-10 kGy.     

Experimental research on sound pulse propagation and channel match in shallow water

Theoretical and experimental research of low frequency pulse compression and channel match in shallow water sound channel were carried out based on 2000-Winter Yellow Sea experiment. Using pulse compression method, signals with high signal to noise ratio (SNR) were received over range of 110 kilometers in the experiment. The SNR gain in the process is consistent with the theoretical prediction. The experimental measurement indicated that the channel is highly coherent over a length of 500 s. Channel match method was used to compensate the degradation of pulse compression SNR caused by the multi-path propagation. And the SNR gain in the channel match process can be theoretically predicted. Experimental results show that low frequency pulse compression and channel match method can be used in shallow water sound channel to improve the SNR.     

Critical behaviour in the commensurate-incommensurate phase transition of pure and γ-irradiated LiRbSO4 crystals

The effect of γ-irradiation on the incommensurate phase of LiRbSO₄ crystals has been studied by measuring the specific heat C_p . As a result of γ-irradiation, the values of C_p decreased and the transition temperature T_c shifted to lower values. The values of ΔH and ΔS decreased with increasing dose rate. The results are explained on the basis of an energy change due to induced lattice defects.     

Experimental and theoretical study of the IR spectrum and barriers to internal rotation of 4-hydroxypropyl-4′-cyanobiphenyl

The IR absorption spectrum of polycrystalline 4-hydroxypropyl-4′-cyanobiphenyl is measured in a KBr pellet over the range 400–4000 cm^?1. The structure of the molecule and the frequencies and the intensities of the bands in the spectrum are calculated in the approximation of the B3LYP hybrid density functional with the 6-31 G(d) and 6-31+G(d) basis sets. The normal vibrations are reliably assigned by the method of linear scaling of frequencies, which made it possible to reproduce the experimental IR spectrum with high accuracy. The barriers to internal rotation of phenyl rings and three barriers for the hydroxypropyl radical are calculated.     

Experimental and theoretical study of long counters on the departure of “point” assumption and scattering background influence

A new long counter has been constructed and calibrated with the inherent efficiency of 11.5 cm² in the 2.5 MeV neutron field, and a relative flat energy response of 20% disparity within 0.5 MeV–15 MeV. Using this detector and another commercial DePangher counter, the departure of “point” assumption at near distance and the scattering background influence are investigated by performing three groups of experiments in low, middle and high scattering room. Simulation studies are also performed to supplement the experimental data.Two conclusions are deduced. First, the direct efficiency η is very sensitive when the source is very near, and the departure of point assumption is very evident at this situation. So, a revising method is tried to put forward, employing the on-site calibration with a known neutron source and theoretical calculated coefficient D = (η/ε)/(η_cf252/ε_cf252). And second, scattering backing counts are found mainly from the nearest wall or scatterers. However, the relatively uniform isotropic scattered neutrons contribute insensitive to the source-detector distance, which means the background tally can be eliminated by some simple ways.     

Electron spin resonance study of γ-irradiated single crystal and powder of LiH3(SeO3)2 and LiD3(SeO3)2

Gamma-irradiated monoclinic single crystals and powders of LiH₃(SeO₃)₂ and LiD₃(SeO₃)₂ have been investigated at room temperature by ESR in both the X and the Q band. Twelve species consisting of six pairs of inequivalent radicals have all been identified as SeO₂⁻-type radicals pairwise located in two different sites. The origin of the difference in the principal values of the g-tensors for the radicals is attributed to a difference between the SeO bond lengths, which in fact gives a lower symmetry of the radicals. The generation of the radicals has been explained as a rupture of a SeO bond, which can occur in six different ways due to the crystal structure. The orientations of the radicals in the crystal are different compared to corresponding SeO₂ groups in the host crystal, and this phenomenon presumably depends either on a reorientation of the radicals or on a radical reaction. One extra splitting of peaks originating from two of the radicals in LiH₃(SeO₃)₂ is absent in LiD₃(SeO₃)₂, thus indicating hydrogen bonding to the radicals.     

PBE–DFT theoretical study of organic photovoltaic materials based on thiophene with 1D and 2D periodic boundary conditions

Conjugated organic systems such as thiophene are interesting topics in the field of organic solar cells. We theoretically investigate π-conjugated polymers constituted by n units (n = 1–11) based on the thiophene (Tn) molecule. The computations of the geometries and electronic structures of these compounds are performed using the density functional theory (DFT) at the 6–31 G(d, p) level of theory and the Perdew–Burke–Eenzerhof (PBE) formulation of the generalized gradient approximation with periodic boundary conditions (PBCs) in one (1D) and two (2D) dimensions. Moreover, the electronic properties (HOCO, LUCO, E _gap, V _oc, and V _bi) are determined from 1D and 2D PBC to understand the effect of the number of rings in polythiophene. The absorption properties—excitation energies (E _ex), the maximal absorption wavelength (λ_max), oscillator strengths, and light harvesting—efficiency are studied using the time-dependent DFT method. Our studies show that changing the number of thiophene units can effectively modulate the electronic and optical properties. On the other hand, our work demonstrates the efficiency of theoretical calculation in the PBCs.     

Synthesis and thermoluminescence characteristics of γ-irradiated K3Ca2(SO4)3F:Eu or Ce fluoride

New halophosphor K₃Ca₂(SO₄)₃F activated by Eu and Ce has been synthesized by a co-precipitation method and characterized according to its thermoluminescence. The formation of traps in rare earth doped K₃Ca₂(SO₄)₃F and the effects of γ-radiation dose on the glow curve are discussed. The glow curve of K₃Ca₂(SO₄)₃F:Ce shows a prominent single peak at 150°C, whereas K₃Ca₂(SO₄)₃F:Eu and K₃Ca₂(SO₄)₃F:Ce,Eu at 142°C and 192°C, respectively. A single glow peak indicates that there is only one set of trap being activated within the particular temperature range. The presented phosphors are also studied because of its fading, reusability and trapping parameters. There was just 2% fading during a period of 10 days, indicating no serious fading problem. Trapping parameters such as order of kinetics (b), activation energy (E) and frequency factor (S) were calculated by using Chen's half-width method. The observations presented in this paper are good for lamp phosphors as well as solid-state dosimeter.     

Nickel deposition on γ-Al2O3 model catalysts: An experimental and theoretical investigation

Recently, surface modifications on a commercial Ni/γ-Al₂O₃ catalyst during the production of methane from synthesis gas were investigated by quasi insitu X-ray photoelectron spectroscopy (XPS) [I. Czekaj, F. Loviat, F. Raimondi, J. Wambach, S. Biollaz, A. Wokaun, Appl. Catal. A: Gen. 329 (2007) 68]. The conclusion was that the reactivity and the observed reaction mechanisms on the different Ni particles are influenced directly by both the size and the composition of the particles on the γ-Al₂O₃ support.In this investigation, Ni deposition and cluster growth on model catalyst samples (10 nm thick, polycrystalline γ-Al₂O₃ on Si(100)) were investigated by XPS. Several steps in the binding energy during Ni deposition indicate changes in the cluster growth. The molecular structure of the catalyst was investigated using Density Functional Theory calculations (StoBe) with a cluster model and non-local functional (RPBE) approach. An Al₁₅O₄₀H₃₅ cluster was selected to represent the γ-Al₂O₃(100) surface. Ni clusters of different size were cut from a Ni(100) surface and deposited on the Al₁₅O₄₀H₃₅ cluster in order to validate the deposition model determined by XPS.     

Study on the mechanism of phase transition and embrittlement for γ-Fe by hydrogen with stress through the first principles method

Because of the influence of hydrogen and the stress corrosion cracking, the damage of metal is quite frequent. It leads to dangerous failures, the loss of property as well as large compensational payments for insurance companies. However, the issue of the precise role of hydrogen in the process is unclear and the mechanism is not available. Based on the binding energy analysis, it was found that H prefers octahedral-like positions for γ-Fe, and could enhance the stability of structure with dissolving into γ-Fe. The higher the concentration of H, the much more remarkable the observation is. Therefore, H is easily soluble in γ-Fe. Under the applied tensile stress, γ-Fe and H doped γ-Fe undergo the stages of elastic and plastic deformations. Meanwhile, H induces γ-Fe phase transition.This process starts from the atomic layer adjacent to H, then gradually extends far. As a consequence, the intergranular embrittlement and cracking happened.     

Experimental and theoretical study of AC electrical conduction mechanisms of Organic–inorganic hybrid compound Bis (4-acetylanilinium) tetrachlorocadmiate (II)

A new organic–inorganic bis (4-acetylaniline) tetrachlorocadmate [C₈H₁₀NO]₂[CdCl₄] can be obtained by slow evaporation at room temperature and characterized by X-ray powder diffraction. It crystallized in an orthorhombic system (Cmca space group). The material electrical properties were characterized by impedance spectroscopy technique in the frequency range from 209 Hz–5 MHz and temperature 413 to 460 K. Besides, the impedance plots show semicircle arcs at different temperatures and an electrical equivalent circuit has been proposed to interpret the impedance results. The circuits consist of the parallel combination of a resistance (R), capacitance (C) and fractal capacitance (CPE). The variation of the exponent s as a function of temperature suggested that the conduction mechanism in Bis (4-acetylanilinium) tetrachlorocadmiate compound is governed by two processes which can be ascribed to a hopping transport mechanism: correlated barrier hopping (CBH) model below 443 K and the small polaron tunneling (SPT) model above 443 K.     

Experimental study of sono-crystallisation of ZnSO4·7H2O, and interpretation by the segregation theory

Power ultrasound is known to enhance crystals nucleation, and nucleation times can be reduced by one up to three orders of magnitude for several organic or inorganic crystals. The precise physics involved in this phenomenon still remains unclear, and various mechanisms involving the action of inertial cavitation bubbles have been proposed. In this paper, two of these mechanisms, pressure and segregation effects, are examined. The first one concerns the variations of supersaturation induced by the high pressures appearing in the neighbourhood of a collapsing bubble, and the second one results from the modification of clusters distribution in the vicinity of bubble. Crystallisation experiments were performed on zinc sulphate heptahydrate ZnSO(4)·7H(2)O, which has been chosen for its pressure-independent solubility, so that pressure variations have no effect on supersaturation. As observed in past studies on other species, induction times were found lower under insonification than under silent conditions at low supersaturations, which casts some doubts on a pure pressure effect. The interfacial energy between the solid and the solution was estimated from induction times obtained in silent conditions, and, using classical nucleation theory, the steady-state distribution of the clusters was calculated. Segregation theory was then applied to calculate the over-concentrations of n-sized clusters at the end of the collapse of a 4 μm bubble driven at 20 kHz by different acoustic pressures. The over-concentration of clusters close to the critical size near a collapsing bubble was found to reach more than one order of magnitude, which may favour the direct attachment process between such clusters, and enhance the global nucleation kinetics.     

Role of molecular interactions and end chain length on the photosensitivity of liquid crystalline alkyl cyanobiphenyl dimers – UV absorption-based approach through DFT calculations

In this paper, the photosensitivity of liquid crystalline alkyl cyanobiphenyl (nCB: n = 6, 7; n is the number of carbon atoms in the alkyl chain) dimers has been presented through density functional theory (DFT) calculations. The nCB structures have been optimized using the Becke, three-parameter, Lee–Yang–Parr hybrid functional with the 6-31+G (d) basis set using the crystallographic geometry as input. The electronic structures of the dimer molecules have been computed using the optimized geometries. The spectra of the dimer molecules have been calculated by employing the DFT method. The excited states have been calculated via configuration interaction singles with the semi-empirical Hamiltonian Zerner intermediate neglect of differential overlap. The influence of molecular interactions and the end chain length on ultraviolet absorption spectral characteristics and the photosensitivity of the compounds has been discussed. These results offer a hint for the protection of various optical devices from the intense light induced damages, and to model photosensitivity.