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This paper focuses on the evaluation of the radiation attenuation properties of 15CaF2-10CaO-5B2O3-(65-x)P2O5-xNiO-5BaO (where 0 ≤ x ≤ 1.0 mol%) bioactive glasses. The radiation attenuation features of these glasses were investigated by determining different factors including mass attenuation coefficient (μ/ρ), exposure and absorption buildup factors (EBF and EABF), neutron removal cross section (NRCS), and effective atomic number (Zeff) for photon, proton, and carbon ion interactions. Geant4 toolkit and Phy-X program were employed for simulations and calculations procedures. The results revealed that NiO content in the studied bioactive glasses has a significant effect on photon interaction and an insignificant effect on the charged particle interactions. The Zeff values of the studied glasses were observed in the range of 18–20 for photon interaction, 10.7–10.9 for proton interaction, and 10.0–10.7 for carbon ion interaction. The NRCS values were 0.087, 0.088, 0.089, 0.090, and 0.091 cm-1 for x = 0, 0.4, 0.6, 0.8 and 1.0 mol%, respectively. The studied bioactive glasses showed a good ability to attenuate gamma radiation at energies of medical applications.

The aim of this study was to determine the principle cause of variation in a measured glass durability using a melt-quenching method. Further goal for this study was to find the optimum level of the factor for producing the glass durability. For that purpose, One-Way Analysis of Variance (ANOVA) was performed. From the analysis, it was found that all longitudinal modulus, shear modulus 2 and shear modulus 3 were the significant parameters that produced high quality of glass durability (p). The mean analysis revealed that the best condition that maximizes the average of Longitudinal Modulus 1, 2 and 3 would be when the erbium concentration was 0.05. It was found that the erbium concentration with 0.03 produced the optimum Longitudinal Modulus 4 and 5. The findings also pointed out that the average of Shear Modulus 2 and 3 was maximized when the erbium concentration was 0.03 and 0.05, respectively.

Melt-quenching method was used to synthesize a series of zinc tellurite glasses doped with erbium oxide and silver oxide. At room temperature, X-ray diffraction (XRD) and density measurement were implemented to characterize the prepared glass samples. The amorphous nature of the glass samples is proven from the XRD spectra obtained in this work. The density of the glass showed an increment trend from 4.4673 to 4.9705 g/cm3 when adding more silver oxide, which can prove that the glass strength is higher. For photoluminescence analysis, blue, green and red emissions were found in the glass series under 375 nm excitation wavelength. According to McCumber theory, higher emission cross-section and higher FWHM are efficient for both broadband amplifier and laser application. More extensive and flatter gain with a maximum gain difference has covered both C and L bands for optical communication, providing a few channels in the wavelength division multiplex network (WDM). The high efficiency of optical amplification is justified with a higher gain figure of merit and larger gain bandwidth. According to McCumber’s theory, all the results proved that 0.03 molar fraction of silver oxide is the most optimum concentration to be applied in the optical application. In Judd-Ofelt analysis, spectroscopic quality factor and shorter lifetime is a crucial parameter for obtaining intense laser transition, strong emission probabilities and encouraging the laser optical transition, which was successfully attained in all glass samples. The present glass system is also applicable for white light application since the standard equal energy point from all glass samples were located near the center of the CIE diagram (0.33, 0.33). In the meantime, higher values of CCT range from 6761 to 6937 K produce light with a better image as compared to lower CCT. Higher CCT is commercially used in LCD (liquid crystal display) and CRT (cathode ray tube) screens. The colour purity is a parameter for better white LED application, whereas low colour purity is for pure white light emission. Therefore, lower colour purity was found around 10.7 around 18.8% in all glass samples.

The investigation involves a comprehensive study on the mechanical and shielding features of the zinc erbium tellurite glasses as a function of doped Ag2O content. The mechanical features are estimated for the examined glasses by utilizing the Makishima-Makinzie model. The results showed the mechanical moduli of Young (E), bulk (B), Shear (K), and longitudinal (L) increased with the increment of the Ag2O substitution ratio. Besides, the radiation shielding properties were also studied and discussed. Among the shielding parameters, the linear attenuation coefficient (LAC), half-value layer (HVL), the lead equivalent and transmission rate (TR) were estimated. The linear attenuation coefficient results illustrated that the TZEAg glasses are better compared to the commercial marketing glasses, especially TZEAg5 glasses. Doping of Ag2O content in zinc erbium tellurite glass improves its ability to attenuate the gamma photons. Also, this study revealed the effectiveness of the examined glasses on the fast neutron, where the fast neutron mass removal cross-section ∑R (cm2/g) computed theoretically. The results offered the maximum value of ∑R = 0.019 cm2/g attained for TZEAg1 while the minimum value ∑R = 0.01884 cm2/g for TZEAg5 glass.

The melt-quenching method was used to synthesize a series of neodymium-doped zinc tellurite glass systems. The ultrasonic velocities, elastic moduli and other elastic parameters of the prepared glasses showed non-linear variations with an increase of Nd2O3 in the glass system. The non-linear variation is associated with the presence of non-bridging and bridging oxygen caused by the network modifier of Nd2O3. Theoretical data sets for the elastic properties of the glass systems were obtained by using the Makishima and Mackenzie theory and the Rocherulle, bond compression and ring deformation models. The values retrieved for the elastic moduli by using the Makishima and Mackenzie, and Rocherulle models are in great agreement with the corresponding experimental data. The recorded bond compression model data for the glass has much higher values for elastic moduli when compared to the corresponding experimental values. Therefore, in this glass system, only the bond compression model is not favoured.

Copper oxide doped TeO2 – B2O3 glass system with empirical formula; [(B2O3)0.3(TeO2)0.7]1-x(CuO)x using the melt quenching method, where x = 0.0, 0.01, 0.015, 0.02, and 0.025 was combined. The glass samples’ density and molar volume were measured, followed by characterizations using the UV-Vis, Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopes. The amorphous or glassy nature of glass samples was proven by the XRD spectra except for the pure borotellurite sample which showed a peak around 2θ = 20o, indicating α-TeO2 crystalline phase presence. The FTIR spectral analysis suggested the presence of BO3, TeO3 and TeO4 as the structural functional units in the glass samples. The UV-Vis spectra showed no presence of any sharply defined edges, affirming the amorphous or glassy nature of the glass materials. Physical parameters e.g. molar volume, density, oxygen packing density (OPD), inter ionic distance of Cu2+ ions, concentration of copper ion per unit volume (N), as well as the polaron radius data were presented and discussed. Also, the direct bandgap (3.8900 to 3.5900 eV) , indirect bandgap (3.3200 to 3.0800 eV), refractive index (2.318 to 2.378), dielectric constant (5.3731 to 5.6549), optical dielectric constant (4.3731 to 4.6549), refractive index based metallization criterion (0.406885 to 0.391916) and the band gap based metallization criterion (0.407431 to 0.392428) were analysed and discussed. Based on the metallization criterion and values of refractive index, the glasses are good candidates for optoelectronic and laser applications. Meanwhile, the dielectric constants’ values of the present glasses indicate their suitability bandpass filters and microelectronic substrates applications.

Reduced graphene oxide (rGO)/bismuth vanadate BiVO

In this research the melt quenching technique method was used to synthesize two series of borotellurite glass systems doped with manganese and strontium. Elastic measurement, X-Ray Diffraction and Fourier Transform Infrared spectroscopy were used to characterize the prepared glass samples. The increment of molar volume confirmed the theory that molar volume is inversely proportional to the density parameters. A broad hump appeared in XRD as the samples shown pure amorphous nature. In FTIR, the functional group vibrations of tellurite network were recorded such as TeO4 trigonal bipyramids and TeO3 trigonal pyramids by addition of both dopants. On the other hand, ultrasonic velocity was used to determine the elastic moduli of the glass such as bulk modulus, shear modulus, longitudinal modulus, Young’s Modulus, microhardness and Poisson’s ratio which showed decreasing and increasing trends with the increased concentration of MnO2 and SrO respectively.

In this paper, we report on the radiation attenuation properties of the essential DNA nucleobases such as guanine, adenine, cytosine, uracil, and thymine. Gamma attenuation parameters such as linear attenuation factor (LAF) and effective atomic number (EAN) are investigated by using FLUKA simulation code for seven chosen photon energies named 0.6, 1.25, 1.5, 2, 3, 5, and 10 MeV. The validation of the simulation results is performed by using XCOM calculations. Moreover, neutron and charge particles attenuation properties are examined for the essential DNA nucleobases. We also compare the radiation attenuation properties of the essential DNA nucleobases to those of liquid water. Our results indicate that the maximum LAF is observed at 0.6 MeV with the value of 0.183, 0.134, 0.130, 0.110, 0.103, and 0.089 cm−1 for guanine, adenine, cytosine, uracil, thymine, and liquid water, respectively. At a given photon energy, the exposure rate (ER) follows the trend: (ER)liquid water > (ER) thymine > (ER)cytosine > (ER)adenine. At 10 MeV, total stopping power (TSP) of electron interactions with the essential DNA nucleobases are 1.952, 1.977, 1.994, 1.990, 2.013, and 2.149 MeVcm2/g for guanine, adenine, cytosine, uracil, thymine, and liquid water, respectively. Comparatively, TSP of electron

This paper reports the effect of lead oxide (PbO) on the optical properties and radiation shielding efficiency of Sb2O3–Na2O–WO3–PbO glasses. The optical properties of the glasses were tested by estimating molar refraction (Rm), molar polarizability (αm), metallization principle (M), optical transmission (T), dielectric coefficients (static and optical), and reflection loss (RL). Additionally, the gamma radiation shielding efficiency of the glasses was evaluated via the Monte Carlo method (Geant4 simulations) and the XCOM program. The mass attenuation coefficient (µ/ρ) and other related factors such as effective atomic number (Zeff), half-value layer (HVL), and mean free path (MFP) were calculated at the energy range of 0.25–1.25 meV. Furthermore, the dependence of radiation protection efficiency (RPE) on the thickness of glasses was discussed in detail. The results revealed that at 40 mol% of PbO, the optical transmission was 0.7774 and the reflection loss was 1.1997. A notable increase in RPE as the thickness of the glass changes from 0.5 to 2 cm. The gamma shielding efficiency of the glasses was compared with those of commonly used shields. The reported glasses showed superior properties to apply for radiation shielding applications.

The gamma-ray shielding parameters for ternary lithium borotellurite systems have been reported using Geant4 code. We simulated the mass attenuation coefficients using Geanr4 code between 284 keV and 1.33 MeV. We checked the accuracy of the simulated results by using XCOM software. The Geant4 and XCOM results showed a reasonable agreement. The maximum linear attenuation coefficient (LAC) values were reported at 284 keV and varied between 0.77914 and 0.81525 cm. The minimum LAC is found at 1.33 MeV and varied between 0.23742 and 0.25005 cm. The LAC reduced by 59.7% for TeLiB1 between 284 and 826 keV, while it reduced by only 6.7% at higher energies. The half-value layer (HVL) decreased due to the increase of B2O3 from 5 to 15 mol%, but the HVL values for the glasses which contain 80 mol% of TeO2 are lower than the HVL for the first three compositions (contain 75 mol% of TeO2). TeLiB6 glass is the best attenuator in this study due to the least HVL values of this sample. The results also revealed that TeLiB1 glass with thickness of 2.94803 cm is required to reduce the photon level carrying energy of 284 keV by a factor of one-tenth. For TeLiB6, it requires a sample with a thickness of 2.82123 cm for this aim at the same energy. The effective atomic number for the ternary lithium borotellurite glasses with 80 mol% of TeO2 is higher than those with 75 mol% of TeO2.

Effects of incorporating (SbS) in the quaternary (CdTe)100-x(SbS)x (x = 0, 8, 16, 20 and 28 at. %) glasses on different physico-chemical properties were investigated using the chemical bond approach. In addition to the estimation of the coordination number, constraint number (Ns), heat of atomization (Hs), cohesive energy and lone pair electrons, one presents theoretically the band gap estimation as well as the valence band (EVB) and conduction band (ECB) positions. The theoretical estimations of band gap are in good agreement with the previously published experimental results, and all compounds have their band gap in the infrared range (from 1.58 to 1.36 eV). Therefore, these materials may be used as an optical absorber in the wavelength range between 0.784 and 0.911 μm. This indicates that the studied compositions could be used for the development of new-generation infrared systems as well as for solar cell devices. Furthermore, the increase of (SbS) content decreases the network rigidity, but due to the decrease in the excess of Cd–Cd, one found, in contrary, an increase in the cohesive energy of the system.

In this paper, we used Geant4 Monte Carlo simulations to investigate the effect of TiO2/V2O5 substitution on the radiation shielding properties of alkali borate glasses in the chemical form of 30Li2O+55B2O3+5ZnO + xTiO2+(10 - x)V2O5, where x = 0, 2.5, 5, 7.5, and 10 mol%. Also, the optical properties were examined by evaluating several factors such as molar refraction (Rm), metallization criterion (M), molar polarizability (αm), dielectric coefficients (static and optical), optical transmission (T), and reflection loss (RL). The radiation shielding properties of the tested glasses were estimated by determining the mass attenuation coefficient, and other related factors such as the tenth value layer (TVL), the mean free path (MFP), the electron total stopping powers (Ψe) and the electron continuous slowing down approximation range (CSDA) (Φe) for different energy values. The results of Geant4 Monte Carlo were compared with the theoretical values calculated by XCOM platform. The results revealed that the TiO2/V2O5 substitution had a remarkable influence on the gamma shielding properties for the tested glasses. On the other hand, the optical properties slightly changed by the TiO2/V2O5 substitution. The gamma shielding properties of the tested glasses were compared with many samples in terms of MFP. The present glasses showed superior features to apply for optical and radiation shielding applications.

Thin amorphous films of Ge5As22Te73–xInx (where x = 0, 3, 6 and 9 at. %) were thermally evaporated on glass substrates. The Seebeck coefficient (S) or simply thermoelectric power, dc electrical conductivity (σd), and photoconductivity (σph) were measured within the temperature (T) range 300–420 K on the prepared thin films. The activation energies for dark conduction (∆Ed), thermoelectric (∆ES) and photoconduction (∆Eph) were estimated using the values of σd, S, and σph, respectively. The current density (J) is found to be directly proportional to applied electric field (E) for the thin films indicating Ohmic behavior for E

Ascertaining plasmonic interaction induced by silver (Ag) and gold (Au) nanoparticles (NPs) in the amorphous system can open a new direction in photonics. In this outlook, various contents of Ag and Au NPs were incorporated into neodymium ions (Nd3+)-doped zinc-sulfate-magnesium-phosphate glasses via the melt-quenching method. The impact of Ag–Au plasmonic coupling on the structures and spectroscopic traits of the prepared glasses were evaluated. As-quenched samples were analyzed using XRD, HRTEM, Raman, absorption and photoluminescence (PL) spectrometer. The Judd-Ofelt (JO) theory was used to evaluate the spectroscopic quality and stimulated emission cross-section of the glasses. HRTEM micrographs verified the existence of Au and Ag NPs in the glass matrix with a mean size ranged 4.47–7.03 nm. The observed thirteen absorption bands centered around 326, 352, 430, 459, 473, 512, 52, 581, 627, 681, 744, 801, and 875 nm were corresponding to electronic transitions from the ground state (4I9/2) to the excited states of 4D7/2, 2D1/2+4D3/2+4D5/2, 2P1/2, 4G11/2, 2D3/2+2P3/2+2G9/2, 4G9/2+2K13/2, 4G7/2, 4G5/2+2G7/2, 2H11/2, 4F9/2, 4F7/2+4S3/2, 4F5/2+2H9/2 and 4F3/2 in Nd3+. Two surface plasmon resonance (SPR) bands assigned to Ag and Au NPs were probed at 442 nm and 503 nm. The addition of Au NPs causes the SPR band of Ag NPs to be red-shifted. The NIR PL bands at 878 nm, 1050 nm and 1322 nm were due to the 4F3/2 → 4I9/2, 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 transitions, respectively. The PMZ1.5Nd0.5Ag0·1Au glass disclosed the highest bandwidth gain of 6.92, 17.05 and 9.10 ( × 10−23 cm3) corresponding to the 4F3/2 → 4I9/2, 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 transitions. It was shown that the PL intensity of the studied glasses could be modified by varying Ag and Au NPs contents. The Ag–Au NPs plasmonic coupling inclusion inside the glass can be beneficial to develop versatile optical materials.

Physical characteristics of new quaternary Heusler alloys (QHAs) CoZrVZ (Z = Al, Ga, In, Sn) are determined employing first-principles calculations. Perdew-Burke-Ernzerhof (PBE) exchange and correlation functional treated with generalized gradient approximation (GGA) within full potential linearized augmented plane wave (FP-LAPW) method. Structural parameters are obtained through geometry optimization process for three non-equivalent configurations and Type I is found the most stable. Calculations for magnetic phases i.e. ferromagnetic (FM), anti-ferromagnetic (AFM) and non-magnetic (NM) are performed. Elastic, thermal and magnetic properties are investigated. All alloys are half-metallic (HM) in nature and magnetic moments are in well agreement to Slater-Pauling rule. The estimated Curie temperature (Tc) is well above the room temperature. The mechanical parameters confirmed that all alloys except CoZrVSn are stable and have ductile nature. Thermal properties predicted that all alloys have high melting temperature (Tm). All determined characteristics envisaged that these QHAs are suitable for technological and spintronic applications.

The extraction of CaO from waste eggshell can be used to produce new product known as calcium borate glass doped manganese (IV) oxide. A tertiary (B2O3)0.6 [(CaO)0.4]1-x (MnO2)x glass system with 0.010 ≥ x ≥ 0 M fraction were prepared using conventional melt-quenching technique. XRF spectroscopy confirms CaO as the main constituent in the calcined eggshell. XRD spectra unveils the two amorphous humps of the glass samples. FTIR analysis reveals the typical features of CaCO3 and B2O3 network. The density has opposite behaviour with molar volume as MnO2 content increases. Next, the optical band gap and refractive index are evidencing the formation of non-bridging oxygen in the glass matrix. The present glass system also has low polarizability, acidic in nature and have tendency to metallizing. The elastic properties of glass samples were determined using the ultrasonic technique. Elastic moduli such as longitudinal modulus, shear modulus, Young's modulus, bulk modulus, Poisson's ratio and hardness of the glass system were discussed.

The impact of the addition of antimony sulfide (Sb2S3) to (0.9GeS2-0.1CdS)100-x(Sb2S3)x chalcogenide glasses (20 ≤ x ≤ 80 at. %) was theoretically investigated. The molar volume and excess volume increased whereas the packing density and compactness decreased. The average coordination number and crosslinking density decreased while the lone pair electrons and floppy modes increased. Furthermore, the cohesive energy, overall mean bond energy and average heat of atomization decreased. Theoretical estimations of the optical band gap were presented. The results showed that adding Sb2S3 content from 20 to 80 % leads to decrease the band gap from 2.143 to 1.563 eV. Therefore, the compositions could be suitable for visible and near infrared technologies. The conduction band and valence band edges were also determined. They were found to shift towards each other with adding Sb2S3 content, which explain the band gap decrease. In addition, we theoretically estimated the glass transition temperature which showed a linear decrease owing the decrement of overall mean bond energy.

The dependence of band gap energy (Eg) and glass-transition temperature (Tg) on physico-chemical properties for the (GeS2)10(Sb2S3)90−x(AgI)x (10 ≤ x ≤ 50 at%) chalcohalide glasses were theoretically investigated. Chalcohalide glasses have wide technological applications owing to the aptitude of tuning their optical band gap through composition change. Therefore, Eg of the studied chalcohalide glasses was estimated using different methods, and it was turned out that it decreased as the AgI amount increases. This decrease was elucidated in terms of physico-chemical properties. In addition, we determined the positions of conduction band (ECB) and valence band (EVB) by using the computed values of Eg. The density and molar volume increased while the packing density decreased by adding AgI. The overall coordination number (CN), crosslinking density (CD), constraints number (Ns), cohesive energy (CE), heat of atomization (Hs) and overall mean bonds energy (〈E〉); computed via the chemical bond approach (CBA); decreased with the increment of AgI amount. In contrary, the floppy (F) and mean bonds energy (Es) increased. Finally, two estimations of Tg were presented based on 〈E〉 and CN. The two estimations showed a decreasing trend when adding AgI content.

Tellurite-lead-tungsten glasses with the chemical composition of (80-x)TeO2-20PbO-xWO3 (where x = 0, 5, 10, 15 and 20 mol%) were reported as high-performance shields for gamma and beta applications. Geant4 toolkit and XCOM program were used to simulate and calculate the gamma attenuation factors. Beta shielding behaviour of the investigated glasses was explored by determining the CSDA range and stopping power (ψe) via ESTAR program. The results showed that the addition of WO3 has a positive influence on density, and as a result, in the shielding capability of the glass against gamma and beta radiations. This influence, however, is much stronger in the case of the shielding against gamma radiation. TPW5 glass with the highest contents of WO3 has the highest MAC, Zeff and the lowest HVL. Moreover, the glasses with low concentrations of WO3 content show the same gamma shielding properties of commercial glasses and concretes.

The effect of iodine content in Ix (As20Se80)100-x where x=0, 4, 8, 12, and 16 atomic % was studied both theoretically and experimentally. The calculated mean coordination number, cohesion energy, mean overall bonding energy, and band gap decrease with iodine content. This is correlated to the decrease of crosslinking by progressive incorporation of iodine. The impact of increasing iodine content on optical properties was studied through the analysis of a single reflection spectrum using Minkov's method. The experimentally evaluated band gap decreases from 1.7 eV to 1.41 eV in good agreement with the different estimations based on Manca's relation. The Urbach energy, related to the structural disorder, increases with the incorporation of iodine. From the measured refraction index, one deduces that the single oscillator energy decreases with iodine content while its dispersion energy increases. The nonlinear optical properties increase substantially with the incorporation of the more polarizable iodine atom.

The ternary compounds Snx(GeSe2)100-x (0 ≤ x ≤ 24 at. %) were prepared in glassy thin films. Using the chemical bond approach, theoretical calculations of effects of Sn content on mean coordination number (CN), constraints number (Ns), molar volume (Vm), compactness (δ), heat of atomization (Hs), cohesive energy (CE), overall difference of electronegativity (Δχ) as well as the degree of iconicity (Ion) were discussed. Optical absorbance has been measured in order to evaluate experimentally the band gap (Eg) and the band tail's width (Ee). In addition, conduction-valence bands positions were estimated when changing Sn content. Increasing Sn content from 0 to 24 at. %, decreases Eg from 2.01 to 1.28 eV. Three theoretical estimations of the variations of the band gap with Sn content were critically compared to experimental values. Obviously, the combination of the estimated band gap from Δχ and contributions of the formed bonds gives the best adjustment.

The reported simulation results could be considered as one of the firsts modeling of the effect of temperature on the electrical breakdown phenomenon in polyethylene nanoscale. The breakdown begins with an abrupt increase of the external current density without a subsequent saturation. Our results show that the increase of temperature at a constant applied DC voltage leads to a breakdown and to a decrease of the insulator's lifetime. These outcomes are strongly linked to the injection of free charges into the sample and to the temporal evolution of the conduction current.

In this paper, we are interested in space charge packet phenomenon generated at submicron scales in insulating polyethylene materials that have not been extensively investigated in all previous theoretical modeling and experimental works. Indeed, a bipolar charge transport model is proposed to simulate space charge dynamics in nano-scale polyethylene material under dc high electric field. For these scales, our results show space charge packet appearance which induces new dynamics that are marked on injected and conduction current oscillations. In addition, our results also show the establishment of post breakdown phenomena that are indicated by an external current abrupt increase without saturation.

In this paper, we present a new numerical formulation that we have applied to the model for bipolar charge transport, trapping and recombination in polymeric insulators, such as low density polyethylene. The numerical model is based on the high precision Runge–Kutta method for determining mobile and trapped charge local density within the sample, during the application of a dc voltage. In addition, we have applied the finite element method considered as the most general one, which can be applied to any sample shape and boundary conditions. It is applied to resolve Poisson's equation, thus providing the potential and its gradient within the sample and at the dielectric–electrode interfaces. In a first step, the new formulation is validated for the charge dynamic under low dc applied voltage. In a second step, model outputs are analyzed under high dc applied voltage. The appearance of charge packets is revealed for the first time in modelling works although they have long been reported in experimental studies on polyethylene materials. The conditions for the appearance of such packets are discussed.

In this paper, we aim to study the repetitive cycle aspect of charge packets observed in nano and macro scale polyethylene under dc applied fields. This aspect is investigated for the first time in modeling works although large research effort has been invested in trying to reproduce the charge packet aspect. Our model results show that the repetitive cycle appearance modifies the local electric field distributions in the sample, and also induces new dynamics observed in injected current and interfacial electric field oscillations. Our model results are validated experimentally for the space charge distribution, for the first time in modeling.

This paper presents bipolar transport model results concerning the recombination phenomenon in a low-density polyethylene under direct current (dc) applied voltages. Results obtained indicate the existence of a threshold value of voltage between two different space charge dynamics. Indeed, we show that under low dc applied voltage, the total recombination rate density is dominated by the recombination between trapped electrons and trapped holes, while under high dc voltage, the recombination is governed by mobile electron-trapped hole and trapped electron-mobile hole recombinations. This is due to the fact that under low dc voltage, trapped charges dominate, while under high voltage, mobile charge density is much higher. In addition, we show the significant effect of the recombination phenomenon on the external current evolution at transient and steady states.

It is well known that space charge accumulation in insulating materials constitutes the principal cause of dielectric breakdown. Though space charge measurements in polymeric materials have been extensively developed over the last two decades, modeling and simulation works have progressed slowly in this respect. In the present study, a model for bipolar charge transport, as a basis for studying breakdown phenomenon in low density polyethylene (LDPE), is presented. Indeed, we are especially interested in external current dynamic which is the witness of the sample post breakdown. Our results show the effect of the high dc applied voltage and the generation of the space charge packets on the apparition of the post breakdown of the insulator. In order for this effect to be revealed, the external current evolutions under low and high dc applied voltages before and at the breakdown are determined. Indeed, these evolutions show an abrupt increase that is observed when the charge packet aspect occurred in the sample under high dc applied voltage. This observed abrupt increase of the external current is attributed to post breakdown phenomenon. These results are obtained for the first time in modeling and show some aspects similar to those observed in some experimental works.

Transient and steady state currents in polyethylene, under low and high dc voltages, are studied. In fact, a bipolar transport physical model is developed in order to characterize the space charge dynamics within an additive-free polyethylene film, under trapping and recombination mechanisms. The numerical computational models, used for the bipolar transport of carriers, are applied to the Poisson's, the continuity and the transport equations with the appropriate physical conditions. The principal and the new numerical results are calculated especially when high dc voltages are applied. Indeed, the net charge density numerical profiles show the appearance of the space charge packets that are revealed for the first time in numerical modelling although they have long been reported in experimental works. These space charge packets induce some new aspects on the external transient current evolutions, produce the oscillations of the conduction and the displacement current before the steady state, and generate a conduction regime that is dominated by the interface electrode-insulator. These numerical results are consistent with those reported in some experimental works. However, under low dc voltage the space charge packets disappear and the space charge limited current aspect appears on the external current profile.

In this paper, we present a bipolar transport model in low-density polyethylene under high direct-current voltage in order to investigate the charge packet dynamic generated under high injection. These charge packets, observed by our model for the first time, have already been seen in some previous experimental works for a long time. Our model results show that applied electric field and sample thickness play important roles on the apparition of space charge packets.