Concentration Of Impurity Ions Research Articles

Gain in Thermoelectric Figure of Merit of Al<sub>x</sub>Ga<sub>1-x</sub>As/GaAs Type Superlattices Induced by Strong Impurity Screening

In multi-layer structures impurity scattering is effectively reduced by the modulation doping in order to achieve high charge carrier mobility and, as a consequence, better device performance. In this paper, the thermoelectric properties of superlattices when electrons are scattered by strongly screened ionized impurities are discussed. In low-temperature and strong screening circumstances, dependence of the thermopower, power factor, and figure of merit on the superlattice period, miniband width, and screening radius is found. For the specified superlattice parameters and ionized impurity concentration, the figure of merit reaches the value of 2.6. The thermopower of the superlattices five times exceeds that of bulk samples.

In-situ direct seawater electrolysis using floating platform in ocean with uncontrollable wave motion

Direct hydrogen production from inexhaustible seawater using abundant offshore wind power offers a promising pathway for achieving a sustainable energy industry and fuel economy. Various direct seawater electrolysis methods have been demonstrated to be effective at the laboratory scale. However, larger-scale in situ demonstrations that are completely free of corrosion and side reactions in fluctuating oceans are lacking. Here, fluctuating conditions of the ocean were considered for the first time, and seawater electrolysis in wave motion environment was achieved. We present the successful scaling of a floating seawater electrolysis system that employed wind power in Xinghua Bay and the integration of a 1.2 Nm3 h−1-scale pilot system. Stable electrolysis operation was achieved for over 240 h with an electrolytic energy consumption of 5 kWh Nm−3 H2 and a high purity (>99.9%) of hydrogen under fluctuating ocean conditions (0~0.9 m wave height, 0~15 m s−1 wind speed), which is comparable to that during onshore water electrolysis. The concentration of impurity ions in the electrolyte was low and stable over a long period of time under complex and changing scenarios. We identified the technological challenges and performances of the key system components and examined the future outlook for this emerging technology.

Selective separation of lithium from the hydrochloric acid leachate of lithium ores via the extraction system containing TBP-FeCl3

The elevation of comprehensive lithium recovery remains a formidable challenge in lithium extraction from lithium bearing ores due to the equilibrium solubility constraints affecting the lithium precipitation reaction. Hence, this work drew inspirations from lithium extraction techniques in salt lakes by characterizing the hydrochloric acid leachate of lithium ores as a distinct brine. The leachate composition was regulated and solvent extraction technology for selective lithium extraction was developed. By employing the loaded organic phase with Fe3+ (2TBP-NaFeCl4) to extract the leachate, and utilizing a four-stage countercurrent extraction process, the extraction efficiency of lithium could be achieved at 99 % at least. Following three-stage scrubbing and two-stage countercurrent stripping experiments, the stabilized stripping efficiency of lithium was 99.24 %. The concentration of Li+ in the stripping solution was enriched up to 16.404 g/L, while the total concentration of impurity ions was only 0.424 g/L. The resulting lithium-enriched solution could be utilized to prepare high-purity lithium chloride. This process has achieved a highly selective and efficient extraction of lithium, thereby enhancing the overall lithium extraction efficiency. The Density Functional Theory results indicate that the loaded organic phase selectively extracted lithium through ion exchange.

Diverse carrier mobilities in halide perovskites: The role of conductive network and ionized impurity scattering

In past decades, ABX3 halide perovskites have attracted great interest in solar cells due to excellent optoelectronic properties, such as high carrier mobility. However, instability and toxicity are obstacles on the commercial route for perovskites. Many studies have turned to exploring A2BX6 and A3B2X9 for better stability. Unfortunately, the carrier mobilities of these two types are inferior to ABX3, lower by an order of magnitude. Furthermore, the mobility of ABX3 is distributed over a large range of 1.78–4500 cm2 V−1 s−1 in experiments, which contributes to another diversity of mobilities. In this paper, we aim at revealing the physical origin of the above-mentioned diversities by theoretical studies on CsBX3, Cs2BX6, and Cs3B2X9 (B=Sn, Pb, Sb, Bi, X=Br, Cl). The difference in group velocities is the major reason responsible for the variation in these types. The unique three-dimensional connected conductive network of CsBX3 determines its large group velocity. As for carrier scattering, ionized impurity scattering dominates at low carrier and high ionized impurity concentrations. Detailed analysis reveals that band degeneracy is strongly related to the impurity scattering rate, while dielectric constant is almost immune. Our study provides a better understanding of the relationship between electronic structures and mobilities for potential applications in photovoltaics.

Multi-ion magnetized sheath properties with non-extensive electron distribution

Magnetized plasma sheath plays an important role in semiconductor processing, material surface modification, film deposition, etc. In plasma experiments and discharge applications, multi-ion plasma consisting of more than two kinds of ions often exists. For a long range interacting plasma system, non-Maxwellian electrons can be described by the non-extensive distribution of Tsallis. In this work, a fluid model with one-dimensional spatial coordinates and three-dimensional velocity coordinates is established for the multi-ion plasma sheath. It is assumed that the electron velocity in the sheath follows a non-extensive distribution, and the background helium ions and different kinds of impurity ions are magnetized in a magnetic field with a certain tilt angle. The effects of non-extensive parameters, impurity ions and oblique magnetic field on the number density, velocity, wall potential and kinetic energy of ions in the multi-ion magnetic sheath are investigated by numerical simulation. The results show that in the helium-hydrogen or helium-argon mixed plasma sheath, the ionic velocity along the vertical wall direction decreases with the increase of the non-extensive parameters, the number density of ions and electrons in the sheath, the sheath thickness , and the kinetic energy of ions at the wall decrease. When the concentration of impurity ions increases, the kinetic energy of ions on the wall is independent of the type of ions. With the increase of magnetic field intensity, the number density of helium ions and the velocity along the vertical wall fluctuate along the sheath edge, and the fluctuation amplitude increases with the decrease of non-extensive parameters, while the heavy ions have no obvious fluctuation. In addition, the effects of the types and concentrations of impurity ions on the related properties of the sheath are also analyzed. With the increase of the magnetic field intensity, the number density and the velocity along the vertical wall direction fluctuate at the sheath edge, and the fluctuation amplitude increases with the decrease of the non-extensive parameter, whereas there are no significant fluctuations for heavy ions. In addition, when impurity ions are heavy ions, the absolute value of wall potential increases with the increase of impurity ion concentration and the decrease of non-extensibility parameters, and the kinetic energy of background ions increases at the wall surface. When the impurity ion is a light ion, the absolute value of the wall potential decreases with the increase of the impurity ion concentration and the decrease of the non-extensibility parameter, and the kinetic energy of the background ion at the wall decreases.

PROCESSES OF DEFECT FORMATION IN SILICON DIFFUSIONALLY DOPED WITH PLATINUM AND IRRADIATED WITH PROTONS

In this work, we studied the effect of technological regimes and proton implantation on the processes of defect formation in single-crystal n-type silicon (n-Si) doped with platinum using the method of impedance spectroscopy. It has been established that radiation-induced changes in the electrical conductivity of silicon depend significantly on the technological regimes of doping with impurities in silicon. Hodographs show that doping with platinum leads to a decrease in the electrical resistance of silicon samples. Irradiation with 2 MeV protons at a dose of 5.1 × 1014 particles / cm2 leads to a significant (2-3 times) increase in the electrical resistance of the silicon samples under study. It is concluded that the relatively high resistance to radiation exposure (resistance change of no more than 16%: from 55 kΩ to 65 kΩ as a result of ion implantation) of samples doped at 1200°C is presumably due to a higher concentration of impurity ions (platinum) in the samples volume compared to 1100°C.

Electron mobility of heavily doped semiconductors including multiple scattering by ionized impurities

A theoretical treatment of the multiple scattering problem for electrons in heavily doped semiconductors is developed for the purpose of resolving a long-standing discrepancy between theory and experiment on electron transport in semiconductors and semimetals. The scattering strength term in the traditional Brooks–Herring formula for ionized impurity scattering is modified to take into account the effect of the spatial proximity of ionized donors leading to an additional scattering term proportional to the cube of ionized impurity concentration, whereas the Brooks–Herring theory varies strictly linearly with the ionized impurity concentration. Comparisons between theory and experiment for GaAs, GaN, ZnO, and α-Sn are presented, showing significant improvement overall. In some cases, improvements greater than an order of magnitude are achieved. The agreement between theory and experiment for heavily doped ZnO over the temperature range of 21–322 K is within about 1%, depending on temperature.

LITHIUM HYDROXIDE FORMATION BY MEMBRANE ELECTROLYSIS

The production of high-purity lithium hydroxide (LiOH) solution by electrochemical conversion of soluble lithium salts (membrane electrolysis) was tested on semi-industrial scale. Stainless steel (cathode) and lead (anode) were used as electrode materials. Lithium sulphate solution was utilised as anolyte and water - as catholyte. During membrane electrolysis, water oxidation takes place in the anode compartment with the formation of gaseous oxygen and protons. Lithium ions permeate through the cationic membrane into the cathode compartment, where gaseous hydrogen and hydroxide ions are formed as the products of water decomposition on the cathode, so lithium hydroxide gets concentrated up to 33-36 g/dm3 with respect to lithium oxide. Electrolysis efficiency is 50-55 % for one process cycle. Sulphuric acid formed in the anode compartment may be then neutralised by adding lithium carbonate, and the formed lithium sulphate may be re-used in membrane electrolysis, which means anolyte recycling. Five successive electrolysis cycles with recycled anolyte allow an increase in the degree of lithium ion transfer from the anode to cathode compartment to 95-98 %. It is established that, in addition to lithium, other metal ions (sodium, potassium, calcium, etc.) and sulphate ions migrate through the cation-exchange membrane into the cathode compartment from anolyte solution. To evaluate the quality of the obtained lithium hydroxide monohydrate (LiOH•H2O), lithium hydroxide solutions obtained both by membrane electrolysis and by the traditional lime causticisation process were evaporated. Comparison between the concentrations of impurity ions in lithium hydroxide monohydrate samples obtained using different methods shows that the product of better purity may be synthesized from lithium sulphate solution by membrane electrolysis.

Electrocatalytic and green system coupling strategy for simultaneous recovery and purification of uranium from uranium-containing wastewater

The recycling of uranium in wastewater is not only beneficial to the protection of ecological safety but also has great significance for the sustainable development of nuclear energy. However, there is no satisfactory method to recover and reuse uranium efficiently up to now. Here, we have developed an efficient and economical strategy that can achieve uranium recovery and direct reuse in wastewater. The feasibility analysis verified that the strategy still had good separation and recovery ability in acidic, alkaline, and high-salinity environments. The purity of uranium recovered from the separated liquid phase after electrochemical purification was up to about 99.95%. Ultrasonication could greatly increase the efficiency of this strategy, and 99.00% of high-purity uranium could be recovered within 2 h. We further improved the overall recovery rate by recovering the residual solid-phase uranium, and the overall recovery of uranium was increased to 99.40%. Moreover, the concentration of impurity ions in the recovered solution met the World Health Organization guidelines. In summary, the development of this strategy is of great importance for the sustainable use of uranium resources and environmental protection.

Влияние внутреннего электрического поля на накопление подвижного заряда в МОП-структурах

Using the developed quantitative model, the influence of the internal electric field on the process of accumulation of a mobile charge in MOS structures is shown. The distribution of the mobile charge over the depth of SiO2 is calculated for various times of thermal field exposure and impurity concentrations. Using Na+ ions as an example, the numerical calculation is compared with the analytical and experimental dependences. It is shown that at high concentrations of impurity ions, the internal electric field induced by them increases near the cathode surface and causes excessive accumulation of impurities at the interface.

Sensitivity study of thermal hydraulics to corrosion of heat exchange tubes in steam generator

A leakage accident occurs in the circulating water system in PWRs, impurity ions enter the SG with the secondary circuit feed water and cause electrochemical corrosion of the heat transfer tubes (HTTs). Based on the hide out and return mathematical model in the SG, a coupled mathematical model of mass transfer-electromigration-hydrodynamics of impurity ions in the secondary boiling channel of SG is deduced. The accuracy of the mathematical model is verified by experiments, and the effects of heat flux density (Peq), flow velocity (Peu), impurity ion concentration (Pec) and relative solubility of impurity ions (Kp) on impurity ions migration and electrochemical corrosion are analyzed and discussed. The results show that Peq mainly controls the diffusion of impurity ions and thus affects the migration rate of impurity ions. The mass transfer of impurity ions driven by Peq can enhance the reduction of H+, thereby accelerating the corrosion rate of HTTs. Peu mainly affects the synergistic effect of convective mass transfer and electromigration during the migration of impurity ions, and charge transfer mainly controls the electrochemical corrosion of HTTs surface with the increase of Peu. The Pec on the surface of HTTs changes linearly with time, and the corrosion rate increases with the increase of Pec. The corrosion rate of HTTs is proportional to Kp, and Kp is a main factor that causes different corrosion rates in different location of HTTs. In this paper, a coupled model for the sensitivity of thermal-hydraulic parameters (Peq, Peu, Pec and Kp) in SG to electrochemical corrosion of HTTs is proposed for the first time. The research results can provide important support for the development of corresponding response strategies, schemes for the life prediction of HTTs and the safety maintenance of nuclear power plants.

The effect of impurity ions on the pH adjustment for vanadium-bearing acid leaching solution by selective electrodialysis

Leaching of vanadium shale with sulfuric acid results in a vanadium acid leaching solution with low pH and many impurity ions. Monovalent selective electrodialysis was employed to adjust the pH of the acid leaching solution by recovering the sulfuric acid. The results demonstrated that CIMS monovalent selective cation exchange membrane had good performance in separating H+ and VO2+ for various vanadium shale acid leaching solutions without Fe3+. The effect of the concentration of impurity ions was investigated. Under the optimum concentration of impurity ions, The treatment time was 125 min, the V rejection ratio reached 98.06%, the water loss rate was controlled at 5.25%, and the pH was adjusted from 0.08 to 1.8. Mg2+ had the best optimization effect on vanadium rejection. Al3+ had the best optimization effect in reducing water loss. F− had the best optimization effect on the treatment time. Meanwhile, the effect of impurity ions on the pH adjustment of acid leaching solution was discussed qualitatively. SEM-EDS analysis confirmed that Fe3+ fouled the membrane and caused the loss of vanadium. Since Fe3+ and PO43− in the acid leaching solution formed FePO4 precipitates. Selective electrodialysis was used to treat vanadium-bearing acid leaching solution, the pH could meet the requirements of separation and purification without consuming any reagent. This process is clean and efficient, and the recycled acid is reused without producing waste water or residue.

Tungsten impurity effects on the coupling of TEM and ITG mode in reversed magnetic shear tokamak plasmas

The trapped electron mode (TEM) and ion temperature gradient (ITG) mode may couple into one hybrid mode or coexist simultaneously, depending on the regime of tokamak plasma parameters. A gyrokinetic integral eigenvalue equation is applied to investigate the coupling of TEM and ITG mode in the presence of tungsten (W) impurity in tokamak geometry of reversed magnetic shear (RMS). Systematic analysis of W impurity effects on the mode characteristics and induced quasi-linear particle flux has been performed in a wide regime of plasma parameters such as density gradient , charge concentration , and charge number of impurity ions, and poloidal wave number spectrum. It is found that both RMS and the impurity ions with inwardly peaked density profile and high charge concentration have strongly stabilizing effects on the modes. Furthermore, the increasing tends to decouple the hybrid mode into coexisting modes or dominating TEM/ITG mode in different parameter regions. The significance of the results for the particle transport of impurity and main ions as well as electrons in advanced tokamaks with W components is discussed.

Quasi-linear heat transport induced by ITG turbulence in the presence of impurities

The impurity effects on turbulent transport induced by ion temperature gradient (ITG) turbulence are numerically studied in tokamak plasmas, using a gyrokinetic quasi-linear model. The characteristics of the instability and heat fluxes in the presence of impurity ions are investigated for a broad parameter regime, including temperature and density gradients of main and impurity ions, concentration, charge and mass numbers of impurity ions, magnetic shear as well as wave vector spectrum. The heat fluxes are demonstrated to depend not only on the saturation amplitude of the instability but also on the phase shift between and . The peaking factor of temperature/density profile, defined as the ratio of major radius to gradient scale length when the total turbulent heat flux equals zero, is fitted with linear/quadratic functions. In addition, the contributions from diagonal and off-diagonal terms to heat fluxes are identified in detail, i.e. the main ion heat diffusion are proved to be dominated by off-diagonal (diagonal) terms for regions of weak (strong) ITG. In general, steep temperature gradients of main ions as well as hollow density profiles of impurity ions significantly enhance instability and heat fluxes. However, it is interesting to find that the effect of impurity ions with positive density gradient may transit from the enhancement to reduction of the quasi-linear heat flux of main ions in regions of steep ITG, corresponding to transport barriers (e.g. pedestal of H-mode and I-mode plasmas). Both strong and weak positive magnetic shear decrease heat transport.

Recent progresses on the boron species in aqueous solution: structure, phase equilibria, metastable zone width (MZW) and thermodynamic model

Abstract The complexity of boron species in aqueous solution becomes the bottleneck in development of boron resources from brine. The concentrations of different boron species and transformation mechanism among boron species are mainly affected with the total boron concentration, temperatures, pH of the solution, and cations in the solution. The change trends for concentration of total boron in the complicated aqueous solution can be obtained with the phase equilibrium results, but the accurate concentration of boron species in the solution cannot be obtained. The metastable zone width (MZW) of borates and H3BO3 changed with the concentrations of impurity ions, the stirring rate, cooling rate, and original temperature for the saturated solution. The Pitzer model is the effective method to calculate the concentration of boron species. More thermodynamic data at temperatures below and above 298.15 K are needed for model parameterization. The main problems existed in the systems containing boron species were summarized, and the future development direction is also discussed. The progresses on boron species in the aqueous solution can provide fundamental data in the comprehensive exploitation of the brine boron resource.

The influence of synthesis modes of alumina ceramics doped with manganese on sensitivity to ionizing radiation

A temperature growth and a decrease in impurity ion concentration result in a sensitivity increase of Al2O3:Mn ceramics to the ionizing radiation. The highest sensitivity to the ionizing radiation for Mn-doped alumina ceramics is observed for minimum dopant concentration and a maximum of temperature sintering (maximum sintering temperature). A sublinear increase in a thermoluminescence intensity with a growing dose is observed in the range of 1–400 Gy for the peak at 460 K and in the range of 1–100 Gy for the peak at 620 K for the Mn-doped alumina ceramic (1 wt % of Mn in a solution) annealed under vacuum at the temperature of 1700°С for 2 h.

“Triangular Antiferromagnet” RbFe(MoO4)2 with the Replacement of Nonmagnetic Ions

The magnetization curves, as well as electron spin resonance and nuclear magnetic resonance spectra of 87Rb+ ions, have been measured in the quasi-two-dimensional antiferromagnet RbFe(MoO4)2 on a triangular lattice with the random modulation of the exchange bond network. Random modulation has been performed by means of the partial substitution of nonmagnetic Rb+ ions for K+ ions. It has been shown that random static disorder thus created at an impurity ion concentration of 15% drastically changes the spin structure. A noncollinear structure with significant sublattice magnetization components transverse to the magnetic field occurs in the doped compound. At the same time, the spin structure in the pure compound has the same magnetic moment, but transverse spin components disappear near a magnetic field of one third of the saturation field (three-sublattice structure with two upward sublattices and one downward sublattice). The revealed doping-induced drastic rearrangement of the spin structure of the triangular antiferromagnet has been explained by the interplay between the contribution of dynamic fluctuations, which makes maximally collinear states favorable in free energy, and the contribution from freeze-in disorder, which ensures the energy gain for the maximally noncollinear arrangement of sublattices.

Thermal ionization energy of hydrogen-like impurities in semiconductor materials

In the work the dependence of the thermal ionization energy of hydrogen-like donors and acceptors on their concentration in n- and p-type semiconductors is analyzed analytically and numerically. The impurity concentrations and temperatures at which the semiconductors are on the insulator side of the concentration insulator – metal phase transition (Mott transition) are considered. It is assumed that impurities in the crystal are distributed randomly (according to Poisson), and their energy levels are distributed normally (according to Gauss). In the quasi-classical approximation, it is shown, for the first time, that the decrease in the ionization energy of impurities mainly occurs due to the joint manifestation of two reasons. Firstly, from the excited states of electrically neutral impurities, a quasicontinuous band of allowed energy values is formed for c-band electrons in an n-type crystal (or for v-band holes in a p-type crystal). This reduces the energy required for the thermally activated transition of electron from the donor to the c-band (for the transition of the hole from the acceptor to the v-band). Secondly, from the ground (unexcited) states of impurities a classical impurity band is formed, the width of which at low temperatures is determined only by the concentration of impurity ions. In moderately compensated semiconductors (when the ratio of the concentration of minority impurities to the concentration of majority impurities is less than 50 %) the Fermi level is located closer to the edge of the band of allowed energy values than the middle of the impurity band, that issue reduces thermal ionization energy of impurities from states in the vicinity of the Fermi level (transition of electron from a donor to the c-band, or hole from an acceptor to the v-band). Previously, these two causes of decrease in the thermal ionization energy due to increase in the concentration of impurities were considered separately. The results of calculations according to the proposed formulas are quantitatively agree with the known experimental data for a number of semiconductor materials (germanium, silicon, diamond, gallium arsenide and phosphide, silicon carbide, zinc selenide) with a moderate compensation ratio.

Magnetic and electrical properties of yttrium substituted manganese ferrite nanoparticles prepared via micro-emulsion route

Polycrystalline oxide YxMnFe2−xO4 was prepared via low-cost micro emulsion method. As concentration of yttrium ions increased, their electrical and magnetic properties were changed. Effect of secondary phase YFeO3 on the electrical and magnetic properties of the material were also studied and discussed in detail. As concentration of impurity ions increased, variation in resistivity was observed. This variation also affected the magnetic behavior of the prepared Mn-based spinel ferrites. Various parameters such as the saturation magnetization (Ms), retentivety (Mr), coercivity (Hc), anisotropic constant (k1), magnetic moments (μB) have been calculated from recorded M-H loops of all unsubstituted and substituted MnFe2O4 nanoparticles. Ms and Mr values found in the range 27–50 emu/g and 1.8–7.6 emu/g respectively.

Preparation of electrolyte for vanadium redox flow battery from sodium-polyvanadate precipitated wastewater

In order to reduce pollution from wastewater and recycle the valuable metal in the vanadium precipitation process, sodium polyvanadate precipitated wastewater was utilized to prepare an electrolyte for the vanadium redox flow battery after two-stage purification via solvent extraction, which removed most of the impurities, especially Mn. The concentration of impurity ions was less than 10 ppm, as obtained by using inductively coupled plasma-optical emission spectroscopy, and the electrolyte obtained from the wastewater complied with the Chinese national standard. The method applied herein can simplify the preparation process compared to the conventional method and avoid ammonia nitrogen pollution. Electrochemical analysis showed that the properties of the prepared electrolyte were similar to those of the standard electrolyte. From the charge/discharge test, the energy efficiency and coulombic efficiency of the electrolyte reached nearly 90% of those of the standard electrolyte, which indicates that the electrolyte prepared from wastewater has the potential for commercial applications.