Effects of Mg doping in the quantum barriers on the efficiency droop of GaN based light emitting diodes

The effects of Mg doping in the quantum barriers（QBs） on the efficiency droop of GaN based light emitting diodes（LEDs） were investigated through a duel wavelength method. Barrier Mg doping would lead to the enhanced hole transportation and reduced polarization field in the quantum wells（QWs）, both may reduce the efficiency droop. However,heavy Mg doping in the QBs would strongly deteriorate the crystal quality of the QWs grown after the doped QB. When increasing the injection current, the carriers would escape from the QWs between n-GaN and the doped QB and recombine non-radiatively in the QWs grown after the doped QB, leading to a serious efficiency droop.

Thermodynamic equilibrium theory-guided design and synthesis of Mg-doped LiFe_(0.4)Mn_(0.6)PO_(4)/C cathode for lithium-ion batteries

Mn-rich LiFe_(1-x)Mn_(x)PO_(4)(x>0.5),which combines the high operation voltage of LiMnPO_(4)with excellent rate performa nce of LiFePO4,is hindered by its sluggish kinetic properties.Herein,thermodynamic equilibrium analysis of Mn^(2+)-Fe^(2+)-Mg^(2+)-C_(2)O_(4)^(2-)-H_(2)O system is used to guide the design and preparation of insitu Mg-doped(Fe_(0.4)Mn_(0.6))_(1-x)Mg_(x)C_(2)O_(4)intermediate,which is then employed as an innovative precursor to synthesize high-performance Mg-doped LiFe_(0.4)Mn_(0.6)PO_(4).It indicates that the metal ions with a high precipitation efficiency and the stoichiometric precursors with uniform element distribution can be achieved under the optimized thermodynamic conditions.Meanwhile,accelerated Li+diffusivity and reduced charge transfer resistance originating from Mg doping are verified by various kinetic characterizations.Benefiting from the contributions of inherited homogeneous element distribution,small particle size,uniform carbon layer coating,enhanced Li+migration ability and structural stability induced by Mg doping,the Li(Fe_(0.4)Mn_(0.6))_(0.97)Mg_(0.03)PO_(4)/C exhibits splendid electrochemical performance.

Improved efficiency and stability of perovskite solar cells with molecular ameliorating of ZnO nanorod/perovskite interface and Mg-doping ZnO

Despite the advanced efficiency of perovskite solar cells(PSCs),electron transportation is still a pending issue.Here the polymer polyvinylpyrrolidone(PVP)is used to enhance the electron injection,which is thanks to the passivation of the defects at the interface between the ZnO electron transporting layer(ETL)and the perovskite.The application of the PVP layer inhibits the device degradation,and 80%of the primary efficiency is kept after 30 d storage in air condition.Additionally,the efficiency of the device is further enhanced by improving the conductivity and crystallinity of the ZnO ETL via Magnesium(Mg)doping in the ZnO nanorods(ZnO NRs).Moreover,the preparation parameters of the ZnO NRs are optimized.By employing the high-crystallinity ZnO ETL and the PVP layer,the power conversion efficiency(PCE)of the champion device is increased from 16.29%to 19.63%.These results demonstrate the advantages of combining mesoscale manipulation with interface modification and doping together.

Influence of Cu doping in Magnesium Hydroxide Nanoparticles for Bandgap Engineering

Cu doped Mg(OH)_(2) nanoparticles were synthesized with varying concentrations from 0 to 10%by a chemical synthesis technique of coprecipitation.X-rays diffraction (XRD) of the samples confirms that all the samples acquire the hexagonal crystal structure.XRD results indicated the solubility limit of dopant in the host material and the secondary phase of CuO was observed beyond 3%Cu doping in Mg(OH)_(2).The reduction in the size of nanoparticles was observed from 166 to 103 nm for Mg(OH)_(2) and 10% Cu doped Mg(OH)_(2)samples,respectively.The shift in absorption spectra exhibited the systematical enhancement in optical bandgap from 5.25 to 6.085 eV.A good correlation was observed between the bandgap energy and crystallite size of the nanocrystals which confirmed the size induced effect in the nanoparticles.The transformation in the sample morphology was observed from irregular spherical particles to sepals like shapes with increasing the Cu concentration in the host material.The energy dispersive X-Ray (EDX) analysis confirmed the purity of mass percentage composition of the elements present in the samples.

Mg acceptor activation mechanism and hole transport characteristics in highly Mg-doped AlGaN alloys

The Mg acceptor activation mechanism and hole transport characteristics in AlGaN alloy with Mg doping concentration(~ 1020 cm-3) grown by metal–organic chemical vapor deposition(MOCVD) are systematically studied through optical and electrical properties. Emission lines of shallow oxygen donors and(VⅢ complex)1- as well as VN3+ and neutral Mg acceptors are observed, which indicate that self-compensation is occurred in Mg-doped AlGaN at highly doping levels. The fitting of the temperature-dependent Hall effect data shows that the acceptor activation energy values in Mgdoped AlxGa1-xN(x = 0.23, 0.35) are 172 meV and 242 meV, and the hole concentrations at room temperature are 1.2×1018 cm-3 and 3.3× 1017 cm-3, respectively. Therefore, it is believed that there exists the combined effect of the Coulomb potentials of the dopants and screening of the Coulomb potentials by a high hole concentration. Moreover, due to the high ionized acceptors’ concentration and compensation ratio, the impurity conduction becomes more prominent and the valence band mobility drops sharply at low temperature.

GaInP/GaAs tandem solar cells with highly Te- and Mg-doped GaAs tunnel junctions grown by MBE

We report a GaInP/GaAs tandem solar cell with a novel GaAs tunnel junction（TJ） with using tellurium（Te） and magnesium（Mg） as n- and p-type dopants via dual-filament low temperature effusion cells grown by molecular beam epitaxy（MBE） at low temperature. The test Te/Mg-doped GaAs TJ shows a peak current density of 21 A/cm2. The tandem solar cell by the Te/Mg TJ shows a short-circuit current density of 12 m A/cm2, but a low open-circuit voltage range of1.4 V^1.71 V under AM1.5 illumination. The secondary ion mass spectroscopy（SIMS） analysis reveals that the Te doping is unexpectedly high and its doping profile extends to the Mg doping region, thus possibly resulting in a less abrupt junction with no tunneling carriers effectively. Furthermore, the tunneling interface shifts from the intended Ga As n＋＋/p＋＋junction to the AlGaInP/GaAs junction with a higher bandgap AlGaInP tunneling layers, thereby reducing the tunneling peak. The Te concentration of ~ 2.5 × 1020 in GaAs could cause a lattice strain of 10-3 in magnitude and thus a surface roughening,which also negatively influences the subsequent growth of the top subcell and the GaAs contacting layers. The doping features of Te and Mg are discussed to understand the photovoltaic response of the studied tandem cell.

Preparation and characterization of Mg-doped CaCu_(3)Ti_(4)O_(12) thin films

Mg-doped CaCu_(3-x)Mg_(x)Ti_(4)O_(12)(x=0,0.05,0.1,0.15,0.2,at.%)thin films were prepared by a modified sol−gel method.A comparative study on the microstructure and electrical properties of Mg-doped CaCu_(3)Ti_(4)O_(12)(CCTO)thin films was carried out.The grain sizes of the Mg-doped CCTO thin films were smaller in comparison to the undoped CCTO films.Furthermore,compared to undoped CCTO films,Mg-doped CCTO thin films obtained higher dielectric constant as well as excellent frequency stability.Meanwhile,Mg doping could reduce the dielectric loss of CCTO thin films in the frequency range of 104−106 Hz.The results showed that the Mg-doped CCTO thin films had the better electrical characteristics compared with the undoped CCTO films.The nonlinear coefficient of Mg-doped CCTO thin films at x=0.15 and x=0.1 was improved to 7.4 and 6.0,respectively.

Magnesium doping to improve the light to heat conversion of OMS-2 for formaldehyde oxidation under visible light irradiation

Mg-doped manganese oxide octahedral molecular sieve(Mg-OMS-2)catalysts were prepared by hydrothermal method.The photothermal degradation performance of these catalysts for formaldehyde(HCHO)in batch system and continuous system was investigated.The light absorption of OMS-2 was increased by Mg-doped,especially for near infrared light,which promoted surface temperature reach a maximum of 214.8℃ under xenon irradiation.At this temperature,the reinforced surface lattice oxygen and oxygen vacancy that formed by lattice distortion via Mg-doped were activated.The best HCHO elimination efficiency was achieved over Mg_(0.2)/OMS-2 catalyst with Mg^(2+)/Mn^(2+)=1/5,which could reduce HCHO from 250 ppm to 10 ppm within 20 min.The in situ DRIFTS was also carried out to monitor the changes in the content of reaction intermediates and analyze the degradation paths of HCHO.It was found the HCHO was attacked by formed·OH and·O^(2-) to generate formate species and carbonate species,and finally transformed to CO_(2) and H_(2)O.This photothermal catalytic oxidation process exhibited a high efficiency purification of HCHO without the help of extra energy consumption.

LiFePO_4 doped with magnesium prepared by hydrothermal reaction in glucose solution

Lithium iron phosphate （LiFePO4） doped with magnesium was hydrothermally synthesized from commercial LiOH, FeSO4, H3PO4 and MgSO4 with glucose as carbon precursor in aqueous solution. The samples were characterized by X-ray powder diffraction, scanning electron microscopy and constant charge-discharge cycling. The results show that the synthesized powders have been in situ coated with carbon precursor produced from caramel reaction of glucose. At ambient temperature （28±2℃）, the electrochemical performances of LiFePO4 prepared exhibit the high discharge capacity of 135 mAh g^-1 at 5C and good capacity retention of 98% over 90 cycles. The excellent electrochemical performances should be correlated with the intimate contact between carbon and LiFePO4 primary and secondary particles, resulting from the in situ formation of carbon precursor/carbon, leading to the increase in conductivity of LiFePO4.

Boosting the electrochemical performance of LiNi_(0.6)Mn_(0.2)Co_(0.2)O_2 through a trace amount of Mg-B co-doping

The extended cycle life of cells is often sacrificed at the expense of high specific energy for high-nickel materials.Cation doping is a promising method to build high-nickel cathode with high energy density and long cycle life.Herein,a trace amount of Mg-B co-doping in LiNi_(0.6)Mn_(0.2)Co_(0.2)O_2(NMC622)is investigated in this work,which shows improved structural and electrochemical stability of 1%Mg-0.5%B co-doped material at both 30 and 55℃in coin-cell.Comprehensive chemical composition,structural,and surface analysis are carried out in this paper.It was found that all the selected materials have a similar composition to the target.Moreover,Mg and B doping have different effects on the crystal structural change of NMC622,to be more specific,the c-lattice parameter increases with Mg doping,while the Li^(+)/Ni^(2+)mixing content increases when B was incorporated into the lattice.Furthermore,the microstructure of primary particles was changed by B doping significantly as confirmed by the SEM images.There were marginal benefits in terms of structural and electrochemical stability of materials introduced by Mg or B sole doping.In comparison,incorporating a suitable amount of both Mg and B into NMC622,we found the capacity retention of cells was noticeably improved by reducing the impedance growth and preventing cation mixing during cycling.This study demonstrates the importance of co-incorporation of Mg,B,and optimizing the co-dopant content to stabilize NMC622 as cathode for lithium-ion batteries.

Improving ionic conductivity of von-Alpen-type NASICON ceramic electrolytes via magnesium doping

NASICON (sodium (Na) superionic conductor) compounds have attracted considerable attention as promising solid electrolyte materials for advanced Na-based batteries. In this study, we investigated the improvement in ionic conductivities of von-Alpen-type NASICON (vA-NASICON) ceramic electrolytes by introducing a magnesium ion (Mg^(2+)) as a heterogeneous element. The optimal Mg-doped vA-NASICON exhibited a high ionic conductivity of 3.64×10^(−3) S·cm^(−1), which was almost 80% higher than that of un-doped vA-NASICON. The changes in physicochemical properties of the vA-NASICONs through the Mg introduction were systematically analyzed, and their effects on the ionic conductivities of the vA-NASICON were studied in detail. When the optimal ratio of Mg^(2+) was used in a synthetic process, the relative density (96.6%) and grain boundary ionic conductivity (σgb) were maximized, which improved the total ionic conductivity (σt) of the vA-NASICON. However, when Mg^(2+) was introduced in excess, the ionic conductivity decreased because of the formation of an undesired sodium magnesium phosphate (NaxMgyPO_(4)) secondary phase. The results of this study are expected to be effectively applied in the development of advanced sodium-based solid electrolytes with high ionic conductivities.

Structure and Raman scattering of Mg-doped ZnO nanoparticles prepared by sol-gel method

Mg-doped ZnO （MgxZn1-xO, x=0-0.10） nanoparticles were prepared by sol-gel method. Structural characterization by X-ray diffraction （XRD） indicates that the lattice parameter a increases and c decreases linearly with the increase in Mg content （x） due to the substitution of Mg2＋ for Zn2＋ in ZnO lattice. The blueshift of Raman modes is observed, impling the increase in force constant of atom vibration in the MgxZn1-xO （MgZnO） nanoparticles. Resonant Raman spectra show longitudinal optical phonon overtones up to fifth order, revealing that the short part of the electron-phonon interaction is enhanced and long-range part is weakened by Mg doping.

Layered K_(0.54)Mn_(0.78)Mg_(0.22)O_(2)as a high-performance cathode material for potassium-ion batteries

Layered Mn-based oxides are one of the promising cathode materials for potassium-ion batteries(KIBs)owing to their high theoretical capacities,abundant material supply,and simple synthesis method.However,the structural deterioration resulting from the Jahn-Teller effect of Mn ions hinders their further development in KIBs.Herein,a novel Mn-based layered oxide,K_(0.54)Mn_(0.78)Mg_(0.22)O_(2),is successfully designed and fabricated as KIBs cathode for the first time.It delivers smooth charging/discharging curves with high specific capacity of 132.4 mAh·g^(‒1)at 20 mA·g^(‒1)and good high-rate cycling stability with a capacity retention of 84%over 100 cycles at 200 mA·g^(‒1).Combining in-situ X-ray diffraction(XRD)and ex-situ X-ray photoelectron spectroscopy(XPS)analysis,the storage of K-ions by K_(0.54)Mn_(0.78)Mg_(0.22)O_(2)is revealed to be a solid-solution processes with reversible slip of the crystal lattice.The studies suggest that the rational doping of inactive Mg2+can effectively suppress the Jahn-Teller effect and provide outstanding structure stability.This work deepens the understanding of the structural evolution of Mn-based layered materials doped with inactive materials during de/potassiation processes.

Potential use of magnesium industrial waste for synthesis of Li and Mg co-doped LiMn_(2)O_(4)nanoparticles as cathode material for Li-ion batteries:Effect of sintering temperature

Potential advantages of active electrode nanomaterials have led to development of high energy and power density lithium-ion(Li-ion)batteries.However,under increasing demand for critical resources such as lithium and cobalt,it is necessary to use abundant raw materials,which can be obtained from industrial waste.In this work,purified Mg(OH)_(2)from waste generated in the production of Li2CO3 with natural brines from the Salar de Atacama(Chile)is used as a doping agent for synthesis of LiMn_(2)O_(4)(LMO)spinel octahedral nanoparticles co-doped with excess Li and Mg.Crystallization of a pure cubic spinel phase(Fd3m)takes place at 500℃and sintering temperature effect at 580 and 750℃,thus the elemental composition and the structural,morphological,and electrochemical properties are studied in detail.Optimum electrochemical performance at room temperature is obtained for Li_(1.03)Mg_(0.05)Mn_(1.92)O_(4)spinel sintered at 750℃with an initial discharge capacity of 121.3 mAh·g^(-1)and capacity retention of 94.0%after 100 cycles at C/3.A locally ordered spinel structure is obtained at 750℃,and doping with Mg^(2+)improves structural rigidity.Synergy between both effects resulted in a high Li^(+)diffusion rate(1.29×10^(-9)cm^(2)·s^(-1))significantly improving cycling performance at elevated C-rates in 50℃.

Thermal properties of Y1-xMgxTaO4-x/2 ceramics via anion sublattice adjustment

A systematic investigation concerned with Y1-xMgxTaO4-x/2(x=0,0.08,0.12,0.16 and 0.20,respectively)ceramics was fabricated by a solid-state reaction method and characterized by X-ray diffraction(XRD),Raman spectroscopy,scanning electron microscopy(SEM)and thermal analysis.XRD spectra display that all of the samples are excellently consistent with the standard XRD spectrum of monoclinic YTaO4(PDF No.24-1415;space group:I2(5)).The Raman peaks of the samples doped with Mg2+just widen slightly compared with those of pure YTaO4,which are in agreement with the results of XRD.The thermal conductivity of dense 7 wt%–8 wt%yttria-stabilized zirconia(7–8 YSZ)ceramic is about 2.5 W·m-1·K-1at 900°C,while the Y1-xMgxTaO4-x/2(x=0,0.08,0.12,0.16 and 0.20)ceramics possess lower thermal conductivity in the range of 1.45–1.57 W·m-1·K-1at 900°C,which declines by35%compared with that of 7–8 YSZ.The lower thermal conductivities of Y1-xMgxTaO4-x/2(x=0,0.08,0.12,0.16and 0.20)ceramics are originated from the enhanced phonon scattering caused by oxygen vacancy and Mg2+ions defect complex.However,the thermal expansion coefficients are about 9.0910-6–9.5910-6K-1along with the different amounts of Mg2+doping at 1200°C.Compared to the pure sample,the thermal expansion coefficient decreases slightly when the Mg2+doping amount is over 20%.The systematic investigations on the phase,microstructure,elastic and thermal properties of Y1-xMgxTaO4-x/2(x=0,0.08,0.12,0.16 and 0.20)ceramics will provide guidance for its application at high temperature,especially as thermal barrier coatings.

Electrochemical performance of La_(2–x)Sm_xMg_(16)Ni+200 wt.% Ni(x=0, 0.1, 0.2, 0.3, 0.4) alloys

Nanocrystalline and amorphous La_（2–x）Sm_xMg_（16）Ni＋200wt.% Ni（x=0, 0.1, 0.2, 0.3, 0.4） alloys were prepared by mechanical milling technology. The structures of as-cast and milled alloys were investigated by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. Electrochemical performance of the alloy was studied by using an automatic galvanostatic system. The electrochemical impedance spectra（EIS） and Tafel polarization curves were measured by electrochemical workstation. The results indicated that the structures of the as-cast and milled alloys presented a multiphase structure with nanocrystalline and amorphous phase, moreover, transforming from nanocrystalline to amorphous phase with Sm doping. With the increase of Sm content, the maximum discharge capacity of the alloy was decreased from 922.6 to 649.1 m Ah/g, the high-rate discharge ability（HRD） was decreased, the cycle stability was strengthened, and the alloy exhibited excellent electrochemical kinetics. In addition, the charge-transfer resistance（R_（ct）） of alloy was lessened from 0.05874 to 0.02953 ？ and the limiting current density（I_L） was descended from 2.08366 to 1.04592 A/g with increasing Sm content.

Almond gum assisted synthesis of Mg doped Fe_(2)O_(3) NPs:Structural analysis,electrochemical sensing,and optical applications

Mg-doped Fe_(2)O_(3)nanoparticles(M-FNPs)are successfully prepared first time by facile green-aided(almond gum)combustion route.The structural analysis of synthesized nanoparticles was well analyzed by Powder X-ray Diffrac-tion(PXRD),Fourier Transform Infrared spectroscopy(FT-IR),Scanning Electron Microscope(SEM),Raman spec-troscopy and UV-Visible spectral studies.PXRD showed a nanocrystalline nature and determined the average particle size to be 85 nm.The surface morphologies of the prepared nanocomposite was measured by SEM tech-nique reveals the porous and spongy like structure.The photodegradation activity on 20×10^(−6)of Fast Orange Red(FOR)organic model dye using M-FNPs(50 mg)under UV light irradiation was investigatedin detail.Elec-trochemical examination of the prepared material was conducted using graphite-M-FNP electrode paste in 0.1 M KCl solution,and its performance in redox reaction was determined to be very good via cyclic voltammetry and electrochemical impedance spectroscopy.Further,an extension to sensor studies revealed broad differences in redox positions for paracetamol sensors,at 0.64 V and 0.41 V,confirming highly chemical sensor activity in alkaline medium for 1∼5 mM concentrations.