Doping Effects on the Crystal Structure and Electrochemical Performance of LiFePO4/C

LiFe_0.98M_0.02PO₄/C (M = Mg, Ni, Co, Sr) composite materials were prepared by solid‐state synthesis method using Fe₂O₃ as one of the starting materials. The structures and electrochemical performance of samples were carried out by means of XRD, SEM, TEM, and constant‐current charge–discharge method. The results showed that the ion doping did not change the crystal structure and morphology of LiFePO₄. Unit‐cell volume gradually increased, which was good for embedding and disembedding of Li⁺, and improving conductivity and charge–discharge performance. The electrical conductivity of powders was increased by carbon coating and ion doping. The initial discharge capacity of Ni²⁺‐doped sample reached 156.6 mA·h/g and 149.4 mA·h/g at 0.2C and 1C rate. After 30 cycles, the capacity retention rate was still 98.8% and 97.2%.     

Structural Characteristics and Electrical Conductivity of Spark Plasma Sintered Ytterbia Co‐doped Scandia Stabilized Zirconia

The effect of replacing Sc₂O₃ with Yb₂O₃ on the structural and electrical properties of xYb₂O₃–(12–x)Sc₂O₃–88ZrO₂ has been investigated. Spark plasma sintering technique is employed to fabricate dense bulk samples from the nano‐sized powders. X‐ray diffraction and transmission electron microscopy performed on pellets indicate the existence of cubic and rhombohedral phases in 12ScSZ, and a single cubic phase in all the co‐doped compositions. However, Raman spectroscopic studies suggest the presence of a metastable tetragonal t″‐phase along with rhombohedral phases in 12ScSZ, whereas a single cubic phase in all the co‐doped compositions. Significant enhancement in the conductivity of grain and grain boundary is observed on replacing Sc₂O₃ with Yb₂O₃. In the intermediate temperature range, 1Yb11ScSZ exhibits the highest, while 12ScSZ shows the lowest conductivity values, which is attributed to corresponding phases present in that range. Through co‐doping with >1 mol% Yb₂O₃ leads to conductivity decrease, but the value remains higher than that of 12ScSZ. A sharp conductivity change is observed in 12ScSZ and 1Yb11ScSZ samples, which is attributed to partial phase transition as well to the formation of cation‐vacancy complexes. In this work, the beneficial effect of Yb₂O₃ co‐doping in 12ScSZ on the phase and conductivity has been highlighted.     

Controllable microstructure tailoring for regulating conductivity in Al-doped ZnO ceramics

Structural and electrical behavior of Al₂O₃ doped ZnO-based ceramics were investigated as function of the aluminum doping ratios under reducing sintering atmosphere (N₂+CO). With Al₂O₃ doping from 0.1 mol% to 0.55 mol%, the electrical conductivity increases firstly to a maximum (1.52 × 10⁵ S·m⁻¹) at 0.25 mol%, and then decreases gradually. The increased conductivity is explained by the formation of shallow donors as Al_Zn-Zn_i complexes with doping to 0.25 mol%. As Al₂O₃ doping further increasing to 0.55 mol%, ZnAl₂O₄ spinel phase and more ZnO-ZnO grain boundaries are formed, hindering charge carriers transport, to decrease charge carrier mobility, thus to decrease the conductivity of ZnO ceramics. Therefore, the Al_Zn-Zn_i complexes, grain boundaries and ZnAl₂O₄ spinel can be adjusted by doping different Al₂O₃ amount, thus the carriers’ concentration and their mobility are optimized to increase the conductivity. Our work, as a fundamental research, is of great significance to control conductivity by regulating Al₂O₃ doping.     

Structural analysis and electrode performance of Ce doped SrMnO3 synthesised by EDTA citrate complexing process

Abstract

Sr_1?xCe_xMnO₃ (SCM, 0·1≤x≤0·4) powders were synthesised by an ethylenediaminetetraacetic acid citrate complexing process, and their properties were investigated. The synthesised Sr_1?xCe_xMnO₃ powders showed a pure perovskite phase, whereas the composition with x?=?0·4 had second phases. The unit cell volumes increased with increasing Ce content because substituted Ce ions formed some Mn³⁺ ions, which have a larger ionic radius than Mn⁴⁺. The electrical conductivity improved with increasing Ce content up to x?=?0·3 (291 S cm^?1 at 750°C), revealing a double exchange interaction. Although the electrical conductivity was increased by doping Ce ions, the polarisation resistance increased due to the increase in lattice distortion with doping Ce content. The substitution of Ce ions for Sr in SrMnO₃ led to the formation of larger Mn³⁺ ions than Mn⁴⁺ ions and lattice distortion, which would affect the electrical and oxygen ion conductivity.     

Multifunctional behavior of acceptor-cation substitution at higher doping concentration in PZT ceramics

The Fe-doped PZT, Pb (Zr, Ti)_1-xFe_xO₃, ceramics have gathered plenty of attention because of the interplay of ferroelectric and ferromagnetic properties. In the present study, we report the properties of Pb(Zr_0.52Ti_0.48)_1-xFe_xO₃ prepared by conventional solid-state reaction route with varying Fe³⁺ doping concentrations, x = 0, 0.05, 0.10, 0.15 and 0.20. Study of X-ray diffraction patterns confirmed the tetragonal crystal structure along with reduction in tetragonality and unit-cell size with doping. It also showed formation of secondary magneto-plumbite phase at higher doping concentrations. The SEM micrographs exhibited decrease in grain size with increase in doping concentration (for x > 0.05). The increase in oxygen vacancies and the formation of secondary magneto-plumbite phase and Fe³⁺–VO²⁻–Fe³⁺ defect dipole complexes introduced with the acceptor (Fe³⁺) doping, caused clamping of the domain walls and hence reduced the room temperature dielectric constant as the doping concentration was increased. The coexistence of electrical polarization and magnetic moment at room temperature in all PFZT compositions confirmed the multiferroic characteristic in the ceramic samples. Electric polarization (P_r) and coercive fields (E_c) decreased with increase in Fe³⁺ concentration in PFZT sample. However, magnetization (M) and magnetic coercive fields (E_c) increased with the increasing Fe³⁺ concentration due to the dominant effect of F-center exchange mechanism in Fe³⁺–VO²⁻–Fe³⁺ and formation of ferromagnetic secondary magneto-plumbite phase.     

Tuning of conductive type and magnetic properties of Ca3Co2O6 ceramics through Pb‐doping

The effect of Pb doping on structural, electrical, magnetic, and thermal transport properties of Ca_3?xPb_xCo₂O₆ (x=0‐0.3) ceramics has been investigated systemically. It is found that the substituted Pb‐ions have a mixed valence state of +2 and +4, and a small amount of Co³⁺ ions will transfer into Co²⁺ due to the substitution of Pb⁴⁺ for Ca²⁺. The resistivity decreases monotonically with increasing Pb content, which is related to the variation in carrier concentration and the enhanced grain connectivity. The signs of both Hall coefficient and thermopower changed from positive to negative by a proper Pb doping, indicating the conductive type of Ca₃Co₂O₆ can be effectively tuned from p to n through the doping. The low‐temperature magnetization, the magnetic exchange coupling constant J and Weiss temperature θ decrease monotonically with the increase in Pb‐doping content, indicating the strength of the ferromagnetic interaction between adjacent high spin Co³⁺ ions has been weakened due to the reduced magnetic correlation length in these Pb‐doped samples.     

High‐Performance Small‐Amount Fe2O3‐Doped (K,Na)NbO3‐Based Lead‐Free Piezoceramics with Irregular Phase Evolution

[(K_0.43Na_0.57)_0.94Li_0.06][(Nb_0.94Sb_0.06)_0.95Ta_0.05]O₃ + x mol% Fe₂O₃ (KNLNST + x Fe, x = 0~0.60) lead‐free piezoelectric ceramics were prepared by conventional solid‐state reaction processing. The effects of small‐amount Fe₂O₃ doping on the microstructure and electrical properties of the KNLNST ceramics were systematically investigated. With increasing Fe³⁺ content, the orthorhombic‐tetragonal polymorphic phase transition temperature (T_O‐T) of KNLNST + x Fe ceramics presented an obvious “V” type variation trend, and T_O‐T was successfully shifted to near room temperature without changing T_C (T_C = 315°C) via doping Fe₂O₃ around 0.25 mol%. Electrical properties were significantly enhanced due to the coexistence of both orthorhombic and tetragonal ferroelectric phases at room temperature. The ceramics doped with 0.20 mol% Fe₂O₃ possessed optimal piezoelectric and dielectric properties of d₃₃ = 306 pC/N, k_p = 47.0%, = 1483 and tan δ = 0.023. It was revealed that the strong internal stress in the KNLNST + x Fe ceramics with higher Fe³⁺ contents (x = 0.40, 0.60) stabilized the orthorhombic phase, leading to the irregular “V” type rather than the usually observed monotonic phase transition with composition change in the ceramics.     

Ba and Gd Doping Effect in (BaxSr1–x)0.95Gd0.05Co0.8Fe0.2O3–δ (x = 0.1–0.9) Cathode on the Phase Structure and Electrochemical Performance

In this study, Ba_xSr_1–xCo_0.8Fe_0.2O_3–δ (BSCF) doped with trace of Gd were studied for phase structures and properties about thermal expansion, electrical conductivity, and electrocatalytic activity. The solution range of barium in Ba_xSr_1–xCo_0.8Fe_0.2O_3–δ can be extended to 0.1 ≤ x ≤ 0.7 after the introduction of small amount of Gd³⁺ ions (only for 5%) into the Ba/Sr‐site. The calculation results of the crystal structure and the crystal lattice energy show that the ratio of Ba/Sr and doping of Gd³⁺ lead to increase the lattice parameter and the Co/Fe ionic average valence state in B‐site. Moreover, the ratio of Ba/Sr and doping of Gd³⁺ were found to have significant impacts on the high‐temperature physical properties and electrochemical characteristics. All oxides exhibited decreases in the thermal expansion coefficient (TEC) and electrical conductivity with increasing Ba/Sr ratio. Barium insertion was found to change the area‐specific resistance (ASR) of porous (not dense) cathodes. An ASR values of 0.048, 0.072, 0.064, 0.121, and 0.059 Ω cm² under air condition were observed at 650 °C for BSGCF with x = 0.1, 0.2, 0.3, 0.5, and 0.7, respectively.     

Dual Doping: An Effective Method to Enhance the Electrochemical Properties of Li10GeP2S12‐Based Solid Electrolytes

Multiple doping is widely used to improve the performance of a material, including its electrical transport, mechanical, and photovoltaic properties. In this paper, Sn–Se dual‐doped Li₁₀GeP₂S₁₂ (LGPS, thio‐LISICON II analogue) electrolytes were synthesized via ball milling and sintering and compared with those Sn or Se single‐doped. Successful Sn and/or Se substitution expanded the unit cell and formed units, which were verified by X‐ray powder diffraction, energy‐dispersive X‐ray spectroscopy, and Raman spectroscopy. In contrast to the limited benefits of Se single doping and the negative effects of Sn single doping, Sn–Se dual doping demonstrated up to 53% enhancement in ionic conductivity. More importantly, Sn–Se dual‐doped LGPS showed an extremely low activation energy of 16 kJ/mol, which is one of the lowest known values for lithium ion conductors; as well as one of the widest electrochemical windows of 8 V. Sn–Se dual‐doped LGPS is a promising electrolyte for advanced all‐solid‐state batteries.     

Structures and electrical conductivities of Gd3+ and Fe3+ co-doped cerium oxide electrolytes sintered at low temperature for ILT-SOFCs

Gd³⁺ and Fe³⁺ co-doped cerium oxide electrolytes, Ce_0.9Gd_0.1‐xFe_xO_2-δ (x?=?0.00, 0.01, 0.03, 0.05, 0.07, 0.10), were prepared by co-precipitation for ultrafine precursor powders and sintering for densified ceramic pellets. The crystal and microscopic structures were characterized by XRD, FESEM and Raman spectroscopy and their electrical properties were studied by AC impedance spectroscopy and the measurement of single cell's outputs. In comparison with Ce_0.9Gd_0.1O_1.95, the ceramic pellets of Ce_0.9Gd_0.1‐xFe_xO_2-δ with a relative density of 95% can be obtained after sintered at 1000?°C for 5?h, showing a remarkably enhanced sintering performance with a sintering temperature reduction of 500?°C, which might be ascribed to the highly activated migration of constituent species in the cerium oxide lattice doped with Gd³⁺ and Fe³⁺ions. Moreover, the electrical conductivity of Ce_0.9Gd_0.1‐xFe_xO_2-δ can be significantly enhanced depending on the mole fraction x, with Ce_0.9Gd_0.07Fe_0.03O_1.95 exhibiting the highest electrical conductivity of 38 mS/cm at 800?°C, about 36% higher than that of Ce_0.9Gd_0.1O_1.95 electrolyte sintered at 1500?°C for 5?h. So, The Gd³⁺ and Fe³⁺ co-doped cerium oxide would be an excellent candidate electrolyte for ILT SOFCs due to its prominent sintering performance and enhanced electrical conductivity.     

Magnetic and conducting Fe3O4–polypyrrole nanoparticles with core‐shell structure

Magnetic and conducting Fe₃O₄–polypyrrole nanoparticles with core‐shell structure were prepared in the presence of Fe₃O₄ magnetic fluid in aqueous solution containing sodium dodecylbenzenesulfonate (NaDS) as a surfactant and dopant. Both the conductivity and magnetization of the composites depend strongly on the Fe₃O₄ content and the doping degree. With increase of Fe₃O₄ content in the composite, the conductivity at room temperature decreases, but the saturated magnetization and coercive force increase. Transmission electron microscopy (TEM) images of Fe₃O₄ and Fe₃O₄–polypyrrole particles show almost spherical particles with diameters ranging from 20 to 30 and 30 to 40 nm, respectively. The thermal stability of Fe₃O₄–polypyrrole composites is higher than that of pure polypyrrole. Studies of IR, UV–visible and X‐ray photoelectron spectroscopy (XPS) spectra suggest that the increased thermal stability may be due to interactions between Fe₃O₄ particles and polypyrrole backbone. Copyright © 2003 Society of Chemical Industry     

Synthesis and Enhanced Electrochemical Performance of Sm‐Doped Sr2Fe1.5Mo0.5O6

Sr₂Fe_1.5Mo_0.5O₆ (SFM) is a mixed ionic and electronic conductor which can be used as both anode and cathode materials in intermediate‐temperature solid oxide fuel cell. By doping Sm into the Sr‐site, the electrical conductivity of SFM is enhanced effectively. The single cell with a configuration of Sr_1.8Sm_0.2Fe_1.5Mo_0.5O₆|La_0.8Sr_0.2Ga_0.83Mg_0.17O_2.815| Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃ obtained maximum power densities of 459, 594, and 742 mW cm⁻² with H₂ as the fuel at 750, 800, and 850 °C, respectively. The results suggest that doping with Sm is a very promising way in enhancing the electrical conductivity of SFM and consequently can greatly improve its anode performance.     

Increased electrical conductivity and the mechanism of samarium‐doped ceria/Al2O3 nanocomposite electrolyte

To further enhance the electrical conductivity of doped ceria, the samarium‐doped ceria (SDC)/Al₂O₃ nanocomposites were prepared through sintering the coprecipitated powders in 1100°C‐1300°C. The grain sizes of all composites are less than 100 nm and decrease with alumina addition. Besides the main phases of SDC and Al₂O₃, the SmAlO₃ can precipitate in the composites if sintered at higher temperatures or for longer dwell time. The deviations of SDC diffraction peak positions demonstrate the solid solution of alumina into SDC lattice. The total electrical conductivities of the composites increase with alumina content until 30% alumina is added. The SDC/30%Al₂O₃ presents the higher total conductivity than the pure SDC by about five times. Specifically, the grain interior conductivity generally decreases with the alumina addition while the grain‐boundary conductivity increases with that. The introduction of the conductive SDC/Al₂O₃ interface can contribute to the rise of total conductivity, yet the excessive alumina addition also blocks the oxygen ion conduction. The SmAlO₃ precipitation is detrimental to the ion conduction for it consumes part of alumina and leads to the decrement in Sm concentration of SDC grain. Appropriate alumina addition not only enhances the conductivity of SDC but also lowers the material cost.     

Structural and optical study of Fe3+-doped Al2O3 nanocrystals prepared by new sol gel precursors

Pure and Fe-doped Al₂O₃ nanoparticles (NPs) were synthesized with different iron doping percentage of 1, 3, and 5 mol% employing sol gel technique with AlCl₃, FeCl₃ as well as ethylene glycol (EG) and Polyvinylpyrrolidone (PVP) stabilizers as precursors. The XRD results indicated that the hexagonal structure of Fe/Al₂O₃ nanocomposite with alpha phase was formed by the substitution of Fe³⁺ ions in the alumina network. The sizes of the NPs obtained for the pure samples and doped samples at percentage dopant of 5% were 35 and 28 nm, respectively. The results of FTIR optical analysis showed the vibrational bond at the wavelength of 448 cm⁻¹, indicating the Al-O band in the sample. The UV-DRS analysis showed that the energy band gap for the pure NPs was 4 eV, but with increase in iron dopant up to 5%, it decreased to 3.42 eV. In addition, the results of photoluminescence (PL) analysis demonstrated that with increase in doping percentage, the PL intensity diminished. VSM magnetic analysis showed that with increase in iron dopant, the ferromagnetic state emerged in the NPs at saturation magnetism of 0.136 emu/g. Finally, photocatalytic experimental results demonstrated that 5% Fe-doped Al₂O₃ NPs effectively degrade MB approximately 53%.     

Synthesis,structural characterization,and photoluminescence properties of TTB‐type PbTa2O6:Eu3+ phosphor

Undoped and Eu³⁺‐doped tetragonal tungsten bronze (TTB) PbTa₂O₆ phosphors were synthesized by using solid‐state reaction method. Synthesized samples were characterized by XRD, SEM‐EDS, and photoluminescence analyses. XRD results revealed TTB‐type crystal structure with single phase up to 10 mol% Eu³⁺ doping concentration. In SEM‐EDS analyses, elemental composition of Pb decreased with the increasing concentration of Eu³⁺. Emissions at the excitation wavelength of 398.5 nm were observed at 593.2 and 618.8 nm due to ⁵D₀→⁷F₁ transitions and ⁵D₀→⁷F₂ transitions, respectively. Emission increased with the increasing Eu³⁺ doping concentration up to 10 mol% and not observed concentration quenching.     

Phase Stability and Optoelectronic Properties of the Bixbyite Phase in the Gallium–Indium–Tin–Oxide System

X‐ray diffraction techniques were used to determine the phase boundaries of the In₂O₃ solid solution phase in the Ga₂O₃–In₂O₃–SnO₂ ternary system. The effects of Ga and Sn content on the unit cell dimensions of the bixbyite phase were calculated by a linear regression fit, the results of which indicate the two substitutive cations have opposite and independent effects on the lattice parameter. These results suggest that the cations do not strongly interact with each other in the crystal. Measurements of optoelectronic properties were also taken on single‐phase bulk specimens within the solid solution to establish their dependence on composition. As anticipated, Sn doping yields corresponding increases in conductivity, reduction in the absolute value of Seebeck coefficient, and increase in optical band gap. In contrast, these properties are not significantly affected by varying Ga content, confirming that Ga behaves as an isovalent dopant at the low doping levels involved.     

Valence state and ionic conduction in Mn‐doped MgO partially stabilized zirconia

The mechanism of the enhancement in the ionic conductivity resulting from cubic phase stabilization in MgO partially stabilized zirconia (MgPSZ) by Mn doping was studied by examining the local Zr‐O structure. Cubic phase (14 vol%) in MgPSZ was increased with the addition of MnO₂, and 10 mol% Mn‐doped MgPSZ exhibited the highest cubic phase fraction (98.72%), which was analyzed by Rietveld refinement. In addition, only the cubic phase, not the monoclinic and tetragonal phases, was observed in the TEM‐SAED pattern of 10 mol% Mn‐doped MgPSZ. Doped Mn exhibited a high Mn²⁺/Mn⁴⁺ ratio, which was identified by X‐ray photoelectron spectroscopy (XPS). In addition, it indicates that oxygen vacancy formation by substitution of Mn²⁺ in the Zr⁴⁺ site in MgPSZ increased cubic phase fraction. Ionic conductivity of MgPSZ was improved by the cubic phase increase attributed to Mn doping, and 10 mol% Mn‐doped MgPSZ exhibited higher ionic conductivity than MgPSZ. To investigate the mechanism of the ionic conductivity improvement, Zr‐O local structure in Mn‐doped MgPSZ was analyzed by Zr K‐edge EXAFS of MgPSZ, and the number of bonding of the Zr‐O first shell decreased with increased Mn substitution. Therefore, it was considered that the oxygen vacancy generation led to an increase in the cubic phase and the number of ionic conduction sites.     

NIR photoluminescence and radioluminescence characteristics of Nd3+ doped BaTa2O6 phosphor

Barium tantalate phosphors activated with different concentrations of Nd³⁺ ion were synthesized via conventional solid state reaction method. The synthesized ceramic powders were characterized by X–ray diffraction (XRD), scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS), laser diode (LD) excited near infrared (NIR) photoluminescence and X‐ray induced radioluminescence (RL) analyses. In XRD results, Nd³⁺ doped BaTa₂O₆ structure with tetragonal tungsten bronze (TTB) symmetry was observed to continue up to 10 mol%. In the examination of ceramic powders by SEM, grain size decreased with the increasing doping concentration. By using laser diode excited NIR photoluminescence of BaTa₂O₆:Nd³⁺ phosphor exhibited characteristic emissions at 877, 1080, and 1376 nm wavelengths due to ⁴F_3/2 → ⁴I_11/2, ⁴F_3/2 → ⁴I_11/2, and ⁴F_3/2 → ⁴I_11/2 band transitions respectively. Scintillation properties of Nd³⁺ doped samples from UV to near‐IR spectral region were carried out by the radioluminescence analysis. NIR and scintillation emissions initially increased by the doping concentration, and then decreased due to concentration quenching effect.     

Boosting the photovoltaic performance of Zn2SnO4‐based dye‐sensitized solar cells by Si doping into Zn2SnO4

In the present work, Zn₂SnO₄ nanoparticles were doped with silicon to improve their electrical and optical properties by the conventional solid‐state reaction method. The results showed that the minimum electrical resistivity of about 0.09 Ωcm was obtained for Zn₂SnO₄ nanoparticles with 3% Si doping. The decrease in the electrical resistivity can be attributed to the insertion of Si⁺⁴ atoms into the Zn⁺² and/or Sn⁺⁴ sites and also the formation of more oxygen vacancies in the Zn₂SnO₄ lattice. The formation of the more oxygen vacancy defect states in Si‐doped Zn₂SnO₄ nanoparticles was verified by photoluminescence spectroscopy. The efficiency of a dye‐sensitized solar cell based on 3% Si‐doped Zn₂SnO₄ was significantly better, by about 81%, compared to that of a cell based on the undoped Zn₂SnO₄. The enhancement in the efficiency can be ascribed to the facilitation of electron transport throughout a photoelectrode due to increase in the charge carrier concentration which was caused by Si doping.     

Visible light active Cu-doped iron oxide for photocatalytic treatment of methylene blue

In recent work, pure α-Fe₂O₃ (F-1) and series of 5% Cu doped Fe₂O₃ (CF-5) , 10% Cu doped Fe₂O₃ (CF-10) and 15% Cu doped Fe₂O₃ (CF-15) nanoparticles by facile chemical coprecipitation method were synthesized to study the effect of concentration of doping for photocatalytic activity. As prepared F-1, CF-5, CF-10, CF-15 nanoparticles were subjected to X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) techniques to analyse the structural and functional groups features. These characterization techniques confirmed the successful doping of Cu ²⁺ ions in α-Fe₂O₃. The crystallite size of synthesized samples was calculated by Scherrer formula. Gradually decline in crystallite size from 18 to 15 nm was observed for undoped to doped samples. Scanning electron microscopic (SEM) analysis expressed that doping of Cu reduced the aggregation of particles and enhanced the surface area of nanoparticles. UV–Visible spectroscopic analysis of synthesized samples was used to calculate the bandgap energy of F-1, CF-5, CF-10, CF-15 nanoparticles i.e., 2.0, 1.7, 1.5, 1.4eV respectively. Narrowing bandgap energy of doped hematite supported to perform excellent photocatalytic activity. Maximum degradation of methylene blue was recorded via CF-10 within 140 min. Higher degradation rate of methylene blue by optimal concentration of CF-10 is due to effective electron trapping ability of photocatalyst.