Cerium Substitution Research Articles

Enhancing the electro catalytic activity of manganese ferrite through cerium substitution for oxygen evolution in KOH solutions

Alkaline water electrolysis (AWE) is the simplest way of producing hydrogen, an attractive fuel for the future.

Cerium Doped NiO Nanoparticles: A Novel Electrode Material for High Performance Pseudocapacitor Applications

The present study demonstrates a novel electrodeposition approach by which Ce 3+ doped NiO nanoparticles coated on titanium foils can be processed into a high surface area electrode for rechargeable energy storage applications. A detailed study has been performed to elucidate how cerium substitution doping and redox reaction behaviors underlying these electrodes impact the cyclic and capacitive behavior of the electrode. These nanoparticles were synthesized via molten salt technique and exhibited particle size of ∼ 65 nm. From the analysis of the relevant electrochemical parameters, an intrinsic correlation between the substitutional doping amount, capacitance and the internal resistance has been deduced and explained on the basis of relative contributions from the faradic properties of the Ce 3+ doped NiO nanoparticles in different electrolytes of varied concentrations. These thin film electrodes exhibited specific mass capacitance value as high as 1500 Fg −1 and 1077 Fg −1 (1 Ag −1 ) measured from cyclic voltammetry and charge discharge curves respectively, which was found to be 5 times higher than the pristine NiO nanoparticles with a capacitance retention of >70% at the end of 2000th cycle. Further, a working model button cell employing these rechargeable electrodes is also demonstrated exhibiting an energy and power density of 92 Wh Kg −1 and 10 kW Kg −1 , respectively. It has been shown that electrodes based on such nanoparticles can allow significant room for improvement in the cyclic stability and performance of a hybrid capacitor/battery system.

Cerium Substitution in Yttrium Iron Garnet: Valence State, Structure, and Energetics

The garnet structure is a promising nuclear waste form because it can accommodate various actinide elements. Yttrium iron garnet, Y3Fe5O12 (YIG), is a model composition for such substitutions. Since cerium (Ce) can be considered an analogue of actinide elements such as thorium (Th), plutonium (Pu), and uranium (U), studying the local structure and thermodynamic stability of Ce-substituted YIG (Ce:YIG) can provide insights into the structural and energetic aspects of large ion substitution in garnets. Single phases of YIG with Ce substitution up to 20 mol % (Y3–xCexFe5O12 with 0 ≤ x ≤ 0.2) were synthesized through a citrate–nitrate combustion method. The oxidation state of Ce was examined by X-ray absorption near edge structure spectroscopy (XANES); the oxidation state and site occupancy of iron (Fe) as a function of Ce loading also was monitored by 57Fe–Mossbauer spectroscopy. These measurements establish that Ce is predominantly in the trivalent state at low substitution levels, while a mixture of trival...

Modified Pechini Synthesis of Proton‐Conducting Ba(Ce,Ti)O3 and Comparative Studies of the Effects of Acceptors on its Structure, Stability, Sinterability, and Conductivity

The phase structure, chemical stability, sinterability, and electrical performance of the proton‐conducting Ba(Ce,Ti)O3 solid solution with a series of acceptors M (M = In, Y, Sm) synthesized by a modified Pechini method were systematically investigated. The substitution of cerium with titanium was proved as an effective way to improve the stability of BaCeO3. Especially for the BaCe0.95Ti0.05O3−δ sample doped with In, no change in the phase was found even after treatment in the atmosphere containing both CO2 and H2O at 700°C for 10 h. Thanks to the highly sinteractive powders with particle size of ~100 nm, dense ceramics were easily acquired. Moreover, compared with the undoped BaCe0.95Ti0.05O3 sample, In, Y, and Sm dopants further improved the sinterability of the solid solution. In particular, In played a role of sintering aid and led to the largest linear shrinkage of the ceramics. As to the electrical performance, the transport properties of the samples under various atmospheres were analyzed and compared. The impedance tests demonstrated the best electrical performance of the Y‐doped samples.

Structure and electrical properties of SrBi2Nb2O9-based ferroelectric ceramics with lithium and cerium modification

• (LiCe) modified SBNBN ceramics was synthesized by using solid state reaction method firstly. • The d 33 and T c of the SBNBN-LC10 are 28 pC/N and 583 °C, respectively. • The better piezoelectric activities are induced by the co-contribution of crystal lattice distortion and oxygen vacancy . Aurivillius-type ceramics, Sr 0.6 (BiNa) 0.2 Bi 2 Nb 2 O 9 (SBNBN) with lithium and cerium modification, were synthesized by using conventional solid-state processing. X-ray diffraction analyses (XRD) and Raman spectroscopy revealed that the lithium and cerium modified SBNBN ceramics had a single phase with perovskite-type orthorhombic structure. The effect of lithium and cerium substitution for A site on structure and electric properties of the SBNBN-based ceramics was investigated. Piezoelectric properties of the SBNBN ceramics were significantly improved by the modification of lithium and cerium. Curie temperature T c and piezoelectric coefficient d 33 of the Sr 0.5 (BiNa) 0.2 (LiCe) 0.05 Bi 2 Nb 2 O 9 ceramics were 583 °C and 28 pC/N, respectively. Reasons for enhancement in piezoelectric properties of the SBNBN ceramics were discussed.

Synthesis and catalytic properties of iron-cerium phosphate prepared in ethylene glycol using additives

The effects of cerium substitution, use of additives, and heating temperature on the chemical composition and catalytic activity of iron phosphate were evaluated. Iron-cerium phosphate was prepared from iron nitrate, ammonium cerium nitrate, and sodium phosphate in ethylene glycol using sodium dodecyl-sulfate or acetylacetone as additive. The chemical composition, particle shape and size distribution of the obtained samples were respectively evaluated based on ICP and XRD, SEM, and laser diffraction/scattering analysis. The catalytic activity was evaluated based on the decomposition of the complex formed from formaldehyde, ammonium acetate, and acetylacetone. XRD peaks corresponding to FePO4 were observed for the samples heated at 600 °C whereas samples treated at lower temperatures were amorphous. Iron-cerium phosphates heated at 200 °C and 400 °C exhibited high catalytic activity for the decomposition of the aforementioned complex.

Modified titania and titanium-containing composites as fillers exhibiting an electrorheological effect

SiO2/TiO2 nanocomposites and individual titania (S = 30–500 m2/g) have been prepared through cohydrolysis of organomineral silicon and titanium derivatives in the presence of templates. We demonstrate that heterovalent substitution of chromium or cerium for titanium increases the thermal stability of TiO2 in terms of its crystallite size and specific surface area. After drying at 120°C, fillers based on SiO2/TiO2 composites (coprecipitated and core-shell SiO2/TiO2 particles) exhibit a significant electrorheological response due to appreciable hydrate and hydroxyl layers on the surface of the particles. Structural modification of titania also allows one to increase the electrorheological effect through an increase in specific surface and defect formation.

Study of Superconducting Properties in Bismuth-Based Cerium Doped High-T c Superconductors

Superconductivity in bismuth-based high-Tc superconducting materials attracts the researchers for their unique properties. Bismuth-based superconductors commonly called BSCCO have great importance among the superconducting family. These are divided into three phases among them 2223 phase is highly studied in order to investigate its superconducting properties by substitution of different elements. We have studied the substitution of cerium (Ce) on the calcium site of bismuth-based Bi(Pb)Sr(Ba)-2223 high-Tc superconductor. The nominal compositions of Bi1.6Pb0.4Sr1.6Ba0.4(Ca1−xCex)2Cu3Ox ceramic superconductor were prepared by the sol–gel method. X-ray diffraction (XRD) was done at room temperature for structural analysis and different parameters were calculated. Surface morphology was done by scanning electron microscopy (SEM). DC resistivity measurements for the transition temperature of synthesized superconducting samples were taken by the standard four-probe method, apparatus for which was developed in our laboratory. Current density measurements were also taken by the same apparatus. The synthesized superconducting samples were also characterized by thermogravimetric analysis (TG) and Fourier transformation infrared radiations (FTIR). It is observed that the substitution of cerium on the calcium site favors the formation of single high-Tc 2223 phase.

Effect of Ce substitution on structural and superconducting properties of Bi-2212 system

In this study, Bi2Sr2Ca1−xCexCu2Oy, where x = 0, 0.01, 0.05, 0.1 and 0.25, superconducting samples were prepared by solid state method and subsequently used as feed in a laser induced directional solidification (LFZ) process. The physical properties of the samples were investigated by powder X-ray diffraction, scanning electron microscopy, dc-electrical resistance, magnetization, and magnetic-hysteresis loops measurements. It has been found that no significant difference has been observed in the critical transition temperatures of samples except for the sample with the highest Ce additions, which shows the lowest T C compared with the other doped samples. Magnetic hysteresis measurements have shown that the hysteresis loop is greater than the doped samples. In addition, critical current density values obtained from the hysteresis loops measurements by using Bean’s critical state model show a decrease with Ce-addition. All the results indicate that Cerium substitution for Ca produces the deterioration on the superconducting properties, compared with the undoped sample.

Improved the Electrochemical Performance of LiCe1−xNixO2 Cathode Material for Rechargeable Lithium Ion Battery

Cerium substituted LiCe(1-x)Ni(x)O2 (0.00 < X < 0.20) (Ce = 0.00 < X < 0.20) nano-particles were synthesized by sol-gel method using nitrate as precursor at 800 degrees C for 12 hrs. XRD studies were revealed a well defined layer structure and a linear variation of lattice parameters with the addition of Cerium confirmed phase pure compounds in a rhombohedral structure for all materials. The surface morphological and particles agglomeration changes by the substitution of Cerium in LiNiO2 particles were examined by scanning electron microscope technique and TEM techniques. Ce3+ has prevented Jahn-Teller distortion and contained the NiO6 in LiCe(1-x)Ni(x)O2 through charge transfer from Ce-3d orbital to nearby Ni-3d orbital. The preferential occupation of Ce3+ in the Li sites was decreased the mixing of Ni2+ into the Li sites and improved the electrochemical properties of LiNiO2. The galvanostatic charge/discharge studies using assembled cells were carried out at 0.5 C rates. Cyclic voltammetric studies were carried out in the potential range between 3.5 V and 4.7 V at a scan rate of 0.1 mV s(-1). Electrochemical impedance spectroscopy revealed that, LiCe0.15Ni0.85O2 augmented charge transfer resistance upon cycling. The variations of cerium mixing and hexagonal ordering with the element (increase in R-factor) were favoured the first discharge capacity with the substituted element. LiCe0.15Ni0.85O2 nano cathode materials have superior electrochemical performances, such as, high charge-discharge capacity, high coulombic efficiency, high electrical conductivity and low irreversible capacity loss.

Cerium Doped Bismuth Based High T&lt;sub&gt;c&lt;/sub&gt; Superconductor: Synthesis and Study of Superconducting Properties

High-Tc superconductivity has been an emerging field for researchers since its discovery. Bismith based superconductors commonly called BSCCO have great importance among the superconducting family. It is divided into three phases among them 2223 phase is highly studied in order to investigate its superconducting properties by substitution of different elements. We have studied the substitution of cerium (Ce) on calcium site of bismuth based Bi (Pb)Sr (Ba)-2223 high-Tc superconductor. The nominal compositions of Bi1.6Pb0.4Sr1.6Ba0.4(Ca1-xCex)2Cu3Ox ceramic superconductor were prepared by wet chemical method. Stoichiometric amounts of Bi2O3, PbO, Sr (NO3)2, BaCO3, CaCO3, CuO and CeO2 were used as starting materials. Structural analysis was done by X-ray diffraction (XRD) at room temperature and different parameters were calculated. DC resistivity measurements for the transition temperature of synthesized superconducting samples were taken by the standard four-probe method, apparatus for which was developed in our laboratory. It is observed that with the substitution of cerium on calcium site the single high-Tc 2223 phase is obtained.

Synthesis and enhancement of current density in cerium doped Bi(Pb)Sr(Ba)-2 2 2 3 high Tc superconductor

Bismuth based superconductors (BSCCO) having 2223 phase is highly carried by the researchers to study the structural and other properties. The effect of substitution of cerium element on calcium site of bismuth based Bi(Pb)Sr(Ba)-2223 high Tc superconductor for the enhancement of superconducting properties like critical temperature(Tc) and critical current density (Jc) are studied. The nominal compositions of Bi1.6Pb0.4(Sr1−yBay)2(Ca1−xCex)2Cu3OY (where x=0.0, 0.1, 0.2, 0.4 and y=0.0, 0.4) ceramic superconductor were prepared by wet chemical method. Stoichiometric amounts of Bi2O3, PbO, Sr(NO3)2, BaCO3, CaCO3, CuO and CeO2 were used as starting materials. The effect of substitution of cerium on calcium site and its effect on current density of Bi-2223 phase were studied. To study the structural morphology and surface analysis X-ray diffraction (XRD) and scanning electron microscopy (SEM) was done. It is observed that with the substitution of cerium on calcium site not only the phase pure material is obtained but also the current density increases.

Universal Superconducting Ground State in Nd1.85Ce0.15CuO4and Nd2CuO4

Superconducting Nd1.85Ce0.15CuO4 (Tczero = 24 K) and Nd2CuO4 (Tczero = 25 K) thin films have been grown by molecular beam epitaxy and their magneto-transport and structural properties have been investigated. The as-grown films are insulators irrespective of the substitution level, and superconductivity is induced after the samples are treated by an annealing process under reducing atmospheres. Though the metallic conductivity is higher in the Ce4+ substituted sample, the superconducting properties are quite similar between Ce4+ substituted and substitution-free samples. A similar upper critical magnetic field as well as a similar superconducting transition temperature of Nd1.85Ce0.15CuO4 and Nd2CuO4 shows that the addition of electrons merely influences the superconducting state. Consequently, the appearance of an antiferromagnetic Mott insulating state solely depends on the annealing process, not on the electron doping or cerium substitution level.

Universal Superconducting Ground State in Nd1.85Ce0.15CuO4 and Nd2CuO4

Superconducting Nd1.85Ce0.15CuO4 (Tczero = 24 K) and Nd2CuO4 (Tczero = 25 K) thin films have been grown by molecular beam epitaxy and their magneto-transport and structural properties have been investigated. The as-grown films are insulators irrespective of the substitution level, and superconductivity is induced after the samples are treated by an annealing process under reducing atmospheres. Though the metallic conductivity is higher in the Ce4+ substituted sample, the superconducting properties are quite similar between Ce4+ substituted and substitution-free samples. A similar upper critical magnetic field as well as a similar superconducting transition temperature of Nd1.85Ce0.15CuO4 and Nd2CuO4 shows that the addition of electrons merely influences the superconducting state. Consequently, the appearance of an antiferromagnetic Mott insulating state solely depends on the annealing process, not on the electron doping or cerium substitution level.

Effect of Ce‐Doping on the Electrical and Electrocatalytical Behavior of La/Sr Chromo‐Manganite Perovskite as New SOFC Anode

AbstractThe effect of cerium substitution on the electrical and electrochemical characteristics of a new anode material La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) was examined by synthesizing CexLa0.75–xSr0.25Cr0.5Mn0.5O3 for x = 0–0.375). From x = 0–0.25, the structure is rhombohedral (S.G. R‐3c), and with a higher cerium content (x = 0.375) it becomes cubic (S.G. Pm‐3m). These materials are stable in the operating conditions of an SOFC anode. CexLa0.75–xSr0.25Cr0.5Mn0.5O3 and LSCM materials are p‐type semi‐conductors. Cerium substitution improves the conductivity in neutral atmosphere from 18.3 to 35.4 S cm–1 for x = 0 and 0.375, respectively, at 1,173 K. In reducing conditions, the conductivity is not influenced by cerium substitution, and it is about 1 S cm–1 at 1,173 K. High temperature XRD shows that structure becomes cubic at 1,073 K in operating (reducing) conditions. Cerium substitution positively enhances the electrochemical behavior, as proved by studying the properties of dense cone‐shaped electrodes.

First-principles calculations of oxygen vacancies and cerium substitution in lutetium pyrosilicate

Cerium-doped lutetium pyrosilicate (LPS:Ce) has attracted much attention for its extensive applications. However, oxygen vacancies will lower its luminescent efficiency. The charge transfer transition between cerium ions and neighboring oxygen vacancies has a long decay time. First-principles calculations on oxygen vacancies, cerium substitution and their complexes in LPS have been performed to research their influence on luminescence. The bridging-oxygen vacancy has the lowest formation energy among oxygen vacancies. We discuss the process of luminescence quenching due to oxygen vacancies. The cerium substitution is less favorable in the oxygen-rich condition. The defect complex of the cerium substitution and bridging-oxygen vacancy has the lowest formation energy among defect complexes. The charge transfer transition between cerium ions and neighboring oxygen vacancies is not related to it but to other two defect complexes. All defect complexes have high formation energies in oxygen-rich condition. We discuss the density of states of perfect and defective crystals.

Catalytic combustion of methane over cerium-doped cobalt chromite catalysts

Cerium modified cobalt chromite catalysts were prepared via co-precipitation method and investigated for the catalytic combustion of methane. Characterization studies by X-ray diffraction (XRD), Raman spectroscopy, BET, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction mass spectroscopy (CH 4 TPR-MS) and temperature-programmed desorption of oxygen (O 2-TPD) were carried out. An improvement of the catalytic activity was observed over cerium-substituted cobalt chromite catalysts with appropriate cerium substitution degrees. The best result has been attained with 5% cerium modified catalyst, for which 5% chromium in CoCr 2O 4 was substituted by cerium, and the catalytic activity reached 90% of methane conversion at 465 °C. The characterization results indicated that cerium doping could deform the spinel structure and cause redistribution of metal ions with different oxidation states; consequently, they would increase crystal defects and oxygen vacancy concentration, which facilitate oxygen mobility and thus increase the catalytic performance of cerium modified cobalt chromite catalysts.

Influence of Ce Doping on Structural and Transport Properties of Ca1−x Ce x MnO3 (x=0.2) Manganite

We have investigated structural, electric, magnetic and thermal transport properties of electron doped Ca1−xCexMnO3 (x=0.2) manganites. The Cerium substitution for Ca2+causes electron doping into insulating CaMnO3 without eg electron. At room temperature the polycrystalline Ca0.8Ce0.2MnO3 is in the crystallographic orthorhombic structure, with Pnma space group symmetry from the refinement of x-ray powder diffraction patterns. The electrical resistivity data infers that Ca0.8Ce0.2MnO3 manganite is in the semiconducting phase. A smooth linear behavior of log plot values is obtained and is well fitted with adiabatic small polaron conduction model. Nearest-neighbor hopping of a small polaron leads to a mobility with a thermally activated form. The negative values of thermopower infer electron as carriers in Ca0.8Ce0.2MnO3. From susceptibility measurements the Ce doped CaMnO3 shows a transition from antiferromagnetic (AFM) to paramagnetic (PM) phase.

Effect of Complexing Agent on Morphology and Crystal Structure of La1-xCexCoO3 (x=0, 0.2, and 0.4) Perovskite-Type Mixed Oxides Catalyst Prepared by Sol-Gel Method

. La1-xCexCoO3 (x=0, 0.2, and 0.4) perovskite-type mixed oxides using polyvinyl alcohol (PVA) as complexing agent at two molar ratio of metal ion to PVA (1:1 and 1:2) were successfully prepared by sol-gel process. The precursor included lanthanum (II) nitrate hexahydrate, cerium (II) nitrate hexahydrate, and cobalt (II) nitrate hexahydrate where polyvinyl alcohol was added as complexing agent. The suitable condition of Cerium (Ce) substitution and PVA molar ratio were established for further application in hydrocarbon conversion to high value added products. TGA thermogram of as-prepared precursor showed that PVA absolutely decomposed at temperature higher than 500°C. XRD patterns of calcined catalyst showed both LaCoO3 rhombohedral and CeO2 cubic structures that confirmed the formation of mixed crystal structure. Nevertheless, Co3O4 slightly appeared with low peak intensity which came from the oxidation reaction of as-prepared catalyst during calcinations. XRD showed that PVA did not effect to crystal structure of synthesized catalyst. Higher PVA content added in the precursor cause the reduction of crystal growth of catalyst in calcinations step. In contrast, morphology of catalyst is directly related with PVA content such that the spongy and sheet-like structure were formed with increasing PVA content which prevented the agglomeration of particles. The results showed that PVA content play an important role in morphology of perovskite-type mixed oxide catalysts but did not affected to their crystal structures.

Improving the dielectric constant of Al2O3 by cerium substitution for high-k MIM applications

Abstract Process compatible high- k dielectric thin films are one of the key solutions to develop high performance metal–insulator–metal (MIM) structures for future microelectronic devices. Engineered cerium–aluminate (Ce x Al 2– x O 3 ) thin films were deposited on titanium nitride metal electrodes by electron-beam co-evaporation of ceria and alumina in a molecular beam deposition chamber. X-ray photoelectron spectroscopy clearly reveals that Ce cations can be stabilized in the 3+ valence state in Ce x Al 2– x O 3 up to x = 0.7 by accommodation in the alumina host matrix. Higher Ce content was observed to result in cerium dioxide segregation in cerium aluminate matrix, probably due to the chemical tendency of Ce cations to exist rather in the 4+ than in the 3+ state. Electrical characterization of the X-ray amorphous Ce 0.7 Al 1.3 O 3 films reveals a dielectric constant value of about 11 and leakage current lower than 10 −4 A/cm 2 . No parasitic low- k interface formation between the high- k Ce 0.7 Al 1.3 O 3 film and the TiN metal electrode is detected.