Synthesis of nanocrystalline Ce(0.8)Gd(0.2)O(2-delta) electrolyte materials for IT-SOFC

We successfully synthesized nano-sized Ce(0.8)Gd(0.2)O(2-delta) powders by combustion method, using gelatin as fuel. The calcined powders showed high-quality characteristics, i.e., nano-scale size (14-35 nm) and narrow size distribution. The structural, morphological, and electrical characteristics of the sintered Ce(0.8)Gd(0.2)O(2-delta) were studied systematically, depending on sintering temperature. The crystal structure of the Ce(0.8)Gd(0.2)O(2-delta) belonged to the cubic fluorite structure. The gelatin-assisted combustion synthesized Ce(0.8)Gd(0.2)O(2-delta) powders allowed to sinter well at low temperature for dense and ultra-fine Ce(0.8)Gd(0.2)O(2-delta) electrolyte with good electrical conductivity. The sintering temperature of the Ce(0.8)Gd(0.2)O2 powder was approximately 300 degrees C lower than that of conventional solid-state synthesized powder. The nanopowder produced was sintered into pellets with relative densities over 99.1% of the theoretical value even at 1400 degrees C. The Ce(0.8)Gd(0.2)O(2-delta) sintered at 1400 degrees C exhibited a conductivity of 0.101 S/cm at 800 degrees C in air.     

Synthesis and microstructural characterization of Ce1-xTb(x)O2-delta (0 < or = x < or = 1) nano-powders

Ce1-xTb(x)O2-delta nano-powders have been successfully synthesized by using the ammonium carbonate coprecipitation method in an entire compositional range of 0 < or = x < or = 1 by adjusting the preparation conditions. Studies of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the powders with different compositions mainly consist of fluorite structure. In addition, a small amount of secondary phase was observed in the powders with x > or = 0.7. TEM observation indicated that the secondary phase could have a superstructure formed by a structural modulation of the fluorite structure.     

Electronic structure and magnetic properties of the Ni0.2Cd0.3Fe(2.5-x)A1(x)O4 (0 < or = x < or = 0.4) ferrite nanoparticles

The structural, magnetic, and electronic structural properties of Ni0.2Cd0.3Fe(2.5-x)Al(x)O4 ferrite nanoparticles were studied via X-ray diffraction (XRD), transmission electron microscopy (TEM), DC magnetization, and near-edge X-ray absorption fine-structure spectroscopy (NEXAFS) measurements. Nanoparticles of Ni0.2Cd0.3Fe(2.5x)Al(x)O4 (0 < or = x < or = 0.4) ferrite were synthesized using the sol-gel method. The XRD and TEM measurements showed that all the samples had a single-phase nature with a cubic structure, and had nanocrystalline behavior. From the XRD and TEM analysis, it was found that the particle size increases with Al doping. The DC magnetization measurements revealed that the blocking temperature increases with increased Al doping. It was observed that the magnetic moment decreases with Al doping, which may be due to the dilution of the sublattice by the doping of the Al ions. The NEXAFS measurements performed at room temperature indicated that Fe exists in a mixed-valence state.     

Thermoelectric properties of nanocrystalline Ca(3-x)Cu(x)Co4O9 (0 < or = x < or = 0.32) for power generation

We successfully synthesized nano-sized Ca(3-x)Cu(x)Co4O9 (0 < or = x < or = 0.32) powders by solution combustion process. Plate-like grains and porous structure were observed in the sintered Ca(3-x)Cu(x)Co4O9 ceramics. The sintered Ca(3-x)Cu(x)Co4O9 showed a monoclinic symmetry. The electrical conductivity of the Ca(3-x)Cu(x)Co4O9 increased with increasing temperature, indicative of a semiconducting behavior. The added Cu led to a significant increase in the electrical conductivity. The Seebeck coefficient of the Cu-added Ca(3-x)Cu(x)Co4O9 was much higher than that of the Cu-free Ca3Co4O9. The highest power factor (9.99 x 10(-4) Wm(-1)K-2) was obtained for Ca2.76Cu0.24Co4O9 at 800 degrees C.     

Nanocrystalline sensor-grade Sn1-xInxO2 (0 < or = x < or = 0.2)

Nanocrystalline Sn1-xInxO2 (0 < or = x < or = 0.2) has been successfully prepared by a solution chemical route. High-resolution transmission electron microscopy studies show that the average grain size of Sn0.8In0.2O2 heated at 310 degrees C, 500 degrees C, and 800 degrees C for 12 h is about 3-4 nm, 5-6 nm, and 7-10 nm, respectively. The corresponding values for pure SnO2 are 3-4 nm, 7-10 nm, and 50-90 nm, respectively. Powder X-ray diffraction and electron diffraction studies confirm the existence of solid solution only in the nanocrystalline state (the average particle size is in the range of 5-10 nm) with the solubility limited to 20% of In2O3. Indium ions stabilize the nanocrystalline nature of Sn1-xInxO2 (0 < or = x < or = 0.2) and prevent the grain growth by entering the SnO2 lattice. The thermal characteristics of nanocrystalline Sn1-xInxO2 (0 < or = x < or = 0.2) investigated by thermogravimetric (TG) and differential thermal analysis (DTA) show that the solid solution decomposes at 820 degrees C into SnO2 and In2O3, which is accompanied by a rapid crystal growth. The electrical conductivity and activation energy of Sn1-xInxO2 (0 < or = x < or = 0.2) undergo significant changes when the average grain size is less than or equal to 2 x the Debye length, LD.     

Novel wet-chemical synthesis and characterization of nanocrystalline CeO2 and Ce0.8Gd0.2O1.9 as solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO₂ and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO₂ powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO₂ powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH₄)₂Ce(NO₃)₆ and urea. The grain size achieved by the hydrothermal technique is ∼7 nm which is smaller than that of commercial nano CeO₂ powders. Conventional or microwave sintering was used to prepare dense Ce_0.8Gd_0.2O_1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd₂O₃ as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400 °C is 1 × 10⁻² and 2.4 × 10⁻² S/cm at 700 °C and 800 °C respectively.     

La0.3Sr0.2Mn0.1Zn0.4 oxide-Sm0.2Ce0.8O1.9 (LSMZ-SDC) nanocomposite cathode for low temperature SOFCs

Nanocomposite based cathode materials compatible for low temperature solid oxide fuel cells (LTSOFCs) are being developed. In pursuit of compatible cathode, this research aims to synthesis and investigation nanocomposite La0.3Sr0.2Mn0.1Zn0.4 oxide-Sm0.2Ce0.8O1.9 (LSMZ-SDC) based system. The material was synthesized through wet chemical method and investigated for oxide-ceria composite based electrolyte LTSOFCs. Electrical property was studied by AC electrochemical impedance spectroscopy (EIS). The microstructure, thermal properties, and elemental analysis of the samples were characterized by TGA/DSC, XRD, SEM, respectively. The AC conductivity of cathode was obtained for 2.4 Scm(-1) at 550 degrees C in air. This cathode is compatible with ceria-based composite electrolytes and has improved the stability of the material in SOFC cathode environment.     

(Ba(x)La(1-x)(2))In(2)O(5+x) (0.4 < or = x < or = 0.6) electrolyte-supported mixed-potential CO sensors

The dense (Ba(x)La(1-x)(2))In(2)O(5+x) electrolytes with different compositions (x = 0.4, 0.5, 0.6) were synthesized by Pechini method. The obtained sintered (Ba(x)La(1-x)(2))In(2)O(5+x) electrolytes showed a high relative density of approximately 98%, and the major phase of three electrolyte compositions was indexed as a cubic phase. The CO sensing properties of as-fabricated planar-type (Ba(x)La(1-x)(2))In(2)O(5+x)-based sensors coupled with ITO and Pt as the sensing electrode and reference electrode, respectively, were investigated. The effects of factors such as gas flow rate, chemical compositions, and density of the electrolytes on the sensing performance were investigated. The sensors showed good sensitivity to different concentrations of CO from approximately 100 to approximately 500 ppm and excellent selectivity over low concentrations of methane (<500 ppm). Linear relationships between emf of the sensors and CO gas concentrations from approximately 100 to approximately 400 ppm were observed. However, the sensors indicated more sluggish response compared with the sensors coupled with a corresponding porous electrolyte. The probable reason has been discussed. The long-term stability of the sensor for the detection of CO was also investigated, which indicated a reasonably stable sensor signal after an initial decline during the incubation period.     

Room temperature co-precipitation of nanocrystalline CeO2 and Ce0.8Gd0.2O1.9−δ powder

This paper describes a simple method to co-precipitate CeO₂ and Ce_0.8Gd_0.2O_1.9−δ with ammonium hydroxide from solvents such as: water, ethylene glycol, ethyl alcohol and isopropyl alcohol. Characterization by Raman spectroscopy and XRD evidenced the formation of a solid solution of gadolinium-doped ceria at room temperature. Nanometric particles with crystallite size of 3.1 nm were obtained during synthesis using ethyl alcohol as solvent. This is a promising result compared with those mentioned in the literature, in which the smallest crystallite size reported was 6.5 nm.     

Nanostructural control in solution-derived epitaxial Ce(1-x)Gd(x)O(2-y) films

A novel mechanism based on aliovalent doping, allowing fine tuning of the nanostructure and surface topography of solution-derived ceria films, is reported. While under reducing atmospheric conditions, non-doped ceria films are inherently polycrystalline due to an interstitial amorphous Ce(2)C(3) phase that inhibits grain growth, a high quality epitaxial film can be achieved simply by doping with Gd(3+) cations. Gd(3+) [Formula: see text] Ce(4+) substitutions within the lattice are accompanied by charge-compensating oxygen vacancies throughout the volume of the crystallites acting as an efficient vehicle to reduce the barrier for grain boundary motion caused by interstitial Ce(2)C(3). In this way, the original nanostructure is self-purified by pushing the amorphous Ce(2)C(3) phase towards the free surface of the film. Once a full epitaxial cube-on-cube oriented ceria film is obtained, its surface morphology is dictated by the interplay between faceting on low energy {110} and/or {111} pyramidal planes and truncation of those pyramids by (001) ones. The development of the latter requires the suppression of their polar character which is thought to be achieved by charge compensation between the dopand and oxygen along [Formula: see text] directions.     

Magnetic and magnetocaloric properties of nanocrystalline Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) manganites

Structural, magnetic and magnetocaloric properties of sol-gel prepared, nanocrystalline oxides Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) (cubic, space group Fm3m) have been studied. From the X-ray data, the crystallite size of Pro.7Ca0.3Mn0.5Co0,503 and Pr0.7Sr0.3Mn0.5Co0.5O3 samples is found to be approximately 24 nm and approximately15 nm respectively. High resolution transmission electron microscopy image shows average particle size of approximately 34 nm and approximately 20 nm. Magnetization measurements indicate a Curie temperature of approximately 153 K and approximately172 K in applied magnetic field of 100 Oe for Pr0.7Ca0.3Mn0.5Co0.5O3 and Pr0.7Sr0.3Mn0.5Co0.O3 compounds. The magnetization versus applied magnetic field curves obtained at temperatures below 150 K show significant hysteresis and magnetization is not saturated even in a field of 7 T. The magnetocaloric effect is calculated from M versus H data obtained at various temperatures. Magnetic entropy change shows a maximum near T(c) for both the samples and is of the order approximately 2.5 J/kg/K.     

Oxygen permeability of Sr1-x Ce x Co0.2Fe0.8O3-δ ceramic membranes

Sr_1-x Ce _x Fe_0.8Co_0.2O_3-δ (x = 0, 0.05, 0.10, 0.15) ceramics were prepared by solid-state reactions, and their oxygen permeability was measured as a function of cerium content and membrane thickness at temperatures from 400 to 1000‡C and oxygen partial pressures from 10² to 10⁵ Pa. The oxygen permeability of the ceramics was found to decrease systematically with increasing Ce content. The oxygen transport was shown to be limited by volume diffusion. Doping of the ceramics with 20 wt % Ag notably improves their cracking resistance during thermal cycling.     

烧结助剂Co2O3对Ce0．8Gd0．2O1.9性能的影响

采用传统固相反应法制备陶瓷试样,借助EIS、XRD及SEM等技术手段研究了烧结助剂Co2O3对Ce.8Gd0.2O1.9(CGO)的体密度、导电性能、相组成及微观结构的影响.结果表明,当CGO中添加2.5%(质量分数)Co2O3时,可使CGO试样的烧结温度降低200℃.添加0.75%(质量分数)Co2O3时,试样的晶粒电导率明显增大,晶界电导率下降,添加量为1.0%～2.5%(质量分数)时,晶粒电导率趋于不变,晶界电导率稍微有所增加.XRD图谱表明,试样在1100～1200℃烧结时表现为CGO纯相,在1300～1400℃的较高温度烧结时,为CGO相及少量的Ce24Co11相.     

Photoluminescence of CaxSr(1-x) (NbO3)2:Pr3+ (0 < or = x < or = 1) nanophosphors

Nanoparticles of CaxSr(1-x) (NbO3)2 doped with Pr3+ have been synthesized by sol-gel method. Particles have sizes in the range of 50-70 nm. The CaxSr(1-x) (NbO3)2:Pr3+ phosphors showed a white emission under the near-ultraviolet excitation (254 nm). There is a large photoluminescence enhancement of the CaxSr(1-x) (NbO3)2:Pr3+ phosphor samples when added with 0.5% KCl. X-ray diffraction (XRD), transmission electron microscope (TEM), photo luminescent (PL) analysis were utilized to characterize the CaxSr(1-x) (NbO3)2:Pr+ particles. The concentration quenching of the samples was discussed as well. The optical concentration and the calcination temperature were 0.8 mol% of Ca2+ and 900 degrees C for these phosphors, respectively, the possible mechanism was discussed. CaxSr(1-x) (NbO3)2:Pr3+ is a promising white phosphor under near-ultraviolet excitation for various applications.     

Composition and temperature dependence of the optical properties of Zn(1-x) Cd(x)Se (0 < or = x < or = 0.34) below the fundamental bandgap

The II-VI ternary semiconductor alloy system Zn(1-x) Cd(x) Se with 0 < or = x < or = 0.2 has important applications as the active material in blue-green light-emitting diodes and lasers. For the wavelength and temperature ranges over which these devices are designed to operate, a knowledge of the optical properties of the alloys is important. We report the results of spectroscopic ellipsometry measurements of the real part of the dielectric function epsilon1 for Zn-rich Zn(1-x) Cd(x) Se layers deposited epitaxially on (100) GaAs. We derive compact expressions that allow one to calculate accurate epsilon1 spectra from 1.5 eV, the low-energy limit of our ellipsometer, to E0-0.05 eV, where E0 is the fundamental bandgap energy, for any composition and temperature within the ranges 0 < or = x < or = 0.34 and 25 < or = T < 260 degrees C. Furthermore, we expect that the results can also be extrapolated to cover the substrate temperature range typically used for the growth of these films (250-300 degrees C). Hence the results presented here are also useful in future real-time spectroscopic ellipsometry studies of Zn(1-x) Cd(x) Se film growth.     

Studies on semiconductive (Ba0.8Sr0.2) (Ti0.9Zr0.1)O3 ceramics

In order to produce semiconductive (Ba_0.8Sr_0.2) (Ti_0.9Zr0.1)O₃ ceramics (BSZT), providing low resistivity for boundary-layer capacitor applications, a controlled valency method and a controlled-atmosphere method were applied and studied. In the controlled-valency method, trivalent ions (La³⁺ Sb³⁺) and pentavalent ions (Nb⁵⁺, Sb⁵⁺, Ta⁵⁺) were doped into BSZT ceramics, while in the controlled-atmosphere method, samples were sintered in air and a reducing atmosphere. The doped BSZT ceramics sintered in the reducing atmosphere showed much lower resistivities and smaller temperature coefficient of resistivity (TCR) than those sintered in air, indicating that low partial pressure of oxygen will increase the solubility of the donor dopant and enhance the grain growth. In addition, a small negative TCR at low temperature, as well as a small positive TCR at higher temperature, are also observed for specimens fired in a reducing atmosphere. The former is attributed to the semiconductive grain and the latter to the small barrier layer formed at the grain boundary.     

Morphology and magnetic properties of diluted magnetic semiconductor 1D nanostructure Ni(x)Sn(1-x)O(2-delta)

SnO2 and Ni(x)Sn(1-x)O(2-delta) (x = 0.007-0.043) 1D nanostructures are fabricated using a catalyzer assisted chemical vapor deposition (CVD). The morphology of the 1D nanostructure is sensitive to the fabrication conditions. As the Ar flux rate is decreased from 50 sccm to 40 sccm, the 1D nanostructure changes from nanowire to nanobelt. All of the Ni(x)Sn(1-x)O(2-delta) 1D nanostructures exhibit room temperature ferromagnetism (RTFM). With the increasing x, magnetic moment per Ni ion increases at first, reaches a maximum of 3.33 microB in x = 0.025, then decreases. The results of annealing in vacuum and oxidizing atmospheres reveal that oxygen vacancies play a crucial role in introducing ferromagnetism, which implies that the origin of RTFM can be understood by the bound magnetic polaron model (BMP).