Study on rare earth electrolyte of SDC

The grain boundaries of polycrystalline oxygen ion conductors presented a blocking effect on the oxygen ionic transport across them.It was found that the apparent specific grain boundary conductivity was 2-3 orders of magnitude lower than the bulk conductivity in the temperature range of 200-500 ℃ for normal purity Ce0.85Sm0.15O1.925(SDC)with an average grain size of 320-580 nm.The apparent specific grain boundary conductivity increased with decreasing average grain size.It was found that the space charge potential was nearly independent of grain size,and the reason was analyzed.The increase of the conduction path width was resportsible for the increase in the apparent specific grain boundary conductivity.     

Electrical properties of iron doped apatite-type lanthanum silicates

The effect of Fe doping on the electrical properties of lanthanum silicates was investigated. The apatite-type lanthanum silicates La10Si6-xFexO27-x/2 (x=0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via sol-gel process. The unit cell volume increased with Fe doping because the ionic radius of Fe3+ ion is larger than that of Si4+ ion. The conductivities of La10Si6-xFexO27-x/2first increased and then decreased with the in-creasing of Fe content. The increase of the conductivity might be attributed to the distortion of the cell lattice, which assisted the migration of the interstitial oxygen ions. The decrease of the conductivity might be caused by the lower concentration of interstitial oxygen ions. The op-timum Fe doping content in lanthanum silicates was 0.6. La10Si5.4Fe0.6O26.7 exhibited the highest ionic conductivity of 2.712×10-2 S/cm at 800 ℃. The dependence of conductivity on oxygen partial pressure p(O2) suggested that the conductivity of La10Si6-xFexO27-x/2 was mainly con-tributed by ionic conductivity.     

Electrical and electronic conductivity of CaO-SiO2-FeOx slags at various oxygen potentials: Part II. Mechanism and a model of electronic conduction

The experimental results obtained for ionic and electronic conductivity of ‘FeO’-CaO-SiO₂ melts have been analyzed considering the mechanism of each conduction process. The Nernst-Einstein equation was employed to calculate diffusion coefficients of Fe²⁺ and Ca²⁺ cations from ionic conductance. A “diffusion-assisted charge transfer” model was developed to explain the dependence of the electronic conductivity on the oxidation state of iron in the slag. The model considers the electronic conduction as a two-step process: in one step, ferrous ions diffuse from their initial position to a proper distance from ferric ions; in the next step, an electron is transferred between Fe²⁺ and Fe³⁺. The optimum distance of the iron ions for electron hopping was found to be approximately 4 Å, in great consistency with the values reported for electron transfer between Fe²⁺ and Fe³⁺ in aqueous solutions and solid glasses.     

Structural,Electrical, and Optical Behavior of Strontium Bismuth Titanate Ceramic

In this report, we present the structural, electrical, and optical study of layer-structured SrBi₄Ti₄O₁₅ (SBT) ceramic prepared by solid-state reaction route. The X-ray diffraction and Rietveld refinement studies show a single-phase orthorhombic structure with space group A₂₁am. The scanning electron micrograph shows plate-like grains. The various Raman peaks originated due to the TiO₆ octahedron confirm the orthorhombic structure. The temperature-dependent dielectric study shows a normal ferroelectric phase transition with a transition temperature at 813 K (540 °C). Impedance studies show a non-Debye-type relaxation and relaxation frequency shift to higher side with increase in temperature. The Nyquist plot shows overlapping semicircles which results the existence of both for grain and grain boundary effect in SBT ceramic. The frequency-dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated and the spectra follow the universal power law. The variation of DC conductivity confirms that the SBT ceramic exhibits negative temperature coefficient of resistance behavior. The Ferroelectric behavior is studied by hysteresis loop. The optical band gap is found to be 2.93 eV from the UV–Visible spectroscopy study. The room-temperature photoluminescence study shows a strong red emission.     

Preparation of hybrid perovskite-type Li0.33La0.56TiO3 by adding ionic liquids

Perovskite-type Li_0.33La_0.56TiO₃ (LLTO) shows greater advantages than organic liquid electrolytes to be used in all-solid-state lithium-ion batteries with high energy densities. Ionic liquid [BMIM][BF₄] was used to improve the properties of Li_0.33La_0.56TiO₃ by attrition milling in this study. The microstructure, crystallinity and lithium-ion conductivity of the samples were measured by scanning electron microscopy (SEM), X-ray diffraction (XRD), and impedance spectroscopy (IS). The total ionic conductivities of the samples LLTO + x wt% [BMIM][BF₄] increase upon adding [BMIM][BF₄] and the maximum conductivity reaches 4.71 × 10⁻⁴ S/cm when x = 12.5 wt%. The enhancement of the total conductivity is ascribed to the bridging role of the ionic liquid among grains, as evidenced by the low activation energy of 0.17–0.25 eV and the SEM observation. The Li⁺ transference numbers of the hybrid samples are all lower than that of the pure LLTO, indicating the existence of electronic conductions. The hybrid material with a mixed conductivity and good stability in the atmosphere can find uses in all-solid-state lithium-ion batteries to improve the interface contact between electrolytes and electrodes.     

Effect of Yttrium Doping in Barium Zirconium Titanate Ceramics: A Structural, Impedance, and Modulus Spectroscopy Study

In the current article, we studied the effect of yttrium [Y³⁺] ions’ substitution on the structure and electric behavior of barium zirconate titanate (BZT) ceramics with a general formula [Ba_1?x Y_2x/3](Zr_0.25Ti_0.75)O₃ (BYZT) with [x = 0, 0.025, and 0.05] which were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that these ceramics have a single phase with a perovskite-type cubic structure. Rietveld refinement data confirmed [BaO₁₂], [ZrO₆], [TiO₆], and [YO₆] clusters in the cubic lattice. The Y³⁺ ions’ effects on the electric conductivity behavior of BZT ceramics as a function of temperature and frequency are described, which are based on impedance spectroscopy analyses. The complex impedance plots display a double semicircle which highlights the influences of grain and grain boundary on the ceramics. Impedance analyses showed that the resistance decreased with the increasing temperature and resulted in a negative temperature coefficient of the resistance property in all compositions. Modulus plots represent a non-Debye-type dielectric relaxation which is related to the grain and grain boundary as well as temperature-dependent electric relaxation phenomenon and an enhancement in the mobility barrier by Y³⁺ ions. Moreover, the electric conductivity increases with the replacement of Ba²⁺ by Y³⁺ ions may be due to the rise in oxygen vacancies.     

The Recrystallization Behavior of Unalloyed Mg and a Mg-Al Alloy

The static recrystallization behavior of pure Mg and Mg-4Al was characterized over a range of annealing temperatures. The electron backscatter diffraction grain orientation spread technique was used to quantify the level of recrystallization at various annealing times. Recrystallization kinetics were characterized using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) relationship and it was found that two sequential annealing stages exist. Stage 1 involves heterogeneous nucleation of recrystallization in regions with a high stored energy, including twins and grain boundaries, and can be represented by an Avrami exponent of n₁ ranging from 0.35 to 0.6. During Stage 2, recrystallization occurred predominately in the interior of deformed grains with incomplete recrystallization generally observed even at annealing times in excess of two weeks. The second recrystallization stage exhibited a much lower Avrami exponent, n₂, ranging from 0.02 to 0.2. Increasing the starting grain size in the pure Mg condition led to a significant delay in recrystallization. The addition of Al had a minimal effect on the recrystallization kinetics of Mg.     

Synthesis and Electrical Conductivities of Sm2O3-CeO2 Systems

Solidoxidefuelcell(SOFC)hasattracteda greatattentionasapromisingtechniqueforelectrical powergeneration[1].Thecurrentstate of the art SOFCsusesyttriastabilizedzirconia(YSZ)electro lyte,operatesat800～1000℃duetothelowoxy genionicconductivityoftheYSZelect…     

Fabrication, characterization, and electrical conductivity properties of Pr6O11 nanoparticles

Pr6O11 nanoparticles were obtained by subsequent thermal decomposition of the as-prepared precipitate formed under ambient temperature and pressure using NaOH as precipitant.The calcination process was affected,for 1 h in static air atmosphere,at 400-700 °C temperature range.The different samples were characterized using X-ray diffraction(XRD),transmission electron microscopy(TEM),field emission scanning electron microscopy(FE-SEM),thermogravimetric analysis(TGA),in situ electrical conductivity,and N 2 adsorption/desorption.The obtained results demonstrated that nano-crystalline Pr6O11,with crystallites size of 6-12 nm,started to form at 500 °C.Such value increased to 20-33 nm for the sample calcined at 700 °C.The as-synthesized Pr6O11 nanoparticles presented high electrical conductivity due to electron hopping between Pr(III)-Pr(IV) pairs.     

Study of Sm0.2Ce0.8O1.9 （SDC） electrolyte prepared by a simple modified solid-state method

Sm0.2Ce0.8O1.9(SDC) electrolyte was prepared by a modified solid state method at relatively low sintering temperatures without any sintering promoters. The phase composition and microstructure of the electrolytes were investigated by X-ray diffraction(XRD) and field emission scanning electron microscopy(FESEM) technologies. A relative density of SDC electrolyte sintered at 1300 oC reached 97.3% and the mean SDC grain size was about 770 nm. Their ionic conductivity and thermal expansion coefficient were also measured by electrochemical workstation and dilatometer. The electrolyte attained a high conductivity of 5×10–2 S/cm at 800 oC with an activation energy of 1.03 eV and a proper thermal expansion coefficient of 12.6×10–6 K–1.     

Conductivity enhancement of yttria doped ceria by spark plasma and ac assisted sintering methods

Abstract

CeO₂ doped with lower valence cations, such as Y³⁺, Sm³⁺, Gd³⁺, etc., is considered as electrolyte material for low temperature solid oxide fuel cells. Doping introduces additional oxygen vacancies and improves ionic conductivity. This work describes the preparation of yttria–calcia doped ceria precursor material, its sintering in DC and AC field methods, and characterisation of sintered electrolytes with respect to the ionic conductivity. Doped precursor materials were prepared by a controlled co-precipitation process. Sintering of prepared, pelletised particulates was carried out using three different methods such as: conventional, spark plasma sintering, and an alternating current field at 1125°C (AC assisted sintering). The conductivity was determined as a function of defect density, grain boundary area and phase stability. It was found that the applied field during sintering, either via pulsed DC (spark plasma), or AC, produced marginal effects on yttria doped ceria microstructure. However, it should be noted that because the sintering conditions were not optimised there is room for substantial conductivity improvements.

On considère le CeO₂ dopé avec des cations à valence plus faible, comme le Y³⁺, le Sm³⁺, le Gd³⁺, etc., comme matériau électrolyte pour les piles à combustible d’oxyde solide à basse température. Le dopage introduit des lacunes additionnelles d’oxygène et améliore la conductivité ionique. Ce travail décrit la préparation de matériau précurseur d’oxyde cérique dopé à l’oxyde d’yttrium-calcia, son frittage par des méthodes de champ CD et CA et la caractérisation des électrolytes frittés par rapport à la conductivité ionique. On a préparé les matériaux précurseurs dopés au moyen d’un procédé de co-précipitation contrôlée. On a effectué le frittage des particules préparées en boulette en utilisant trois méthodes différentes: conventionnelle, frittage au plasma à étincelles et un champ de courant alternatif à 1125°C (frittage assisté au CA). On a déterminé la conductivité en fonction de la densité de défaut, de la superficie de joint de grain et de la stabilité de phase. On a trouvé que le champ appliqué lors du frittage, soit par CD à impulsion (plasma à étincelles) ou par CA, produisait des effets marginaux sur la microstructure de l’oxyde cérique dopé à l’oxyde d’yttrium. Cependant, on doit noter que parce que les conditions de frittage n’étaient pas optimisées, il y a place pour des améliorations substantielles de la conductivité.     

A strategy for improving sinterability and electrical properties of gadolinium-doped ceria electrolyte using calcium oxide additive

In this study,Gd and Ca co-doped ceria electrolytes with the compositions of Ce_(0.8)Gd_(0.2-x)Ca_xO_(2-δ)(x=0-0.08) were prepared by a novel gel-casting method.The effects of the addition of Ca on the phase compositions,sintering behavio r,and electrical prope rties of samples were investigated.According to the scanning electron microscope results and relative density measurement results,it is found that the addition of particular quantity of CaO can promote the sintering densification with a uniform grain growth.When the sintering temperature is 1400℃,the sample with 6 mol% addition of Ca has the highest relative density,which reaches 98.5% of the theoretical density.The electrical properties testing results confirm that the electrical conductivity of the samples can be improved significantly by doping appropriate CaO content.The maximum conductivity of 0.082 S/cm can be obtained at 800℃ in the Ce_(0.8)Gd_(0.12)-Ca_(0.06)O_(1.87) sample.It suggests that CaO can be used as an effective sintering aid and a codopant on the optimization of electrical properties for ceria-based electrolytes.     

Er and Gd Co-Doped Ceria-Based Electrolyte Materials for IT-SOFCs Prepared by the Cellulose-Templating Method

Ce_0.9?x Gd_0.1Er _x O_1.9?x/2 (0 ≤ x ≤ 0.1) (EGDC) powders were successfully synthesized with a fast and facile cellulose-templating method for the first time and characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The samples were calcined at a relatively low calcination temperature of 773 K (500 °C). The sintering behavior of the calcined EGDC powders was also investigated at 1673 K (1400 °C) for 6 hours. Calcined Ce_0.9?x Gd_0.1Er _x O_1.9?x/2 (0 ≤ x ≤ 0.1) powders and sintered Ce_0.9?x Gd_0.1Er _x O_1.9?x/2 (0 ≤ x ≤ 0.1) pellets crystallized in the cubic fluorite structure. It was found that the relative densities of the sintered EGDC pellets were over 95 pct for all the Er contents studied. Moreover, the effect of Er content on the ionic conductivity of the gadolinium-doped ceria (GDC, Ce_0.9Gd_0.1O_1.90) was investigated. The highest ionic conductivity value was found to be 3.57 × 10^?2 S cm^?1 at 1073 K (800 °C) for the sintered Ce_0.82Gd_0.1Er_0.08O_1.91 at 1673 K (1400 °C) for 6 hours.     

Preparation and characterization of Ce_(0.8)La_(0.2–x)Y_xO_(1.9) as electrolyte for solid oxide fuel cells

In this study, ultrafine Ce0.8La0.2–x Y x O1.9（for x=0, 0.05, 0.10, 0.15, 0.20） powders were successfully prepared by the sol-gel method.The samples were characterized by fourier transform infrared（FTIR）, thermogravimetric and differential scanning calorimetry（TG-DSC）, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, AC impedance and thermal expansion measurements.Experimental results indicated that highly phase-pure cubic fluorite electrolyte Ce0.8La0.2–x Y x O1.9 powders were obtained after calcining at 600 °C.The as-synthesized powders exhibited high sintering activity, the Ce0.8La0.2–x Y x O1.9 series electrolytes which have higher relative densities over 96% could be obtained after sintered at 1400 °C for 4 h.Ce0.8La0.15Y0.05O1.9 electrolyte sintered at 1400 °C for 4 h exhibited higher oxide ionic conductivity（σ800 oC=0.057 S/cm）, lower electrical activation energy（E a=0.87 e V） and moderate thermal expansion coefficient（TEC=15.5×10-6 K-1, temperature range 25–800 °C）.     

Preparation and thermoelectric transport properties of Ba-, La- and Ag- doped Ca3Co4O9 oxide materials

The Ba-, La- and Ag-doped polycrystalline Ca2.9M0.1Co4O9 (M=Ca, Ba, La, Ag) thermoelectric bulk samples were prepared via citrate acid sol-gel synthesis method followed by spark plasma sintering technique. The bulk samples were characterized and analyzed with regard to their phase compositions, grain orientations as well as microstructures. The high temperature thermoelectric transport properties of the bulk samples were studied in detail. All bulk samples were found to be single-phased with modified body texture. The electrical resistivity was modulated as a result of carrier concentration modification, however the carrier transport process was not influenced; the Seebeck coefficient was deteriorated simultaneously. The total thermal conductivity was remarkably reduced, on account of the decreasing of phonon thermal conductivity. The thermoelectric properties of the Ba-, La-, and Ag-doped bulk samples were optimized, and the Ba-doped Ca2.9Ba0.1Co4O9 system was found to have the highest dimensionless figure of merit ZT0.20 at 973K, which was remarkably higher than that of the un-doped sample.     

Structural and electrical transport properties of a rare earth double perovskite oxide：Ba2ErNbO6

The double perovskite oxide barium erbium niobate,Ba2ErNbO6(BEN) was synthesized by solid state reaction technique.Rietveld refinement of the X-ray diffraction pattern of the sample showed cubic(Fm3m) phase at room temperature.Fourier transform infrared spectrum showed two primary phonon modes of the sample at around 387 and 600 cm–1.Raman spectrum of the sample taken at 488 nm excitation wavelength showed four primary strong peaks at 106,382,747 and 814 cm–1.Lorentzian lines with 10 bands were used to fit the Raman spectrum.A group theoretical study was performed to assign all the Raman modes.Impedance spectroscopy was applied to investigate the ac electrical conductivity of BEN in a temperature range from 303 to 673 K and in a frequency range from 100 Hz – 1 MHz.The dielectric relaxation mechanism was discussed in the frame work of permittivity,conductivity,modulus and impedance formalisms.The complex plane plot of the impedance data was modeled by an equivalent circuit consisting of two serially connected R-CPE units,(one for the grain and the other for the grain boundary),each containing a resistor(R) and a constant phase element(CPE).The R-CPE units were used to incorporate the non-ideal character of the polarization phenomenon instead of an ideal capacitive behaviour.The relaxation time corresponding to dielectric loss was found to obey the Arrhenius law with activation energy of 0.85 eV.The frequency dependent conductivity spectra followed the Jonscher power law.The Cole-Cole model was used to investigate the dielectric relaxation mechanism in the sample.     

Grain boundary segregation and its influences on ionic conduction properties of scandia doped zirconia electrolytes

Solid oxide fuel cell is a promising energy conversion system which converts chemical energy into electrical energy directly. Electrolyte is the key component and determines the working temperature. In this paper,ceria and scandia co-doped zirconia electrolytes sintered from 1300 to 1550 ℃ were chosen as research objects. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were performed to characterize the ceramic samples. The effects of grain size and grain boundary element segregation on the electrical conductivity were focused. Electrochemical impedance spectroscopy was used to calculate the bulk, grain boundary and specific grain boundary conductivity. Results show that the bulk and grain boundary ionic conductivity increases with the increasing grain size.However, the specific grain boundary conductivity decreases with the increasing grain size. This is explained by the fact that Sc~(3+) is segregated at the grain boundary, which leads to higher oxygen vacancy concentration when sintered at lower temperature.     

Mitigating Electronic Current in Molten Flux for the Magnesium SOM Process

The solid oxide membrane (SOM) process has been used at 1423 K to 1473 K (1150 °C to 1200 °C) to produce magnesium metal by the direct electrolysis of magnesium oxide. MgO is dissolved in a molten MgF₂-CaF₂ ionic flux. An oxygen-ion-conducting membrane, made from yttria-stabilized zirconia (YSZ), separates the cathode and the flux from the anode. During electrolysis, magnesium ions are reduced at the cathode, and Mg_(g) is bubbled out of the flux into a separate condenser. The flux has a small solubility for magnesium metal which imparts electronic conductivity to the flux. The electronic conductivity decreases the process current efficiency and also degrades the YSZ membrane. Operating the electrolysis cell at low total pressures is shown to be an effective method of reducing the electronic conductivity of the flux. A two steel electrode method for measuring the electronic transference number in the flux was used to quantify the fraction of electronic current in the flux before and after SOM process operation. Potentiodynamic scans, potentiostatic electrolyses, and AC impedance spectroscopy were also used to characterize the SOM process under different operating conditions.     

Synthesis and characterization of calcium and manganese-doped rare earth oxide La_(1-x)Ca_xFe_(0.9)Mn_(0.1)O_(3-δ) for cathode material in IT-SOFC

In order to develop novel cathode materials with high performance for intermediate temperature SOFC(IT-SOFC),Ca and Mn doped rare earth oxides La1-xCaxFe0.9Mn0.1O3-δ(x=0.1,0.3 and 0.5,denoted as LCFM9191,LCFM7391 and LCFM5591) were synthesized by solid state reaction(SSR) method.The formation process,phase structure and microstructure of the synthesized samples were characterized using thermogravimetry/differential scanning calorimetry(TG/DSC),X-ray diffraction(XRD) and scanning electron microscopy(SEM).The thermal expansion coefficients(TEC) of the samples were analyzed at 100-900 oC by thermal dilatometry.The electrical conductivities of the samples were measured with direct current(DC) four-terminal method from 300 to 850 oC.The results indicated that the samples(x=0.1 and 0.3) exhibited a single phase with orthorhombic and cubic perovskite structure,respectively after being sintered at 1200 oC for 3 h.The electrical conductivity of the samples increased with temperature up to a maximum value,and then decreased.The small polaron hopping was regarded as the conducting mechanism for synthesized samples at T≤600 oC.The negative temperature dependence occurring at higher temperature was due to the creation of oxygen vacancies for charge balance.LCFM7391 had higher mixed conductivity(>100 S/cm) at intermediate temperature and could meet the demand of cathode material for IT-SOFC.In addition,the average TECs of LCFM9191 and LCFM7391 were 11.9×10-6 and 13.1×10-6 K-1,respectively,which had good thermal match to the common electrolytes.     

The internal stress in titanium deformed at low temperatures (T<0.33TM)

The internal stressσ _i at 300 K produced by deforming commercial Ti-50A titanium (0.5 at. pct O _eq ) wire of 2 and 22μm grain size to 1 pet strain at temperatures of 78 to 650K was investigated employing the back-extrapolation and decrementai unloading techniques. Concurrent observations of the amount of twinning and the dislocation structure were made by transmission electron microscopy,σ _i by the decrementai unloading method was higher, and was inferred to have a stronger temperature dependence, than that by back-extrapola tion, the difference inσ _i being relatively independent of grain size.σ _i by both methods was found to be relatively independent of the deformation temperature and neither twinning nor dynamic strain aging was found to have a noticeable influence on its value. Since no pro nounced changes in dislocation structure or slip mode were observed for the present material as a function of deformation temperature, the difference inσ _i obtained here between the decremental unloading and the back-extrapolation methods could not be correlated with such changes as was possible by Williamset al. for titanium sheet material of higher in terstitial solute content.