Characterization and Stability of La0.5Sr0.5CoO2.91 Perovskite-Type Oxide

Compositely doped oxide La0.5Sr0.5CoO2.91 （LSC） was synthesized using solid state reaction and citric acid-nitrate low temperature self-propagating combustion methods. The crystal structure and the particle size micrograph of LSC powders synthesized by different methods were investigated with XRD and SEM. The experimental results show that the single perovskite phase of LSC can be synthesized by solid state reaction method, but LaSrCoO4 phase appears in LSC powder synthesized by citric acid-nitrate low temperature self-propagating combustion method. The LSC particle by citric acid-nitrate low temperature self- propagating combustion method has smaller size. To analyze the character of cathode material based on Ceo.gGdo.101.95（GDC） electrolyte, two types of cathode wafers were fabricated with the two kinds of LSC and GDC powders at the mass rate of 6：4, respectively. The electrical conductivity of the sintered samples was measured by four probe DC method from 300 to 800 ℃. The cathode with LSC particle by citric acid- nitrate low temperature self-propagating combustion method has higher electrical conductivity. In order to investigate the stability, the two samples were put into the muffle furnace to heat up in air at 800℃for 800 h. To analysis the reason for reduced electrical conductivity, the crystal structure and the particle micrograph of the cathode wafers before and after an exposure were investigated with XRD and SEM. The result shows that new crystal structure appears in both the two kinds of cathode wafers and crystal micrographs change a lot.     

Electrical Properties and Microwave Synthesis of Mixed Rare Earth Oxide Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ

In order to lower the raw materials cost and develop a novel cathode materials for intermediate temperature solid oxide fuel cell(ITSOFC), using mixed rare earth replacing the expensive pure La2O3 as the raw materials, the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ (Ln=the mixed rare earth, x=0.05, 0.10, 0.15) for the applications as the cathode materials were prepared by microwave sintering process. The crystal structure and the particles morphology of the obtained powders were characterized by XRD and SEM, the electrical conductivity of all samples sintered at 1200 ℃ for 3 h was also measured as the function of the temperature from 100 to 800 ℃ by DC four-probe method in air. The experimental results show that due to the influence of mixed rare earth the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ synthesized at 1200 ℃ for 0.5 h with the mean particle size of 1～20 μm was of perovskite and cubic fluorite phase as well a little SrO phase, the electrical conductivity of the samples decreases with the adding Ca2+ content, and are all higher than 100 S·cm-1 from 500 to 700 ℃ when x≤0.10. Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ. Can meet the demand of the electrical properties for the cathode materials in ITSOFC.     

Thermogravimetric Study on Oxygen Adsorption/Desorption Properties of Double Perovskite Structure Oxides REBaCo2O5+δ (RE= Pr, Gd, Y)

The oxygen adsorption/desorption properties of double perovskite structure oxides PrBaCo2O5+δ, GdBaCo2O5+δ, and YBaCo2O5+δ were investigated by the thermogravimetry (TG) method in the temperature range of 400～900 ℃. The calculated oxygen adsorption/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides, such as Ba0.95Ca0.05Co0.8Fe0.2O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ, whereas, the oxygen permeation flux was comparable to that of the latter, which was attributed to the smaller difference of oxygen vacancy in oxygen and nitrogen atmosphere (Δδ/Vmol) in these double perovskite structure oxides. The large oxygen adsorption/desorption rate constants of GdBaCo2O5+δ and PrBaCo2O5+δ made them nice catalyst coating materials, on other membrane surfaces, to improve the oxygen permeability.     

Thermogravimetric Study on Oxygen Adsorption/Desorption Properties of Double Perovskite Structure Oxides REBaCo2O（5＋δ）（RE= Pr,Gd,Y）

The oxygen adsorption/desorption properties of double perovskite structure oxides PrBaCo2O5＋δ,GdBaCo2O5＋δ,and YBaCo2O5＋δ were investigated by the thermogravimetry（TG）method in the temperature range of 400~900 ℃.The calculated oxygen adsorption/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides,such as Ba0.95Ca0.05Co0.8Fe0.2O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ,whereas,the oxygen permeation flux was comparable to that of the latter,which was attributed to the smaller difference of oxygen vacancy in oxygen and nitrogen atmosphere（Δδ/Vmol）in these double perovskite structure oxides.The large oxygen adsorption/desorption rate constants of GdBaCo2O5＋δ and PrBaCo2O5＋δ made them nice catalyst coating materials,on other membrane surfaces,to improve the oxygen permeability.     

Solid state reaction synthesis and total electrical conductivity of La_(0.7)Sr_(0.3)Cr_yMn_zCo_(1-y-z)O_(3-δ)

The La0.7Sr0.3CryMnzCo(1-y-z)O3-δ samples were prepared by solid state reaction.The phases,microstructure and properties of the samples were investigated by XRD,SEM,DC four-probe method and iodometry method.The single orthorhombic phase La0.7Sr0.3CryMnzCo(1-y-z)O3-δ perovskite oxides were obtained when sintered at l350 °C for 10 h.The oxygen nonstoichiometry of the materials varied inversely with the total electronic conductivity.The sample with composition of La0.7Sr0.3Cr0.5Mn0.35 Co0.15O3-δ had the maximal total electronic conductivity and the lowest oxygen nonstoichiometry which were 22.4 S/cm and 0.040 at 850 °C,respectively.The low total electronic conductivity is related to the low relatively density of the samples directly.The activation energy of conduction changed at 550 °C,and the activation energy of conduction at high temperature(T550 °C) was higher than that at low temperature range(T550 °C).     

Characterization of A-site excessive perovskite La0.7-xSmx＋0.02Ca0.3CrO3-δ

La0.7-xSmx+0.02Ca0.3CrO3-δ(0≤x≤0.4) powders with A-site excessive perovskite structure were synthesized by auto-ignition process and characterized. X-ray diffraction (XRD) patterns of samples after sintering at 1400℃ for 4 h were indexed as tetragonal structure. The relative densities were all above 96% although decreased slightly with the increasing content of samarium, indicating that the excessive A-site element was helpful to enhance their sinterability. Conductivities of the specimens in air increased with increasing content of samar-ium. The conductivity of La0.6Sm0.12Ca0.3CrO3-δ was 33.6 S/cm in air at 700 ℃ which was about 1.7 times as high as that of La0.7Ca0.3CrO3-δ (20.1 S/cm). Average thermal expansion coefficients (TECS) of the specimens increased from 11.06×10-6 to 12.72×10-6 K-1 when x in-creased from 0 to 0.4, and they were close to that of Y doped ZrO2 (YSZ). La0.7-xSmx+0.02Ca0.3CrO<3-δ>(0.1≤x≤0.3) were good choices for in-termediate temperature solid oxide fuel cells (IT-SOFCs) interconnect materials.     

Defect structure and electrical properties of LaSr_3Fe_3O_(10-δ)

As a mixed conductor,LaSr3Fe3O10-δ with triple layer perovskite intergrowth structure can be used as an oxygen separation membrane material and cathode material in solid oxide fuell cells.LaSr3Fe3O10-δ was synthesized via citrate acid route.Iodine titration method was used to determine the average valence of transition metal Fe and oxygen nonstoichiometry δ.Conductivities of LaSr3Fe3O10-δ were measured in the oxygen partial pressure range from 10-2×105 to 1×105 Pa,by Ac four probe method.Seebeck coefficient...     

Synthesis and photoluminescent properties of Sr2Si5N8：Eu^2＋red phosphors for white light-emitting diodes

Highly efficient Sr2Si5N8：Eu^2＋red emitting phosphor was successfully synthesized by a cost-effective direct silicon nitrida-tion and gas-reduction method. The effects of synthesis parameters, including reaction temperature, heating rate and gas species, on the crystal structure and photoluminescence of the prepared phosphors were studied. Single-phase Sr2Si5N8：Eu^2＋phosphor was ob-tained at 1500℃ with a heating rate of 300℃/h under NH3-1 vol.%CH4 atmosphere using starting silicon and oxide powders. Silicon powder and high heating rate favored the achievement of the pure Sr2Si5N8 phase. Under near-UV to blue light excitation, the obtained Sr2Si5N8：Eu2＋phosphor showed a board red emission band centered at about 625 nm, which agreed well with the phosphors prepared by the conventional solid-state reaction. The possible reaction mechanism was also proposed based on the experimental observations.     

Preparation and Electrical Transport Properties of Perovskite Oxide Ln0.5Sr0.5CoO3

The superfine powders of Ln0.5 Sr0.5 CoO3 （Ln = La, Pr, Nd, Sm, Eu） were obtained by solid state reactions. The crystal structure and electrical transport properties of samples doped with different rare earth elements as well as the forming process of the Perovskite structure were studied. The result shows that when the temperature reaches 1200 ℃, the samples will become a steady and unitary Perovskite phase by solid state reactions. The conductive behavor at low temperature is consistent with small polaron mechanism （i. e., localized electronic carriers having a thermally activated mobility）. However, the maximum of conductivity appears at about 700 ℃, and the conductivity of La0.5Sr0.5CoO3 is the biggest in the intermediate-temperature （600 - 850 ℃ ）, so it is fit for cathode material of intermediate-temperature solid oxide fuel cells.     

Structural and electrical properties of La2-xSrxMo2O9-δ

Sr-doped La2Mo2O9 were prepared by solid state reaction and characterized by XRD,impedance spectroscopy and HebbWagner polarization method.XRD patterns of the samples indicated that the solubility limit of Sr2+ in La2-xSrxMo2O9-δ was in the range of 7 mol.% to 7.5 mol.%,i.e.,the maximum stoichiometric coefficient x in La2-xSrxMo2O9-δ was larger than 0.14 and less than 0.15.The cubic lattice parameter of La2-xSrxMo2O9-δ(0相似文献   

Chemical stability and electrical property of Ba_(1.03)Ce_(0.6)Zr_(0.2)Yb_(0.2)O_(3-α) ceramic

Ba1.03Ce0.6Zr0.2Yb0.2O3-α ceramic was prepared by solid state reaction. Phase composition, surface and cross-section morphologies of the material were characterized by using X-ray diffractometer (XRD) and scanning electron microscopy (SEM), respectively. Its chemical stability against carbon dioxide and water steam at high temperature was tested. Ionic conduction of the material was investigated by ac im-pedance spectroscopy and gas concentration cell methods under different gas atmospheres in the temperature range of 500-900 ℃. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at the tem-perature from 500 to 900 oC was examined. The results indicated that Ba1.03Ce0.6Zr0.2Yb0.2O3-α was a single-phase perovskite-type ortho-rhombic system, with high density and good chemical stability under carbon dioxide and water steam atmospheres at high temperature. In wet hydrogen, the material was a pure protonic conductor with the protonic transport number of 1 from 500 to 700 ℃, a mixed conductor of pro-ton and electron with the protonic transport numbers of 0.945-0.916 from 800 to 900 ℃. In wet air, the material was a mixed conductor of proton, oxide ion and electronic hole. The protonic transport numbers were 0.013-0.003, and the oxide ionic transport numbers were 0.346-0.265. Under hydrogen-air fuel cell conditions, the material was a mixed conductor of proton, oxide ion and electron, the ionic trans-port numbers were 0.945-0.848. The fuel cell could work stably, and at 900 ℃, the maximum power output density was 36.5 mW/cm2.     

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.     

Wet chemical synthesis of La9.83–xSrxSi6O26+δ（0≤x≤0.50） powders,characterization of intermediate and final products

In this paper we reported the preparation and extensive characterization of La9.83–x Sr x Si6O26+δ(0≤x≤0.50) precursors, intermediate and final products. The sintering reactions, the phase formation, the structure as well as the powders’ morphology were studied by means of thermogravimetric analysis, X-ray diffraction(XRD), Fourier-transform infrared spectroscopy(FTIR) and scanning electron microscopy(SEM). Moreover, the effect of stoichiometry on precursor’s structure and morphology as well as on intermediate and final products was reported. As was concluded pure La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ and La9.33Sr0.50Si6O26+δ could be prepared after sintering at 1400 °C for 20 h while La9.68Sr0.15Si6O26+δ and La9.53Sr0.30Si6O26+δ compounds contained minor traces(<3.5%) of La2Si2O7 secondary phase. Concerning the synthesis, there have been no previous reports on the preparation of pure La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ and La9.33Sr0.50Si6O26+δ compounds. The final powders consisted of spherical particles and an increase of Sr content seemed to inhibit sintering phenomena. The existence of interstitial oxygen at intermediate crystallographic positions of apatite structure had great effect on Si O4 sub-structure distortion. The increase of Sr content led to a major reduction of interstitial oxygen quantity and the refutation of silicon tetrahedron distortion.     

Preparation and performance of Pr-doped Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) cathode for IT-SOFCs

(Ba0.5Sr0.5)1-xPrxCo0.8Fe0.2O3-δ(BSPCFx;x=0.00-0.30) oxides were synthesized by a sol-gel thermolysis process using combination of PVA and urea,and were also investigated as cathode material for intermediate temperature solid oxide fuel cells(IT-SOFCs).X-ray diffraction(XRD) results showed that all the samples formed a single phase cubic pervoskite-type structure after being calcined at 950 oC for 5 h and the lattice constant decreased with the Pr content increasing.The electrical conductivity of Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) was greatly enhanced by Pr-doping.The thermal expansion coefficient(TEC) of BSPCFx was increased with the content of Pr increasing,and all the thermal expansion curves had an inflection at about 250-400 oC due to the thermal-induced lattice oxygen loss and the reaction of Co and Fe ion.Ac impedance analysis indicated that BSPCFx possessed better electrochemical performance.The polarization resistance of the sample with x=0.2 was only ～0.948 Ω cm2 at 500 oC,significantly lower than that of BSCF(～2.488 Ω cm2).     

Synthesis and characterization of Ce_(0.6)Sr_(0.4)Fe_(0.8)Co_(0.2)O_(3–δ) perovskite material:Potential cathode material for low temperature SOFCs

A sol-gel method and a modified chemical vapour deposition technique were used to produce nanostructured Ce_(0.6)Sr_(0.4)Fe_(0.8)Co_(0.2)O_(3–δ) materials at temperatures as low as 400 °C. Powders were characterized using Fourier transform infrared spectroscopy(FTIR), Raman spectroscopy, thermo gravimetric analysis, powder X-ray diffraction(XRD), scanning electron microscopy(SEM) with energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy(HRTEM), and nitrogen sorption at 77 K. FTIR spectra showed that the sol-gel method resulted in residual carbon groups on the materials after calcination, while the Raman and XRD analysis confirmed that both synthesis methods resulted in cubic perovskite structure. However, the chemical vapour deposition(CVD) method resulted in materials with a smaller crystallite size when compared to those prepared via the sol-gel route. The overall morphology of the powders was irregularly shaped aggregated particles as observed by SEM and HRTEM. In addition, HRTEM analysis showed that the materials were highly crystalline. Textural analysis revealed the powders had some mesoporosity, and the surface areas were 76.69 and 65.90 m~2/g for materials synthesized using the CVD and sol-gel methods, respectively. The synthesized perovskite powders were used to fabricate button cells employing samarium doped ceria(SDC) as the electrolyte and NiO/SDC as the anode materials. As cathode materials, the maximum power density observed was 308.4 mW/cm~2 at 500 oC.     

A New Combustion Process for Nanosized BaCeo.95Yo.o5O3-δ Powders

Nanosized BaCeo.95Yo.o5O3-δ powders with the homogeneous composition were synthesized by a new combustion process based on the Pechini method. A polymeric precursor sol was formed by use of citric acid and ethylene glycol as the chelating agents of metal ions. The perovskite-type BaCeo.95Yo.o5O3-δ powders with uniform shape and smaller than 40 nm in sized were obtained through the combustion of the polymeric precursor sol at the existence of nitric acid and ammonium hydroxide. It was found the particle size could be controlled by modulating the quantities of nitric acid and ammonium hydroxide, the quantities of the residue, carbonate ions were also affected by the quantities of the citric acid and ethylene glycol.     

Synthesis,structural and optical properties of SrZrO3：Eu3＋phosphor

Eu3+ activated Sr1–xEuxZrO3(x=0.01–0.04) phosphor with perovskite structure was successfully synthesized by using combustion method.The structure,morphology and optical properties of the material were characterized by X-ray diffraction,scanning electron microscopy and fluorescence spectrometry.The XRD results indicated that crystals of SrZrO3:Eu3+ belongs to tetragonal perovskite system.The phosphor could be effectively excited by UV light and the emission spectra results indicated that reddish-orange luminescence of SrZrO3:Eu3+ due to magnetic dipole transition 5D0→7F1 at 593 nm was dominant.Thus,the prepared phosphor showed remarkable luminescent properties which find applications in field emission display(FED) and plasma display panel(PDP) devices.     

Crystal structure and magnetic behavior of the La0.1Bi0.9FeO3 compound

The nano-crystalline La_(0.1)Bi_(0.9)FeO_3 compound was successfully synthesized by starch-based combustion method. The crystal structure and magnetic behavior were studied by temperature-dependent X-ray diffraction(XRD), scanning electron microscopy(SEM), differential scanning calorimetry(DSC) and magnetic measurements. The La_(0.1)Bi_(0.9)FeO_3 compounds crystallized in a rhombohedrally distorted perovskite structure with space group R3 c. The substitution of La for Bi reduced the rhombohedral distortion. The structural phase transitions in La_(0.1)Bi_(0.9)FeO_3 driven by temperature showed that the extraordinary two-phase coexistence state of BiF eO 3 and LaF eO 3 was observed in a narrow temperature range of 630–700 oC. The magnetization of the La_(0.1)Bi_(0.9)FeO_3 sample was improved by heat treatment in the temperature range. When the heat treatment temperatures rose from 25 to 600 oC, the remanence(Mr) and coercivity(Hc) of the La_(0.1)Bi_(0.9)FeO_3 compound almost remained the same, and increased rapidly to 0.134 emu/g and 7.1 KOe on further increasing the heat treatment temperature to 650 oC.     

Effects of the penetration temperature on structure and electrical conductivity of samarium modified BaTiO3 powders

Gaseous penetration technique was adopted to improve the electrical conductivity of BaTiO3 powders and the effects of penetration temperature on the structure and electrical conductivity of Sm-modified BaTiO3 powders were studied.It was observed that the penetration of Sm made the resistivity of BaTiO3 powders decrease with the increase in the penetration temperature and decreased to the lowest point of 4.20×102 ?·m when the penetration temperature was 950 oC.The relationship curve of the temperature and resistivity of the samples was also established preliminarily to get the mathematical expression by the fitting method.Through X-ray diffraction (XRD) analysis,the new phases of Sm2O3 and Ba4Ti2O27 were detected.It was indicated that intricate reactions related to Sm took place during the penetration process and led to the Ti-rich state of the system.The Fourier transform infrared (FTIR) spectrum illustrated that the bonds of Ti–O octahedron was strengthened by substitution of Sm3+ at Ti4+ sites,which led to the growth of Ti:Ba ratio.The analysis results of scanning electron microscopy (SEM) indicated that the particle size of Sm-modified BaTiO3 powders progressed with the penetration temperature increasing.     

Magnetic properties of samarium and gadolinium co-doping Mn-Zn ferrites obtained by sol-gel auto-combustion method

Mn-Zn ferrites doped with different contents of Sm~(3+) and Gd~(3+) ions were prepared by sol-gel auto-combustion method and characterized by Fourier transform infrared spectroscopy(FTIR), thermogravimetric analysis(TG), X-ray diffraction(XRD), scanning electron microscopy(SEM) and vibrating sample magnetometer(VSM). When samples were calcined in a relatively low temperature below 1100 °C, secondary phases(α-Fe_2O_3) could be identified. Therefore, in order to acquire pure and better crystallinity, the suitable calcining temperature of powders was selected at 1200 °C. It was also found that all the samples consisting of ferrite phases of typical spinel cubic structure and average crystallite sizes between 31.5 and 38.2 nm were obtained after calcining at 1200 oC for 4 h. The lattice parameters increased almost linearly with increasing Sm content. A dense microstructure was obtained after sintering at 1250 °C for 4 h. Through the analysis of magnetic properties, hysteresis loops for all the samples were narrow with low values of coercivity and retentivity, indicating the paramagnetic nature of these samples. And saturation magnetization Ms strongly depended on the type of additive to reach a maximum of 47.99 emu/g for x=0.015, which showed a great promise for hyperthermia applications.