Dy3+- and Eu3+-doped LaGaO3 nanocrystalline phosphors for field emission displays

Nanocyrstalline LaGaO3 and Dy3+- and Eu3+-doped LaGaO3 were prepared through a Pechini-type sol-gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence, cathodoluminescence spectra, and lifetimes were utilized to characterize the samples. XRD reveals that the samples begin to crystallize at 900 degrees C and pure LaGaO3 phase can be obtained at 1000 degrees C. FE-SEM images indicate that the Dy3+- and Eu3+-doped LaGaO3 samples are both composed of aggregated spherical particles with sizes ranging from 40 to 80 nm. Under the excitation of ultraviolet light and low voltage electron beams (1-5 kV), the undoped LaGaO3 sample shows a strong blue emission peaking at 433 nm, and the Dy3+- and Eu3+-doped LaGaO3 samples show their characteristic emissions of Dy3+ (F-4(9/2)-H-6(15/2) and F-4(9/2)-H-6(13/2) transitions) and Eu3+ (D-5(0,1,2)-F-7(1,2,3,4) transitions), respectively. The relevant luminescence mechanisms are discussed.

The thermal cycling behavior of Lanthanum-Cerium Oxide thermal barrier coating prepared by EB-PVD

Bulk material and coatings of Lanthanum-Cerium Oxide (La2Ce2O7) with a fluorite structure were studied as a candidate material for thermal barrier coating (TBC). It has been showed that such material has the properties of low thermal conductivity about four times lower than YSZ, the difference in the thermal expansion coefficient between La2Ce2O7 and bond coat is smaller than that of YSZ in TBC systems, high phase stability between room temperature and 1673 K, about 300 K higher than that of the YSZ. The coating prepared by electron beam physical vapor deposition (EB-PVD) showed that it has good thermal cycling behavior, implying that Such material can be a promising thermal barrier coating material. The deviation of coating composition from ingot can be overcome by the addition of excess La2O3 during ingot preparation and/or by adjusting the process parameters.

Neodymium-cerium oxide as new thermal barrier coating material

Neodymium-cerium oxide (Nd2Ce2O7) was proposed as a new thermal barrier coating material in this work. Monolithic Nd2Ce2O7 powder was prepared by the solid-state reaction at 1400 degrees C. The phase composition, thermal stability and thermophysical properties of Nd2Ce2O7 were investigated. Nd2Ce2O7 with fluorite structure was thermally stable in the temperature range of interest for TBC applications. The results indicated that the thermal expansion coefficient (TEC) of Nd2Ce2O7 was higher than that of YSZ (6-8 Wt-% Y2O3 + ZrO2) and even more interesting was the TEC change as a function of temperature paralleling that of the superalloy bond coat. Moreover, the thermal conductivity of Nd2Ce2O7 is 30% lower than that of YSZ, which was discussed based on the theory of heat conduction. Thermal barrier coating of Nd2Ce2O7 was produced by atmospheric plasma spraying (APS) using the spray-dried powder. The thermal cycling was performed with a gas burner test facility to examine the thermal stability of the as-prepared coating.

Synthesis, structural characterization and electrical property of new oxide ion conductors: La3MMo2O12 (M = In, Ga and Al)

New series of oxides, La3MMo2O12 (M = In, Ga and Al), have been prepared by the solid-state reaction. The composition and elemental distribution were analyzed by the energy-dispersive X-ray (EDX) analysis. As determined by the X-ray diffraction (XRD), these compounds have similar crystal structures that can be indexed on a monoclinic cell at room temperature. AC impedance spectra and the DC electrical conductivity measurements in various atmospheres indicate that they are oxide ion conductors with ionic conductivities between 10(-2) and 10(-3) S/cm at 800 degrees C. The conductivity decreases in the order of La3GaMo2O12 > La3AlMo2O12 > La3InMo2O12, implying that the effect of cell volume and polarization associated with In3+, Ga3+ and Al3+ play an important role in the anion transport of these materials. The reversible phase transition was observed in all these compounds as confirmed by the differential thermal analysis (DTA) and dilatometric measurements.

New double-ceramic-layer thermal barrier coatings based on zirconia-rare earth composite oxides

A series of La2O3-ZrO2-CeO2 composite oxides were synthesized by solid-state reaction. The final product keeps fluorite structure when the molar ratio Ce/Zr >= 0.7/0.3, and below this ratio only mixtures of La2Zr2O7 (pyrochlore) and La2O3-CeO2 (fluorite) exist. Averagely speaking, the increase of CeO2 content gives rise to the increase of thermal expansion coefficient and the reduction of thermal conductivity, but La-2(Zr0.7Ce0.3)(2)O-7 has the lowest sintering ability and the lowest thermal conductivity which could be explained by the theory of phonon scattering. Based on the large thermal expansion coefficient of La2Ce3.25O9.5, the low thermal conductivities and low sintering abilities of La2Zr2O7 and La-2(Zr0.7Ce0.3)(2)O-7, double-ceramic-layer thermal barrier coatings were prepared. The thermal cycling tests indicate that such a design can largely improve the thermal cycling lives of the coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature thermal barrier coatings, double-ceramic-layer coating may be an important development direction of thermal barrier coatings.

Synthesis, structural and electrical characterizations of Sr2Fe1-xMxNbO6 (M = Zn and Cu) with double perovskite structure

Sr2Fe1-xZnxNbO6-x/2 (0 <= x <= 0.5) and Sr2Fe1-xCuxNbO6-x/2 (0.01 <= x <= 0.05) with the double perovskite structure have been synthesized. The crystal structures at room temperature were determined from Rietveld refinements of X-ray powder diffraction data. The plots of the imaginary parts of the impedance spectrum, Z '', and the electric modulus, M '', versus log (frequency), possess maxima for both curves separated by less than a half decade in frequency with associated capacities of 2 nF. The enhancement of the overall conductivity Of Sr2Fe1-xMxNbO6-x/2 (M = Cu and Zn) is observed, as increases from 2.48 (3) x 10(-4) S/cm for Sr2FeNbO6 to 3.82 (5) x 10(-3) S/cm for Sr2Fe0.8Zn0.2NbO5.9 at 673 K. Sr2Fe0.8Zn0.2NbO5.9 is chemically stable under the oxygen partial pressure from 1 atm to 10(-22) atm at 873 K. The p and n-type electronic conductions are dominant under oxidizing and reducing conditions, respectively, suggesting a small-polaron hopping mechanism of electronic conduction.

A new oxide ion conductor: La3GaMo2O12

A new oxide ion conductor, La3GaMo2O12, with a bulk conductivity of 2.7 X 10(-2) S.cm(-1) at 800 degrees C in air atmosphere was prepared by the traditional solid-state reaction. The room temperature X-ray diffraction data could be indexed on a monoclinic cell with lattice parameters of a=0.5602(2) nm, b=0.3224(1) nm, c= 1.5741(1) nm, beta= 102.555(0)degrees, V=0.2775(2) nm(3) and space group Pc(7). Ac impedance measurements in various atmospheres further support that it is an oxide ion conductor. This material was stable in various atmospheres with oxygen partial pressure P(O-2) ranging from 1.0 X 10(5) to 1.0 X 10(-7) Pa at 800 degrees C. A reversible polymorphic phase transition occurred at elevated temperatures as confirmed by the differential thermal analysis and dilatometric measurement.

Electrochemical study of PW12O403- in poly(ethylene glycol) electrolyte

The electrochemical properties Of PW12O403- (abbreviated as PW12) anion in poly(ethylene glycol) (PEG) have been studied by cyclic voltammetry, complex impedance and FT-IR spectroscopy. The PW12 anion in PEG-LiClO4 electrolyte shows reasonable facile electrochemistry, and the diffusion coefficients Of PW12 were measured with microelectrode. It is shown that ionic conductivity of polymer electrolytes based on low molecular weight PEG can be improved by the addition of PW12. The increase of conductivity is coupled with decrease of transient cross-links density of polymer chains which is evidenced by the downshift of C-O-C stretching mode. The phenomena are explained in view of ion-ion and ion-polymer interactions.

Electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40), in polyethylene glycol

The electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40) (abbreviated as PMo12-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol(-1)) and containing LiClO4 (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo12-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo12-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo12-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO4-PMo12-Co, and well described the reason that the PMo12-Co nanoparticles could promote the conductivity of the PEG-LiClO4-PMo12-Co system.

Confining conducting polyaniline in a stable inorganic network

Water soluble conducting polyaniline with electrical conductivity of 10(-1)-10(-2) S/cm was prepared employing dopant induced water solubility technology. The water resistance of the conducting film was significantly improved employing,sol-gel hybrids method, especially when the conductive polyaniline loading was below 30 wt%. The reason for the improvement is that the conducting polyaniline chains are confined in a stable inorganic network.

Synthesis, characterization and electrical properties of the new solid electrolyte materials Ce6-xErxMoO15-delta (0.0 < x < 1.5)

A new series of oxides, Ce6-xErxMoO15-delta (0.0 less than or equal to x less than or equal to 1.5), was synthesized using wet-chemistry techniques. The precursors and resultant oxide powders were characterized by differential thermal analysis/thermogravimetry, x-ray diffraction, and IR, Raman and x-ray photoelectron spectroscopy. The formation temperature of the powders was found to be as low as 350degreesC. Ce6-xErxMoO15-delta crystallized to a fluorite-related cubic structure. The electrical conductivity of the samples was investigated by using ac impedance spectroscopy. This showed that the presence of Er was related to the oxygen-ion conductivity, and that the highest oxygen-ion conductivity was found in Ce6-xErxMoO15-delta (x = 0.4), ranging from 5.9 x 10(-5) S cm(-1) at 300degreesC to 1.26 x 10(-2) S cm(-1) at 700degreesC, respectively. This kind of material shows a potential application in intermediate-temperature solid oxide fuel cells.

Synthesis of new solid solutions on neodymium-stabilized La2Mo2O9

A new ionic conductor La2-xNdxMo2O9 (x=0.0-2.0) has been synthesized by wet-chemistry method. The precursors and the resultant oxide powders were characterized by DTA/TG, DSC, XRD and XPS techniques. Effect of substituting Nd for La reveals that the phase transition which occurs in La2Mo2O9 around 565degreesC disappears when x>0.2. And the maximum amount of Nd stabilized the high temperature phase of beta-La2Mo2O9 from cubic to tetragonal is about x=1.6. The measurements of impedance spectroscopy indicate that the ionic conductivity becomes considerably higher in comparison to that of La2Mo2O9.