Abstract: Monodispersed cerium(IV) oxide (CeO2) particles composed of an agglomeration of primary nanocrystalline particles with a cubic fluorite structure could be synthesized from relatively concentrated cerium(IV) sulfate solutions up to 0.5 mol dm−3 by thermal hydrolysis at 120 to 240 °C. The influences of the presence of urea and its concentration on their crystallite size and morphology were investigated. Upon the addition of urea and increasing its concentration, the morphology gradually changed from monodispersed particles to dispersed ultra-fine particles that had no definite shape and tight agglomeration. The mechanisms for the growth and agglomeration of the particles formed by thermal hydrolysis were discussed. The existence of a dopant such as Gd was effective for suppressing the grain growth of the ceria particles during the calcining and sintering.

Abstract: Cerium-doped lithium niobate crystals are tested for holographic recording. A photochromic effect is observed in crystals doped with cerium and manganese. But two-center recording in the sample is not as effective as in iron and manganese doubly doped crystals. Photocurrent measurements in cerium and iron singly doped crystals indicate that the photovoltaic constant in the cerium-doped crystal is only one third of that of the iron-doped one. This is the main reason accounting for the low sensitivity of cerium-doped lithium niobate crystals. However, in the diffusion dominated case, i.e., for reflection geometry, cerium-doped lithium niobate may give a strong effect.

Abstract: The effect of small amounts (<5 mol %) of cobalt oxide on the electrical properties of cerium oxide solid solutions has been evaluated. Ce0.8Gd0.2O2-x (CGO) powder with an average crystallite size of 20 nm served as a model substance for the electrolyte material with a high oxygen ion conductivity and low electronic conductivity in its densified state. Doping the CGO powder by transition metal oxides (MeO) with concentrations below 2 mol % did not change the ionic conductivity nor the electrolytic domain boundary. After long sintering times (2 h) at temperatures above 900°C, MeO and CeO2 form solid solutions. However, short sintering times or high dopant concentrations lead to an electronic conducting grain boundary phase short circuiting the ionic conductivity of the CGO grains. Choosing proper doping levels, sintering time and temperature allows one to tailor mixed conducting oxides based on CGO. These materials have potential use as electrolytes and/or anodes in solid oxide fuel cells and ion separation membranes.

Abstract: Precursors of formula [Ce(hfac)3{MeO(CH2CH2O)nMe}], 1 (n = 1), 2 (n = 2), and 3 (n = 3), and [{Ce(hfac)3}2{μ-MeO(CH2CH2O)4Me}], 4 (hfac = CF3COCHCOCF3), have been prepared and used as precursors for chemical vapor deposition (CVD) of films of cerium oxides on the substrates Si, Pt, and TiN. Thermal CVD at 450 °C with oxygen as carrier gas gave mixed Ce(III)/Ce(IV) oxides, and the main crystalline component was Ce4O7, but with fluoride impurity. The fluoride impurity was not observed if CVD was carried out using moist oxygen as carrier gas or if the as-deposited films were annealed in oxygen. Codeposition with [Y(hfac)3{MeO(CH2CH2O)2Me}] gave films of the mixed Ce(IV)Y(III) oxide Ce2Y2O7. The depositions of cerium oxides could be enhanced by use of a palladium precursor catalyst [Pd(2-methylallyl)(acetylacetonate)] and could then be carried out at 250 °C, giving films of CeO2. Under carefully controlled conditions, films of ceria-supported palladium could be prepared by this method. The films were characte...

Abstract: A detailed analysis of the microstructural properties of nanocrystalline cerium(IV) oxide powders produced by thermal dehydration of two hydrated ceria precipitated from the ceric ammonium and sulfate salts in ammonia solutions is described. In addition, it is shown that the diffraction pattern of hydrated ceria can be modeled with the structure data of CeO 2 and that the average crystallite size for the precursor CeO 2 .1.6H 2 O is 19 A. The analysis of nanocrystalline CeO 2 is based on the modern developments of X-ray powder diffraction line broadening analysis, using 16 Bragg reflections. It is shown that, on average, the crystallites have a spherical shape with volume-weighted and area-weighted diameters in the ranges 264-1349 A and 178-1079 A for CeO 2 (am-CeO 2 ) obtained from the ammonium-based ceria and 263-1756 A and 195-927 A for CeO 2 (sul-CeO 2 ) obtained from the sulfate-based ceria. The early stages of the crystallite growth have been studied up to 775°C and 900°C, respectively. While sul-CeO 2 is strain-free over the temperature range investigated, am-CeO 2 contains a small amount of strains decreasing with temperature until 700°C, where strains are negligible. The kinetics of the crystallite growth has been studied for the two samples, from which activation energies have been calculated. Crystallite sizes are also compared to the values from SEM and BET measurements. Strain-free sul-CeO 2 is suggested as a potential candidate as reference material for crystallite size in powder diffraction.

Abstract: A method of making a YAG:Ce3+ phosphor includes adding an AlF3 fluxing agent to a yttrium, cerium, aluminum and oxygen containing starting powder and sintering the powder in a weak reducing atmosphere generated by evaporating charcoal. The resulting phosphor has a luminosity of greater than 435 lumens per watt.

Abstract: Mixed oxidic and perovskite-type materials based on the La, Sr, Ce and Fe elements were prepared using a mixture of nitrates salts and heating at 1000°C. Three groups of solids were synthesized: (i) La1−yCeyFeO3 (y=0.2, 0.3, 0.5), (ii) La1−xSrxFeO3 (x=0.2, 0.3, 0.5) and (iii) La1−x−ySrxCeyFeO3 (x/y=0.05/0.15, 0.15/0.05, 0.1/0.2, 0.2/0.1, 0.2/0.3 and 0.3/0.2). The structure of the solids was examined by XRD and the main crystal phases determined were LaFeO3, α-Fe2O3 and CeO2 in group (i), LaFeO3 and SrFeO3−x in group (ii), and LaFeO3, α-Fe2O3, SrFeO3−x and CeO2 in group (iii), while traces of La(OH)3 and SrFe12O19 were also detected. The precise determination of the percentage amount of the iron-containing crystal phases in each solid composition was determined by Mossbauer spectroscopy at 20 K. The ceramic materials had low surface areas and were tested for their catalytic activity for the NO+CO reaction in a flow reactor in the range of 280–560°C. Conversions as high as 90% were achieved at 550°C at a GHSV=54 000 h−1. The reaction rate of NO conversion is favored by the increased amount of CeO2 in groups (i) and (iii) of solids that contain cerium. In the case of solids without CeO2 (group ii), the NO conversion is favored by the existence of SrFeO3−x phase at low temperatures (280–440°C), while it decreases at high temperatures (440–560°C). The double substituted solids La1−x−ySrxCeyFeO3 with x+y>0.3 and y>x were found to be the best catalysts for the NO+CO reaction as compared to the single substituted mixed oxides. Temperature programmed desorption (TPD) studies of NO and CO2 support the view that a synergistic effect takes place between the two phases of CeO2 and SrFeO3−x, whose co-existence results in the maximum enhancement of activity, via alternative oxidation–reduction cycles in the two phases.

Abstract: The present invention relates to high oxygen ion conducting/oxygen storage (OIC/OS) capacity materials, a catalyst employing the OIC/OS materials, and a method for converting hydrocarbons, carbon monoxide and nitrogen oxides using the catalyst. The OIC/OS materials have stable cubic crystalline structures such that after aging for greater than about 36 hours at temperatures up to about 1,200° C., greater than about 60-95% of the cerium present is reducible. These materials comprise up to about 95 mole percent (mole %) zirconium, up to about 50 mole % cerium, up to about 20 mole % of a stabilizer such as yttrium, rare earths, and the like; and about 0.01 to about 25 mole % of a base metal selected from the group consisting of iron, copper, cobalt, nickel, silver, manganese, bismuth and mixtures comprising at least one of the foregoing metals.

Abstract: Cerium complexes of Umbellipherone, Mendiaxon, Warfarin, Coumachlor, and Niffcoumar have been synthesized by reaction of the ligands with cerium nitrate in a stoichiometric ratio of 1:2. The formation of the complexes has been proved on the basis of elemental analysis, conductivities, IR spectroscopy, and 1H-NMR spectroscopy. The molecules of the ligands were optimized by means of the semiempirical quantum mechanical method PM3 to the energetically most stable conformers. All the ligands were characterized by molecular and submolecular electronic indices and the putative donor centers are proposed. It is concluded that the lactone- and the keto-carbonyl groups of Warfarin, Coumachlor, and Niffcoumar are bonded to the metal ion as bidentate ligands. The other two coumarins are bonded as monodentate ligands. Conductivity measurements show the non-electrolytic nature of the complexes. Cytotoxic screening by MTT assay was carried out. The cerium complexes were found to be more active than the inorganic salts.

Abstract: An epitaxial rare earth oxide (001)/silicon (001) structure is realized by epitaxially growing a rare earth oxide such as cerium dioxide in the (001) orientation on a (001)-oriented silicon substrate. For this purpose, the surface of the (001)-oriented Si substrate is processed into a dimer structure by 2×1, 1×2 surface reconstruction, and a rare earth oxide of a cubic system or a tetragonal system, such as CeO2 film, is epitaxially grown in the (001) orientation on the Si substrate by molecular beam epitaxy, for example. During this growth, a source material containing at least one kind of rare earth element is supplied after the supply of an oxidic gas is supplied onto the surface of the Si substrate. If necessary, annealing is conducted in vacuum after the growth.

Abstract: Reactive radio frequency (RF) sputtering was used to grow cerium-doped yttrium iron garnet (YIG) films on magnesium oxide substrates. Magnesium oxide has been proven to be a good buffer material for semiconducting substrates. Reactive sputtering was not effective for cerium doping because the cerium target reacted with the oxygen in the sputtering gas. The films were amorphous as deposited. Stoichiometric compositions yielded smooth, polycrystalline garnet films on annealing. The effects of fluctuations in the yttrium-to-iron ratio were studied. Separate iron and yttrium targets were cosputtered in order to tailor the composition systematically along the iron-yttrium binary phase diagram. Oxygen content was found to be important in the formation of garnet and in the prevention of secondary phases. The garnet films had strong in-plane magnetizations and small coercive fields, which have promise for waveguide and switch devices, respectively.

Abstract: Abstract New intermetallic cerium compounds Ce2T2Mg (T = Ni, Cu, Pd), C2T2Cd (T=Pd, Pt, Au), and C2T2Pb (T = Pt, Au) were prepared by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. Most C2T2X (X = Mg, Cd, Pb) compounds are stable after annealing at about 1000 K, while Ce2Pd2Mg is obtained as single phase only after melting and quenching. A thermal treatment at about 1000 K leads to decomposition in CePdMg and CePd. The eight compounds were investigated by X-ray diffraction both as powders and single crystals, and most structures were refined from single crystal data. They adopt an ordered U3Si2 type structure with space group P4/mbm: a = 759.6(1), c = 376.71 (9) pm, wR2 = 0.0562, 294 F2 values, 12 parameters for Ce2Ni2Mg, a = 787.41(9), c = 387.23(7) pm, wR2 = 0.0438, 222 F2 values, 12 parameters for Ce2Cu2Mg, a = 777.14(8), c = 400.03(7) pm, wR2 = 0.0276, 221 F2 values, 13 parameters for Ce2Pd2.03Mg0.97, a = 777.90(6), c = 393.28(6) pm, wR2 = 0.0360,317 F2 values, 12 parameters for Ce2Pd2Cd, and a = 779.90(7), c = 389.97(7) pm, wR2 = 0.0453, 315 F2 values, 12 parameters for Ce2Pt2Cd. Refinement of the occupancy parameters revealed full occupancy for most sites. A mixed palladium/magnesium (97 % Mg / 3 % Pd) occupancy was observed only for the 2a site of Ce2Pd2.03Mg0.97, indicating a small homogeneity range for this compound. Ce2Au2Cd (a = 804.93(7), c =393.36(6) pm) and the plumbides Ce2Pt2Pb (a = 794.63(7), c = 381.50(6) pm) and Ce2Au2Pb (a = 810.70(7), c = 394.85(7) pm) were characterized through their Guinier powder data. The structures of the Ce2T2X compounds can be interpreted as an intergrowth of distorted AIB2 and CsCl related slabs of compositions CeT2 and CeX. The course of the lattice parameters and chemical bonding within the series of Ce2T2X compounds are briefly discussed.

Abstract: A method for producing a cerium oxide, characterized as comprising heating a cerium salt at a high speed up to a burning temperature, followed by burning; a cerium oxide abrasive comprising a cerium oxide produced by the method and pure water; an abrasive containing a slurry comprising a medium and, dispersed therein, cerium oxide particles having, in a powder X-ray diffraction chart, an intensity ratio of the area of a primary peak appearing at 27 to 30° to that of a secondary peak appearing at 32 to 35° (primary peak/secondary peak) of 3.20 or more; an abrasive containing a slurry comprising a medium and, dispersed therein, cerium oxide particles having a bulk density of 6.5 g/cm3 or less; an abrasive containing a slurry comprising a medium and, dispersed therein, abrasive grains having pores; a method for polishing a substrate, characterized as comprising polishing a specific substrate using the above abrasive; and a method for manufacturing a semiconductor device, characterized as comprising a step of polishing with the above abrasive.

Abstract: The chemical and surface behaviour of cerium oxide, a candidate material for MCFC applications is analysed in Li2CO3–Na2CO3 carbonate eutectic in reducing (H2:CO2:H2O:CO) and oxidizing (O2:CO2) atmospheres. The electrochemical stability domains of cerium species are established at different temperature on the basis of thermochemical calculations. CeO2 is the stable species whatever the acidity level in both the anode and cathode conditions; nevertheless, a partial solubility of Ce2O3 in CeO2 can be predicted. The solubility of cerium and cerium oxide samples, determined by absorption spectrophotometry, is about 5 × 10−4 mol kg−1 in cathodic conditions and 3 × 10−4 mol kg−1 in anodic conditions. X-ray diffraction (XRD) confirmed the presence of CeO2 at the surface of the samples. Incorporation of sodium species in the CeO2 lattice is likely; the presence of Ce(III) in long endurance tests was detected by X-ray photoelectron spectroscopy (XPS).

Abstract: Three novel monomeric glyme adducts of cerium hexafluoroacetylacetonate (Ce(hfa) 3 .diglyme, Ce(hfa) 3 .diethyldiglyme, and Ce(hfa) 3 .dibutyldiglyme have been synthesized adopting a one-pot procedure and characterized by elemental analyses, mass spectrometry, and infrared spectroscopy. Single-crystal X-ray diffraction (XRD) studies provide evidence of a mononuclear nine-coordinated complex with a monocapped square antiprismatic structure of the Ce(hfa) 3 .diglyme (monoclinic system, space group = P2 1 /c; a = 10.037(2) A, b = 15.643(5) A, c = 21.080(5) A, β = 103.460(5)°, Z = 4). The thermal analyses of all three compounds revealed high volatility and good thermal stability with low residue. The adducts 1-3 have better mass transport properties and thermal behavior than conventional cerium metal-organic chemical vapor deposition (MOCVD) precursors, and have been successfully applied to CeO 2 film depositions. The good quality of the deposited layers indicates that the adducts are very attractive precursors for MOCVD applications.

Abstract: A series of catalysts containing 20 wt.% of Mn, Ce and Zr oxides deposited on Al 2 O 3 , SiO 2 and TiO 2 has been studied in ketonisation of heptanoic acid. The most pronounced effect of alumina support on catalysts activity has been noted. Manganese oxide catalysts have shown the highest activity. The dependence of the concentration of MnO 2 active phase on catalyst activity has been determined. A chemical constitution of the side products accompanying 7-tridecanone has been assigned. Stability of MnO 2 /Al 2 O 3 catalyst activity in ketonisation of heptanoic acid in long-time test has been measured.

Abstract: A method for producing a nitrogen oxide storage material that contains at least one storage component in the form of particles of an oxide, carbonate or hydroxide of the elements magnesium, strontium, barium, lanthanum and cerium on a carrier material from the group consisting of doped cerium oxide, cerium/zirconium mixed oxide and aluminum oxide or mixtures of these. The method is carried out by suspending the support material in an aqueous solution of precursors of the storage components, this suspension is then introduced into a hot gas stream, the temperature of which is calculated so that, during a residence time of the suspension in the hot gas stream of less than one minute, the solvent of the suspension is evaporated out and the precursors of the storage components are thermally broken down and converted to the storage components before the storage material that forms in this way is separated from the stream of hot gases.

Abstract: A catalyst for the selective catalytic reduction of nitrogen oxide compounds with ammonia comprising iron exchanged zeolites. The catalyst may further include promoters ion exchanged, or doped with the zeolites. Preferably the promoter ions are rare earth metals such as cerium.