Effect Of Cerium Concentration Research Articles

The local and average structure of Ba(Ti, Ce)O3 perovskite solid solution: effect of cerium concentration and particle size.

The amazing properties of ferroelectric perovskite BaTiO3 (BT) and its solid solutions make them indispensable for many technological applications (e.g. multilayer capacitors). Unfortunately, the so-called `size effect' limits their use. Indeed, under a certain critical particle size, these materials show a suppression of the spontaneous polarization and thus of the ferroelectric properties. In pure nanometric BaTiO3, this is related to a certain local structural disorder. However, only a few studies have explored BT solid solutions, where the doping effect, coupled to the reduced particle size, can play an important role. Therefore, in this work, the structure of BaCexTi1-xO3 (x = 0.02-0.20) was explored by traditional Rietveld method and Pair Distribution Function. Samples present a particle size from 80-160 nm to 400-1000 nm depending on increasing x. The carbox approach was applied, investigating the evolution of the local structure, its modifications and the structural coherent correlation length, as a function of cerium amount. Results demonstrate a cooperative effect of composition and reduced size in the ferroelectricity loss. The two, in fact, contribute to intensify the local structural disorder, decreasing the structural coherent correlation length. The local structural disorder is thus confirmed to be a relevant factor in the ferroelectric properties degradation.

Photoluminescence and γ-Ray Induced Thermoluminescence Investigation of Phase Pure Cerium Doped Yttrium Silicate Nanophosphors

Y2SiO5:Ce3+ (1-7 mol %) nanophosphors were prepared by solution combustion method using oxalyldihydrazide fuel. The phosphors were characterized by X-ray diffraction, scanning electron microscopy, UV-visible and Fourier transform infrared spectroscopy. The XRD patterns confirm the monoclinic structure of the prepared phosphors, with crystallite size of 66-74 nm. The surface morphology and elemental composition were evaluated by SEM and energy dispersive X-ray analysis. The optical band gap was calculated and is between 4.66 eV – 4.9 eV. The presence of Si-O-Si and Y-O bonds was confirmed by the FTIR spectra. Effect of cerium concentration on photoluminescence and thermoluminescence intensity were interpreted. The photoluminescence emission spectrum was recorded under excitation wavelength of 370 nm, the emission spectra showed three significant peaks positioned at 418 nm, 459 nm and 485 nm, which are ascribed to electronic transitions between 5d-4f levels. The nature and activity of trap centers were evaluated from the parameters obtained from Chen′s peak shape method. The intense blue emission by phosphor makes it a competent material for blue emission display devices. Also, its thermoluminescence properties make it a good material for dosimetric applications.

Effect of Cerium Concentration on the Corrosion Resistance of Electro-Less Ni-P-PTFE Composite Coatings

In order to improve the corrosion resistance of electro-less Ni-P-PTFE composite coating, electro-less Ni-P-PTFE composite coatings were prepared on 45# carbon steels specimen with addition of rare element cerium (Ce). Surface morphology of the coatings was observed by scanning electron microscope (SEM). Effect of cerium concentration on PTFE content of the coatings was investigated. The results indicated that properly added cerium into the bath increases the PTFE content of the coatings, decrease the corrosion rate, made the corrosion resistance improved of the coatings. And effect of cerium concentration on corrosion resistance of the composite coatings was evaluated by immersion test with 3.5% NaCl and 5% NaOH solutions respectively. With the rare element cerium concentration exceeding, the corrosion rate gradually increase. At the cerium concentration was 0.01 g.L-1, the corrosion rate of coating in the solutions were lowest, at 0.00186 mg·cm-2·h-1 and 0.00109 mg·cm-2· h-1. But with the cerium concentration go on increasing, the corrosion resistance of the coatings then decreases.

The Effect of Cerium Reduction on Light Emission in Cerium-containing 20Y2O3-25Al2O3-55SiO2 Glass

The effect of cerium concentration and the addition of Sb2O3 on the light emission of cerium-contained glass were investigated. The glass matrix composition was 20Y2O3-25Al2O3-55SiO2, the CeO2 concentration ranged from 0.05 to 0.5 mol%, and Sb2O3 was added at concentrations of 0.02 to 0.1 mol%. The Ce3+ and Ce4+ absorption bands were observed at approximately 330 nm and 240 nm, respectively. A broad emission band at 400 nm, due to the 4f-5d transition of the Ce3+ ion, was observed under illumination by a UV light at 330 nm. The photoluminescence intensity of Ce3+ had a maximum value at a CeO2 concentration of 0.1 mol%. Adding Sb2O3 decreased the Ce4+ absorption intensity and enhanced the light emission intensity of Ce3+ by about 45%.

Effect of cerium concentration on corrosion resistance and polymerization of hybrid sol–gel coating on martensitic stainless steel

Stainless steels are increasingly used in the aeronautics field for the manufacture of structural parts. One of them, the X13VD martensitic stainless steel (X12CrNiMoV12-3), known for its good mechanical properties, has a poor corrosion resistance in confined or severe environments. In the past years, Cr(VI) based pre-treatments have been currently used for corrosion protection of different metals, however, they are toxic and due to environmental regulations, they will be definitely banned in a near future. Alternatives to replace Cr(VI) show advantages and drawbacks considering key properties such as: corrosion resistance, adhesion of coatings, fatigue resistance, durability and reliability. However, some of their possible alternatives show high potential.In this paper, a process was developed to improve the corrosion resistance of the martensitic stainless steel. Organic–inorganic hybrid coatings with different cerium concentrations were deposited onto stainless steel by sol–gel process. Corrosion resistance of the coatings was evaluated by electrochemical impedance measurements and it has been proved that cerium concentration of 0.01M into hybrid coating was an optimal content. Adhesion tests were also carried out by “nanoscratchtest” to characterize the coatings mechanical properties as a function of cerium concentration but results do not clearly show the influence of cerium for the coating adhesion toward the substrate. To try to correlate with the electrochemical properties, liquid 29Si NMR spectroscopy was then performed to investigate hydrolysis and condensation reactions of sol–gel process, and by this method, it was demonstrated that for higher cerium concentration (>0.01M) there is a modification of the chemical structure of the sol–gel network.

Investigating the luminescence properties as a function of activator concentration in single crystal cerium doped Lu2SiO5: Determination of the configuration coordinate model

The effect of cerium concentration on single crystal lutetium orthosilicate (Lu2SiO5, LSO) was investigated with temperature-dependent steady state and time resolved luminescence spectroscopy. The results were used to determine the thermal quenching activation energies and the phonon energies responsible for the thermal broadening of the luminescence spectra. The measured phonon values were used to calculate configuration coordinate (CC) diagrams of the luminescence centers. The nature of single crystal LSO:Ce concentration quenching was determined to be due to radiative energy transfer by self-absorption. The observed broadening of the excitation spectra and narrowing of the emission spectra with increasing cerium was explained via a CC model. A combination of the CC model and concentration quenching explained the measured thermal quenching activation energies.

Effect of cerium concentration on the structural and ferroelectric properties of Bi4−xCexTi3O12 thin films for ferroelectric random access memories

The effect of cerium concentration on the structural and ferroelectric properties in Bi4−xCexTi3O12 (BCT) thin films grown using pulsed-laser deposition was studied. The BCT films with x=0.25 and 0.5 have a pure layered structure after annealing at 650°C in an oxygen ambient. On the other hand, films with x=0.75 still contained a pyrochlore phase as well as a layered structure. The remanent polarization of BCT thin films decreased with increasing Ce concentration. The BCT films with x=0.25 and 0.5 exhibit no polarization fatigue after electric field cycling up to 6×1010 switching cycles. The leakage current densities of samples measured at 100kV∕cm decreased slightly with decreasing Ce concentration.

Preparation and electrochemical study of cerium–silica sol–gel thin films

Design and development of suitable multilayered systems for delaying corrosion advance in metals requires that both the alteration mechanisms of the metal and the behaviour and properties of the protective coatings be known. Coatings prepared by the sol–gel method provide a good approach as protective layers on metallic surfaces. This kind of coatings can be prepared from pure chemical reagents at room temperature and atmospheric pressure, with compositions in a very wide range of environmentally non-aggressive precursors. Sol–gel coatings based on siloxane bonded units were prepared starting from an organic–inorganic hybrid system. The precursors were γ-methacryloxypropyltrimethoxysilane (MAP) and tetramethoxysilane (TMOS). Cerium nitrate hexahydrate in three different concentrations was added. Cerium salts may perform a similar protective effect to that carried out by the well-known lead oxides and chromium salts, even though in this case a negative environmental impact is not expected. Application of coatings upon pure zinc substrates and common glass slides were performed by spinning. Coated samples were heat treated at 40°C for 6 days. Optical measurements (UV-Vis absorption and diffuse reflectance spectroscopies) pointed out that the coatings were colourless and transparent, reducing the diffuse reflectance of the metallic surface up to ∼60%. Optical and scanning electron microscopies (SEM) allowed observation of the texture and microstructure of the coated samples, both before and after the corrosion tests were carried out. Likewise, the remaining sols were kept to gelify at 60°C for 4 days and then powdered to obtain suitable samples for analysing them by other characterisation techniques (Fourier transformed infrared, FTIR and differential thermal analysis, DTA). Electrochemical measurements were performed by impedance spectroscopy. This technique was used to clarify the anticorrosive protection role of cerium ions incorporated into the hybrid sol–gel network. The effect of cerium concentration on the impedance spectra was analysed, as well as the system behaviour against the corrosive medium (0.6M NaCl aqueous solutions), as a function of exposure time. From the electrochemical point of view, the sol–gel films behave as a conversion coating on the metallic surface.