Lanthanum Cerium Oxide Research Articles

Effects of Post-Deposition Annealing Time on Metal-Organic Decomposed Lanthanum Cerium Oxide Film Spin-Coated on Si Substrate

Metal-oxide-semiconductor characteristics of MOD-derived lanthanum cerium oxide (LaxCeyOz) film deposited on n-type Si substrate have been studied. Post-deposition annealing of the oxide was performed in argon atmosphere for a dwell time, ranging from 15 to 120 min at a fixed temperature of 400°C. Results demonstrated presence of positively charged oxygen vacancies in all of the oxides post-deposition annealed for different dwell time. Acquisition of the lowest effective oxide charge as well as the lowest interface trap density and total interface trap density in oxide annealed for 120 min has led to the attainment of the highest breakdown voltage, surpassing other oxides.

Synthesis of La2Ce2O7 nanoparticles by co-precipitation method and its characterization.

Lanthanum cerium oxide nanoparticles have been synthesized by co-precipitation method. In this method, nanoparticles in hydroxide form are obtained and then these nanoparticles are calcined at high temperature. Thermo gravimetric analysis (TGA), X-ray diffraction (XRD), electron dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FT-IR) were utilized to characterize the thermal decomposition, phase structure and morphology of the products. Thermo gravimetric analysis (TGA) of the as prepared material shows almost 37% wt losses, which may be due to the presence of water and nitrate. X-ray diffraction (XRD) analysis of sample calcined at 600 °C shows the formation of standard cubic fluorite phase of lanthanum cerium oxide (La2Ce2O7). Electron dispersive spectroscopy (EDS) confirms the presence of both La and Ce. From Transmission electron microscopy (TEM) morphology, it is observed that particles are in the nano dimension having diameter in the range of 55 to 80 nm with cubic shape. Fourier transform infrared spectroscopy (FTIR) analysis shows the presence of residual nitrate, and absorption of water in the sample.

Oxygen vacancy formation and annihilation in lanthanum cerium oxide as a metal reactive oxide on 4H-silicon carbide

A mechanism regarding the redox reaction in lanthanum cerium oxide (LaxCeyOz) post-deposition annealed in reducing and oxidizing atmosphere was schematized and discussed in association with the presence of lanthanum as a substitutional cation. Analyses have been performed using X-ray diffraction, energy-filtered transmission electron microscopy, scanning transmission electron microscope-energy dispersive spectroscopy line scan, and capacitance-voltage measurements. The results showed the presence of an oxygen vacancy when La(3+) was in its substitution site, while annihilation of oxygen vacancy was accompanied by a displacement of La(3+) from the substitutional site to the interstitial site via a kick-out mechanism prior to its disappearance from the CeO2.

Study of molar ratio on the characteristics of metal–organic decomposed LaxCe1−xOz film as a metal reactive oxide on Si substrate

A metal–organic decomposition technique was employed in this study for the preparation of a solution precursor using different molar ratios of lanthanum (La) to cerium (Ce), which was spin-coated on an n-type Si substrate. Post-deposition annealing was subsequently performed at 1000°C for 15min in argon on the samples to transform the precursor into lanthanum cerium oxide (LaxCe1−xOz) film. This work correlated the influence of decreasing content of La3+ in the LaxCe1−xOz film with formation of oxygen vacancies. Generation of higher amounts of oxygen vacancies in LaxCe1−xOz has evoked an interest in the study of LaxCe1−xOz as a metal reactive oxide on Si substrate for oxygen gas sensing. These oxygen vacancies would serve as active sites for capturing oxygen ions, which were formed as a result of chemisorption of oxygen atoms originating from oxygen gas. The response of oxygen gas sensing for the fabricated Al/LaxCe1−xOz/Si metal–oxide–semiconductor structures was characterized and discussed.

Effects of post-deposition annealing temperature on metal-organic decomposed lanthanum cerium oxide film as metal reactive oxide layer on 4H-SiC

Investigation of metal-organic decomposed LaxCeyOz film was performed on n-type 4H-SiC substrate by varying post-deposition annealing (PDA) temperature from 400 to 1000 °C. The LaxCeyOz acting as a metal reactive oxide layer was demonstrated, explained, and justified via X-ray photoelectron spectroscopy (XPS) through its effect in performing catalytic oxidation of the substrate with temperature as low as 400 °C and the removal of excess carbon, originated from the substrate itself, accumulated at the oxide/4H-SiC interface via formation of CO. Williamson–Hall approach has revealed an increment in crystallite size for LaxCeyOz with decreasing microstrains as PDA temperature increased. High resolution transmission electron microscopy showed the formation of a distinct amorphous interfacial layer in between the bulk oxide and SiC substrate. XPS analysis proved that the bulk oxide with a mixture of amorphous and crystalline regions was comprised of an intermixing of La, Ce, O, C, and La, Ce, O, Si, C elements while interfacial layer consisted of La, Ce, O, Si, and C elements.

Metal-oxide-semiconductor characteristics of lanthanum cerium oxide film on Si

Metal-organic decomposed lanthanum cerium oxide (La x Ce y O z ) film had been spin-coated on n-type Si substrate. Effects of post-deposition annealing temperature and time on the metal-oxide-semiconductor (MOS) properties of the film were studied. As temperature increased from 400 to 1000°C for 15 minutes dwell time, La x Ce y O z demonstrated a decrease in interface trap density (D it) and total interface trap density (D total), which were related to the formation of SiO x /silicates interfacial layer (IL). The lowest leakage current density and highest dielectric breakdown voltage (V B) was obtained in 1000°C-annealed sample. When longer annealing times (30–120 minutes) were studied on the 1000°C-annealed sample, the sample annealed at 1000°C for 120 min showed the best MOS characteristics with V B of 30 V. Reasons contributing to such observation were discussed.

Aqueous CSD approach for the growth of novel, lattice-tuned LaxCe1−xOδ epitaxial layers

Lanthanum–cerium oxide (LCO) films were deposited on Ni-5%W substrates by chemical solution deposition (CSD) from water-based precursors. LCO films containing different ratios of lanthanum and cerium ions (from CeO2 to La2Ce2O7) were prepared. The composition of the layers was optimized towards the formation of LCO buffer layers, lattice-matched with the superconducting YBa2Cu3Oy layer, useful for the development of coated conductors. Single, crack-free LCO layers with a thickness of up to 140 nm could be obtained in a single deposition step. The crystallinity and microstructure of these lattice-matched LCO layers were studied by X-ray diffraction techniques, RHEED and SEM. We find that only layers with thickness below 100 nm show a crystalline top surface although both thick and thin layers show good biaxial texture in XRD. On the most promising layers, AFM and (S)TEM were performed to further evaluate their morphology. The overall surface roughness varies between 3.9 and 7.5 nm, while the layers appear much more dense than the frequently used La2Zr2O7 (LZO) systems, showing much smaller nanovoids (1–2 nm) than the latter system. Their effective buffer layer action was studied using XPS. The thin LCO layers supported the growth of superconducting YBCO deposited using PLD methods.

Effects of Post-Deposition Annealing Temperature on Band Alignment and Electrical Characteristics of Lanthanum Cerium Oxide on 4H-SiC

ABSTRACTInvestigation of lanthanum cerium oxide as a gate oxide on 4H-SiC was performed by varying post-deposition annealing temperature from 400 to 1000°C. Energy band alignment and band gap of bulk oxide and interfacial layer (IL) with respect to SiC were extracted using X-ray photoelectron microscopy. Two band alignment structures were proposed and the change of band alignment was affected by the changes in chemical composition in bulk oxide and in IL that may induce lattice strains and dipoles. A conduction band offset of IL/SiC was 0.97 eV for sample annealed at 1000°C, which was comparable to the value extracted from Fowler-Nordheim model. The acquisition of sufficient conduction band offset, coupled with the lowest slow trap density, effective oxide charges, interface trap density, as well as total interface trap density, yielded the lowest leakage current density for this sample.

Density functional theory study of La2Ce2O7: Disordered fluorite versus pyrochlore structure

The crystal structure of Lanthanum Cerium Oxide (La$_2$Ce$_2$O$_7$) is investigated using \textit{ab initio} density functional theory (DFT) calculations. The relative stability of fluorite- and pyrochlore-like structures is studied through comparison of their formation energies. These formation energies show the pyrochlore structure to be favored over the fluorite structure, apparently contradicting the conclusions based on experimental neutron and X-ray diffraction (XRD). By calculating and comparing XRD spectra for a set of differently ordered and random structures, we show that the pyrochlore structure is consistent with diffraction experiments. For these reasons, we suggest the pyrochlore structure as the ground state crystal structure for La$_2$Ce$_2$O$_7$. %we show that among the structures considered in this work, the pyrochlore geometry is clearly favorable over the disordered fluorite geometry.

Effects of post-deposition annealing temperature and time on physical properties of metal-organic decomposed lanthanum cerium oxide thin film

Lanthanum cerium oxide (La xCe yO z) precursor was prepared using metal-organic decomposition method. The effects of post-deposition annealing temperatures (400–1000 °C) and annealing time (15–120 min) in argon ambient on physical properties of the deposited film were investigated. X-ray diffraction was employed to detect the presence of phase and crystal orientation in the films. Williamson–Hall plot was used to determine the grain size and microstrains of the film. The grain size increased with the increase of annealing temperature and time while microstrains showed an inverse relationship. High resolution transmission electron microscopy (HRTEM) revealed the formation of three layers on top of the Si substrate.

Segmented lanthanum cerium oxide thermal barrier coatings by atmospheric plasma spray

Recently, efforts have been focussed on seeking for new candidates as ceramic topcoat in thermal barrier coating (TBC) system, instead of yttria stabilised zirconia (YSZ) currently used for TBC topcoat. Among the candidates, lanthanum cerium oxide (La2Ce2O7, LCO) is a promising TBC topcoat material, because of its higher temperature stability and better thermal insulation performance relative to yttria stabilised zirconia. In this work, the LCO TBC with high segmentation crack density was prepared by atmospheric plasma spraying, while keeping the stoichiometric composition of the coating. High plasma power and high substrate temperature Ts contribute to the formation of the segmentation structure. The segmented LCO TBC had a lifetime of >730 cycles, exhibiting a significant improvement in thermal shock resistance as compared to the nonsegmented coating. Spallation failure of the segmented TBC was caused by both chipping and delamination cracking.

Lanthanum-cerium Oxide Thermal Barrier Coatings Prepared by Atmospheric Plasma Spraying

Lanthanum-cerium oxide(La2Ce2O7,LC) thermal barrier coatings(TBCs) were prepared by atmospheric plasma spraying(APS).The actual composition of the as-sprayed coating is La2Ce1.66O4.32,due to the volatilization of CeO2 phase during the spray process.A little decomposition of the LC coating takes place after annealing at 1400℃ for 240h.The thermal conductivity of bulk LC material is about 0.51W/(m·K) at 1000℃,which is one fourth of that of typical bulk YSZ.The coefficient of thermal expansion(CTE) of the LC coating ranges from 10×10-6K-1 to 13×10-6K-1 at the temperature from 450℃ to 1100℃,which is relatively higher than that of the YSZ coating.Dilatometric measurements show that there is slight shrinkage in the coating till 1250℃,however,a remarkable sintering process happens during holding period at 1250℃.A spallation of the LC TBC occurs after 60 cycles at 1100℃ by typical delaminating cracking within the LC topcoat.

Thermal Cycling Behavior of Lanthanum-Cerium Oxide Thermal Barrier Coatings Prepared by Air Plasma Spraying

Lanthanum-cerium oxide (La2Ce2O7, LC) is considered as a new candidate material for thermal barrier coatings (TBCs) because of its low thermal conductivity and high phase stability between room temperature and 1673K. The LC coatings with different La2O3 contents were prepared by air plasma spraying (APS) and their lifetime was evaluated by thermal cyclic testing from room temperature to 1373 K. The structures of the coatings were characterized by XRD and SEM and the deviation of the composition from the powder was determined by EDS analysis. Long time annealing for the freestanding coating at 1673K reveals that the near stoichiometric LC coating is stable up to 240h, and the stability decreases with increasing the deviation from stoichiometric LC composition. During thermal cyclic testing, spallation was observed within the top coat near the bond coat. It is considered that the effect of intrinsic stress caused by the coefficient of thermal expansion (CTE) mismatch between top coat and bond coat is larger than that of thermally grown oxide (TGO) and the bond adherence of top coat with TGO.

Hollow Fibers of Lanthanum Cerium Oxide Prepared by Electrospinning

The lanthanum cerium in the fiber is formed by calcination of the electrospinning fibers of polymer/inorganic composite at 600 °C and a polycrystalline hollow fiber with diameter of 1∼5 μm can be obtained at 1000 °C for 12 h. After calcination at 1400 °C, the lanthanum cerium grains are closely connected to each other with clear grain boundaries and the hollow structure can be observed in the cross-section of the fiber.

On improving the phase stability and thermal expansion coefficients of lanthanum cerium oxide solid solutions

Abstract The phase stability of lanthanum cerium oxide (La 2 Ce 2 O 7 ), which is stable up to 1400 °C, and the thermal expansion coefficient of La 2 Ce 2 O 7 doped with Ta 2 O 5 or WO 3 were studied. The thermal expansion coefficient of La 2 Ce 2 O 7 below 400 °C was increased by adding more CeO 2 or doping with either Ta 2 O 5 or WO 3 .

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

Bulk material and coatings of Lanthanum–Cerium Oxide (La 2Ce 2O 7) 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 La 2Ce 2O 7 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 La 2O 3 during ingot preparation and/or by adjusting the process parameters.

Polarization Characteristics of Composite Electrodes in Electrochemical Cells with Solid Electrolytes Based on CeO2 and LaGaO3

For two types of electrochemical cells with oxygen-conducting solid electrolytes based on lanthanum gallate (LSGM) and cerium oxide (SDC) studied are the temperature dependences of the polarization conductivity of air electrodes prepared from lanthanum-strontium manganite (LSM) and composites LSM-LSGM, LSM-SDC, and LSM-SSZ (SSZ is zirconium dioxide-based electrolyte). Effect of praseodymium oxide, added into these electrodes as a modifier, on their electrochemical properties is examined. Electrochemical systems with an LSM/LSGM interface exhibit low electrochemical activity toward the oxygen reaction, because during the formation of electrodes, LSM interacts with LSGM to form a poorly conducting product.

Lanthanum—Cerium Oxide as a Thermal Barrier‐Coating Material for High‐Temperature Applications.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Lanthanum–Cerium Oxide as a Thermal Barrier‐Coating Material for High‐Temperature Applications

La2Ce2O7 is proposed as a new material for thermal barrier coating that has a higher thermal expansion coefficient and a lower thermal conductivity than traditional coating materials. After long‐term annealing at 1400 °C, the crystal structure of La2Ce2O7 was maintained (see Figure). Below 300 °C, thermal contraction occurs, and the material has a comparable thermal cycling life to yttria‐stabilized zirconia coatings.

Kinetics and mechanism of hydrogen oxidation over lanthanum-cerium oxide catalyst using deuterium and oxygen-18

The kinetics of oxidation of stoichiometric mixtures of hydrogen and oxygen with different isotope compositions was studied on La 2O 3 doped with CeO 2 (ratio La Ce = 99 ) in the temperature range between 250 and 400 °C. It was found that during the oxidation the rate constant of H 2 + D 2 = 2HD exchange is equal to the rate of the oxidation under all experimental conditions. 16O 2 + 18O 2 = 2 16O 18O exchange and exchange of 18O between gas and catalyst did not occur during oxidation. The data obtained led to the conclusion that the limiting step of the oxidation reaction is the interaction between hydrogen in molecular form and adsorbed oxygen.