Lanthanum Content Research Articles

Investigation of LaxSr1−xCoyM1−yO3−δ (M = Mn, Fe) perovskite materials as thermochemical energy storage media

Materials in the LaxSr1−xCoyMn1−yO3−δ (LSCM) and LaxSr1−xCoyFe1−yO3−δ (LSCF) families are candidates for high-temperature thermochemical energy storage due to their facility for cyclic endothermic reduction and exothermic oxidation. A set of 16 LSCM and 21 LSCF compositions were synthesized by a modified Pechini method and characterized by powder X-ray diffraction and thermogravimetric analysis. All materials were found to be various symmetries of the perovskite phase. LSCM was indexed as tetragonal, cubic, rhombohedral, or orthorhombic as a function of increased lanthanum content. For LSCF, compositions containing low lanthanum content were indexed as cubic while materials with high lanthanum content were indexed as rhombohedral. An initial screening of redox activity was completed by thermogravimetric analysis for each composition. The top three compositions with the greatest recoverable redox capacity for each family were further characterized in equilibrium thermogravimetric experiments over a range of temperatures and oxygen partial pressures. These equilibrium experiments allowed the extraction of thermodynamic parameters for LSCM and LSCF compositions operated in thermochemical energy storage conditions.

Degradation of Electrical Conductivity in Lanthanum Silicate Oxyapatite

Degradation of electrical conductivity in lanthanum silicate oxyapatite (La9.33+x Si6O26+1.5x ) was observed at 600 ~ 1000oC. Small particles were detected on the surface of pellets after electrical conductivity measurements for 100~201 h. These particles were identified as La2SiO5 phase using micro-raman spectroscopy. Lanthanum content in the oxyapatite phase is strongly related to its conductivity, because the excess oxygen is incorporated by charge compensation according to excess lanthanum composition. This study suggests that the decrease in electrical conductivity may be attributed to reduction in electrical charge carriers as a result of the phase degradation of La2SiO5 phase from oxyapatite phase.

Formation mechanism and characteristics of lanthanum-doped BaTiO3 powders and ceramics prepared by the sol–gel process

Pure and lanthanum-doped barium titanate nanopowders described by two different formulae, as Ba1−xLaxTiO3, for lower La concentrations (0≤x≤0.005) and Ba1−xLaxTi1−x/4O3 for higher La concentration (x=0.025) were prepared by an alkoxide sol–gel method. Single phase compositions were obtained after annealing at 900°C for 2h, in air. The increase of the lanthanum content causes structural and morphological changes in the oxide powders, including the evolution of the unit cell from tetragonal toward a cubic symmetry, the particle size decrease and a higher aggregation tendency.SEM investigations of the ceramics sintered at 1300°C for 4h indicate significant changes of the microstructural features (strong decrease of the average grain size and increase of the intergranular porosity) with the raise of La amount. Lanthanum addition to barium titanate prepared by sol–gel induces a more significant shift of the Curie temperature toward lower values, than that one reported in literature for ceramics of similar compositions, but processed by the conventional solid state method. The compositions with smaller La amount (x≤0.005) show semiconducting properties at room temperature and high relative dielectric permittivity values, while the undoped ceramics and those doped with higher La content (x=0.025) are good dielectrics. The ceramic with x=0.025 exhibits acceptable low losses, a very diffuse ferroelectric–paraelectric transition and Curie temperature closed to the room temperature, being thus susceptible for high tunability applications.

Photoluminescence properties of cerium oxide nanoparticles as a function of lanthanum content

The structural and photoluminescent properties at room temperature of CeO2 and La-doped CeO2 particles were undertaken. The obtained particles were synthesized by a microwave-assisted hydrothermal method (MAH) under different lanthanum contents. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman), Ultra-violet spectroscopy (UV–vis) and photoluminescence (PL) measurements were carried out. XRD revealed that the powders are free of secondary phases and crystallize in the cubic structure. Raman data show that increasing La doping content increase oxygen vacancies due to lattice expansion. The UV/vis absorption spectroscopy suggested the presence of intermediate energy levels in the band gap of structurally ordered powders. Lanthanum addition creates oxygen vacancies and shifts the photoluminescence in the low energy range leading to intense PL emission.

Dielectric properties of neodymium-modified PLZT ceramics

Relaxor ferroelectrics or relaxors are a class of disordered single crystals and ceramic materials, of peculiar structure as well as properties. The commonly known examples of such materials are Pb(Mg,Nb)O3 (PMN) ceramics as well as single crystals. The second most extensively studied relaxor ceramics is lanthanum-doped lead zirconate–titanate, described as x/65/35 PLZT when lanthanum content is x = 6–10 at%. Throughout the last few decades, there has been an increasing interest in rare-earth-doped PLZT ceramics, because PLZT can be easily substituted with lanthanide elements for La3+ ions. For this reason, the present studies concern the changes in microstructure and crystal structure as well as in dielectric properties, caused by modification of 8/65/35 PLZT with neodymium dopant. Modification of this material with Nd3+ influences the microstructure, electrooptical and dielectric properties, whereas the changes in crystal structure are slight. It was also observed that the maximum value of dielectric properties decreases and moves to a low temperature. Described changes in physical properties are associated with the significant improvement of relaxor properties, characteristic for pure 8/65/35 PLZT ceramics.

Oxygen nonstoichiometry and defect equilibrium in electron doped Ca0.6−уSr0.4LaуMnO3−δ

The perovskite-like electron doped manganites Ca0.6−уSr0.4LaуMnO3−δ (0⩽y⩽0.15) were synthesized in order to study oxygen content variations with composition, temperature and oxygen partial pressure. The samples are characterized with orthorhombic Pnma structure at 0<у<0.1 and tetragonal I 4/mcm structure at у⩾0.13 according to room temperature powder X-ray diffraction (XRD). The high-temperature data of XRD in air show transition to cubic Pm3¯m structure at heating above 550°С. The variations of oxygen content in Ca0.6−уSr0.4LaуMnO3−δ with temperature and oxygen pressure were measured using thermogravimetry and coulometric titration at temperatures between 650 and 950°С in the oxygen pressure range 10−4–0.7atm. The oxygen nonstoichiometry δ changes in Ca0.6−уSr0.4LaуMnO3−δ are observed to considerably decrease with the increase in lanthanum content. In order to explain the nonstoichiometry data, a thermodynamic model is developed based on defect formation reactions 2Mn3++VO+½O2=2Mn4++O2− and 2Mn4+=Mn3++Mn5+. The respective equilibrium constants, defect formation enthalpies and entropies are obtained. The concentrations of different defects are calculated as functions of temperature, oxygen pressure and lanthanum content. The high-temperature conductivity measurements are carried out for independent verification of the suggested model.

Influence of La3+ additions on the phase behaviour and antibacterial properties of ZrO2–SiO2 binary oxides

The present study reports the influence of lanthanum (La3+) content on the phase stability and antibacterial activity of ZrO2–SiO2 binary oxides. Four different concentrations of La3+ additions in ZrO2–SiO2 binary oxides were synthesized using a sol–gel technique. Heat treatment of the synthesized powders resulted in the formation of t-ZrO2 phase at 1000°C. Heat treatment beyond 1000°C resulted in the phase degradation of t-ZrO2 to yield m-ZrO2 and ZrSiO4. Results from antibacterial tests confirmed the potential activity of La3+ doped ZrO2–SiO2 binary oxides in countering the microbial invasion.

Investigation of carbonates in oxygen-transporting membrane ceramics

The performance of perovskite-type oxygen-transporting membranes during CO2 sweeping has been investigated. The series of La1−xSr xCo0.8Fe0.2O3−δ (LSCF) materials with x=1, 0.8, 0.6 and 0.4 (SCF, LSCF2882, LSCF4682, LSCF6482) were synthesized by the sol–gel method and characterized by X-ray diffraction (XRD). To investigate the poisoning effect of CO2 on the phase composition and microstructure of the membranes after long-term oxygen permeation experiments (more than 200h) at 1173K under a CO2 atmosphere, transmission electron microscopy (TEM) investigations were carried out. Electron-energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDXS) revealed the formation of carbonate at the outer surface of the LSCF materials with low lanthanum content, which correlates with a decrease in oxygen permeation flux. Nevertheless, the LSCF 6482 material is tolerant to CO2 gas. No carbonate layer was found after 200h of operation, and the oxygen flux remained stable.

Mg-La-Zr合金の延性と変形組織

In order to gain insight for developing fine-grained magnesium alloy materials through plastic deformation, Mg-Zr, Mg-La, and Mg-La-Zr alloys, prepared from pure magnesium and lanthanum metals, and a Mg-33Zr master alloy were tensile tested at room temperature and 150ºC. The microstructures were examined by optical microscopy, X-ray diffraction analysis, and EBSD analysis to establish the characteristics of deformed portions of the tensile-tested specimens. Whereas the elongation values of Mg-La and Mg-La-Zr materials tested at room temperature decreased with lanthanum content, the materials tested at 150ºC maintained a similar level of elongation regardless of lanthanum content. EBSD analysis of the deformed materials of the Mg-La-Zr alloys tensile-tested at room temperature and 150ºC revealed that the microstructures of primary αMg consisted of approximately 50% ultrafine grains of 0.5 to 1.5 μm in size. About 70% of the eutectic αMg grains was found to be approximately 0.1 μm in size, suggesting that microstructural transformations that take place through deformation processes may help to enhance ductility.

Ferroelectric and piezoelectric properties of La-modified lead-free (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–SrTiO3 thin films

Lead-free piezoelectric 0.9(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)–0.1SrTiO3 thin films doped with x mol% La (abbreviated as BNT–BKT–ST–xLa) (x=0, 0.5, 1.0, 1.5) were prepared by a sol–gel method on Pt(111)/Ti/SiO2/Si substrates. The effects of La content on the microstructure, ferroelectric and piezoelectric properties were investigated systematically. The X-ray diffraction patterns indicated that all films had a single-phase perovskite structure. Meanwhile, we found that lanthanum content had great influence on the grain size and electrical properties. The thin film with a composition of BNT–BKT–ST–0.5La showed the optimal electrical properties with a remnant polarization, dielectric constant and effective piezoelectric constant of 10μC/cm2, 560, and 83pm/V, respectively. The results indicated that 0.5mol% La-doped BNT–BKT–ST thin films would be of great interest for lead-free piezoelectric devices.

Studies of sulphated mixed oxides (ZrO2–SO4–La2O3) in the isomerization of n-hexane

A series of mixed oxides (ZrO2–La2O3) was investigated to establish the effect of the source of the sulphate ion and the modification of sol–gel zirconia with La2O3. Supports were synthesized varying the content of La2O3 (2, 3, 5 and 10wt.%). Sample sulphation took place in situ, maintaining the amount at 20wt.% using concentrated H2SO4 and a 1M (NH4)2SO4 solution as the sulphating agents. These catalytic materials were characterized by: X-ray diffraction, nitrogen adsorption (BET), FTIR pyridine, 2-propanol dehydration, Scanning Electron Microscopy (SEM) and isomerization of n-hexane. The modification of sol–gel zirconia with La2O3 originated an increase in the surface area. When increasing the content of La2O3 (3, 5 and 10wt.%) a diminution of the surface area for samples sulphated with H2SO4 (CASLn) occurred. On the contrary, for samples sulphated with (NH4)2SO4 (CSALn) a not defined behavior was presented. In mixed oxides, the tetragonal phase was present which is characteristic of sulphated zirconia. By SEM, the morphology of the support can be perfectly observed showing the presence of clusters in each of them. It was observed that the crystallite size did not change when increasing the lanthanum content for the CASLn supports. According with the FTIR pyridine technique all the samples exhibited the presence of Brönsted and Lewis sites, and the support that achieved the highest acidity was the one containing 2wt.% of La2O3 (CASL2). It was determined that the effect of the sulphate agent generated more active catalysts in terms of conversion of n-hexane and it was also observed that La2O3 provided a higher catalytic selectivity toward isomerization products.

Effect of A-site La3+ modified on dielectric and energy storage properties in lead zironate stannate titanate ceramics

(Pb1-1.5xLax)(Zr0.66Sn0.23Ti0.11)O3 (PLZST) ceramics with different lanthanum (La3+) content (x = 0–6%) were prepared by conventional solid state reaction process, and exhibited excellent electrical properties with high switching field from AFE to FE phase and electric breakdown strength. The maximum dielectric constant (εm) and its corresponding temperature (Tm) decreased with La3+ doping and a phase transition from rhombohedral ferroelectric (FE) to tetragonal antiferroelectric (AFE) state was found at 2% La3+ doping. At room temperature, a maximum energy density of 1.47 J cm−3 was obtained for x = 4%. In addition, electric-field-dependent energy storage properties of PLZST (x = 4%) ceramics have been investigated, which could be ascribed to the AFE–FE phase transition associated with the increase of strain.

Effects of adding basic oxides of La and/or Ce to SiO2-supported Co catalysts for ethanol steam reforming

In this study, cobalt catalysts supported on La2O3–CeO2–SiO2 were synthesized by the method of impregnation of the support with aqueous solution of the active phase precursor. These materials were tested in ethanol steam reforming (ESR). The catalysts were characterized by in situ X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR), temperature-programmed hydrogen desorption (H2-TPD), temperature-programmed oxidation (O2-TPO), adsorption–desorption of nitrogen (BET) and energy-dispersive X-ray spectroscopy (EDS). After reaction, the spent materials were characterized by XRD, SEM and elemental analysis. The in situ XRD analysis showed the formation of the solid solution CexLa1−xO2−δ and identified cobalt oxide in the spinel structure (Co3O4) and metallic cobalt (Co0). The H2-TPR analysis showed the reduction of cobalt oxide, and it was observed that the peaks of cobalt oxide shifted to lower temperatures as the content of lanthanum increased. The H2-TPD analysis showed that metal surface area and metal dispersion decreased as the percentage of lanthanum oxide in the supports increased. The O2-TPO analysis showed that La2%Ce48%Si50% consumed the most oxygen. The SEM analysis identified filamentous carbon after reaction. The catalysts were active for H2 and CO2 production. The best catalytic performance was shown by Co10%La2%Ce48%Si50%, which gave the highest H2 yield.

Characterization and kinetic study of BiMoLax oxide catalysts for oxidative dehydrogenation of 1-butene to 1,3-butadiene

BiMoLax oxide catalysts with a variation of lanthanum component were prepared by a co-precipitation method, and applied to the oxidative dehydrogenation (ODH) of 1-butene to 1,3-butadiene (BD). The results reveal that the lanthanum content has significant effects on the catalyst performance. BiMoLa0.2 exhibits the superior activity and stability during the 100h test. H2 temperature-programmed reduction (H2-TPR), 1-Butene temperature-programmed re-oxidation (TPRO) and temperature-programmed desorption (TPD) characterization show that the oxygen mobility and the adsorption ability of 1-butene of catalysts are two crucial factors determining catalytic performance in ODH reaction. The kinetics analysis finds that the ODH reaction over BiMoLa0.2 can occur more easily.

Effect of La doping in transparent 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 ceramics fabricated by conventional sintering

Abstract

CH4 reforming with CO2 for syngas production over La2O3 promoted Ni catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al2O3 with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N2 adsorption-desorption, TPR, TPO, TPH, NH3-TPD and SEM techniques. The BET analysis showed a high surface area of 204 m2·g−1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and O2 to dry reforming feed increased the methane conversion and led to carbon free operation in combined processes.

Effect of Dielectric Properties and Elastic Strain Behavior on x/65/35 PLZT Ceramics in Lanthanum (x) Ions Contents

In this paper the effect of lanthanum addition on the phase formation, dielectric and ferroelectric characteristics of x/65/35 PLZT. This ceramics were prepared using mixed-oxide synthetic route via a rapid vibro-milling method. All samples were sintered at 1200°C for 12 h. X-ray diffraction was used to observe the crystal structure. It was found that when increasing lanthanum content, the structure remained rhombohedral. It can be seen that the change of behavior to ferroelectric relaxor with the increasing of lanthanum content resulted in the change of elastic strain

Cathodes based on rare-earth metal nickelate ferrites prepared from industrial raw materials for solid oxide fuel cells

Powders of composite materials based on lanthanum nickelate-ferrite with different contents of lanthanides were synthesized using Ln-Ni-Fe-O (LnNF) mischmetal. The phase composition of the powders was determined by XRD. The crystal structure of the main phase in LnNF obtained using a mischmetal with a high lanthanum content is perovskite-like, while the structure with a high cerium content is fluorite-like. The temperature coefficients of linear expansion of the synthesized materials were determined by dilatometry. The temperature dependences of electric conductivity of the compact samples and porous electrodes from these materials were studied by the DC four-probe method. The electric conductivity of compact samples from materials prepared using the mischmetal with the perovskite-like structure of the main phase exceeds the electric conductivity of the materials based on the mischmetal with a high cerium content by approximately three orders of magnitude. The temperature dependences of polarization conductivity of electrodes in cells with the Ce0.8Sm0.2O1.9 (SDC) electrolyte at 600–900°C in air were studied by impedance spectroscopy. The LnNF electrodes with a perovskite-like crystal structure of the main phase showed high electrochemical activity.

Evolution of structure and electrical properties with lanthanum content in [(Bi1/2Na1/2)0.95Ba0.05]1−xLaxTiO3 ceramics

Abstract Lead-free perovskite [(Bi 1/2 Na 1/2 ) 0.95 Ba 0.05 ] 1− x La x TiO 3 ( x = 0.00–0.10) ceramics were fabricated via the solid state reaction method and their crystal structures and electrical properties were systematically studied. Transmission electron microscopy examination reveals a transition from a rhombohedral R3c phase with micron-sized complex domains to a mixture of rhombohedral R3c and tetragonal P4bm phases with nanodomains as La content was increased. X-ray diffraction analysis on bulk samples, however, indicates a pseudocubic structure in La-doped compositions. Electrical poling seems to transform the pseudocubic structure to a rhombohedral phase in compositions with 0.00 x T d ) is observed to decrease and the dielectric constant ( ɛ r ) within 100–350 °C becomes more temperature independent, promising for applications in high-temperature capacitors. Electric field-induced polarizations and strains display complex changes with respect to La concentration, with the highest strain of 0.35% achieved in the composition x = 0.04 under 70 kV/cm at room temperature. The piezoelectric coefficient d 33 initially increases with La content, reaching a maximum value of 151 pC/N in the composition x = 0.02, and then diminishes.

Analysis of Structural and Microstructure of Lanthanum Ferrite by Modifying Iron Sand for Microwave Absorber Material Application

Analysis crystal structure of lanthanum ferrite by modifying iron sand has been carried out. Lanthanum ferrite included one of the functional materials which had composition of ABO3 perovskite system. The lanthanum ferrite is prepared by iron sand and lanthanum oxide powders. The mixture was milled for 10h with the various composition of lanthanum content. The samples are sintered at a temperature of 1000 °C for 10h. The microstructure analyses showed that the particle shapes was polygonal with the varied particle sizes and uniform distribution on the surface of the sample. The phase composition of refinement result showed that the lanthanum ferrite formed empirical compound of La0.8Mg0.2Fe0.7Ti0.2Si0.1O3. The La0.8Mg0.2Fe0.7Ti0.2Si0.1O3 phase has a structure orthorombic (P b n m) with lattice parameters a = 5.513(1) Å, b = 5.549(1) Å and c = 7.849(2) Å, α = β = γ = 90°, the unit cell volume of V = 240.2(9) Å3, and the atomic density of ρ = 6.293 gr/cm3. We concluded that this study has been successfully synthesized lanthanum ferrite material from modifying iron sand and has been understood changes in the parameters of the crystal structure and phase composition of this material. It was a great opportunity that the material can be used as a material candidate of absorber electromagnetic waves.