Lanthanum Content Research Articles

Effect of Lanthanum Content and Zirconium Addition on Cast Structure and Mechanical Properties of Mg-La Alloy

Effect of Lanthanum Content and Zirconium Addition on Cast Structure and Mechanical Properties of Mg-La Alloy

A novel electrolyte for intermediate solid oxide fuel cells

Scheelite-type, La x Ca 1− x MoO 4+ δ electrolyte powders, are prepared by the sol–gel process. The crystal structure of the samples is determined by employing the technique of X-ray diffraction (XRD). According to XRD analysis, the continuous series of La x Ca 1− x MoO 4+ δ (0 ≤ x ≤ 0.3) solid solutions have the structure of tetragonal scheelite. Their lattice parameters are greater than that of the original sample, and increase with increasing values of x in the La-substituted system. Results of sinterability and electrochemical testing reveal that the performances of La-doped calcium molybdate are superior to that of pure CaMoO 4. La x Ca 1− x MoO 4+ δ ceramics demonstrate higher sinterability. The La 0.2Ca 0.8MoO 4+ δ sample that achieved 96.5% of the theoretical density was obtained after being sintered at 1250 °C for 4 h. The conductivity increases with increasing lanthanum content, and a total conductivity of 7.3 × 10 −3 S cm −1 at 800 °C could be obtained in the La 0.2Ca 0.8MoO 4+ δ compound sintered at 1250 °C for 4 h.

Influence of composition and pressure on the electric field-induced antiferroelectric to ferroelectric phase transformation in lanthanum modified lead zirconate titanate ceramics

The electric field-induced phase transformation behavior in lanthanum-doped lead zirconate titanate ceramics was examined by polarization versus electrical field (P-E) measurements carried out from room temperature to 130 degrees C and under hydrostatic pressures from 20 to 300 MPa. The samples with composition (Pb(1-x)La(x))(Zr(0.90)Ti(0.10))(1-x/4)O(3) [PLZT x/90/10; x = 2,3,4 at%] were prepared by the standard solid-state reaction method. The analysis at room temperature under atmospheric pressure showed that the increase in the lanthanum content induces a transformation from the typical ferroelectric hysteresis, observed for PLZT 2,3/90/10, to double-hysteresis loops, typical of antiferroelectric phases, for PLZT 4/90/10 under a strong electric field. Hydrostatic pressure- induced and temperature-induced ferroelectric (FE) to antiferroelectric (AFE) phase transformations were examined. The measured hysteresis loops indicated that the FE-AFE phase transformation depends on both temperature and hydrostatic pressure for PLZT 3/90/10. This composition, which is in a ferroelectric state at room temperature under atmospheric pressure, can be transformed into the antiferroelectric phase by the application of a hydrostatic pressure of 100 MPa or by increasing the temperature to around 90 degrees C. The PLZT 2/90/10 and 4/90/10 compositions displayed predominantly ferroelectric and antiferroelectric behavior, respectively, over the ranges of temperature and hydrostatic pressure examined in the present study.

Phase transition and dielectric properties of La-doped Pb(Zr, Ti)O 3 antiferroelectric ceramics

Lanthanum modified lead zirconate titanate (PLZT) ceramics with a Zr/Ti (90/10) ratio were investigated for a 7 and 8 at% lanthanum content by dielectric spectroscopy, the Sawyer–Tower polarization technique and x-ray diffraction measurements. The ceramics were obtained using a standard ceramic method, showing an antiferroelectric (orthorhombic) phase ( Pbam). Electric field dependence of polarization ( P – E ) studies revealed slim-like hysteresis loop characteristics. The temperatures corresponding to the maximum real and imaginary parts of the dielectric permittivity were not only coincident, but also shown to be frequency independent. Results on dielectric response suggest a thermodynamic phase transition rather than a dipole glass/relaxor ferroelectric transition. On the other hand, the Curie temperature ( T C ) was found to be negative. Using Landau’s theory considerations, the obtained results have been interpreted in terms of an antiferroelectric–paraelectric (AFE–PE) phase transition.

Sintering behaviour of La 1− xSr xCo 0.2Fe 0.8O 3− δ ( [formula omitted]) mixed conducting materials

The sintering behaviour of different materials within the system La 1− x Sr x Co 0.2Fe 0.8O 3− δ ( 0.3 ≤ x ≤ 0.8 ) was investigated. Shrinkage curves were measured up to 1350 ° C using a vertical high-resolution dilatometer. The measurements showed that the influence of the heating rate on the shrinkage curves is negligible. Furthermore, the relative shrinkage increases with decreasing lanthanum content in the perovskite lattice at a constant sintering temperature. Sintering experiments showed that the influence of the sintering temperature on the microstructure and densification is more significant than the influence of the dwell time. Increasing the sintering temperature led to a higher densification even at low sintering dwell times. There seems to be no influence of the lanthanum content on the final sintering temperature and dwell time. Nevertheless, sintering at the highest sintering temperature led to the formation of cobalt oxide in case of La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ and La 0.7Sr 0.3Co 0.2Fe 0.8O 3− δ .

Structural and spectroscopic investigation of lanthanum-substituted strontium-oxybritholites

Lanthanum-substituted strontium-oxybritholites, Sr10−x La x (PO4)6−x (SiO4) x O with x = 0, 2 and 4, prepared by solid state reaction were investigated by chemical analysis, powder X-ray diffraction, Raman and 29Si MAS NMR spectroscopies. The refinements of powder XRD patterns of the substituted compounds by the Rietveld method showed that the lanthanum occupied the two metal sites, i.e. (4f) and (6h) sites into the apatite structure, with a clear preference for the (6h) sites. A progressive shift of the free oxygen O(4) towards the centre of the triangles formed by the metal-atoms in the (6h) positions was observed when the lanthanum content increased. It led to the formation of a Sr/La(2)-O(4) strong bond, which might have increased the stability of these compounds. The bands of Raman spectra were assigned to the vibration modes of PO4 and SiO4 groups. The comparison of the results of 29Si MAS NMR analysis with those obtained with the 31P previously reported, suggested that both species occupied the same crystallographic sites.

Influence of lanthanum doping on the dielectric, ferroelectric and relaxor behaviour of barium bismuth titanate ceramics

Barium lanthanum bismuth titanate (Ba1−(3/2)xLaxBi4Ti4O15, x = 0–0.4) ceramics were fabricated using the powders synthesized via the solid-state reaction route. X-ray powder diffraction analysis confirmed the above compositions to be monophasic and belonged to the m = 4 member of the Aurivillius family of oxides. The effect of the partial presence of La3+ on Ba2+ sites on the microstructure, dielectric and relaxor behaviour of BaBi4Ti4O15 (BBT) ceramics was investigated. For the compositions pertaining to x ⩽ 0.1, the dielectric constant at both room temperature and in the vicinity of the temperature of the dielectric maximum (Tm) of the parent phase (BBT) increased significantly with an increase in x while Tm remained almost constant. Tm shifted towards lower temperatures accompanied by a decrease in the magnitude of the dielectric maximum (εm) with an increase in the lanthanum content (0.1 < x ⩽ 0.4). The dielectric relaxation was modelled using the Vogel–Fulcher relation and a decrease in the activation energy for frequency dispersion with increasing x was observed. The frequency dispersion of Tm was found to decrease with an increase in lanthanum doping, and for compositions corresponding to x ⩾ 0.3, Tm was frequency independent. Well-developed P(polarization)–E(electric field) hysteresis loops were observed at 150 °C for all the samples and the remanent polarization (2Pr) was improved from 6.3 µC cm−2 for pure BBT to 13.4 µC cm−2 for Ba0.7La0.2Bi4Ti4O15 ceramics. Dc conductivities and associated activation energies were evaluated using impedance spectroscopy.

Electrochemical behavior and application of lead–lanthanum alloys for positive grids of lead-acid batteries

The effects of different lanthanum content (0, 0.00600, 0.0112, 0.0195 and 0.0540 wt.%) on the electrochemical behavior of lead–lanthanum alloy in sulfuric acid solutions were investigated by linear potential sweep (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The morphology of the corrosion layer and corrosion section of Pb and Pb–La alloys were analyzed by scanning electron microscope (SEM) after corrosion testing. It was found that the addition of La inhibits the oxygen evolution reaction on the surface of Pb alloy electrodes, and La amounts of 0.00600 and 0.0540 wt.% in Pb–La alloy electrodes can lead to a more effective inhibition. The results of the LSV, CV and EIS experiments show that the addition of La can inhibit the growth of the anodic Pb(II) oxides and PbO 2 film. The resistance of the anodic film on the Pb–La electrodes is much lower than that on the Pb electrode. SEM for the corrosion layer indicates that the corrosion product on pure Pb and Pb–0.0195% La alloy is uniform and compact. The corrosion products on the alloys with La contents of 0.00600, 0.0112 and 0.0540 are loose and porous that the active materials can easily sit in the apertures to contact the grid surface intimately with the effective. The results demonstrate that Pb–La alloys show the potential for application as the positive grid material in maintenance-free lead-acid batteries.

Nanosized lead lanthanum titanate (PLT) ceramic powders synthesized by the oxidant peroxo method

For the first time it is reported the synthesis of lead titanate modified with rare earth by the oxidant-peroxo method (OPM). Lanthanum was added up to 20% in mol through the dissolution of lanthanum oxide in nitric acid, followed by the addition of a solution of lead and lanthanum nitrate into an aqueous solution of titanium peroxo complexes. The amorphous precipitate formed was heat-treated at different temperatures in the range from 400 to 900 °C for crystallization. Powders were characterized by Raman spectroscopy and X-ray diffraction. Tetragonal perovskite structure was observed for the samples up to 15% of lanthanum substitution and cubic perovskite for sample with 20% of lanthanum. Crystallographic domains calculated by Scherrer equation showing a probable suppression of the crystallite growth in function of lanthanum content. It was observed shifting to lower frequencies of Raman modes in the range between 100 and 400 cm −1 and the vanishing of the A1(2TO) and E(1LO) modes could be attributed to transition phase from tetragonal to cubic. Electronic microscopy image revealed that the powders annealed at height temperature are spherical with sharp size distribution.

Effects of lanthanum modification on dielectric properties of Pb(Zr0.90,Ti0.10)O3 ceramics: enhanced antiferroelectric stability

Lanthanum modified lead zirconate titanate ceramics with lanthanum content changing from 2 to 6 at% La and a Zr/Ti ratio of 90/10 (PLZT x/90/10) have been analyzed by using X-ray diffraction, dielectric response, differential scanning calorimetry, and ferroelectric hysteresis. An antiferroelectric state was found to be stabilized, whereas the long-range ferroelectric state was disrupted by lanthanum substitution on the lead sites. A ferroelectric state is shown to be stable over an antiferroelectric state for low lanthanum contents in a wide temperature range, where both phases coexist. With the increase of the lanthanum concentration, the long-range coherency of the ferroelectric state is suppressed, i.e., the temperature range of the ferroelectric state stability decreased, disappearing for x > 3 at% La.

Influence of deposition parameters on composition and refractive index of femtosecond and nanosecond pulsed laser deposited gallium lanthanum oxysulphide

The influence of the deposition parameters on femtosecond and nanosecond pulsed laser deposited gallium lanthanum oxysulphide (GLSO) glass films has been investigated. A comparison between films deposited by femtosecond and nanosecond pulsed laser deposition (PLD) shows that the compositional range of each ablation regime varies significantly; in particular, femtosecond PLD shows a unique potential for selective fabrication of films with a high lanthanum content well outside the conventional glass-melting region. We demonstrate how manipulation of the PLD growth parameters can influence the stoichiometric transfer of the PLD process, leading to films with compositions that differ significantly from the GLSO target material. We also reveal how the refractive index of as-deposited films is dependent upon the composition and briefly discuss the thermal properties of bulk GLSO material of various compositions which indicate the potential for films grown by PLD to be used in optical data-storage device applications.

AC conductivity in rare earth ions doped vanadophosphate glasses

Room temperature density and AC conductivity in the temperature range 300–525 K and frequency range 50 Hz to 5 MHz have been investigated in a set of La2O doped vanadophosphate glasses. The density decreased and total conductivity increased with increase of La2O content. The high temperature electrical conductivity has been analyzed using Mott’s small polaron model and polaron activation energies were determined. The polaron activation energy decreased marginally with increase of lanthanum content, at all frequencies of interest. These results have been attributed to the presence of mixed ion–polaron conduction in the present glasses. It is for the first time that La2O doped vanadophosphate glasses have been investigated for AC conductivity and despite heaviness of lanthanum ions, the mixed ion–polaron conduction has been detected. Frequency dependence of AC conductivity has been considered under the correlated barrier hopping (CBH) model of single electron hopping.

Influence of synthesis route and composition on electrical properties of La 9.33 + xSi 6O 26 + 3 x/2 oxy-apatite compounds

Oxy-apatite materials La 9.33 + x Si 6O 26 + 3 x/2 are thought as zirconia-substitutes in Solid Oxide Fuel Cells due to their fast ionic conduction. However, the well-known difficulties related to their densification prevent them from being used as such. This paper presents strategies to obtain oxy-apatite dense materials. First, freeze-drying has been optimized to obtain ultrafine and very homogeneous La 9.33 + x Si 6O 26 + 3 x/2 (0 ≤ x ≤ 0.67) nanopowders. From these powders, conventional and Spark Plasma Sintering (SPS) have been used leading to very dense samples obtained at temperatures rather lower than those previously reported. For instance, SPS has allowed to prepare fully dense and transparent ceramics from 1200 °C under 100 MPa. The microstructure and transport properties of such samples have been then evaluated as a function of sintering conditions and lanthanum content. It will be show that for lanthanum content higher than 9.60 per unit formula, the parasitic phase La 2SiO 5 appears leading to a degradation of conduction properties. We also show that grain boundaries and porosity (for conventionally-sintered materials) seem to have blocking effects on oxygen transport. The highest overall conductivity values at 700 °C, i.e. σ 700 °C = 7.33.10 − 3 S cm − 1 , were measured for La 9.33Si 6O 26 material conventionally-sintered at 1500 °C which contains bigger grains' size by comparison with σ 700 °C = 4.77.10 − 3 S cm − 1 for SPS-sintered materials at the same temperature but for few minutes. These values are associated with activation energies close to 0.83–0.91 eV, regardless of sintering condition, which are commonly encountered for anionic conductivity into such materials.

Role of lanthanum in the gate stack: Co-sputtered TaLaN metal gates on Hf-based dielectrics

We examine the characteristics of TaLaN metal gates in direct contact with HfO 2 dielectric, in particular focusing on the effect of La in the gate stack for NMOS applications. Effective work functions (EWF) and vacuum work functions (WF) are measured as a function of lanthanum content in TaLaN without any intentional heating using X-ray photoelectron spectroscopy, U-V photoelectron spectroscopy, and electrical C– V measurements. We find that the addition of lanthanum to tantalum nitride lowered both the EWF and the WF of the metal gate by ∼0.2 eV and ∼0.9 eV, respectively. Furthermore, XPS indicates that lanthanum in TaLaN at the interface with HfO 2 is primarily bonded to nitrogen rather than oxygen and not reacting with the dielectric.

Development of structural stability and the electrochemical performances of ‘La’ substituted spinel LiMn 2O 4 cathode materials for rechargeable lithium-ion batteries

The LiLa x Mn 2 − x O 4 ( x = 0.00 to 0.10) cathode materials for rechargeable lithium ion batteries were synthesized by simple sol–gel technique using aqueous solutions of metal nitrates and succinic acid as the chelating agent. The gel precursors of metal succinates were dried in vacuum oven for 10 h at 110 °C. After drying, the gel precursors were ground and heated at 900 °C. The structural characterization was carried out by X-ray powder diffraction and Laser Raman spectroscopy. The sample exhibited a well-defined spinel structure and the lattice parameter was linearly increased with the increasing lanthanum contents in LiLa x Mn 2 − x O 4. Surface morphology of the synthesized materials was determined by Scanning electron microscope and it was found that the cathode materials consisted of highly-ordered single crystalline particles with cubic spinel structure. Electrochemical properties were characterized by the assembled test cells using Galvanstatic charge/discharge studies which were carried out at a current rate 0.1C and Cyclic voltammetry was carried out in the potential range of 2.75 to 4.5 V at a scan rate 0.1 mVs − 1 . Among them, lanthanum doped spinel LiLa 0.05Mn 1.95O 4 has improved the structural stability, high reversible capacity and excellent electrochemical performance of rechargeable lithium batteries.

The Gd2-yLayZr2O7 Solid Solution as a New Electrolyte for High and Intermediate-Temperature SOFC's

Different compositions in the Gd2-yLayZr2O7 solid solution (0 {less than or equal to} y {less than or equal to} 1) were prepared at room-temperature, by mechanically milling stoichiometric mixtures of the corresponding oxides. We found that irrespective of their lanthanum content, as-prepared powder samples consist of single-phase anion deficient fluorite materials, although post-milling thermal treatments at 1200ºC facilitates the long-range ordering of cations and anion vacancies characteristic of pyrochlores for y {greater than or equal to} 0.4. Interestingly, activation energy for oxygen migration in the series decreases from 1.13 {plus minus} 0.02 eV (Gd2Zr2O7) to 0.84 {plus minus} 0.03 eV (GdLaZr2O7) as La-content and the RA/RB ratio increase. These results are explained in terms of weaker ion-ion interactions in better ordered and highlight the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions.

Thermoelectric Properties of Iron-and Lanthanum-Doped CoSb3 Compounds by Pulse Discharge Sintering

of fossil fuels. In this regard, thermoelectric power generation that can directly convert the thermal energy to electrical energy is one of the attractive methods. Skutterudite compounds of CoSb3 have been investigated as promising candidate materials for thermoelectric power generation. In this research, CoSb3 compounds were synthesized from raw metal powders by using a pulse discharge sintering process. To improve the thermoelectric properties, iron was doped as an element substituting for cobalt of the CoSb3 compound. The syntheses of FexCo1xSb3 were confirmed by x-ray diffraction analysis. The Seebeck coefficient, electric resistivity, and thermal conductivity were measured as the thermoelectric properties. Optimum content of iron was decided from the maximum thermoelectric figure of merit. Furthermore, filling of lanthanum into Fe0:1Co0:9Sb3 was attempted to decreasethethermalconductivity.Thelanthanum-filledFe0:1Co0:9Sb3 compoundsweresynthesizedfromrawmetal powders and LaSb powder by the pulse discharge sintering process. The optimum lanthanum content that leads to the maximum thermoelectric performance is discussed. The substitution of iron for cobalt improved the thermoelectric performance. The lanthanum-filling decreased the thermal conductivity at a low lanthanum content and led to higher thermoelectric performance in spite of low lanthanum content.

A Model of the Kinetics of Lanthanum in Human??Bone, Using Data Collected during the Clinical Development of the Phosphate Binder Lanthanum Carbonate

Lanthanum carbonate (Fosrenol) is a non-calcium phosphate binder that controls hyperphosphataemia without increasing calcium intake above guideline targets. The biological fate and bone load of lanthanum were modelled with the aid of a four-compartment kinetic model, analogous to that of calcium. The model used data from healthy subjects who received intravenous lanthanum chloride or oral lanthanum carbonate, and bone lanthanum concentration data collected from dialysis patients during three long-term trials (up to 5 years). Infusion of lanthanum chloride or ingestion of lanthanum carbonate led to a rapid rise in plasma lanthanum concentrations, followed by an exponential decrease. Comparison of oral and intravenous exposure confirmed that lanthanum is very poorly absorbed. On a typical intake of lanthanum (3000 mg/day as lanthanum carbonate), the rate of absorption was calculated as 2.2 microg/h, with a urinary excretion rate constant of 0.004-0.01 h(-1). The faecal content of endogenous lanthanum was estimated to be 8- to 20-fold greater than that of urine, compared with a ratio of only about 1 for calcium. The model predicts that upon multiple dosing, plasma lanthanum concentrations rise rapidly to a near plateau and then increase by about 3% per year. However, this small change is obscured by the variability of the study data, which show that a plateau is rapidly attained by 2 weeks and is thereafter maintained for at least 2 years. The initial deposition rate of lanthanum in bone was 1 microg/g/year and, after 10 years of lanthanum carbonate treatment, the model predicts a 7-fold increase in total bone lanthanum (from 10 mg to 69 mg [from 1 microg/g wet weight to 6.6 microg/g wet weight]), with lanthanum cleared after cessation of treatment at 13% per year. The model indicates that lanthanum flow from bone surface to bone interior is much lower than that of calcium. Bone is the major reservoir for metals, but bone lanthanum concentrations are predicted to remain low after long-term treatment because of very poor intestinal absorption.

Analysis of a Superconductor: Development of a Practical Exam for the International Chemistry Olympiad

In July 2004 the 36th International Chemistry Olympiad was held in Kiel, Germany. Competition for medals included 236 students from 61 countries, accompanied by about 150 teachers and other mentors. During this Olympiad the students performed qualitative and quantitative analyses of a superconductor, based on lanthanum barium cuprate. In the quantitative determination the students assessed the lanthanum and copper content by complexometric and iodometric titration; the alkaline earth metal was identified by qualitative analysis. From these results, the formula of the superconductor could be calculated. New procedures were developed, which in contrast to classical procedures, did not require the use of toxic chemicals. We report on the development and the results of our practical task and the reasons why we chose it for the Olympiad.

Characterization and electrical properties of new perovskite films of Ba(Ti,Zr)O3 type doped with lanthanum (BLZT)

AbstractIn the current work, we characterized a new family of compounds with perovskite‐type structure with the general formula: Ba1–yLa2y/3Ti1–xZrxO3 (BLZT). Through XRD on crystalline powder we detected a single perovskite cubic phase, Pm3m (221), for the compounds with zirconium content (x) lower than 0.15 and lanthanum content (La) lower than 0.17. Upon increasing the x value in BLZT compounds, the value of La falls to 0.13. Morphology studies through SEM revealed that the incorporation of lanthanum into the composition of Ba(Ti,Zr)O3 (BZT) compounds produces the formation of bigger grains and materials with greater density. The stoichiometry for each compound was corroborated by atomic emission spectroscopy (AES‐ICP). The lanthanum‐doped compounds demonstrated higher relative permittivity values with respect to the BZT and a decrease of the Curie temperature (Tc) with relation to the amount of La3+ ion present in the structure. Finally, we grew thin films by using a target of the compound Ba0.90La0.067Ti0.91Zr0.09O3 over three different substrates under two atmospheres (Ar and O2), using the Magnetron Sputtering technique by Radio Frequency (RF), showing the best results when growth is over the substrate SrTiO3.Nb 0.1% in the [00l] direction under an O2 atmosphere. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)