Barium Lanthanum Research Articles

Synthesis and microwave characterization of Bi- substituted barium lanthanum titanate

Synthesis and microwave characterization of Bi- substituted barium lanthanum titanate

Magnetoresistance studies on barium doped nanocrystalline manganite

An energetically attractive, simple, fast and a novel low temperature (300 °C) solution combustion route for the synthesis of crystalline and homogeneous nanoparticles of lanthanum barium manganese oxide La 0.9Ba 0.1MnO 3+ δ (LBMO) is reported. Formation and homogeneity of the solid solutions have been confirmed by powder X-ray diffraction (PXRD) and energy dispersive X-ray analysis (EDS) respectively. The Rietveld analysis shows both as-formed as well as calcined samples are in cubic phase with space group pm3 m. The microstructure and agglomerated particle size of the compounds are examined by scanning electron microscope. Infrared spectroscopy revealed that both Mn O Mn bending mode and Mn O stretching mode are influenced by calcination temperature. The magnetoresistance measurement on sintered LBMO pellet exhibits a broad metal–insulator transition ( T M-I) at around 228 K. At 1 T applied magnetic field, LBMO shows magnetoresistance (MR) of 10%, whereas for 4 and 7 T, the negative magnetoresistance values are in the range 51 and 59% respectively at T M-I. The experimental resistivity data of the present investigation are fitted to a simple empirical equation in order to understand conduction mechanism in this compound.

Ferroelectric transitions in valence compensated Ba1−x La x Ti1−x Cr x O3 ceramics

An attempt has been made to investigate the solid solubility limit between barium titanate, BaTiO3 and lanthanum chromite, LaCrO3. Compositions with x ≤ 0.15 have shown solid solution formation in the system Ba1−xLaxTi1−xCrxO3. Compositions with 0.01 and 0.05 are found to have a tetragonal structure, whereas those with x = 0.10 and 0.15 are found to have a cubic structure at room temperature. Dielectric measurements have been carried out at different frequencies in the temperature range 100–550 K. Plots of er versus temperature for composition with x = 0.01 show dielectric anomalies at 376 K (TC-T) and 275 (TT-O) where TC-T and TT-O denote the temperature for cubic to tetragonal and tetragonal to orthorhombic transition. Dielectric anomaly corresponding to the ferroelectric to paraelectric transition has been found to shift to lower temperatures with increasing concentration of lanthanum and chromium. For compositions with x ≤ 0.05, TC has been found to be frequency independent while for x = 0.10 and 0.15, TC has been found to be frequency dependent in a manner similar to relaxor ferroelectrics.

Electrocatalytic Studies of Oxygen Reduction by Lanthanum Barium Manganate

The electrocatalysis of the oxygen reduction reaction by Lanthanum Barium Manganate, (La0.5Ba0.5MnO3) (LBM) has been studied by cyclic voltammetry using the rotating ring-disc electrode technique (RRDE) in alkaline medium. From the ring-disc data and other kinetic parameters it has been assumed that the oxygen reduction occurs by dissociative chemisorption at low overpotentials. At higher overpotentials, the formation of hydrogen peroxide (HO2 - in this case) has been observed on this electrocatalyst. The apparent exchange current density value for oxygen reduction on LBM has been found to be 4 x 10-8 Acm-2, while the corresponding Tafel slope is 0.115 V per decade. The possible reaction mechanism for electroreduction of oxygen on this oxide catalyst has been discussed.

Monoclinic La1‐xBaxMnO3 (x = 0.185) at 160 K.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Monoclinic La1−xBaxMnO3(x= 0.185) at 160 K

Single-crystal X-ray diffraction has shown that lanthanum barium manganese trioxide, La0.815Ba0.185MnO3, is monoclinic (I2/c) below a first-order phase transition at 187.1 (3) K. This result differs from the Pbnm symmetry usually assigned to colossal magnetoresistance oxides, A1-xA'xMnO3 with x approximately 0.2, which adopt a distorted perovskite-type crystal structure. The Mn atom lies on an inversion center, the disordered Li/Ba site is on a twofold axis and one of the two independent O atoms also lies on a twofold axis.

Carbon combustion synthesis of complex oxides: Process demonstration and features

AbstractCarbon combustion synthesis of oxides (CCSO) is a novel process to rapidly produce high‐purity, submicron, and porous powders of complex oxides. It is a modified form of self‐propagating high temperature synthesis (SHS) that uses carbon as the fuel instead of a pure metal. The CO2 release increases the porosity and friability of the products. Like SHS, it is much faster (order of minutes) than the calcination processes (order of hours). CCSO has several advantages over SHS (the initial components are less expensive, porosity of the products is up to 70%). CCSO can produce complex oxides, such as LaGaO3, which cannot be produced by SHS. The feasibility and features of CCSO are illustrated by its use in producing barium titanate, lithium manganese, and lanthanum gallium oxides. The carbon concentration enabled control of the moving front temperature and average velocity and the particle size and surface area. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Cooling to 208K by optical refrigeration

We report cooling to record low temperatures by optical refrigeration with ytterbium-doped zirconium–barium–lanthanum–aluminum–sodium-fluoride glass. The glass cooling element was mounted in vacuum in a low-thermal-emissivity chamber and pumped with the light from a diode-pumped solid state Yb:YAG (ytterbium-doped yttrium-aluminum-garnet) laser. Starting from room temperature, the glass cooling element reached a minimum temperature of ∼208K when pumped with ∼10W of 1026-nm light. The heat load at minimum temperature was ∼29mW.

Eu1.8La0.2BaZnO5: a Rietveld refinement using X-ray powder diffraction

The families of oxides with stoichiometry RE2BaMO5 (where RE is a trivalent rare earth, and M is Co2+, Ni2+, Cu2+, Zn2+, Pd2+ or Pt2+) are known as the green phases in studies of Y–Ba–Cu–O superconductor ceramics. These oxides are not superconductors but nevertheless present interesting structural types. In this work, the synthesis and structural characterization using the Rietveld method applied to X-ray powder diffraction data for Eu1.8La0.2BaZnO5 (europium lanthanum barium zinc oxide) are presented. The compound is isostructural with Y2BaZnO5. The two sites for Y3+ are occupied by Eu3+, while La3+ ions partially occupy one of these sites.

High-Resolution Transmission Electron Microscopy Observations on Antiphase Boundaries in Barium Lanthanum Magnesium Niobate

Atomic structural observations on the antiphase boundaries (APBs) in the complex barium lanthanum magnesium niobate perovskite compound Ba 0.7 La 0.3 (Mg 0.43 Nb 0.57 )O 3 (BLMN), which has a 1:1 chemical ordering of B-site cations, were conducted using high-resolution transmission electron microscopy. Using APB contrast, the curved APB was determined to have a ledged structure, with a terrace that was composed of the (111) plane at an atomic level. In APBs with finite widths, microfacets on the (111) planes also were observed.

Synthesis of Single-Crystalline La1-xBaxMnO3 Nanocubes with Adjustable Doping Levels

We report a hydrothermal synthesis of single-crystalline nanocubes composed of lanthanum barium manganite (La1-xBaxMnO3) with three different doping levels (x = 0.3, 0.5, and 0.6). The synthesis yields clearly faceted nanocubes with a pseudo-cubic perovskite structure. Typical nanocubes have sizes ranging between 50 and 100 nm irrespective of doping level. Magnetic measurements performed on nanocube ensembles show that the magnetic properties depend on the doping level. The ability to synthesize nanoscale manganites of a desired doping level should enable detailed investigations of the size-dependent evolution of magnetism, colossal magnetoresistance, and nanoscale phase separation.

High resolution depth profiling of thin STO in high- k oxide material

High k-dielectrics have become an important material in the development of ultra shallow junctions. In addition, strontium titanium oxide (STO) has been used as an interposer material to grow GaAs on Si for MESFETs [RF devices implemented on GaAs on Si substrates using a SrTiO 3 buffer layer, Motorola knowledge base, 14 September 2001]. Also, SrTiO 3 has a potential to be used as insulating material between ferromagnetic electrodes in magnetic tunnel junctions for magnetic random access memory devices (M-RAM). In this study we have investigated a multilayer system of STO with lanthanum barium manganese oxide (LBMO). The layer thickness was down to 0.8 nm, corresponding to two unit cells of SrTiO 3. With low energy Cs bombardment a depth resolution down to 2 nm per decade and a peak width of 2 nm FWHM was achieved. Since the erosion rates of STO and LBMO differ greatly, we will discuss a depth calibration procedure based on actual material composition.

CVD of oxide materials for thermal imaging ? the role of precursor chemistry

Thermal detectors exploiting ferroelectric lead zirconate titanate (PZT) or the metal insulator phase change material vanadium oxide are used widely to detect infra red radiation. Higher performance systems need to exploit improved materials as the detector element. Such materials are the ferroelectric perovskite, lead scandium tantalate (PST) and the metal insulator phase change material lanthanum barium manganite (LBMO). This paper presents work on the selection of precursors for liquid injection CVD of PZT and the high performance detector materials PST and LBMO. Control of the chemistry for the CVD process is an important step in the realisation of the large area, high quality deposition. In order to achieve this it is necessary to tailor the precursor properties so that vaporisation is efficient and decomposition leads to the desired material composition. It demonstrates how through careful precursor selection it is possible to match precursors in order to deposit high quality materials. It is shown that CVD offers a competitive route for the large area uncooled infrared devices.

Solution synthesis and spectroscopic characterization of high Er3+ content LaF3 for broadband 1.5 μm amplification

Erbium-doped LaF3 transparent gels have been synthesized by the solution synthesis of metal inorganic precursors. The solid solubility of Er3+ can reach 60 mol %, which is almost double the solubility limit of Er3+ in LaF3 synthesized by the Bridgman technique. A quantitative analysis of the absorption and emission spectral data shows that the quantum efficiency of the 1.55 μm emission band is comparable to that of melt grown single crystal. However, the emission spectral width of the 1.55 μm band is found to be 40% greater than that of the melt grown single crystal, which extends the spectral bandwidth to 11 THz. The high solid solubility of Er3+ supports 36 cm−1 single pass optical gain, which is three times higher than that in zirconium barium lanthanum aluminum sodium glass. The high Er3+ concentration and spectral bandwidth enable LaF3:Er amplifiers to be made by a low-temperature solution-based technique.

Synthesis of nanoparticles of barium lanthanum hafnium oxide by a modified combustion process.

Barium lanthanum hafnium oxide, a complex perovskite ceramic, has been synthesized as nanoparticles by a modified combustion process for the first time. The Ba, La, and Hf ions required for the formation of Ba2LaHfO5.5 were obtained in solution by dissolving in boiling nitric acid a stoichiometric mixture of BaCO3, La2O3, and HfO2 that had been heated at 1200 degrees C for 4 h. By complexing the ions with citric acid and using ammonia as fuel, it was possible to get Ba2LaHfO5.5 as nanoparticles in a single-step combustion process. The powder obtained by the present combustion process was characterized by X-ray diffraction, BET surface area analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and scanning and high-resolution transmission electron microscopy. According to the results of X-ray and electron diffraction, the powder synthesized through the combustion process showed single-phase barium lanthanum hafnium oxide. The transmission electron microscopic investigations showed a grain size of 42 nm, with a standard deviation of 8 nm. The nanoparticles of Ba2LaHfO5.5 synthesized by the present combustion technique could be sintered to > 97% of the theoretical density at a relatively low temperature of 1425 degrees C. Scanning electron microscopic studies on the sintered Ba2LaHfO5.5 samples showed that the final grain size of the sintered specimen was < 500 nm.

Enhanced Infrared Absorption by Ferroelectric-Conducting Oxide Thin-Film Structures

Infrared absorbing free-standing bridge structures are anticipated to be used in the next generation of ferroelectric uncooled infrared detectors. These structures will consist of resonant cavities with an absorbing bridge element, which contains the ferroelectric detector and the contact electrodes. An oxide electrode is preferable to a metallic electrode, because the metallic electrode reflects too much of the incoming radiation at reasonable thickness. For this paper, spectral transmission and reflection of lanthanum nickelate (LNO), barium ruthenate (BRO) and strontium ruthenate (SRO) films were measured, and it was found that the properties could be described as a simple two-dimensional conducting sheet. The optical absorption of several free-standing bridge structures was modeled, and optimized dimensions and electrode conductivity are presented which yield greater than 80% absorption over the full 8-14 w m band.

Thermal analysis of La–Ba oxalate and role of γ-irradiation there on

Lanthanum–barium oxalate was prepared and characterised by chemical and thermal analysis, X-ray diffraction and plasma emission spectroscopy. X-ray analysis showed the presence of a uniphase system. The kinetics of decomposition of oxalates of La and Ba as well as coprecipitated La–Ba oxalate have been investigated in air using dynamic thermogravimetry. The decomposition of mixed oxalate occurred with two over-lapping exotherms, corresponding to the decomposition of lanthanum oxalate followed by that of barium. The kinetics of decomposition of the irradiated salt was studied over the same temperature range as that of the unirradiated one in air and activation energies obtained from the slopes of Coat–Redfern’s plot. Kinetic analyses following various theoretical models of solid state reactions showed that the best fit was obtained for a third order reaction and geometrical models. It was evident that though there was increase in the activation energy as well as frequency factor with increasing radiation dose, reverse phenomenon takes place in the case of reaction rate. The effect of γ-irradiation on the process and the mechanism involved therein has been discussed.

Structural, thermal and dielectric properties of barium lanthanum niobate: A potential material for substrate application

Barium lanthanum niobate has been prepared as single phase compound by solid-state route. The structure of Ba2LaNbO6 has been studied by power X-ray diffraction method and was found to have a cubic perovskite (A2BB′O6) structure with a lattice constant a=8.60A. Ba2LaNbO6 did not show any phase transition in the temperature range 30-1300 °C as revealed by DTA studies. Thermal expansion coefficient of Ba2LaNbO6 measured by TMA studies was 8.1×10-6°C-1. The specific heat capacity of Ba2LaNbO6 obtained from DSC measurements was 383Jkg-1K-1 and the thermal diffusivity measured following the photoacoustic technique was found to be equal to 0.25cm2s-1. Ba2LaNbO6 has a moderately low dielectric constant and loss factor values making it suitable as substrate for microwave applications.

Colossal magnetoresistance in La0.7Ba0.3MnO3 thin films prepared by spray pyrolysis

Barium–lanthanum–manganite (La0.7Ba0.3MnO3) thin films that exhibit a colossal magnetoresistance (CMR) effect have been prepared by spray pyrolysis of solutions of aqueous nitrates. Structural, optical, and magnetotransport properties of the films were studied as a function of growth conditions and postgrowth treatments. In a magnetic field of 600 mT, the maximum CMR effect amounted to a 15% decrease in resistivity relative to zero field value. Instead of decreasing at lower temperature, the value of the CMR continued to increase as the temperature decreased to 100 K. This behavior is attractive for practical applications.

A new multi-function thin-film microsensor based onBa1-xLaxTiO3

A new multi-function microsensor with a barium lanthanum titanate(Ba1-xLaxTiO3) thinfilm is developed for the fabrication of a thin-film resistor and a metal-insulator-semiconductor(MIS) capacitor on a SiO2/Si substrate. The results reveal that thethin-film resistor has good sensitivity to visible light and good thermalsensitivity within the temperature range of 28-400 °C. The MIS capacitor issensitive to changes in the relative humidity (RH), with a130% change of the current for a humidity change from 12 to 92% RH at a test frequencyof 500 Hz, and with short response times of 5 and 4.5 s for the adsorption anddesorption of water vapor, respectively. The effects of the test frequency on the photo,thermal and humidity sensitivity performances are also investigated. Since thelifetime of charge carriers of Ba1-xLaxTiO3 thin films is only 16 ms,about half that of Sr1-xLaxTiO3 thin films, the device can detect lightmodulation at higher frequencies.