Effects Of La Content Research Articles

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.

Effect of La Content on the Infrared Stealth Property of ZnO: (La, Al) Coated on Cotton Fabrics

Effects of La content on the infrared stealth of ZnO: (La, Al) coated cotton fabrics were studied through XRD, SEM, ICP, IR_2 dual-band emissivity measuring instrument and the infrared camera instrument, where the content of Al remained unchanged. It was suggested the doping of Al and La was favorable for providing more free electrons, improving scattering of infrared photon, and decreasing the infrared emissivity of ZnO: (La, Al) coated fabric in the range of 8-14μm wavelengths. Thermography indicated that ZnO: (La, Al) coated fabric gave as low thermal radiation as the environment.

Effects of La content on the magnetic, electric and structural properties of BiFeO3

Nano-powders of Bi1−xLaxFeO3 (BLFO) with x=0, 0.1, 0.15 and 0.2 were synthesized by co-precipitation. The as-synthesized powders were characterized by the X-ray diffraction analysis, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer. The dielectric constant and loss factor of the bulk samples were tested between 12Hz and 1MHz by an inductance–capacitance–resistance (LCR) meter. The structural studies showed that the La-doping increases the asymmetry and decreases the second phases noticeably. The magnetic measurements revealed that the La improves the magnetic properties mainly due to the spin cycloid distortion. Furthermore, the La-doping enhances the dielectric properties as a result of the reduction in the Fe2+ ions and oxygen vacancies. The microwave sintering method led to the enhancement of ferroelectric properties due to the higher densities of the sintered samples.

Synthesis and Properties Investigation of Non-equivalent Substituted W-Type Hexaferrite

A novel composed W-type hexaferrite Ba1−x La x Co2Fe16O27 was rapidly synthesized via a sol–gel self-combustion reaction. The effects of lanthanum ions on the oxidation state of iron ions and cobalt ions in hexaferrite were explored by X-ray photoelectron spectroscopy. The changes of the Fe 2p X-ray absorption spectra indicated that the nonequivalent substitution can lead to the transition Fe3+→ Fe2+ in Ba1−x La x Co2Fe16O27. However, the oxidation state of cobalt ions was maintained as Co2+. Moreover, the effects of La content on the phase composition, structural parameters, morphology, and static magnetic properties were also investigated in detail by using the X-ray diffractometer, scanning electron microscope, and vibrating sample magnetometer. The results indicated that the structural parameters decreased regularly with increasing the La content, and the magnetic properties were enhanced after substitution, which is beneficial for their application in various electrical devices employed for industrial and military applications.

Synthesis of dipropyl carbonate over calcined hydrotalcite-like compounds containing La

Dipropyl carbonate (DPC) was selectively synthesized via transesterification of dimethyl carbonate (DMC) and n-propanol over Mg–Al composite oxide containing La catalysts. The catalysts were prepared by calcining the precursors of hydrotalcite-like compounds (HTLcs) from co-precipitation method. The effect of La content (nMg:nAl:nLa=3:1:x) in the catalyst on the synthesis of DPC was investigated. And the catalyst exhibited the highest catalytic activity when x was tuned to 0.7. Under the optimized reaction conditions, the DMC conversion and DPC selectivity were 98.4% and 95.4%, respectively. These catalysts were characterized by thermogravimetry differential thermal analysis (TG-DTA), X-ray diffraction (XRD), nitrogen adsorption–desorption, Fourier transform infrared (FT-IR), temperature programmed desorption with CO2 (CO2-TPD) and scanning electron micrograph (SEM). It was clarified that the amount of basic sites of moderate strength, formed by chelating bidentate carbonate, was enhanced with the La content increasing until x=0.7, which were the catalytically-active sites for this reaction. But when La content x reached 1.0, these sites were transformed to bridging bidentate carbonate, leading to a loss of the catalytic activity to some extent. These findings indicated that La content controlled the catalytic performance of the composite oxides catalysts via structure change of the basic sites. The catalyst was easily prepared and handled, easily separated from the reaction medium and could be reused many cycles.

Piezoelectric properties of La and Nb co-modified Bi4Ti3O12 high-temperature ceramics

Bi4-x La x Ti3O12 + mol4 % Nb2O5 ceramics were prepared by the conventional ceramic method and the effect of La content on their electrical properties was investigated. Density and resistivity of Bi4Ti3O12 ceramics were improved by doping La and Nb. The dielectric constant and the dielectric loss decreased simultaneously with increasing La content. An enhanced piezoelectric behavior of d 33 ~ 16.0 pC/N was obtained in the ceramic with x = 0.50, together with a good temperature stability. As a result, the introduction of La and Nb was considered an effective way to improve the piezoelectric properties of Bi4Ti3O12 ceramics.

Propane dehydrogenation over PtSnNa/La-doped Al2O3 catalyst: Effect of La content

La-doped mesoporous alumina (La-Al) with different content of La was synthesized and then this kind of material was used as the support for platinum–tin catalyst in propane dehydrogenation. It was found that a portion of La had been incorporated into the alumina framework with La-doping. When the content of La in the support was suitable, both the catalyst acidity and the coke amount were decreased. Moreover, in these cases, the presence of La could not only promote the distribution of metallic particles, but also strengthen the interaction between tin species and support. As a result, more amounts of tin could exist in oxidized states, which was beneficial to enhance the interaction of Pt with SnOx species and the reaction activity. In the current study, the PtSnNa/La-Al catalyst with 1.0wt.% La exhibited the best catalytic activity and stability. Compared with pure Al2O3 support, this La-doped Al2O3 support was also favorable for the improvement of the catalytic performance even at higher reaction temperature (605°C). However, with the excessive addition of La, the agglomerations of metallic particles and the increase in percentage of metallic tin (Sn0) on the catalyst were found, which seriously resulted in the deactivation of catalyst.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous Ni–La–Al 2O 3 aerogel catalysts: Effect of La content

Mesoporous Ni–La–Al 2O 3 aerogel catalysts (denoted as (40- x)Ni xLa) with different lanthanum content ( x) were prepared by a single-step sol-gel method and a subsequent CO 2 supercritical drying method. The effect of lanthanum content on the physicochemical properties and catalytic performance of mesoporous (40- x)Ni xLa catalysts in the steam reforming of liquefied natural gas (LNG) was investigated. Physicochemical properties of (40- x)Ni xLa catalysts were strongly influenced by lanthanum content. Dispersion and reducibility of nickel aluminate phase in the (40- x)Ni xLa catalysts increased with increasing lanthanum content. Small amount of lanthanum addition was effective for dispersion of metallic nickel in the (40- x)Ni xLa catalysts, but large amount of lanthanum addition was not favorable for nickel dispersion due to the blocking of active sites. In the steam reforming of LNG, both LNG conversion and hydrogen yield showed volcano-shaped curves with respect to lanthanum content. Average nickel diameter of (40- x)Ni xLa catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, 36Ni4La (36 wt% Ni and 4 wt% La) catalyst with the smallest average nickel diameter exhibited the best catalytic performance and the strongest resistance toward carbon deposition in the steam reforming of LNG.

Effect of La content on microstructure evolution of 20Ag–Cu–Zn–Sn–P–La filler metals and properties of joints

The influence of La content on the microstructure evolution of 20Ag–Cu–Zn–Sn–P (wt-%) filler metals and the mechanical properties of joint was investigated in this study. The typical microstructure of filler metal was analysed by means of scanning electron microscopy, optical microscopy and X-ray diffraction. Microstructural observation indicated that the growth of crystal grains in filler metals was prohibited with increasing the La content. It was found that 0·1–0·3 wt-%La improved the wettability of filler metals on 321 stainless steel and Cu substrates. From mechanical properties tests, the shear strength increased with increasing the La content in the range of 0·1 to 0·5 wt-%. When the La content reached 0·5 wt-%, the maximum of the joint shear strength was achieved. When the content is proper, the La addition had a positive effect on wettability by reducing surface tension of liquid alloys.

Effect of La content on the room temperature ageing behavior of Al 90− xNi 6La 4+ x ( x = 0–3) metallic glasses

The ageing behavior of Al 90− x Ni 6La 4+ x ( x = 0–3) amorphous alloys under ambient temperature (20–50 °C) has been studied. Partial crystallization has been observed in all alloys after several years of ageing under ambient conditions especially in Al 90Ni 6La 4 and Al 89Ni 6La 5 alloys, where the onset of crystallization temperatures are comparatively lower. The transformations have been studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. These alloys showed two stages of crystallization upon heating. A significant decrease of first stage of crystallization enthalpy was observed after 5.5 years of room temperature ageing and showed a mixed structure containing fcc-Al nanocrystals (20–40 nm) in an amorphous matrix. The results are explained in terms of transformation kinetics at the ageing temperatures.

Effects of La content on the properties of Ba1−xLaxTiO3 powders prepared by spray pyrolysis

Nano-sized Ba1−xLaxTiO3 (0 ≤ x ≤ 0.03) powders were prepared by ultrasonic spray pyrolysis from the spray solution with citric acid. The mean sizes of the primary particles decreased from 110 nm to 59 nm when the x of the Ba1−xLaxTiO3 powders was changed from 0 to 0.03. The BET surface areas of the powders changed from 9.1 m2/g to 16.9 m2/g. The pure BaTiO3 and La-doped BaTiO3 powders had both tetragonal and cubic crystal structures. The average grain size of the sintered BaTiO3 specimen was 2.8 µm, while those of the La-doped BaTiO3 pellets ranged from 1.04 µm to 0.68 µm according to the doping concentrations of La. The dielectric constant of Ba1−xLaxTiO3 (0.01 ≤ x ≤ 0.03) pellets ranged from 2500 to 3855 when sintered at 1280 °C.

Effects of La content on the glass transition and crystallization process of Al–Ni–La amorphous alloys

Effects of La content on the glass transition and crystallization process of Al 94− x Ni 6La x ( x = 3–9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. The results show that the thermal stability increases with increasing the La content. The crystallization changes from a two-stage process without glass transition at x = 3–6 to a three-stage one with obvious glass transition at x = 7–9. The first crystallization process results in precipitation of single fcc-Al at x = 3–5, fcc-Al plus metastable phase(s) at x = 6 and 7, and single metastable phase at x = 8 and 9. The first crystallization process at x = 4 and 5 is the growth of quenched-in nuclei, whereas that at x = 6, 7 and 9 is the diffusion-controlled growth with a decreasing, constant and increasing nucleation rate, respectively. The activation energy for the first crystallization process is larger in the eutectic reaction than that in the primary reaction, and is the highest when the number of the products is the most.

Low temperature synthesis and ferroelectric properties of La substituted Bi 4Ti 3O 12 thin films by sol–gel

Bi 4− x La x Ti 3O 12 (BLT) thin films were prepared on p-Si substrates by using sol–gel method. The effect of La content and annealing temperature on structure, morphology, dielectric and ferroelectric properties of BLT films were investigated. Even at low temperatures ranging from 500 to 650 °C, the BLT thin films were uniform and crack free as well as exhibited no preferred orientation analyzed by X-ray diffraction and atomic force microscope. La content and annealing temperature affect greatly on the preferred orientation and ferroelectric properties of BLT thin films. The Bi 3.25La 0.75Ti 3O 12 thin films annealed at as low as 600 °C showed excellent dielectric and ferroelectric properties with a dielectric constant of 288, a dielectric loss of 1.57%, a remanent polarization of 17.5 μC/cm 2 and a coercive field of 102 kV/cm, which are better than those of Bi 4Ti 3O 12 thin films prepared using the same processing. The low processing temperature and the large remanent polarization of BLT are favorable for device application.

Investigation of Cobalt-Free AB<sub>5</sub>-Type Hydrogen Storage Alloy

Co-free AB5-type LaxMm1-x(NiMnSiAlFe)4.9 (x = 0, 0.45, 0.75, 1) hydrogen storage alloys were prepared by casting and rapid quenching. The phase structures and microstructures of the as-cast and quenched alloys were analyzed and observed by XRD and SEM. The electrochemical performances of the as-cast and quenched alloys were measured. The effects of La content and quenching rate on the microstructures and electrochemical properties of the alloys were investigated comprehensivel y. The obtained results indicate that the Co-free AB5-type hydrogen storage alloy with excellent synthetical electrochemical performances can be prepared by adjusting La content and employing appropriate rapid quenching technique.

Effect of La content on characterization of PLZT ceramics

This work has been undertaken with a view to study the effect of lanthanum content on properties of PLZT ceramics. The polycrystalline complex compounds of PLZT with Pb 1− x La x (Zr 0.40Ti 0.60) 1− x/4 O 3, +10% PbO formula were prepared from the nano-size individual oxides powders by hot-pressed process. Transparent PLZT ( x/40/60) bulk ceramics with pure tetragonal phase was obtained. The studies of the microstructures, dielectric and ferroelectric properties of the ceramics were carried out. The experiment results showed that when La content increased from 7 to 13 mol.%, the grain size increased from 2 to 7 μm. La content also effects the dielectric property obviously, the dielectric constant increased with La content increasing. Moreover, the ferroelectric properties are sensitive to the variation of La content.

Site definition and characterization of La-substituted Bi4Ti3O12 thin films prepared by metalorganic chemical vapor deposition

The effects of La content on crystal structure and ferroelectric property of La-substituted Bi4−xLaxTi3O12 were investigated. We utilized as-deposited thin films prepared on (111)Pt/SiO2/Si substrates at 680 °C by metalorganic chemical vapor deposition. The films showed (117) preferred orientation, and the lattice spacing of the (117) plane increased with increasing La content. With the aid of Raman spectroscopy, we found a pronounced site selectivity of La ions for the Bi site (A site) in the pseudoperovskite layer. Even for a small content (x=0.2), an incorporation of La ion into the pseudoperovskite layer greatly enhanced both remanent polarization and coercive field, but improved properties were almost irrespective of La content for x>0.2. For (Bi3.27La0.73)Ti3O12 thin film, we confirmed a good fatigue endurance up to 2×1010 switching cycles.

ELECTRICAL PROPERTIES OF THE PEROVSKITE (PB, LA)TIO3 FILMS DEPOSITED BY ELECTRON CYCLOTRON RESONANCE PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION

The effects of La content and rapid thermal annealing (RTA) on the capacitance (C–V) and leakage current (J–E) properties of the PLT films were investigated. The films were deposited on Pt/Ti/SiO2/Si substrates at 480 °C by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD). The La doped films showed slim P–E hysteresis curves and almost no frequency dependency of permittivity. As the La content increased beyond 11%, Pb was excessively incorporated into the PLT film, resulting in non-stoichiometric compositions with (Pb+La)/Ti>1, degraded crystallinity and decreased capacitance. After RTA at 700 °C, C–V curves became symmetric and leakage current characteristics were improved, but the crystallinity and the ferroelectricity of the films were not so much improved although the film became stoichiometric. The leakage current of the films was controlled by Schottky conduction except for the low electric field region where the trap current of mobile charges or hopping conduction appeared to be dominant. In order to explain the RTA dependence of the C–V shift and the polarity dependence of the J–E characteristics of the PLT films, a physical model was suggested, based on the surface states and Pb vacancies, which affects the width of the space charge region and the height of the Schottky barrier. © 1998 Kluwer Academic Publishers

Preparation and characterization of chemically derived (Pb,La)TiO/sub 3/ thin films

Ferroelectric lead lanthanum titanate (PLT) thin films with composition varying from pure PbTiO(3) to PLT 25/100 (0 to 25 mol.% La) were prepared by spin-casting 0.25M solutions containing metallo-organic precursors of Pb, La, and Ti. The dielectric and ferroelectric properties of the thin (410-nm) films were characterized. The dielectric constants of the films varied from ~80 to ~690 for La contents varying from 0 to 25 mol%, respectively. Dissipation factors varied from ~0.03 to ~0.09 over the same compositional range. The temperature dependence of the dielectric properties was also studied to determine the effects of La content on the Curie point (T(c)). As expected, T(c ) was found to decrease with increasing La concentration. Coercive field and remanent polarization also decreased with increased La concentration.