Amount Of La Doping Research Articles

Study on the physical mechanism of thermoelectric transport on the properties of ZnO ceramics

Herein, ZnO is used as the matrix while La as the doping element, and the band structure of the oxide system is calculated by first-principles. The La doped series oxides are synthesized by powder-metallurgy method. The first-principles calculation results show that La doping can converge the energy band and significantly increase the density of states near the Fermi level, enhanced by the hybridization between d-orbits of La atoms and d-orbits of Zn atoms and p-orbits of O atoms. With the increase of La element content, the electrical conductivity of the oxide gradually increases, and the Seebeck coefficient decreases to a certain extent, which is consistent with the first - principle calculation. As the doping of La element increases, the thermal conductivity of the oxide has been greatly reduced, resulting in a substantial improvement in the thermoelectric properties of the oxide. The best ZT value of ∼ 0.401 (873 K) can be obtained through proper amount of La doping (x = 0.04), which is ∼ 4.09 times as ∼ 0.098 of the pristine oxide ZnO at the same temperature.

La doping of manganese oxide leads to a dramatically promoted catalytic performance for UV–visible-infrared photothermocatalytic ethyl acetate abatement

La-doped manganese oxide catalysts with nanorod morphology, cryptomelane octahedral molecular sieve structure (OMS-2) and La/Mn atomic ratios of 0.0045, 0.0097, and 0.0459 (denoted as La-OMS-2-A, La-OMS-2-B, and La-OMS-2-C) were synthesized with the reaction among KMnO4, La(NO3)3, and Mn(NO3)2 at 90 °C. They were used for photothermocatalytic oxidation of ethyl acetate (typical organic pollutant) merely with UV–visible-infrared (UV–vis-IR) illumination. An appropriate amount of La doping was found to dramatically enhance photothermocatalytic activity and diminish the selectivity of more toxic by-product acetaldehyde. The optimal La-OMS-2-B demonstrated exceptionally large photothermocatalytic activity, low acetaldehyde selectivity, and good catalytic stability. Within initial five minutes, its CO2 formation rate (rCO2) was exceptionally high (1362.0 μmol g−1 min−1), a 67-fold increase as compared to pure OMS-2, while its acetaldehyde selectivity was very low (1.9%), a 37-fold decrease as compared to pure OMS-2. Even with λ > 830 nm IR illumination, it still possessed good photothermocatalytic performance. The photothermocatalytic oxidation abided by a light-driven thermocatalysis mechanism. The dramatic catalytic enhancement by the La-doping arose from a considerable promoted thermocatalytic activity due to the oxygen activity of OMS-2 being substantially improved with La-doping. A photoactivation on La-OMS-2-B, quite unlike photocatalysis on semiconductor photocatalysts, was discovered that further substantially improved catalytic activity and decreased acetaldehyde selectivity due to the oxygen activity of OMS-2 being considerably promoted with UV–vis-IR illumination.

Amorphous LaZnSnO thin films by a combustion solution process and application in thin film transistors

Amorphous LaZnSnO thin films with different La doping concentration are prepared by a combustion solution process and the electrical performances of thin film transistors (TFTs) are investigated. The influence of La content on the structure, oxygen vacancies, optical and electrical performance of LaZnSnO thin films are investigated. At an appropriate amount of La doping (15 mol.%), LaZnSnO-TFT shows a superior electrical performance including a mobility of 4.2 cm2/V s, a subthreshold swing of 0.50 V/decade and an on/off current ratio of 1.9 × 107. The high performance LaZnSnO-TFT is attributed to the better interface between SiO2 and LaZnSnO channel layer and the suppression of oxygen vacancies by optimizing La content. It suggests that La doping can be a useful technique for fabricating high performance solution-processed oxide TFTs.

Effect of La-doping on AgSbTe2 thermoelectric compounds

Ag(Sb1−xLax)Te2 compounds (x = 0, 0.01, 0.02, 0.03, and 0.05) were fabricated to study the effect of La-doping on the thermoelectric properties by using a spark-plasma-sintering process. All specimens were nearly single-phase AgSbTe2 with a small amount of Ag2Te. The La doping in AgSbTe2 resulted in a reduction in the electrical and the thermal conductivity but increased the Seebeck coefficient. A small amount of La doping increased the Seebeck coefficient because of the electron filtering effect. The maximum figure of merit was 1.50 due to the enhanced power factor and extremely low thermal conductivity.

Excellent acetone sensor of La-doped ZnO nanofibers with unique bead-like structures

In this work, Lanthanum (La) doped ZnO nanofibers with bead-like structures were facilely produced by electrospinning technique. The obtained La-doped ZnO products were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The results show that La doping changes the structures of ZnO nanofibers markedly. La-doped ZnO nanofibers have unique bead-like nanostructures, in which two phases of hexagonal La2O3 and wurtzite ZnO coexist along with partially incorporation of La into ZnO lattice. The gas sensing performances of the La-doped ZnO nanostructures to acetone were investigated via static gas sensor testing system. The sensing test results indicate that an appropriate amount of La doping greatly improves the gas sensing properties of ZnO nanofibers. The 1.0wt% La-doped ZnO sensor has the highest selectivity and response (64, to 200ppm acetone at 340°C), in addition to its short response time and recovery time. The unique bead-like structure and the gas sensing mechanism of La-doped ZnO nanofibers are discussed. The La-doped ZnO nanostructures we have produced can be used as a promising material for acetone sensors.

The influence of La doping on the catalytic behavior of Cu/ZrO 2 for methanol synthesis from CO 2 hydrogenation

A series of Cu/ZrO 2 catalysts with various La loadings for methanol synthesis from CO 2 hydrogenation were prepared by a urea–nitrate combustion method. The catalysts were characterized with N 2 adsorption, XRD, reactive N 2O adsorption, XPS, TPR, H 2-TPD and CO 2-TPD techniques, and tested for methanol synthesis from CO 2 hydrogenation. With increasing La loading, the Cu surface area increases first and then decreases, whereas the amount of basic site over catalysts increases continuously. The results of catalytic test reveal that a linear relationship exists between the conversion of CO 2 and the Cu surface area. Moreover, it is found for the first time that the selectivity to methanol is related to the distribution of basic site on the catalyst surface. The presence of La favors the production of methanol, and the optimum catalytic activity is obtained when the amount of La doping is 5% of the total amount of Cu 2+ and Zr 4+.

Hydrogen production by methane tri-reforming process over Ni–ceria catalysts: Effect of La-doping

The objective of the present work is the study of CH4 tri-reforming process (simultaneous carbon dioxide reforming, steam reforming and oxygen reforming) that can contribute to the CO2 abatement producing synthesis gas with the desiderate H2/CO ratio.A series of Ni–CeO2 catalysts with different La loadings is prepared by combustion synthesis and tested as catalysts in CH4 Tri-reforming reaction at 800°C under atmospheric pressure with a GHSV of 30,000h−1.It has been found that during tri-reforming reaction the activity of Ni–ceria catalysts can be enhanced by an appropriate amount of La doping (10at.%), the CH4 and CO2 conversion increases from 93% and 83% to 96% and 86.5%, respectively. The activity enhancement appears to be related to synergic effect of nickel–lanthana–surface oxygen vacancies of ceria via interfacial active sites that contribute to increase the nickel dispersion and create a basic site distribution on the surface able to interact with CO2.

The magnetic properties of La doped and codoped BiFeO 3

La doped BiFeO 3, Bi(Fe 0.95Co 0.05)O 3 and Bi(Fe 0.95Mn 0.05)O 3 ceramics have been prepared by sol–gel method with rapid sintering process. X-ray diffraction spectra show that the impurity phase has been effectively suppressed by La doping. The magnetic measurements show that 10% La doping on Bi sites has little influence on the magnetic properties of BiFeO 3 and Bi(Fe 0.95Co 0.05)O 3, while significantly enhances the magnetization of Bi(Fe 0.95Mn 0.05)O 3. Raman measurements show larger structure distortion by Co doping or La and Mn codoping on BiFeO 3, which explains the significant enhancement of magnetization. Our results suggest that small amount of La doping can be an effective way to prepare high quality BiFeO 3 and its derivatives.

Effects of La on Dielectric and Piezoelectric Properties of Pb1−xLa2x/3(Nb0.95Ti0.0625)2 O6 Ceramics

Ceramics with the chemical compositions of Pb1−xLa2x/3(Nb0.95Ti0.0625)2O6 (0≤x≤0.060) (PLTN) were prepared by the conventional solid‐state reaction method. X‐ray diffraction analysis indicated that Ti and La doping not only decreased the rhombohedral–tetragonal phase transformation temperature, but also stabilized the orthorhombic phase of PLTN ceramics. All ceramics sintered at 1190°–1250°C had shown the pure orthorhombic ferroelectric phase. La doping suppresses grain growth and inhibits the formation of pores and cracks, resulting in an increase in relative density up to 97%. The amount of La doping to PLTN ceramics obviously affect ceramics' piezoelectric constant (d33) and dielectric loss (tanδ). The sample with x=0.015 possesses high Curie temperature (Tc=560°C), low dielectric loss (tanδ=0.0054), and excellent piezoelectric constant (d33=92 pC/N), presenting a high potential to be used in high‐temperature applications as piezoelectric transducers.

Effects of Lanthanum Modification on the Structure and Electrical Properties of PZN-PZT Ceramics

La-modified PZN-PZT compositions with representative formula Pb1-0.7xLa0.7x(Zn1/3Nb2/3)0.3- (Zr0.55Ti0.45)0.7(1-x/4)O3 were prepared by the columbite precursor method. La content, x, was varied from 0 to 8mol%. Effects of La doping on microstructure, dielectric and piezoelectric properties were investigated. The results showed that in present system La doping promotes the formation of pyrochlore phase and the phase shifted from rhombohedral to tetragonal structure with increasing La content. It was also found that La doping makes dielectric permittivity maximum decrease and the degree of diffuse phase transition enhance. Appropriate amount of La doping could improve the piezoelectric properties.

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In order to improve the understanding of the role of rare-earth dopant in BaTiO3, the effect of microstructure and oxygen defect have been investigated on the electrical properties of polycrystalline La- and Ho-doped BaTiO3. The BaTiO3 doped with Ho 2at.% had the core-shell structure in each grain, while La-doped BaTiO3 did not have the core-shell. The core-shell structure in Ho-doped BaTiO3 consists of a ferroelectric core and a nonferroelectric shell. However, the dielectric properties of Ho-doped BaTiO3 with core-shell structure exhibited no temperature-stability as La-doped BaTiO3. Furthermore, the oxygen diffusion related to dielectric properties was also studied from the viewpoint of defect chemistry. The oxygen diffusion coefficients for BaTiO3 specimens were determined by secondary ion mass spectrometry. The oxygen diffusion coefficient for La-doped BaTiO3 was highly influenced by the amount of La-doping, while that for Ho-doped BaTiO3 was independent of the amounts of Ho-doping.

Disordered oxygen octahedral rotations and glasslike polarization characteristics in rhombohedral lead zirconate titanate

Disordered oxygen octahedral rotations have been observed in the low-temperature rhombohedral ferroelectric state in the Pb(Zr1−xTix)O3 crystalline solution. The development of disordered oxygen octahedral rotations within the ferroelectric state was found to result in the interruption of long-range polar order and the development of fluctuation effects. Dielectric relaxation was observed below ∼160 °C for Pb(Zr0.65Ti0.35)O3. In addition, double-looplike characteristics were observed in the polarization electric-field (P–E) response in the same temperature range. The results clearly reveal the nature of the coupling between the polarization and oxygen octahedral rotations in a perovskite ferroelectric structure. It was also shown that a small amount of La doping can enhance the degree of ordering of the octahedral tilted state. The enhancement of the ordering was verified by an intensity increase of the 1/2〈111〉 superlattice reflections in the selected area electron-diffraction pattern.

Improvement on the thermostability of electrostriction in Pb(Mg1/3Nb2/3)O3-PbTio3 relaxor system by La-doping

The thermostability of electrostriction in 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (0.9PMN-0.1PT) relaxor ferroelectric system was improved by enhancing the extent of the 1:1 short-range ordering in the B-site sublattice of perovskite structure. The enhanced short-range ordering was achieved by the partial substitution of La with Pb in the A-site. With increasing La content from 0 to 5 at.%, the diffuseness parameter (δ) increased from 43 K to 81 K, while TCE (temperature coefficient of electrostriction) decreased from 2.61% K-1 to 1.27% K-1. The product of TCE and δ exhibited a constant value regardless of the amount of La-doping, demonstrating that the enhanced 1:1 short-range ordering is directly related to the improvement on the thermostability of electrostriction. A semiempirical functional relationship between the electric field-related electrostrictive coefficient (M) and the polarization-related electrostrictive coefficient (Q) was derived. Based on this semiempirical relationship, practical guidelines on t...

Structure and properties of the La-doped Bi-2201 system

In this article, the influence of La substitution for Sr on structure and physical properties of the 2201 phase is studied. First, the crystal microstructure of the Bi2.1Sr1.9-xLaxCuOy (0 ≤ x ≤ 1.0) is characterized by means of x-ray diffraction and electron diffraction analyses, it is discovered that in the La-doped 2201 system with increasing La content the 2201 phase undergoes tetragnoal-orthorhombic-monoclinic structural transition. With this phase transition, the modulation vector of the 2201 phase transforms from incommensurate to commensurate, and the period of the modulation wave decreases. Secondly, the superconductivity of this system is analyzed systematically. The results of the resistivity measurement show that the appropriate amount of La doping can raise the superconducting transition temperature (Tc) of the 2201 phase, with x=0.2, Tc reaches as high as 25 K. However the excessive doping of La (x ≥ 0.3) leads the 2201 phase to transit from metal to insulator and the superconductivity disappears. The measurement of thermoelectric power (TEP) of this system shows that with increasing La content the TEP value also increases gradually. But the interesting point is that the transition from positive to negative in TEP occurs for x=0.2 sample. In addition, the electronic structure and oxygen content of this system are also studied. Based on these, we analyze the relation between the microstructure, electronic structure of the La-doped 2201 phase and its superconductivity, indicating that the type of element substitution with higher valence, together with the microstructural distortion induced by the substitution affects the electronic states of Cu 3d seriously, that is, changes the degree of coulomb correlation of Cu 3d electrons, thus resulting in the transition of the type of carrier of this system and the decrease of hole carrier concentration, as well as the corresponding variation of the superconductivity of La-doped 2201 phase.