Spectral properties of Ce3+ doped yttrium lanthanum oxide transparent ceramics

Ce3+-doped yttrium lanthanum oxide (Y0.9La0.1)2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce:(Y0.9La0.1)2O3 transparent ceramics are investigated. There appear two characteristic absorption peaks of Ce3+ ions at 230 nm and 400 nm, separately. It is found that Ce3+ ions can efficiently produce emission at 384 nm from (Y0.9La0.1)2O3 transparent ceramic host, while the emission is completely quenched in Re2O3 (Re=Y, Lu, La) host materials.     

Synthesis and characterization of doped apatite-type lanthanum silicates for SOFC applications

A series of iron- and/or aluminium-doped apatite-type lanthanum silicates (ATLS) La_9.83Si_{6 ‐ x ‐ y}Al_xFe_yO_26 ± δ (x = 0, 0.25, 0.75, and 1.5, y = 0, 0.25, 0.75, and 1.5) were synthesized using the mechanochemical activation (MA), solid state reaction (SSR), Pechini (Pe) and sol-gel (SG) methods. The total conductivity of the prepared materials was measured under air in the temperature range 600-850 °C using 4-probe AC impedance spectroscopy. Its dependence on composition, synthesis method, sintering conditions and powder particle size was investigated. It was found that for electrolytes of the same composition, those prepared via mechanochemical activation exhibited the highest total specific conductivity, which was improved with increasing Al- and decreasing Fe-content. The highest conductivity value at 700 °C, equal to 2.04 × 10^− 2 S cm^− 1, was observed for the La_9.83Si₅Al_0.75Fe_0.25O_26 ± δ electrolyte. La_9.83Si_4.5Fe_1.5O_26 ± δ electrolyte samples synthesized using the Pechini method exhibited higher conductivity when sintered conventionally than when spark-plasma sintering (SPS) was used.     

La掺杂诱发层状钙钛矿型铁电体弛豫性相变的介电研究

制备了La掺杂层状钙钛矿铁电体材料SrBi₄Ti₄O₁₅, Sr₂Bi₄Ti₅O₁₈以及共生结构Bi₄Ti₃O₁₂-SrBi₄Ti₄O₁₅，通过研究样品的变温介电特性发现，SrBi_4-xLa_{x 关键词： 弛豫性相变 微畴-宏畴 层状钙钛矿 介电性能}     

First‐principles study on the concentrations of native point defects in high‐dielectric‐constant binary oxide materials

The intrinsic concentrations of point defects in high‐k binary oxide materials of HfO₂, ZrO₂, Y₂O₃ and La₂O₃ are evaluated on the basis of first‐principles calculations. Oxygen defects are found to dominate over a wide range of the oxygen chemical potential. Neutral oxygen vacancies are likely to be responsible for electron trapping in the investigated materials. In HfO₂ and ZrO₂, oxygen Frenkel pairs are likely to form. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamical properties and electronic structure of (LaLi)TiO3 conductors

A computer simulation by a molecular dynamics method is performed to study the properties of structure and Li ion diffusion in La_4/3???x Li (LaLi)TiO₃ ;LLTO;Li ion conductors;Superionic conductors;Perovskite;Off-site;Electronic structureA computer simulation by a molecular dynamics method is performed to study the properties of structure and Li ion diffusion in La_{4/3 − x} Li Ti₂O₆ =(LaLi)TiO₃ =LLTO, which is the perovskite-type Li ion conductor. In the low Li concentration, Li ions conduct a two-dimensional motion, while Li ions diffuse a three-dimensional motion in the high Li ion concentration. The partial distribution function for Li–Ti and the diffusion paths of Li ions suggest that Li ions stay for a long time at off-site positions, which are 2.7? away from a body-centered Ti ion. The Li ion concentration dependence to the conductivity σ is in approximate agreement with experiments. The energy band dispersion and the density of states are calculated using the linear-muffin-tin-orbital method. The energy contour map shows the stable position of Li ions is off center of the vacant La sites. Both calculations suggest that the stable position of Li ions is off center of the vacant La sites. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Electrochemical reduction of NO and O2 on oxide based electrodes

Cyclic voltammetry has been used to investigate the electrocatalytic properties of oxide based electrodes for the reduction of NO and oxygen. Perovskites of compositions La_xSr_1-xMnO_3+δ, (LSMx), with 0.05 ≤ x ≤ 0.5 and La_0.6Sr_0.4Fe_0.8Mn_0.2O_3-δ, (LSFM), the spinels Co₃O₄ and CuCr₂O₄ and the mixed oxide V₂O₅ have been selected and investigated in the temperature range 300 – 500 °C. The materials show good catalytic properties against both NO oxidation and NO reduction. The catalytic activity as well as the selectivity is dependent both on the redox behavior of the compound and on the oxygen defect concentration. Paper presented at 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Inelastic magnetic X-ray scattering from highly correlated electron systems: La1.2Sr1.8Mn2O7, La0.7Sr0.3MnO3 and Fe3O4

Magnetic Compton profiles have been measured for the colossal magnetoresistance manganites La_1.2Sr_1.8Mn₂O₇ and La_0.7Sr_0.3MnO₃, and for magnetite Fe₃O₄, along various crystallographic directions, over a wide range of temperatures and magnetic fields. The experimental results are interpreted via first-principles computations for the double layer manganite, La_1.2Sr_1.8Mn₂O₇, and by using a simple model involving atomic d-orbitals and free electrons for the other two compounds. For all three materials a preference for the occupation of e_g orbitals is found, particularly, for orbitals of dx²−y² symmetry. An itinerant electron contribution is adduced at all temperatures in magnetite; such a contribution also appears in La_1.2Sr_1.8Mn₂O₇, but it is present only at low temperatures in La_0.7Sr_0.3MnO₃.     

La掺杂对Bi4Ti3O12薄膜铁电性能的影响

利用Sol-Gel法在Pt/Ti/SiO₂/Si衬底上制备出Bi₄Ti₃O₁₂和Bi_3.25La_0.75Ti₃O₁₂薄膜，研究了La掺杂对Bi₄Ti₃O₁₂薄膜的晶体结构、铁电性能和疲劳特性的影响，发现La掺杂没有改变Bi₄Ti₃O₁₂薄膜的基本晶体结构，并且提高了Bi₄Ti₃O₁₂铁电薄膜的剩余极化值和抗疲劳性能，对La掺杂改善Bi₄Ti₃O₁₂铁电薄膜性能的机理进行了讨论. 关键词： 铁电性能 4Ti₃O₁₂薄膜')" href="#">Bi₄Ti₃O₁₂薄膜 3.25La_0.75Ti₃O₁₂薄膜')" href="#">Bi_3.25La_0.75Ti₃O₁₂薄膜 sol-gel法 La掺杂     

Interstitial oxide positions in oxygen-excess oxy-apatites

Several oxy-apatites materials, La_8.65Sr_1.35(Si₆O₂₄)O_2.32, La_8.65Sr_1.35(Ge₆O₂₄)O_2.32, La₉Sr₁(Si_5.5Al_0.5O₂₄)O_2.25, La_9.67□_0.33(Si_5.5Al_0.5O₂₄)O_2.25, La_8.5Sr_1.5(Si_5.5Al_0.5O₂₄)O₂ and La_9.5□_0.5(Si_5.5Al_0.5O₂₄)O₂ have been prepared as crystalline phases. The impedance study showed that all samples are oxide ion conductors and their conductivities are similar to those previously reported for related oxy-apatites. A thorough study on the oxygen sublattices for oxygen excess samples has been carried out using neutron powder diffraction data by the Rietveld method. The structural study shows the presence of interstitial oxide anions close to the periphery apatite channels. However, the interstitial oxide position in cation stoichiometric silicates, f. i. La_8.65Sr_1.35(Si₆O₂₄)O_2.32, is different from that in germanates, f. i. La_8.65Sr_1.35(Ge₆O₂₄)O_2.32. This is likely due to the different structural flexibility of the two tetrahedral groups and it explains the previously reported evidence of higher oxygen contents for germanates oxy-apatites. The structural characteristics of these oxide anion conductors are discussed.     

Copper and oxygen vibrations in La2CuO4 and YBa2Cu3O7

We perform eV neutron scattering experiments (neutron energy > 1 eV) on copper metal, CuO, La₂CuO₄ and YBa₂Cu₃O₇, and neutron absorption experiments of HoBa₂Cu₃O₇, and determined the mean kinetic energy of O, Cu and other atoms in these materials. The Debye temperatures of Cu atoms in La₂CuO₄ and YBa₂Cu₃O₇ were estimated to be extremely large, about 1500 and 2000 K, respectively.     

Oxygen ion diffusion measurements in Bi0.775La0.225O1.5

The oxygen transport properties of the Bi_0.775La_0.225O_1.5 electrolyte material have been investigated. Isotopic exchange depth profiling (IEDP) technique with secondary ion mass spectrometry (SIMS) was used in order to measure the oxygen tracer diffusion coefficient D. The activation energy for oxygen tracer diffusion was found to be 115 ± 2 kJ/mol (1.19 ± 0.02 eV). The measured D values were converted using the Nernst-Einstein relationship to conductivity and compared with data from AC Impedance. The agreement of the two sets of data implies that the material is an oxygen ion conductor.     

Effect of different dielectrics on performance of sub-5.1 nm blue phosphorus Schottky barrier field-effect transistor from quantum transport simulation

Two-dimensional materials have attracted great attention because of their ultra-thin atomic layer thickness and high carrier mobility. In this work, we investigated the electronic transport of in-plane (IP) heterojunction based on Cu/Blue Phosphorus (BlueP), and the results suggest the metallization at the IP Cu/BlueP contact interface and a small Schottky barrier. Then, we investigated the performance of 5.1 nm IP BlueP Schottky barrier field-effect transistors (SBFET) with different dielectrics (SiO₂, Al₂O₃, Y₂O₃, and La₂O₃) using quantum transport simulations. The results show that IP BlueP SBFETs with four dielectrics satisfy the off-state requirement of the International Technology Roadmap for Semiconductors (ITRS) for the high-performance (HP) device. However, the on-state current of only IP BlueP SBFET with La₂O₃ satisfies the requirements of ITRS. This will provide a reference for designing BlueP SBFETs.     

Influence of ceramic oxide materials on lithium based potentiometric CO2 sensors

In these potentiometric sensors, a mixed binary carbonate sensing material consisting of 90 mol% Li₂CO₃ and 10 mol% BaCO₃ was modified by adding ceramic oxide materials such as SiO₂, B₂O₃, La₂O₃, Bi₂O₃, CeO₂ and In₂O₃ in different mol% concentrations. Various sensors mixed with these external oxides have shown good performance at operating temperatures below 300 °C. Scanning electron microscopy reveals that a glassy sensing phase is formed in the sensing bi-carbonate by the addition of ceramic oxides and sintered at 600 °C for 1 h. The sensor mixed with SiO₂:B₂O₃:Bi₂O₃ in 1:2:1 mol% showed an excellent response and recovery characteristics and followed a fair Nernstian behavior with a ΔEMF/dec value of −48.18 at as low as 150 °C. The decrease in operating temperature is attributed to the enhanced lithium ion migration through the glassy sensing phase of the sensing electrode.     

La2O3对Yb:Y2O3透明陶瓷光谱性能的影响

研究了La₂O₃对Yb：Y₂O₃透明陶瓷光谱性能的影响，添加适量La₂O₃以后，Yb：Y₂O₃透明陶瓷的吸收峰和发射峰的位置不变，但由于La³⁺的离子半径大于Y³⁺的离子半径，在Y₂O₃中引入La³⁺离子后，导致Y₂O₃晶格常数变大，晶场强度变弱，同时降低了Y₂O₃晶体的有序度，致使发射峰强度有所下降，发射截面变小.过量的La₂O₃（x=0.16）造成Yb³⁺激活离子发射强度明显下降；其荧光寿命在添加La₂O₃后总体增大45%—60%. 关键词： 氧化镧 氧化钇 透明陶瓷 光谱性能     

Luminescence of Ce3+ in lanthanum silicon oxynitride

The luminescence properties of lanthanum silicon oxynitride(La-Si-O-N) series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications.Four compound hosts of LaSiO2N,La4Si2O7N2,La5Si3O12 N,and La2Si6O3N8 were synthesized and examined in this work.Crystallographic examination for the equal amount of Ce 3+ substitution indicated that the covalency degree decreased in a sequence LaSiO2 N > La2Si6O3N8 > La4Si2O7N2 > La5Si3O12 N,not simply in correlation to the ratio of N3/O2.Excitation and emission spectrum measurements showed the main features of Ce3+ luminescence in the series:the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce-N bonding;nephelauxetic effect could not be observed clearly for the investigated series;to some extent Stokes shift was dominated by crystal-field splitting rather than Ce-N covalency degree.     

Nd3+掺杂的氧化镧钇透明激光陶瓷的光谱性能研究

采用传统无压烧结工艺制备了Nd³⁺掺杂的Y_2-2xLa_2xO₃(x=0.08)透明陶瓷并对其光谱性能进行了研究. 结果表明：Nd³⁺:Y_1.84La_0.16O₃透明陶瓷在780—850 nm的波长范围内有较宽的吸收带. 当Nd³⁺掺杂量为1.5at%时，在820 nm和激光二极管抽运的808 nm处的吸收截面分别为σ_abs(820 nm)=1.81×10^-20 cm²，σ_abs(808 nm)=1.54×10^-20 cm². 最强的发射峰位于1078 nm处，并具有荧光寿命长、发射带宽宽、量子效率高等特点. 加入La₂O₃后，基质的光谱品质参数X_Nd由1.6减小到0.46，因此和⁴F_3/2—⁴I_11/2跃迁相对应的荧光分支比β_J,11/2增大为56.82%. Nd³⁺:Y_1.84La_0.16O₃透明陶瓷的这些性质有利于高效率的激光输出和超短锁模激光脉冲的实现. 关键词： 氧化镧钇透明陶瓷 光谱性能 3+')" href="#">Nd³⁺     

Influences of La3+ substitution on the structure and magnetic properties of M-type strontium ferrites

M-type strontium ferrites with substitution of Sr²⁺ by rare-earth La³⁺, according to the formula Sr_1−xLa_xFe₁₂O₁₉, are prepared by the ceramic process. Influences of the substituted amount of La³⁺ on structure and magnetic properties of Sr_1−xLa_xFe₁₂O₁₉ compounds have systematically been investigated by XRD, VSM and Mössbauer spectrum. When the substituted amount x is below 0.30, X-ray diffraction shows that the samples are single M-type hexagonal ferrites. It is found that the suitable amount of La³⁺ substitution may remarkably increase saturation magnetization σ_s and intrinsic coercivity H_cJ. With the La³⁺ addition for the same sintering temperature, σ_s and H_cJ increase at first, then decrease gradually. However, the substituted amount x at the maximum value of H_cJ is bigger than that of σ_s. Mössbauer spectroscopy of ⁵⁷Fe in Sr_1−xLa_xFe₁₂O₁₉ has shown that the substitution of Sr²⁺ by La³⁺ is associated with a valence change of Fe³⁺ to Fe²⁺ at 2a or 4f₂ site. The magnetic properties are reflected in the Mössbauer spectra which indicate that the magnetic hyperfine field (H_hf) is detected with the highest value at x=0.20. The different exchange paths between the iron sublattices are discussed according to the increased hyperfine fields of the 12k- and 2b-site. The Curie temperature of Sr_1−xLa_xFe₁₂O₁₉ decreases linearly with increasing La³⁺ substitution.     

Sintering and electrical properties of Na0.5K0.5NbO3 ceramics modified with lanthanum and iron oxides

Effects of La³⁺, Fe³⁺ doping and their co-doping on the sintering, structures and electrical properties of Na_0.5K_0.5NbO₃ (NKN) ceramics were investigated. A significant modification of sintering behavior can be obtained by the addition of Fe₂O₃. On the contrary, the addition of La₂O₃ and La–FeO₃ tends to degrade the densification. Moreover, Fe³⁺ doping does not change the crystal structure, thus leading to an unchanged Curie temperature. Owing to a transition from orthorhombic to pseudo-cubic structures, the Curie temperatures of NKN ceramics were significantly lowered by doping La₂O₃ and La–FeO₃. NKN ceramics modified with a small amount of Fe₂O₃ and La–FeO₃ (less than 0.5 mol%) exhibit improved ferroelectric, piezoelectric and electromechanical properties.     

A route to transparent bulk metals

Hypothetical compounds based on a sapphire host are investigated with respect to their structural as well as electronic features. The results are obtained by electronic structure calculations within density functional theory and the generalized gradient approximation. A quarter of the Al atoms in Al₂O₃ is replaced by a 4d transition metal M ion, with d⁰ to d⁹ electronic configuration. We perform structure optimizations for all the compounds and analyze the electronic states. Due to the sizeable band gap of the Al₂O₃ host, we can identify promising candidates for transparent bulk metals. We explain the mechanisms leading to this combination of materials properties. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Local relaxation in lanthanum silicate oxyapatites by Raman scattering and MAS‐NMR

To characterize the local relaxation in the structure of lanthanum silicate oxyapatite materials, six compositions with different cation and oxygen stoichiometries (La₈Ba₂Si₆O₂₆, La₉BaSi₆O_26.5, La₁₀Si_5.5Mg_0.5O_26.5, La_9.33SiO₂₆, La_9.67SiO_26.5 and La_9.83Si_5.5Al_0.5O_26.5) were investigated by combining Raman scattering and ²⁹Si and ²⁷Al magic‐angle spinning nuclear magnetic resonance (MAS‐NMR) spectroscopies. Only [SiO₄]⁴⁻ species were evidenced and the hypotheses of [Si₂O₇]⁶⁻ and [Si₂O₉]⁸⁻ entities were ruled out. Both oxygen excess and cation vacancies induce local distortions in the structure, which leads to nonequivalent [SiO₄]⁴⁻ species, characterized by different ²⁹Si MAS‐NMR signals and by splitting of Raman signals. Copyright © 2011 John Wiley & Sons, Ltd.