Synthesis and electrical properties of strontium-doped lanthanum ferrite with perovskite-type structure

In this study, we prepared strontium-doped lanthanum ferrites with the perovskite-type structure for application as solid oxide fuel cell (SOFC) cathodes. We used the Pechini method to prepare strontium-doped lanthanum ferrites with the strontium:lanthanum molar ratios of 20:80 and 40:60. The resulting doped materials were characterized using various analytical tools. The calcination process was conducted at 450 °C because above this temperature, the stabilization of mass loss occurred and no phase transformation was observed. The X-ray diffraction results confirmed the mixing of the powder phases after the calcination process and the presence of a single powder phase in the air-sintered samples. The high-resolution transmission electron microscopy results revealed the presence of agglomerated nanoparticles smaller than 20 nm in size in the samples. The electrochemical impedance spectroscopy results revealed that the sample with 20% strontium exhibited a conductivity of 3.9 × 10⁻³ S cm⁻¹ at 95 °C and activation energy of 0.37 eV. In contrast, the sample with 40% strontium exhibited a conductivity of 3.5 × 10⁻² S cm⁻¹ and activation energy of 0.29 eV. These results suggest that with an increase in the strontium content, the conductivity of the samples increased, where as the activation energy of the conduction process decreased. Therefore, the ferrites synthesized in this work are potential catalysts for SOFC cathodes.     

Resolved-detrimental surface crystallization in yttrium lanthanum gallate glasses for optical fiber applications

Gallium-rich heavy metal oxide glasses have become highly attractive optical materials since they exhibit a wide transparency window spanning from the ultraviolet ∼270 nm up to the mid-infrared (IR) region ∼6 μm making them promising for a future integration in optical fiber devices. Nonetheless, in most composition, surface crystallization is a key limiting factor for optical fiber drawing using the classical preform-to-fiber method. Herein, taking advantage of structural information from vibrational spectroscopies (Raman/IR) and ⁷¹Ga Solid-State Nuclear Magnetic Resonance, we describe the key role of lanthanum and yttrium rare—earth elements on the glass structure and their impact on the capability to draw those new glass compositions into optical fibers. This approach emphasizes that yttrium ions as compared with lanthanum ones favor the glass disorder, increasing significantly the fraction of GaO₅ units with respect to GaO₄. That, combined with thermal analysis and examination of the crystallization behaviors, highlights that Y₂O₃ prevents the glass devitrification during the glass shaping. The smaller yttrium radius is believed to be the key physical parameter preventing the precipitation of the Ba_yGa_5-yGe_y+1La_3-yO₁₄ (y = 0, 1, 2, 3) langasite-type crystal phase. This study remains particularly relevant and opens up the way for the development of highly robust power scaled fiber devices operating from the visible up to the challenging mid-IR domain.     

Synthesis,structure, and reactivity of yttrium complexes with chiral biaryldiamine-based N4-ligands

The chiral biaryl-based N₄-ligands, (R)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-bis(pyrrol-2-ylmethyleneamino)-1,1′-binaphthyl (1H₂) and (S)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), can effectively stabilize the chiral rare earth metal chloride complexes such as 1-YCl(dme) (3) and 2-YCl(dme) (4), which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, treatment of 3 with half equiv of 1Na₂ in THF gives the binuclear complex 1-Y(thf)-1-Y(thf)-1 (5) in 70% yield. These complexes have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides.     

Thermal conductivity of air plasma sprayed yttrium heavily-doped lanthanum zirconate thermal barrier coatings

The yttrium heavily doped La₂Zr₂O₇ solid solutions coatings, with a Y to La molar ratio of 1:1, have been successfully prepared by air plasma spraying technique. The evolution of phase composition, phase structure and thermal conductivity of such coatings with annealing at 1300?°C has been investigated. The results show that, a single pyrochlore structure can be retained for coating after annealing up to 48?h, beyond which the fluorite phase begins to precipitate out. By comparing thermal conductivities to those undoped counterparts at a similar porosity level, we find a considerably flat thermal conductivity versus temperature (k-T) curve, suggesting the existence of a strong phonon scattering source, which is inferred as rattlers. In addition, after the segmentation of the fluorite phase, the thermal conductivity of corresponding coatings rises considerably, indicating that the fluorite phase has a higher thermal conductivity than that of pyrochlore phase. Moreover, while the as-sprayed coatings show a clear indication of radiative thermal conduction beyond 1000?°C, the thermal conductivity of annealed coatings do not show such an uprising trend after 1000?°C, suggesting that the radiative thermal conduction has been greatly suppressed. The reason is proposed as the formation of local dipoles due to local enrichment of certain elements influences the propagation of electromagnetic waves and thus suppresses the radiative thermal conduction.     

Synthesis,structure, and adsorption properties of a three-dimensional porous yttrium–organic coordination network

Deprotonation of 4,4′-biphenyldicarboxylic acid (H₂BPDC) with triethylamine followed by the copolymerization with Y(III) in N,N-dimethylformamide (DMF) at room temperature yields a new three-dimensional (3-D) porous metal–organic coordination network, [Y₂(BPDC)₃(DMF)₂(H₂O)₂]_n · (DMF)_n · (H₂O)_n (1). Compound 1 (C_24.50H₁₉N_1.50O₉Y) crystallizes in the triclinic P-1 space group (a = 8.220 (2), b = 13.998 (4), c = 14.212 (4) Å, α = 111.058 (5)°, β = 90.187 (5)°, γ = 94.318 (5)°, V = 1520.9 (7) ų, and Z = 2). X-ray crystallography reveals that 1 consists of a 3-D framework contained open 1-D channels with the dimension of 5 × 10 Å along the crystallographic a axis. The adsorption measurements show that compound 1 can adsorb N₂, Ar and CO₂ into its pores. The adsorption isotherms for MeOH and H₂O were also measured.     

Crystallization behavior and IR structure of yttrium aluminosilicate glasses

The crystallization of four Y₂O₃-Al₂O₃-SiO₂ (YAS) glasses were investigated to prepare YAS glass ceramics precipitated singly/mainly Y₂Si₂O₇ or Y_4.67(SiO₄)₃O apatite, and to explore the crystallization difference between the stoichiometric parent glass (SPG) and non-stoichiometric parent glass (NSPG). The DSC results revealed that glass locating at the higher liquidus surface temperature has lower crystallization peak temperature, which indicating that the corresponding glass has higher crystallization potential to crystallize easily. Crystallization of the NSPG samples is along surface and caused by phase separation, while SPG sample is the surface crystallization at the first exothermic peak temperature and overall crystallization at the second exothermic peak temperature. Glass ceramics only containing y-Y₂Si₂O₇ or Y_4.67(SiO₄)₃O apatite are obtained successfully, and which are illustrated by fitting FTIR spectra. These results can provide technical guide for controlling the crystallization process and the types of precipitated crystals in YAS glass for different application potentials.     

Synthesis,densification and oxidation study of lanthanum hexaboride

This paper presents the result of investigation carried out on the synthesis, densification and oxidation studies of LaB₆. LaB₆ was synthesized by boron carbide reduction of La₂O₃. Effect of temperature on product quality was investigated. Pure LaB₆ powder was obtained at 1500 °C, in vacuum. Pressureless sintering at 1950 °C of LaB₆ powder resulted in a density of only 85.1% of the theoretical value. Hot pressing resulted in near theoretical density at the same operating temperature. Hardness and fracture toughness of the dense LaB₆ was measured as 20 GPa and 3.02 MPa m^1/2 respectively. Oxidation study by thermogravimetry revealed that oxidation starts slowly at 500 °C and accelerates at 700 °C. Isothermal oxidation study revealed that protective oxide layer forms on LaB₆ surface on oxidation at 900 °C. The presence of protective continuous oxide layer on the surface was observed even after 64 h exposure in air atmosphere.     

固相法合成乙酰丙酮镧

以无机镧盐、固体碱、乙酰丙酮(Hacac)为原料,在室温下无溶剂固相研磨合成乙酰丙酮镧。考察了碱的种类,乙酰丙酮的量,NaOH的量,以及研磨时间对产率的影响。采用红外、热重及X射线衍射对目标产物进行了表征,结果与标准谱图基本一致。实验结果表明LaCl3.6H2O 10mmol,Hacac 40mmol,NaOH 30mmol,室温下研磨1 h所得乙酰丙酮镧的产率达97.48%,高出经典液相法8.48个百分点。     

钇三元配合物的合成、表征及其抗菌活性研究

以YCl3.6H2O、2,6-吡啶二羧酸(PDA)和噻吩甲酰三氟丙酮(TTA)为原料,制备了钇的三元配合物,用元素分析、红外光谱、X射线光电子能谱对配合物进行了表征,确定了配合物的化学组成为:Na[Y(TTA)2(PDA)].3H2O(反应时间为1 h)和Na2[Y(TTA)3(PDA)].3H2O(反应时间为0.5 h)。抗菌实验表明,Na[Y(TTA)2(PDA)].3H2O对大肠杆菌和金黄色葡萄球菌的抑菌圈直径分别约为14,12 mm,Na2[Y(TTA)3(PDA)].3H2O分别约为16,14 mm,说明配合物对大肠杆菌、金黄色葡萄球菌具有一定的抑制作用,且对大肠杆菌的抑制效果较好。     

Synthesis of lanthanum chromite using the sol-gel method

Synthesis of lanthanum chromite using the sol-gel method is considered. The effect of the amount of gel-forming agent and the heat treatment time and temperature on the completion of synthesis is investigated. The optimum parameters of the process are presented. The possibility of replacing the powder obtained by vibration crushing of electrically melted lanthanum chromite with powder synthesized by the sol-gel method in the production of miniature ceramic articles is demonstrated. Translated from Steklo i Keramika, No. 6, pp. 15 – 17, June, 1998.     

低热固相合成磷酸镧及其结晶度

对合成功能材料磷酸镧的新方法进行了研究,以聚乙二醇-400 （PEG-400）为表面活性剂,LaNO₃•6H₂O和(NH₄)₃PO₄•3H₂O为原料,用低热固相反应法成功合成得到磷酸镧。用产物XRD图谱数据计算得到的结晶度作为试验的考察指标,试验中应用了均匀设计试验法及数据挖掘技术,在数据挖掘成果的指导下进行了试验。试验结果表明,用最优工艺条件合成得到的产物为23nm的LaPO₄∙0.5H₂O,结晶度为97.8%与数据挖掘得到的最佳结果相吻合。TG/DTA分析结果表明LaPO₄∙0.5H₂O在300℃下加热脱水可以转变成为LaPO₄。     

Synthesis and characterization of MC nylon/modified yttrium hydroxide nanocomposites

In this article, monomer casting (MC) nylon is synthesized. MC nylon could replace nonferrous metals in certain applications, including gears, wheels, and other moving parts. However, compared with metals, MC nylon products have poor strength and stiffness, and crack easily, especially at low temperatures. In addition, the dimensional stability of MC nylon is poor, especially in the large casting nylon products, causing significant internal stresses due to shrinkage. Thus, MC nylon cracks easily when cast and molded. The yttrium hydroxide particles are modified by stearic acid and dispersed in the caprolactam. The polymerization time is short due to fast anionic polymerization. Copolymerization with different ratios of yttrium hydroxide particles can be used to prepare the copolymer. The effects of different amounts of yttrium hydroxide on the performance of the monomer casting nylon are studied. The products are characterized using X‐ray diffraction, impact, and tensile testing. When the percentage of modified yttrium hydroxide is 0.3 wt %, the composite exhibits the maximum impact strength, thus the 0.3 wt % of modified yttrium hydroxide is the suitable percentage to enhance the impact strength of MC nylon. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43356.     

有机酸镧盐的合成及其改性PA66的性能研究

将自制的2种有机酸镧盐(简称有机镧1、有机镧2)及抗氧剂1010按添加质量分数为1.5%的比例分别与聚酰胺66(PA 66)切片混合、熔融挤出造粒、烘干,采用高速纺丝工艺,制得改性PA 66纤维,研究了改性PA 66及其纤维的热稳定性和抗黄变性能。结果表明:有机镧1和有机镧2为水合配位化合物,有良好的热稳定性,纯PA 66粉体及混有抗氧剂1010、有机镧1、有机镧2的PA 66混合粉体的初始失重温度分别为325,350,340,370℃;抗氧剂1010,有机镧1、有机镧2改善了PA 66粉体的抗黄变性,其改善程度分别为1.9%,22.6%,20.4%;与纯PA 66纤维相比,加入抗氧剂1010及有机镧2的改性PA 66纤维的断裂强度分别降低了6.5%和11.5%,抗氧剂1010改性PA 66粉体的黄变指数增加了10.5%,而有机镧2改性PA 66的黄变指数降低了2.6%。     

Synthesis and characterization of yttrium iron garnet nanoparticles doped with cobalt

In this work, we have synthesized and characterized yttrium iron garnet nanoparticles doped with cobalt. The X-ray diffraction data showed a single phase, belonging to the cubic structure of Y₃Fe₅O₁₂. Rietveld refinement revealed variation of the angles and interionic distances (Fe³⁺(a)-O^2-Y³⁺(c) and Fe³⁺(d)-O^2--Y³⁺(c) when Fe³⁺ ions are replaced by Co³⁺ ions in the tetrahedral (d) and octahedral (a) sites of YIG. In addition, the lattice parameter a, decreases from 12.3846?Å to 12.3830?Å with the increasing of cobalt concentration. The analysis by Infrared and Raman spectroscopies has shown a slight stretching at lower wave numbers as the dopant concentration increased. The magnetic measurements confirm the substitution of Fe³⁺ by Co³⁺ in the a-sites and d-sites with the reduction of the saturation magnetization from 26.63?emu/g to 24.92?emu/g, for 0.000?≤?y?≤?0.030. Changes in the coercive field varying the dopant concentration were related to the particle size and pinning centers existence.     

Synthesis of single-crystalline lanthanum hexaboride nanowires by Au catalyst

Lanthanum hexaboride (LaB₆) nanowires have been successfully fabricated by the facile catalytic reaction of lanthanum (La) powders, and gas mixture of boron trichloride (BCl₃), hydrogen and argon, where Au was used as the catalyst. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED) were used to characterize the composition, morphology and structure of the samples. Single crystal column-shape LaB₆ nanowires were obtained. It is expected that LaB₆ nanowires can provide thermionic emission, field-induced emission, and thermal field-induced emission of electrons for TEM, SEM, flat panel displays, as well as many electronic devices that require high-performance electron source.     

蠕虫形管状镧铝复合介孔材料的合成及表征

The lanthanum aluminum mesoporous materials were synthesized using sodium dodecyl sulfate as a template agent by ultrasonic hydrothermal method.The resulting samples were characterized by low angle X-ray diffraction(XRD),N2 adsorption-desorption studies,transmission electron microscopy(TEM)and surface morphology analysis(SEM),surface acid(NH3-TPD),reducibility properties(TPR),X-ray energy dispersive spectrometer(EDS)and thermogravimetric analysis(TG/DTG).A l/La composite mesoporous material were synthesized with n(Al)︰n(La)=70︰1.0,80°C of reaction temperature,20 h of reaction time,12 h of crystallization time,650°C of calcination temperature.The specific surface area of the sample is 273.90 m 2 ·g ?1 ,with the average diameter 5.642 nm and pore volume 0.2354 cm 3 ·g ?1 .The samples have mesoporous structure and its particles are similar to a worm-shaped tubular structure.The influence of calcination temperature on the surface physical and chemical properties of Al/La composited mesoporous materials was examined,and the results showed that the acid strength was increased but the amount of acidic sites is decreased as the calcination temperature increased.It was found that the sample calcined at 650°C had appropriate acid content,acid strength and better reducibility.     

Effect of modifiers on the structure of yttrium oxide ceramic

Refractories and Industrial Ceramics - The structure-forming process of yttrium oxide ceramic is influenced by the addition of small amounts of the high-melting oxides of zirconium and thorium.