The effect of magnesium compounds (MgO and MgAl2O4) on the synthesis of Lanthanum magnesium hexaaluminate (LaMgAl11O19) by solid-state reaction method

In the present study, the lanthanum magnesium hexaaluminate (LaMgAl₁₁O₁₉)(LaMA) powder was synthesized by the solid–state reaction method using two types of magnesium compounds, including magnesium oxide (MgO) and magnesium aluminate (MgAl₂O₄) spinel (MAS). The effect of substitution of magnesium oxide with MAS on the synthesis temperature, intermediate compounds and morphology of synthesized powders were investigated. The microstructural results showed that the intermediate compounds of lanthanum aluminate (LaAlO₃), aluminum oxide and MAS were formed in the presence of magnesium oxide, whereas in the latter case, the LaAlO₃ intermediate phase was not observed and La₄Al₂MgO₁₀ was formed at about 810 °C. Also in both cases, a single LaMA phase with the platelet-like morphology was formed. The thickness of the LaMA platelets decreased from 300 nm to 125 nm and the synthesis temperature increased from 1330 °C to 1355 °C, by replacing MgO with MAS.     

Synthesis and properties of lanthanum hexaaluminate ceramic La1−xCaxAl11−y−zMgyTizO18

The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La_1−xCa_xAl_11−y−zMg_yTi_zO₁₈ (x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage ceramic technology. By X-ray diffraction and scanning electron microscopy, predominant phase LaAl₁₁O₁₈ and second phases LaAlO₃ and -Al₂O₃ are identified. Ceramic materials are characterized with high physico-mechanical properties and may be find application for production of mill bodies and materials for immobilization of nuclear waste.     

Electrical conductivity of Ca-substituted lanthanum manganites

The physico-chemical properties of substituted perovskites materials have been analyzed with the aim of studying the relationships between structure and properties in this class of materials. Investigations were carried out into the effect of substitution in lanthanum manganites La_1–xCa_xMnO₃ (x = 0; 0.05; 0.1; 0.15) materials obtained through sol-gel method followed by heat treatment at low temperatures and X-ray diffraction, into the surface area thereof, as well as into transmission electron microscopy for purposes of morpho-structural characterization. The results indicated a well-crystallized Pm-3m perovskite-type structure, and 20 nm average crystallite sizes for all samples. By means of complex impedance measurements in the 20 Hz–2 MHz frequency range, the electrical conductivity was determined at temperatures between 30 °C and 120 °C; the results showed that the conductivity obeys a Jonscher's universal law. It was found that below 10 kHz, the dc component of the conductivity increases with temperature for all samples, indicating that electrical conduction processes are activated thermally, in agreement with Mott's variable-range hopping (VRH) model; the model parameters (hopping distance and hopping energy) were also determined. In the high frequency range (f > 200 kHz) the ac conductivity is attributed to charge carriers hopping between the nearest neighboring states, in agreement with the correlated barrier hopping (CBH) model. Using this model, the energy band gap values: 0.364 eV, 0.372 eV and 0.424 eV of the substituted samples were found.     

Novel lanthanide salicylaldimine complexes with unusual coordination mode

The one-step metal promoted reaction between salicylaldehyde and 4-methyl-1,3-phenylenediamine in the presence of lanthanum(III) or gadolinium(III) nitrate yields new salicylaldimine complexes containing N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine as a result of the [2 + 1] Schiff base condensation. The crystal structure of the gadolinium complex reveals a dinuclear species with four unionized ligands coordinating in the monodentate and bridging bidentate fashion, using exclusively the oxygens as donor atoms with the nitrogen atoms not being involved in coordination. The coordination number of nine is achieved by involving three bidentate nitrate counterions in the coordination sphere.     

Tunable photoluminescence of nanostructured LaPO4:Eu3+/Tb3+ synthesized via a microwave-assisted ethylene glycol route

Nanostructured phosphors LaPO₄:Eu³⁺/Tb³⁺ were prepared via a combined approach using microwave heating and a bifunctional solvent (ethylene glycol) acting as both microwave absorber and capping agent. The synthesized samples were characterized by X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM) and photoluminescence (PL) measurements. All samples crystallized in a monoclinic monazite-type structure. Electron microscopy analysis revealed a hierarchical organization of self-assembled seed crystals of lanthanum phosphate into nanoparticles that, in turn, gave rise to sponge-like aggregates. The co-doped samples exhibited self-activated blue luminescence from the host matrix, as well as red and green emissions due to the presence of Eu³⁺ and Tb³⁺ ions, respectively. Furthermore, the spectroscopic analysis indicated energy transfer from terbium to europium ions.The synthetic route described here is efficient to prepare nanomaterials with advanced optical properties, which exhibit a potential for applications in photonics, sensing and biolabelling.     

Improvement of Fracture Toughness Lanthanum Zirconate

Thermalbarriercoatings(TBCs)havefoundan increasingnumberofapplicationsinprotectinghigh temperaturemetalliccomponents,forexample,TBCsaredepositedontransitionpieces,combustion lines,first stagebladesandvanes,andotherhot pathcomponentsofgasturbineseithertoincreasethe inlettemperaturewithaconsequentimprovementof theefficiencyortoreducetherequirementsfora coolingsystem[1].Thereareseveralceramicsthat havebeenevaluatedasTBCmaterials[2].Lanthanum zirconatewasrecentlyproposedasapromisingTBC materia…     

Fabrication of La_(1-x)Ca_xFeO_3 perovskite-type oxides with macro-mesoporous structure via a dual-template method for highly efficient soot combustion

A series of three-dimensionally ordered macro-mesoporous(3DOMM) La_(1-x)Ca_xFeO_3(x=0-0.3)perovskite-type oxides were designed and successfully fabricated for the first time via a dual-template method.In which,PMMA and Brij-56 were employed as the hard template and soft template,respectively.It is found that 3 DOMM La_(1-x)Ca_xFeO_3 exhibits abundant wormlike mesoporous channels about 3 nm in diameter on macroporous skeleton walls.The excellent catalytic activity of soot combustion benefits from not only the well-designed hierarchical porous structure of catalyst,but also the redox electron pair of Fe~(3+)/Fe~(4+) induced by the doping of low-valent alkaline earth metal Ca to A-site of LaFeO_3.3DOMM La_(0.8)Ca_(0.2)FeO_3 exhibits superior catalytic performance for soot combustion,which shows T_(50) of396℃.It is 189℃lower than that without catalyst.A combination of structure and composition in the design of catalyst can be widely extended to other catalytic systems.     

含镧ZA12和ZA27合金相变过程的DSC分析

用差示扫描量热分析（ＤＳＣ）研究了Ｌａ对ＺＡ１２和ＺＡ２７铸态合金加热及冷却相变的影响。结果表明，ＺＡ１２中含０．４％Ｌａ，使合金的凝固温度区间减小，共析转变温度降低，共析转变热增大，表明Ｌａ抑制其共析相变。ＺＡ２７中含０．４％Ｌａ，使合金的凝固温度区间增宽和凝固潜热增加，并使冷却过程中的共晶转变出现双峰，这可能是因为ε相提前析出的缘故。     

Single crystal growth and characterization of LaLuO3

Wide shoulder and fast lateral growth are characteristics of LaLuO₃ during crystallization onto an iridium rod in Czochralski's configuration. Under careful temperature control, necking in and further low-speed pulling provided for single-crystal growth, but spontaneous separation of the growing crystal from the melt is a strongly limiting factor for production of large boules. Ce- and Pr-doped single crystals of up to 0.5 cm³ were obtained and used in measurements of the X-ray data, density, melting point and optical properties and in annealing studies.     

Can lanthanum doping enhance catalytic performance of silver in direct propylene epoxidation over NaMoAg/SiO_2?

In the attempt to reduce surface free energy of silica to improve interaction of silica with silver, silica was doped by different amounts of low surface energy lanthanum, La_2O_3, through impregnation. The doped and undoped silica were used as supports for preparation of Na/Ag/Mo/La_2O_3-SiO_2 catalysts. Catalytic performances of the catalysts were evaluated in direct epoxidation of propylene(DPO) using molecular oxygen under atmospheric pressure and without adding hydrogen. Adding 5 wt%La to the Na/Ag/Mo/SiO_2 catalyst improves both the catalysts electivity in DPO and its stability over 20h of time-on-stream.The characterization results show that La_2O_3 species interact strongly with silver particles on the silica surface which result in significant improvement in the dispersion profile of silver and marked decrease in the size of silver nanoparticles(AgNPs). The estimated mean diameter of AgNPs is ca. 4.0 nm in Na/Ag/Mo/5 wt%La_2O_3-SiO_2, which is smaller than that(53.9 nm) found in Na/Ag/SiO_2. The presence of subnanometer AgNPs on Ag/La_2O_3-SiO_2 prior addition of MoO_3 and NaCl to the sample can enhance the mutual electronic synergism between Ag, MoO_3 and Na for selective production of propylene oxide.