Structure Of La0 Research Articles

Synthesis and characterisation of lanthanide-based dioxide

In the present work, the microstructure and structure of La0·25Ce0·52Nd0·17Pr0·06(OH)3 and La0·25Ce0·52Nd0·17Pr0·06O2 is obtained from transmission electron microscopy and X-ray diffraction measurements. Space group P63/m is assigned to the structure of La0·25Ce0·52Nd0·17Pr0·06(OH)3. Lanthanides are assigned to Wyckoff positions 2c. Cell parameters are a = 6·375(5) Å and c = 3·753(5) Å. The thermal decomposition of this compound was studied by differential scanning calorimetry. The process is exothermal with an enthalpy change ΔH° value of −254±10 kJ mol−1. The decomposition kinetics is complex and two global processes with Ea values of 98±4 and 61±2 kJ mol−1 were observed. The product is a lanthanide dioxide. Space group Fm3m is assigned to the La0·25Ce0·52Nd0·17Pr0·06O2. Lanthanides are distributed in Wyckoff positions 4a. The cell parameter is a = 5·479(5) Å. Nanopores in the oxide surface are obtained using this method and characterised by STEM measurements.

Synthesis of La<SUB>0.6</SUB>Nd<SUB>0.2</SUB>Na<SUB>0.2</SUB>MnO<SUB>3</SUB> Nanowire and Its Magnetism

The colossal magnetoresistance (CMR) manganite La0.6Nd0.2Na0.2MnO3 nanowires were synthesized in porous anodic alumina oxide (AAO) membrane via the sol-gel template route. X-ray diffraction (XRD) results of La0.6Nd0.2Na0.2MnO3/AAO composites verified the purity of the perovskite structure of La0.6Nd0.2Na0.2MnO3. Field emission scanning electron microscopy (FE-SEM) confirmed that the monodisperse cylindrical pores of alumina membrane were filled with manganite nanowire arrays. The nanowires were found to be essentially polycrystalline materials by high-resolution transmission electron microscope (HRTEM) images and selected electron diffraction (SAED) analysis. The Curie temperature of the La0.6Nd0.2Na0.2MnO3 nanowires determined by superconducting quantum interference device (SQUID) was much less than the the Curie temperature of the bulk material. According to our experimental results, we proposed the single domain size should be less than 50 nm conservatively. The result suggested that the finite size effect may play an important role in the reduction of the Curie temperature of the La0.6Nd0.2Na0.2MnO3 nanowires.

Structural change of Li 2S–P 2S 5 sulfide solid electrolytes in the atmosphere

The sulfides Li 2S−P 2S 5 are attractive solid electrolytes for all-solid-state lithium batteries since they have high lithium-ion conductivities and wide electrochemical windows. However, chemical stability of Li 2S-P 2S 5 solid electrolytes in the atmosphere is concerned. In the present study, the structure of Li 2S−P 2S 5 glasses and glass-ceramics after exposure to air was investigated for the first time. Raman spectroscopy demonstrated that the 75Li 2S∙25P 2S 5 (mol%) glass and glass-ceramic composed of Li + and PS 4 3− ions did not exhibit obvious structural changes on exposure to the atmosphere. The amount of H 2S generated from Li 2S−P 2S 5 glasses exposed to air depended on the glass composition. The composition of 75Li 2S∙25P 2S 5 generated the least amount of H 2S of Li 2S−P 2S 5 binary systems. 75Li 2S∙25P 2S 5 glass and glass-ceramic are promising solid electrolytes for all-solid-state lithium batteries in terms of chemical stability and conductivity.

ChemInform Abstract: A Comparative Synthetic and Structural Study of Triphenylmethoxide and Triphenylsiloxide Complexes of the Early Lanthanoids, Including X-Ray Crystal Structures of La2(OCPh3)6 and Ce2(OSiPh3)6.

ChemInform Abstract: A Comparative Synthetic and Structural Study of Triphenylmethoxide and Triphenylsiloxide Complexes of the Early Lanthanoids, Including X-Ray Crystal Structures of La2(OCPh3)6 and Ce2(OSiPh3)6.

Electrochemical Characteristics of Lithium Vanadium Oxide for Lithium Secondary Battery

The pure crystalline Li1.1V0.9O2 powder has been prepared by a simple solid state reaction of Li2CO3 and V2O3 precursors under nitrogen gas containing 10 mol % hydrogen gas flow. The structure of Li1.1V0.9O2 powder was analyzed using Xray diffraction (XRD) and scanning electron microscope (SEM). The stoichiometric Li1.1V0.9O2 powder was used as anode active material for lithium secondary batteries. Its electrochemical properties were investigated by cyclic voltammetry and constant current methods using lithium foil electrode. The observed specific discharge capacity and charge capacity were 360 mAh/g and 260 mAh/g during the first cycle, respectively. In addition, the cyclic efficiency of this cell was 72.2% in the first cycle. The specific capacity of Li1.1V0.9O2 anode rapidly declines as the current rate increases and retains only 30 % of the capacity of 0.1C rate at 1C rate. The crystallinity of the Li1.1V0.9O2 anode decrease as discharge reaction proceeds. However, the relative intensity of main peaks was almost recovered when the cell was charged up to 1.5 V.

Infrared spectroscopy and the structure of La0.33Zr2(Po4)3-Yb0.33Zr2(PO4)3 solid solutions

Solid solutions of double orthophosphates of zirconium and rare earth lanthanum and ytterbium (La 0.33 Zr 2 (PO 4 ) 3 -Yb 0.33 Zr 2 (PO 4 ) 3 ) that belong to the NASICON (NZP) structural type are synthesized and studied by IR spectroscopy. The factor-group analysis of P-O vibrations in phosphates with P3 (La 0.33 Zr 2 (PO 4 )3) and P3c (Yb 0.33 Zr 2 (PO 4 ) 3 ) space groups allows us to assign the intermediate representatives of this series to two different space groups by their IR spectra, which is difficult to perform based on powder X-ray diffraction results. A morphotropic transition P3 → P3 c is found to occur near the La 1/18 Yb 5/18 Zr 2 (PO 4 ) 3 composition.

Magnetic Refrigeration Properties of ${\hbox{La}}_{0.8}\hbox{Ca}_{0.2}\hbox{Mn}_{0.99}{^{57}\hbox{Fe}_{0.01}}\hbox{O}_{3}$

The La0.8Ca0.2Mn0.99 57Fe0.01O3 sample was prepared by sol-gel method. The crystallographic and magnetic properties of La0.8Ca0.2Mn0.99 57Fe0.01O3 have been studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mossbauer spectroscopy measurements. The crystal structure of La0.8Ca0.2Mn0.99 57Fe0.01O3 was found to be orthorhombic (Pnma) structure with lattice constants ao=5.486 Aring, bo=7.761Aring, and co=5.510 Aring at room temperature. The Curie temperature (Tc) is determined to be 160 K by zero field cooled (ZFC) magnetization curve under 5 kOe applied field. The maximum value of magnetic entropy changes, |DeltaSM| is 1.25 J/kgldrK at 157 K under 13 kOe applied field. Mossbauer spectrum at 4.2 K was fitted with two independent magnetic components of the magnetic hyperfine fields Hf,1=526 kOe and Hf,2=501 kOe. Mossbauer spectra show that the two well-resolved sextets show nearly equal intensities between them without any external fields. This unusual phenomenon provides direct evidence of the two-phase character of the metallic state in the mixed valence state of La0.8Ca0.2Mn0.99 57Fe0.01O3 powder.

Direct observations of La ordering and domain structures in La0.61Li0.17TiO3 by high resolution electron microscopy

La0.61Li0.17TiO3 microstructures have been studied by high resolution electron microscopy. A local lattice distortion occurs in the vicinity of the domain boundary region due to the twin with an angle of 89°. The average domain size of La0.61Li0.17TiO3 is greater than 20 nm. The domain size and structures of La0.61Li0.17TiO3 differ greatly from those of La-poor compounds, such as La0.55Li0.35TiO3. At a nanoscopic level, microdomains of 20–100 nm in size construct a two-dimensional structure in La-rich compounds, while microdomains of 5–10 nm in size construct a three-dimensional structure in La-poor compounds. In addition, the Li-ion conduction mechanisms for La-rich and La-poor compounds are two- and three-dimensional, respectively.

Synthesis and structures of complexes with axially chiral isoquinolinyl-naphtholate ligands

The synthesis of axially chiral ligands 1-(3',6'-di-t-butyl-2'-hydroxy-1'-naphthyl)-3-R-isoquinoline (R = H, Pr(i), Bu(t)) (LR-H) is described. Ligands with unsubstituted isoquinolinyl rings tend to give 1:2 metal complexes. The syntheses and crystal structures of Li2(LH)2(THF)2 (9), (LH)2Ti(OPr(i))2 (12), Zn(LH)2 (13) and [Mg(LH)2]2 (14) are reported. Complex formation is highly stereoselective; the ligands in 1:2 complexes have the same stereochemistry (i.e. R,R and S,S but not R,S), whereas in the binuclear magnesium compound 14 the bridging and non-bridging ligands LH have opposite stereochemistry. The reaction of LH-H with Pd(acac)2 afforded the N,O chelate Pd(acac)(LH) (10), whereas towards K2PtCl4 the same ligand acts as an N-donor only, to give trans-PtCl2(LH-H)2 (11) in which the OH groups are hydrogen-bonded to one of the two chloride ligands. The more bulky ligand with a t-butyl substituent in the 3-position of the isoquinolinyl ring reacts with zinc and magnesium bis(amides) to give the mixed-ligand species (LBu)ZnN(SiMe3)2 and (LBu)MgN(SiMe3)2, respectively, which catalyse the ring-opening polymerisation of epsilon-caprolactone (CL) and rac-lactide (LA).

2-Lithio-3,3-dimethyl-2-oxazolinyloxirane: Carbanion or Azaenolate? Structure, Configurational Stability, and Stereodynamics in Solution

Chemical studies have shown that, in ethereal solvents, oxiranyllithium Li-1 is configurationally unstable either on the macroscopic (Hoffmann's text) or microscopic time scale at low temperature (175 K). An optically pure sample of oxazolinyloxirane 1, once deprotonated, racemized within 1 min at -130 degrees C in THF/Et(2)O (3:2) (t(1/2) = 6.05 s); the application of the Eyring equation suggested a barrier to inversion for Li-1 of 8.8 kcal/mol at -130 degrees C. Despite this, Li-1 exhibited an unusual thermal stability undergoing a successfully deuterium incorporation (>98%) also at 25 degrees C with a little decomposition. The structure, configurational stability, and stereodynamics in solution of alpha-lithiated oxazolinyloxirane Li-1 have been also synergically investigated by means of in situ IR and NMR spectroscopy. IR spectroscopic studies showed that lithiation of 1 is complete at -98 degrees C within 1 min and is accompanied by a decrease of the CN wavenumber by only 60 cm(-1), so supporting the idea that the structure of Li-1 may be more similar to that of an "organolithium" rather than an "azaenolate". In addition to this, multinuclear magnetic resonance studies suggested that at least in a range of concentration of 0.08-0.3 M, Li-1 mainly exists in THF as a monomeric eta(3)-aza-allyl coordinated species rapidly equilibrating, on the NMR time scale, with a complex mixture of diastereomeric oxazoline-bridged dimeric species variously intraaggregated. An exchange mechanism by which monomers would interchange their Li atoms via one of the above dimeric species and which may be responsible for the fast racemization Li-1 undergoes as soon as is generated has been proposed.

Effects of amorphous Co–C on the structural and electrochemical characteristics of La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1 hydrogen storage alloy

Abstract Amorphous Co–C powder prepared by ball milling was introduced to improve the performance of La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1 hydrogen storage alloy. The structural and electrochemical properties of the as-prepared La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1–x wt.% Co–C composites were investigated systematically. Scanning electron microscopic images show La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1 alloy was coated by Co–C particles. X-ray diffraction patterns suggest that the composite almost remained original phase structures of La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1 and Co–C in both charge and discharge processes. The maximum discharge capacity of the composites reached 414 mAh g−1 at a current density of 50 mA g−1 at 298 K. The cyclic stability and the discharge capacities of the composite electrodes were noticeably improved in comparison with single La–Mg–Ni-based alloy due to increased corrosion resistance and the catalysis of the Co–C powder. Cyclic voltammogram and potentiodynamic polarization studies on the composite indicate that the electrochemical kinetics was improved and the corrosion resistance was increased. The cycling performance of the composite electrode at high current density is good as well.

Combined high resolution powder and single-crystal diffraction to determine the structure of Li1+xCeIIIxCeIV6-xF25

Combined high resolution powder and single-crystal diffraction to determine the structure of Li_1+xCe^III_xCe^IV_6-xF₂₅

Hole distribution and local structure in La2−xSrxCuO4

Atomistic simulation has been performed on La2−xSrxCuO4 to investigate its hole distribution and local structure in real space lattice. It is found that the holes introduced by Sr doping are more energetically favorable to form stripes than to be disordered. The authors verify two types of hole-stripe models (vertical and diagonal domain walls) and propose some other possible types of hole-stripe models, which are quarter or half filled. The local structure of hole stripes is found to be different from the average structure. Sr2+ ions are also found to have a thermodynamics tendency of ordering.

Phase equilibria and crystal structures of solid solutions in the system LaCoO3−δ-SrCoO2.5±δ-SrFeO3−δ-LaFeO3−δ

The composition region and structure of La1−x Sr x Co1−y Fe y O3−δ solid solutions are determined by x-ray powder diffraction using the Rietveld profile analysis method. The solid solutions based on lanthanum cobaltite, LaCoO3−δ, have a rhombohedrally distorted perovskite-like structure (sp. gr. R $$\bar 3$$ c), and those based on lanthanum ferrite, LaFeO3−δ, have an orthorhombically distorted structure (sp. gr. Pbnm). The rhombohedral distortion decreases with increasing strontium content, and the solid solutions with x ≥ 0.5 have an ideal cubic structure (sp. gr. Pm3m). The composition dependences of lattice parameters for the La1−x Sr x Co1−y Fe y O3−δ solid solutions are presented, and the 1100°C isotherm of the LaCoO3−δ-SrCoO2.5±δ-SrFeO3−δ-LaFeO3−δ system in air is constructed.

Oxygen-deficiency and high-pressure effects on the magnetic and crystal structures of La0.7Sr0.3MnO3−d managanites

The magnetic and crystal structures of anion-deficient La0.7Sr0.3MnO3−d manganites (d = 0.15 and 0.20) are studied by neutron diffraction in the range of high pressures 0–5 GPa and temperatures 10–300 K. It is found that a spin-glass state forms in La0.7Sr0.3MnO2.85 below Tg ∼ 50 K, while magnetic phase separation is observed in La0.7Sr0.3MnO2.80, which is characterized by the coexistence of AFM domains of the C type with spin-glass domains. As distinct from the stoichiometric A0.5Ba0.5MnO3 manganites (A = Nd, Sm), in which the high-pressure effect suppresses the spin-glass state and gives rise to ferromagnetism, the spin-glass state in La0.7Sr0.3MnO2.85 is stable under pressure. The bulk modulus of La0.7Sr0.3MnO2.85 is considerably smaller than that for the stoichiometric La0.7Sr0.3MnO3 compound. The causes of the formation of different types of the magnetic structure in La0.7Sr0.3MnO3−d (d = 0.15 and 0.20) and different high-pressure effects on the magnetic structure of stoichiometric and anion-deficient manganites are analyzed.

Magnetic field dependent evolution of band structure in La1−xCaxMnO3 (x=0.18 and 0.30)

Probing of the evolution of electronic structure in magnetic field is a key issue for the design and realization of manganite-based devices. Here, the shift of the maximum (or minimum) position in unusual magnetoresistance (MR) versus V curves of the heterojunctions composed of La1−xCaxMnO3 (LCMO, x=0.18 and 0.3) and 0.5wt% Nb-doped SrTiO3 (SNTO) was used to investigate the change of band gaps of LCMO with magnetic field. Negative and positive MRs which depend on temperature, bias current (or voltage), and Ca concentration observed in these heterojunctions are directly determined by the band structure at the LCMO-SNTO interface.

Cation distribution in the crystal structure of Li2.32Fe 0.56 3+ [PO4]F—A synthetic structural analog of grandidierite

Cation distribution in the crystal structure of Li2.32Fe 0.56 3+ [PO4]F—A synthetic structural analog of grandidierite

Structural, magnetic and transport properties ofLa0.8Sr0.2MnO3/xNiO composites

The effect of NiO doping on the structure, magnetic and magnetotransport properties ofLa0.8Sr0.2MnO3(LSMO)/xNiO has been investigated.Two types of LSMO/xNiO composites were prepared by different processes using the solid-state reactionmethod. In the first type, the LSMO powders are mixed with small particle size NiO(SAx samples) and in the second type the LSMO powders are mixed with as-powder NiO(SBx samples). These studies show that some part of the Ni goes into the perovskite lattice,substituting Mn in LSMO, and the remainder segregates as a separate phase at the grainboundaries and grain surfaces. The presence of NiO at the grain boundaries increases thenumber of disordered states at the surface of the grains and therefore the low-temperatureresistivity increases very quickly with the increase of NiO doping level. Resultsalso show that the NiO doping has an effect on the low-field magnetoresistance(LFMR). The value of magnetoresistance (MR) increases for a low doping level of0≤x≤3 and decreases at ahigh doping level of x≥5. The spin-dependent tunnelling and scattering at the interfaces ofthe grain boundaries are responsible for the increasing of LFMR atx≤3, while reduction of theLFMR at x≥5 originatesfrom substitution of Ni2+ for the Mn3+ ions, which introduces magnetic dilution into the samples. Also it can be found that, asT<230 K, the MR value ofthe SB3 sample is largerthan that of the SA3 sample due to the presence of a larger amount of NiO at the grain boundaries andsurfaces.

Effect of high-current pulsed electron beam irradiation on the structure of La0.7Sr0.3CoO3 powder

The effect of pulsed electron irradiation on the long- and short-range order in the La0.7Sr0.3CoO3 ceramics is reported. Neutron and X-ray powder diffraction reveal that the unit cell symmetry and single-phase state of single and multiple irradiated La0.7Sr0.3CoO3 are preserved, while the oxygen atoms coordination changes towards the La0.5Sr0.5CoO3 structure. X-ray absorption data confirm this observation and further reveal the details of the shift and splitting of the Co 3+ t2g and eg atomic orbitals. Possible mechanisms of pulsed electron irradiation effect in La0.7Sr0.3CoO3 are discussed.

Ab initio electronic and magnetic structure inLa0.66Sr0.33MnO3: strain and correlation effects

The effects of tetragonal strain on the electronic and magnetic properties of strontium-doped lanthanummanganite, La2/3Sr1/3MnO3 (LSMO), are investigated by means of density-functional methods. As far as the structuralproperties are concerned, the comparison between theory and experiments forLSMO strained on the most commonly used substrates shows an overall goodagreement: the slight overestimate (at most of 1–1.5%) for the equilibriumout-of-plane lattice constants points to possible defects in real samples. The inclusionof a Hubbard-like contribution on the Mn d states, according to the so-called‘LSDA+U’ approach, is rather ineffective from the structural point of view, but much more importantfrom the electronic and magnetic point of view. In particular, full half-metallicity,which is missed within a bare density-functional approach, is recovered withinLSDA+U, in agreement with experiments. Moreover, the half-metallic behaviour, particularlyrelevant for spin-injection purposes, is independent of the chosen substrate and is achievedfor all the considered in-plane lattice constants. More generally, strain effectsare not seen to crucially affect the electronic structure: within the consideredtetragonalization range, the minority gap is only slightly (i.e. by about 0.1–0.2 eV) affectedby a tensile or compressive strain. Nevertheless, we show that the growth on asmaller in-plane lattice constant can stabilize the out-of-plane versus in-planeeg orbital and significantly change their relative occupancy. Sinceeg orbitals are key quantities for the double-exchange mechanism, strain effects are confirmedto be crucial for the resulting magnetic coupling.