Hydrothermal synthesis and structural studies of a new coordination polymer of lanthanum（III） with benzene-1,2,4,5-tetracarboxylic acid and 4,4＇-bipyridine

A new lanthanum complex formulated as {(bpyH₂)[La(btc)(H₂O)₄(NO₃)]·2H₂O}_n (1) (btcH₄=benzene-1,2,4,5-tetracarboxylic acid; bpy=4,4′-bipyridine) was hydrothermally synthesized. The complex was characterized by FT-IR spectroscopy, elemental analysis and X-ray diffraction. X-ray crystal structural analysis revealed that the compound belonged to the monoclinic space group C2/c with cell parameters a= 1.42806(7) nm, b=1.10258(5) nm, c=1.60333(8) nm and β=101.9400(10)°. The complex was polymeric with La^III atoms linked by four O atoms from two carboxylate groups of one benzene-1,2,4,5-tetracarboxylate. The La^III atom was ten coordinated in a distorted tetracapped trigonal prism. In the crystal structure, a wide range of noncovalent interactions consisting of hydrogen bonding (of the types of O—H…O, N—H…O and C—H…O) and ion pairing interactions connected the various components into a supramolecular structure.     

Synthesis, crystal structures and characterization of a pair of TbIII-based enantiomers

A pair of novel Tb^III-based enantiomers, [Tb(dbm)₃·L_SS] (1) and [Tb(dbm)₃·L_RR] (2) (where L_SS=(+)-4,5-pinene bipyridine, L_RR= (-)-4,5-pinene bipyridine, dbm=dibenzoylmethanate), were synthesized and characterized based on single crystal X-ray diffraction, elemental analysis, FT-IR, TG and CD spectra. X-ray diffraction analysis showed that both the complexes crystallized in monoclinic crystal system with P2₁ chiral space group. The Tb^III ion was eight-coordinated by six O atoms of three dbm ligands and two N atoms from one chiral ligand L_SS or L_RR. The CD spectra revealed that complexes 1 and 2 were enantiomers. Thermogravimetric analysis results indicated that 1 and 2 were thermally stable up to 246 °C.     

Enhanced separation of praseodymium and neodymium by kinetic“push and pull”system of[A336][NO_3]-DTPA in a column extractor

A new approach was suggested in present work for improving the separation between Pr(Ⅲ) and Nd(Ⅲ)by a so-called kinetic "push and pull" system consisting of [A336][NO_3] and DTPA in a column extractor.It is revealed that,when organic extractant [A336][NO_3] is continuously pumped into the column extractor in the form of dispersed oil droplets and at the same time DTPA was injected into the aqueous feed solution whet the extraction was just started,the separatiot factor of Pr(Ⅲ) to Nd(Ⅲ),βPr/Nd,increased obviously with the time,and could even achieve 21.7.Such an amazing increase in β_(Pr)/Nd value might be due to the extraction rate of Pr(Ⅲ) by [A336][NO_3] oil droplets being faster than that of Nd(Ⅲ),while the complexing rate of Nd(Ⅲ) with DTPA in the aqueous solutions being faster than that of Pr(III).The opposite order of the two rates for Pr(Ⅲ) and Nd(Ⅲ) result in their kinetic "push and pull" separation.In contrast,the β_(Pr)/Nd value in traditional thermodynamic separation reported in previous literatures is only around 5 or even less,even though using the same extractant [A336][NO3] and DTPA but by previously adding DTPA into the aqueous feed solutions for pre-complexing of Pr(Ⅲ) and Nd(Ⅲ).Various effects from the pH and addition amount of DTPA aqueous solutions,LiNO_3 concentrations in initial aqueous feed solutions,the initial concentration ratios of Pr(Ⅲ) to Nd(Ⅲ) ions,the initial pH of aqueous feed solutions,and the concentrations of [A336][NO_3] in organic phases,on the kinetic separatiot of Pr(Ⅲ) and Nd(Ⅲ) are discussed.The present work highlights a promising approach for separation of rare earths or other targets with extreme similarity in physicochemical properties.     

Synthesis, crystal structure and characterization of one-dimension complex constructed by terbium（III） and 2-iodobenzoate

The complex of [Tb(2-IBA)₃(H₂O)₂]_n (2-IBA=2-iodobenzoate)was prepared by solvent method from TbCl₃·6H₂O and 2-iodobenzoic acid. The crystal structure was determined with X-ray single-crystal diffraction. The X-ray diffraction analysis indicated that the title complex crystallized in triclinic crystal system and Pī space group. The Tb³⁺ ion was coordinated by six oxygen atoms from five 2-IBA ligands and two oxygen atoms from two water molecules, giving a distorted square-antiprism polyhedral geometry. The carboxyl groups were bonded to the Tb³⁺ ions with bidentate-bridging and bidentate-chelating coordination modes. The adjacent Tb³⁺ ions were linked by two bidentate-bridging 2-IBA ligands, forming 1-D chain structure. The fluorescence spectrum of the complex showed four main peaks at 489, 543, 587, and 618 nm, corresponding to ⁵D₄→⁷F_J (J=6?3) transition emissions of the Tb³⁺ ion, respectively.     

Fabrication, characterization, and electrical conductivity properties of Pr6O11 nanoparticles

Pr6O11 nanoparticles were obtained by subsequent thermal decomposition of the as-prepared precipitate formed under ambient temperature and pressure using NaOH as precipitant.The calcination process was affected,for 1 h in static air atmosphere,at 400-700 °C temperature range.The different samples were characterized using X-ray diffraction(XRD),transmission electron microscopy(TEM),field emission scanning electron microscopy(FE-SEM),thermogravimetric analysis(TGA),in situ electrical conductivity,and N 2 adsorption/desorption.The obtained results demonstrated that nano-crystalline Pr6O11,with crystallites size of 6-12 nm,started to form at 500 °C.Such value increased to 20-33 nm for the sample calcined at 700 °C.The as-synthesized Pr6O11 nanoparticles presented high electrical conductivity due to electron hopping between Pr(III)-Pr(IV) pairs.     

Structure and oxygen storage capacity of Pd/Pr/CeOe-ZrO2 catalyst： effects of impregnated praseodymia

Praseodymium （Pr） was impregnated to CeO2-ZrO2 solid solution by an impregnation method. The as-obtained Pr modi- fied CeO2-ZrO2 was impregnated with 1 wt.% Pd to prepare the catalysts. The structure and reducibility of the fresh and hydrother- really aged catalysts were characterized by X-ray diffraction （XRD）, Raman, X-ray photoelectron spectroscopy （XPS）, CO chemi- sorption and H2 temperature-programmed reduction （H2-TPR）. The oxygen storage capacity （OSC） was evaluated with CO serving as probe gas. Effects of impregnated Pr on the structure and oxygen storage capacity of catalysts were investigated. The results showed that the aged Pr-impregnated samples had much higher OSC and better reducibility than the unmodified ones. The scheme of structural evolutions of the catalysts with and without Pr was also established. Partial of the impregnated Pr diffused into the bulk of CeO2-ZrO2 during ageing, which inhibited the sintering, and increased the amount of oxygen vacancies in CeO2-ZrO2 support. Furthermore, those impregnated Pr species which covered on the surface of the support obstructed the strong metal-support interaction between Pd and Ce so as to reduce the encapsulation of Pd as well as the back spill-over of the oxygen during the catalytic process.     

Synthesis and thermal behavior of [Li(thf)_3(μ-Cl)La{N(SiMe_3)_2}_3] and its investigation as spin-coating precursor for lanthanum-based layer formation

The lanthanum(Ⅲ) complex [Li(thf)_3(μ-CI)La{N(SiMe_3)_2}_3](3) was obtained by the reaction of LaCl_3 with three equiv of Li[N(SiMe_3)_2]_3 in a tetrahydrofuran solution. The molecular structure of 3 in the solid state was characterized by a tetracoordinated anionic lanthanide(Ⅲ) amide in form of an adduct with LiCl(thf)_3 as evidenced by single crystal X-ray structure analysis. In order to study the suitability of 3 as a precursor for the deposition of La_2O_3/LiLaSiO4 by thin layer deposition techniques,its thermal behavior was investigated by thermogravimetry(TG) and TG-MS-coupled studies. TG studies show a two-step decomposition process, whereby volatile decomposition products can be detected during the second decomposition step. TG measurements under an atmosphere of oxygen produced La_2O_3, Calcination processes of 3 under ambient atmosphere for 10 h at 1000 ℃ gave La_2O_3 and LiLaSiO_4,which was confirmed by PXRD studies. Metal-organic 3 was applied as spin-coating precursor for La_2O_3 thin film formation giving the as-deposited layers nearly crack-free.     

Theoretical elucidation of rare earth extraction and separation by diglycolamides from crystal structures and DFT simulations

Diglycolamides(DGAs) show excellent application prospects for the extraction and separation of rare earth metals from highly radioactive liquid wastes and rare earth ores.The extraction ability of DGAs for rare earth ions in nitrate or chloride media increases with increasing atomic number of the rare earth metal.To understand the origin of this phenomenon,three binuclear crystals [Ln(TEDGA)3][Ln(NO_3)_6] of N,N,N',N'-tetraethyldiglycolamide(TEDGA) with rare earth ions La(Ⅲ),Pr(Ⅲ) and Eu(III) were prepared and characterized crystallographically.The three complexes belong to the triclinic crystal system,P-1 space group.The bond lengths of Ln-O_(amide) are significantly shorter than those of Ln-O_(ether) in the same crystal.The Ln-O_(amide) and Ln-O_(enher) bond lengths gradually decrease with increasing atomic number of the rare earth ion.The dihedral angle formed by TEDGA and metal ions through the tridentate coordination gradually increases with increasing metal ion atomic number,tending toward the formation of sizeable planar coordination structures for the most massive rare earth ions.The structures of the compounds formed by the extractant and metal ion were optimized by means of DFT simulations.We find that the interaction between TEDGA and the rare earth ion is dominated by electrostatic interaction by analyzing binding energy,WBIs,Mulliken charge,natural electron configurations,and molecular orbital interaction.The covalent component of the Ln-O bonds of the complexes increases with increasing metal atomic number.The observed increase in extraction and separation capacity of diglycolamides for rare earth ions with increasing atomic number might be due to the formation of two fivemember rings by one tridentate ligand.The rare earth ions with large atomic numbers tend to form planar structures with large dihedral angles with DGA ligands.     

Role of localized phonon vibration in luminescence performance of Pr doped Ba(Mg0.28Zr0.16Ta0.56)O3 transparent ceramics

Oxygen-assisted high temperature solid-state reaction approach was employed for the fabrication of Pr activated Ba(Mg_0.28Zr_0.16Ta_0.56)O₃ transparent ceramic phosphor. Retiveld refinement of X-ray diffraction pattern was carried out to reveal the lattice parameters and crystal structural information. Under the blue-light excitation of λ_ex = 473 nm, the phosphor exhibits a sharp intense red emission centered at 645 nm, accompanied by several other weak peaks. PL evolution with temperature shows a significant luminescence quenching behavior, and the underlying multi-phonon interaction with optical center is revealed by proposing an unprecedent theoretical calculation work. Such a phonon effect is further confirmed from the red-shift of peak position with temperature, and the involved phonon energy of 50.7 meV is determined from Raman scattering measurement. More interestingly, the fitted results of transient-state PL spectra show a fluctuation of luminescence lifetime at various temperatures, further indicating a significant effect of phonon vibration in the system.     

Luminescence properties and energy transfer of host sensitized CaMoO4：Tb^3＋ green phosphors

A series of CaMoO 4 :xTb 3+(x=0.01,0.03,0.05,0.07,0.09,0.15 and 0.20) phosphors in pure phase were prepared via high temperature solid-state reaction approach.The crystal structure of the phosphors was investigated by X-ray diffraction(XRD),and the optical properties were investigated by Fourier transform infrared spectroscopy(FT-IR),ultraviolet-visible spectroscopy(UV-Vis) and photoluminescence(PL) spectroscopy.The PL spectra illustrated that these phosphors could be efficiently excited by the charge transfer band of the host and the energy transfer efficiency from the host to the doped activator reached 60% when the doping concentration of the activator Tb 3+ was 20 mol.%.The concentration quenching occurred at x=10 mol.%,from which the critical distance of activator was calculated to be about 1.14 nm.The CIE coordinates were estimated to be close to the standard green value.The host sensitized samples had potential application as green phosphors.     

Structure and mechanical properties of a eutectic high-temperature Nb-Si alloy grown by directional solidification

The structure and the short-term high-temperature strength of Ni-18.7 at % Si (Nb-Nb₃Si eutectic) alloys fabricated by vacuum electron-beam zone melting and induction melting in an argon atmosphere are studied. The structure of the samples prepared by vacuum electron-beam zone melting is characterized by the presence of primary Nb₅Si₃ intermetallic precipitates and the absence of its secondary precipitates. The structure of the samples prepared by induction melting in an argon atmosphere has two characteristic zones, namely, eutectic and eutectoid ones.     

Hybrid DFT study of structural,electronic,magnetic and elastic properties of laves phase binary intermetallics RFe2(R=La,Ce,Pr and Nd)

Hybrid density functional theory was used to investigate the structural,electronic,magnetic and elastic properties of the Laves phase binary intermetallics RFe₂(R=La,Ce,Pr and Nd) in C₁₅ crystal structure.The calculated lattice constants of these materials are found in good agreement with the experiments.The band structures and density of states distribution confirm the metallic nature of all these intermetallics.The optimized energies in different magnetic phases and magne...     

A-site ordered state in manganites with perovskite-like structure based on optimally doped compounds Ln0.70Ba0.30MnO3 (Ln = Pr,Nd)

In this paper, we report on the crystal structure and magnetic properties of the nanostructured Ba-ordered phases of rare-earth manganites obtained from the optimally doped solid solutions Ln_0.70Ba_0.30MnO₃ (Ln = Pr, Nd). The materials were studied by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and SQUID-magnetometry techniques. It is found that states with different degrees of cation ordering in the A-sublattice of the ABO₃ perovskite can be obtained by employing special conditions of chemical treatment. In particular, reduction of the parent compounds results in the formation of a nanocomposite containing ferrimagnetic anion-deficient ordered phase LnBaMn₂O₅. Oxidation of the composite does not change an average size of the nanocrystallites, but drastically alters their phase composition to stabilize ferromagnetic stoichiometric ordered phase LnBaMn₂O₆ and ferromagnetic superstoichiometric disordered phase Ln_0.90Ba_0.10MnO_3+δ. It is shown that the magnetic properties of the materials are determined by the joint action of chemical (cation ordering) and external (surface tension) pressures.     

Characterization of dispersed intermetallic Phases in Rapidly Quenched Al-Ti-Ce Alloys

The microstructures of Al-3Ti-lCe (wt pct) and Al-5Ti-5Ce alloys melt-spun under controlled He atmosphere have been characterized using analytical electron microscopy. The rapidly so- lidified microstructures comprise uniform, fine-scale dispersions of intermetallic phase in an aluminum matrix, and particular attention has been given to identification of the dispersed phases. In the Al-3Ti-lCe alloy, the dispersed particles are polycrystalline with a complex twinned substructure and a diamond cubic crystal structure (α _o = 1.44 ± 0.01 nm) and composition consistent with the ternary compound Al₂₀Ti₂Ce (Al₁₈Cr₂Mg₃ structure type, space group Fd3m). In the Al-5Ti-5Ce alloy, there is, in addition to the dispersed ternary phase, a separate uniform array of fine-scale particles of the binary compound Al₁₁Ce₃. The majority of such particles have the body-centered orthorhombic structure of the low-temperature polymorph, α-Al₁₁Ce₃, but there is evidence to suggest that at least some particles developvia initial formation of the high-temperature body-centered tetragonal phase, β-Al₁₁Ce₃. The accumulated evidence sug- gests that both binary and ternary particles formed as primary phases directly from the melt during rapid solidification, leaving only small concentrations of solute in aluminum matrix solid solution. Both phases are observed to be resistant to coarsening for up to 240 hours at 400 °C.     

Synthesis,characterization and thermolysis of lanthanide metal nitrate complexes with 1, 10-phenanthroline,Part-95

The nitrate complexes of cerium, praseodymium and neodymium with 1,10-phenanthroline(phen) of general formula [Ln(phen)2(NO3)2(H2O)2]·NO3(where, Ln=Ce, Pr and Nd) were prepared and characterized by X-ray crystallography. Thermolysis of these complexes was investigated by simultaneous thermogravimetry(TG) and differential thermal analysis(DTA). Isothermal TG was taken to evaluate the kinetic parameters using model fitting as well as model free isoconversional methods. The thermolytic pathways were also suggested, which involves decomposition followed by ignition. All the three complexes had coordination number ten and showed multistep decompositions. In order to evaluate the response of rapid heating, ignition delay(Di) measurements were undertaken. The activation energies for ignition were found to decrease in the order: NdPrCe.     

Phase relations,microstructure, and valence transition studies on CaZr_(1-x)Ce_xTi_2O_7(0.0≤x≤1.0) system

In this study, Ce-doped zirconolite was synthesized through high-temperature solid-state reaction at 1250 ℃ in air for 96 h. The crystal phase.microstructure and valence transition were studied by X-ray diffraction(XRD), scanning electron microscopy(SEM), and X-ray photoelectron spectroscopy(XPS).Phase relations of CaZr_(1-x)Ce_xTi_2O_7 systems were determined by XRD analyses and Rietveld refinements.Four different phases are identified, namely zirconolite, perovskite, pyrochlore, and cerianite. The phase transformation(2M-zirconolite → 4M-zirconolite → Ce-pyrochlore) is caused by cations rearrangement as cerium content increases. The solubility limit of cerium ions in CaZr_(1-x)Ce_xTi_2O_7 system is estimated to be approximately 0.80. Under sintering air atmosphere, partial reduction of Ce~(4+) in Ce~(3+) is detected in Ce 3d XPS spectra, and the ratio of Ce~(3+) and Ce~(4+) significantly decreases as cerium content increases.     

Effects of praseodymium doping on thermoelectric transport properties of CaMnO3 compound system

The rare earth Pr doped Ca1-x Prx MnO3(x=0,0.06,0.08,0.1,0.12,and 0.14) compound bulk samples were prepared to study the effect of Pr doping on thermoelectric transport properties of CaMnO3 compound system.The doped samples exhibited single phase composition within the experimental doping range,with condensed bulk microstructure and small porosities.The electrical resistivity was remarkably reduced for doped samples,on account of the enhanced carrier concentration;the absolute value of Seebeck coefficient was deteriorated mainly due to enhanced electron carrier concentration.The electrical performances of the doped samples reflected by resistivity and Seebeck coefficient fluctuations were optimistically tuned,with an optimized power factor value of 0.342 mW/(m·K2) at 873 K for x=0.08 sample,which was very much higher comparing with that of the un-doped sample.The lattice thermal conduction was really confined,leading to distinctly repressed total thermal conductivity.The thermoelectric performance was noticeably improved by Pr doping and the dimensionless figure of merit ZT for the Ca0.92 Pr0.08 MnO3 compound was favorably optimized with the maximum value 0.16 at 873 K.     

Synthesis, fluorescence properties of Eu（III） complexes with novel carbazole functionalized β-diketone ligand

A novel carbazole functionalized β-diketone, methyl 6-(9-ethylcarbazole-3-yl)-oxoacetyl-2-pyridinecarboxylate (MEP), and its corresponding binary Eu(III) complexes Eu(MEP)₃·2H₂O and ternary complex Eu(MEP)₃Phen with 1,10-Phenanthroline (Phen) were prepared. The ligand was characterized based on elemental analysis, FT-IR, and ¹H NMR, and the complexes were characterized with elemental analysis, FT-IR and thermogravimetric and differential thermal analysis (TG-DTA). The investigation of fluorescence properties of the complexes Eu(MEP)₃·2H₂O and Eu(MEP)₃Phen showed that the Eu(III) ion could be sensitized efficiently by the ligand to some extent, in particular, in the ternary system, the secondary ligand Phen acting as a light-harvesting center was involved in the highly efficient energy transfer process, and the emission was stronger than the binary complex. In addition, the introduction of the carbazole moiety enlarged the π-conjugated system of the ligand and enhanced the luminescent intensity of the complexes.     

Glycine-nitrate auto-combustion synthesis and magnetic properties of nanocrystalline NdAlxFe1-xO3 perovskites

The effect of substitution of Fe³⁺ by Al³⁺ on the structure and magnetic properties of NdAl_xFe_1-xO₃ perovskite nano-powders(x=0.0,0.1,0.2,0.3,0.4,and 0.5) prepared by the glycine-nitrate auto-combustion method was studied.All samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR),and energy dispersive X-ray spectroscopy(EDX).The magnetic properties of the samples ...     

Hydrophilic and photocatalytic performances of lanthanum doped titanium dioxide thin films

Pure and La-doped TiO2 thin films were prepared on glass by sol-gel method using tetrabutyl titanate as Ti precursors. Their chemical composition, structure and properties were characterized by X-ray d...