Crystal growth, observation, and characterization of the low-temperature structure of the fluorite-related ruthenates: Sm(3)RuO(7) and Eu(3)RuO(7)

The compounds Sm(3)RuO(7) and Eu(3)RuO(7) were grown as single crystals from molten hydroxide fluxes. They crystallize in the orthorhombic space group Cmcm and are part of a well-known family of fluorite-related oxides of stoichiometry Ln(3)MO(7). This structure contains rare earth cations in two different coordination environments, 8-fold pseudocubic and 7-fold pentagonal bipyramidal, and contains Ru(V) cations that are octahedrally coordinated. The RuO(6) octahedra are trans vertex-sharing to yield chains oriented along the c-axis. Upon cooling, single crystals of Sm(3)RuO(7) and Eu(3)RuO(7) undergo a structural transition at 190 and 280 K, respectively, from space group Cmcm to P2(1)nb. The structure transition results in a loss of lattice centering, a doubling of the b-axis, a distortion of the vertex-shared Ru-O chains, and a reduction in the coordination of one of the rare earth cations from 8-fold to 7-fold. Accompanying this structural transition are anomalies in the magnetic susceptibility at about 190 and 280 K for Sm(3)RuO(7) and Eu(3)RuO(7), respectively. The structures of these low-temperature phases of Ln(3)RuO(7) have been determined for the first time and are described.     

Crystal growth,structures, magnetic and photoluminescent properties of NaLnGeO4 (Ln = Sm,Eu, Gd,Tb)

Single crystals of NaLnGeO₄ (Ln = Sm, Eu, Gd) were grown out of a molten sodium hydroxide flux, and their crystal structures were determined by single crystal X-ray diffraction. The lanthanide containing germanates crystallize in the orthorhombic space group of Pnma, and exhibit a complex three-dimensional structure consisting of corner- or edge-shared LnO₆, GeO₄, and NaO₆ polyhedra. UV–vis diffuse reflectance spectra indicated that the reported oxides are insulating materials with wide band gaps. The magnetic susceptibility data shows paramagnetic behavior. For the NaEuGeO₄ and NaTbGeO₄ compositions intense room temperature photoluminescence was observed.     

Crystal growth of Ln3GaO6 (Ln = Nd, Sm, Eu and Gd): Structural and optical properties

Single crystals of Ln₃GaO₆ (Ln = Nd, Sm, Eu, Gd) were grown out of a reactive high temperature hydroxide melt. The structures were solved by single-crystal X-ray diffraction. These gallium oxides crystallize in the polar space group Cmc2₁ where the orientation of the GaO₄ tetrahedra determines the polarity of the structure. The atomic positions along with the determination of the absolute structure are reported. The lanthanide atoms are located in a seven-fold coordination environment forming edge-sharing zigzag-chains. The photoluminescence was investigated and the europium and gadolinium members of this series exhibit intense luminescence in the visible portion of the spectrum.     

Crystal growth of a new series of non-centrosymmetric oxides,Ln3FeO6 (Ln = La,Nd, Sm,Eu and Gd)

Single crystals of Ln₃FeO₆ (Ln = La, Nd, Sm, Eu, Gd) were grown out of a high temperature hydroxide melt. The crystal structures were determined by single crystal X-ray diffraction. These oxides crystallize in the polar space group Cmc2₁ where the orientations of the FeO₄ tetrahedra determine the polarity of the structure. The lanthanide atoms are located in a seven-fold, square face mono-capped trigonal prismatic coordination environment; these polyhedra are edge-shared to form zig-zag chains.     

Crystal structures, magnetic and thermal properties of Ln3IrO7 (Ln=Pr, Nd, Sm, and Eu)

Ternary iridium oxides Ln₃IrO₇ (Ln=Pr, Nd, Sm, and Eu) were prepared and their crystal structures, magnetic and thermal properties were investigated. Powder X-ray diffractions (XRDs) were measured for all samples and neutron diffraction (ND) measurements were performed for Pr₃IrO₇. All the profiles were refined with space group Cmcm (No. 63). The lattice parameters for Pr₃IrO₇ refined by using ND data are a=10.9782(13) Å, b=7.4389(9) Å, and c=7.5361(9) Å. From specific heat and differential thermal analysis (DTA) measurements, Ln₃IrO₇ (Ln=Pr, Nd, Sm, and Eu) show thermal anomalies at 261, 342, 420, and 485 K, respectively. The results of powder high-temperature XRD and ND measurements indicate that these anomalies are due to the structural phase transition. Magnetic susceptibilities of these compounds were measured in the temperature range between 1.8 and 400 K. Nd₃IrO₇ shows an antiferromagnetic transition at 2.6 K. A specific heat anomaly has also been observed at the same temperature. For Ln₃IrO₇ (Ln=Pr, Sm, and Eu), no magnetic anomalies have been found in the experimental temperature range.     

Studies on phase transition temperature of rare earth niobates Ln3NbO7 (Ln = Pr,Sm, Eu) with orthorhombic fluorite-related structure

The phase transition of ternary rare earth niobates Ln₃NbO₇ (Ln = Pr, Sm, Eu) was investigated by the measurements of high-temperature and low-temperature X-ray diffraction, differential scanning calorimetry (DSC) and differential thermal analysis (DTA). These compounds crystallize in an orthorhombic superstructure derived from the structure of cubic fluorite (space group Pnma for Ln = Pr; C222₁ for Ln = Sm, Eu). Sm₃NbO₇ undergoes the phase transition when the temperature is increased through ca. 1080 K and above the transition temperature, its structure is well described with space group Pnma. For Eu₃NbO₇, the phase transition was not observed up to 1273 K Pr₃NbO₇ indicates the phase transition when the temperature is increased through ca. 370 K. The change of the phase transition temperature against the Ln ionic radius for Ln₃NbO₇ is quite different from those for Ln₃MO₇ (M = Mo, Ru, Re, Os, or Ir), i.e., no systematic relationship between the phase transition temperature and the Ln ionic radius has been observed for Ln₃NbO₇ compounds.     

稀土元素Sm、Eu、Gd对Nb掺杂的TiO2压敏电阻电性能的影响

研究了稀土元素Sm、Eu、Gd对于Nb掺杂的TiO₂基压敏电阻电学性能的影响. 几种稀土元素的掺杂量均为体系总量的2%(原子比), 其它原料的掺入量固定不变. 实验样品在1380 ℃烧结, 保温4 h. 实验发现, Sm、Eu、Gd等稀土元素可以有效降低TiO₂基压敏电阻的压敏电压, 但对于非线性系数的影响不很明显. 对于Sm、Eu、Gd掺杂, 实验得到的压敏电压值分别为12.7、14.7和16.1 V. 通过对试样的阻抗分析发现, Sm、Eu、Gd掺杂对于压敏电阻的介电性能有显著影响, 单独掺杂Sm或Gd的试样具有很低的介电常数和介电损耗, 并且具有很高的电阻率.     

Synthesis and properties of europium-based phosphors on the nanometer scale: Eu2O3, Gd2O3:Eu, and Y2O3:Eu

Nanocrystals of oxides containing europium as the main constituent or as a doping element in RE2O3 ( RE=Y, Gd) have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by high-resolution TEM, absorption spectroscopy, and luminescence spectroscopy. The samples obtained consisted of concentrated and colloidally stable suspensions of luminescent oxide nanoparticles with an average grain diameter in the range 2-5 nm. The nanoparticles were found to be highly crystalline despite their ultrasmall size and the low temperature of 180 degrees C applied during the synthesis. Upon UV excitation, the red luminescence relative to the 5D0-->7Fn transition within the cubic form of RE2O3 exhibits some important differences from that usually found in bulk materials.     

Preparation, characterization, magnetic susceptibility (Eu, Gd and Sm) and XPS studies of Ln2ZrTiO7 (Ln=La, Eu, Dy and Gd)

Bulk and nanosized pyrochlore materials Ln₂ZrTiO₇ (Ln=La, Eu, Dy, Gd and Sm) have been prepared by the sol-gel method. All the samples were characterized by powder X-ray diffraction, Raman and X-ray photoelectron spectroscopy. Magnetic susceptibility (χ) measurements of Gd₂ZrTiO₇, Sm₂ZrTiO₇ and Eu₂ZrTiO₇ were carried out by vibrating sample magnetometer in the temperature range 2-320 K. The variation of χ⁻¹ (or χ) with temperature of Gd₂ZrTiO₇, Sm₂ZrTiO₇ and Eu₂ZrTiO₇ follows the Curie law, intermediate formula and the Curie-Weiss law, respectively. From the linear portion of χT vs. T⁻¹ plot of Eu₂ZrTiO₇ from 2 to 15 K, the classical nearest neighbor exchange (J^cl) and dipolar interactions (D_nn) are obtained. The XPS of Ln₂ZrTiO₇ (Ln=La, Eu, Dy and Gd) gave characteristic peaks for Ln, Ti, Zr and O. The satellite peaks are observed only for 3d La of La₂ZrTiO₇.     

Crystal growth and anisotropic magnetic properties of V3O7

Needle-like crystals of V₃O₇ up to 2 mm in length were grown by a chemical vapor transport method using NH₄Cl as a transport agent. The anisotropic magnetic susceptibility was measured for the first time. At 2 K, a spin-flop transition occurs under a magnetic field of 0.1 T. V₃O₇ is proved to be a uniaxial antiferromagnet with its easy axis parallel to the b-axis of monoclinic structure. A spin structure with antiferromagnetic interaction between layers and ferromagnetic interaction in the layers below the Néel temperature (5.2 K) is suggested.     

Crystal structures and magnetic properties of fluorite-related oxides Ln3NbO7 (Ln=lanthanides)

Crystal structures and magnetic properties of the ternary oxides Ln₃NbO₇ (Ln=La, Pr, Nd, Sm-Lu) are reported. Their powder X-ray diffraction measurements and Rietveld analyzes show that they have the fluorite-related structures with space group Pnma (Ln=La, Pr, Nd), C222₁ (Ln=Sm-Tb), or Fm-3m (Ln=Dy-Lu). Magnetic susceptibility measurements were carried out from 1.8 to 400 K. The Ln₃NbO₇ compounds for Ln=Pr, Gd, Dy-Yb show Curie-Weiss paramagnetic behavior, and Sm₃NbO₇ and Eu₃NbO₇ show van Vleck paramagnetism. On the other hand, two magnetic anomalies were observed for both Nd₃NbO₇ (0.6 and 2.7 K) and Tb₃NbO₇ (2.0 and 3.2 K). From the results of specific heat measurements, it was found that these anomalies are due to the antiferromagnetic ordering of Ln ions in two different crystallographic sites (the 8-coordinated and 7-coordinated sites).     

Cationic lanthanide monoporphyrinates with Sm, Eu, Gd and Tb, synthesis and spectroscopic properties in aqueous and non-aqueous media

The synthesis of a new series of cationic monoporphyrinates with “light” lanthanide ions is reported. The meso-tetrakis(4-pyridyl)porphyrin, (tpyp)H₂, was used as the tetrapyrrole ligand, and the metallation reaction with the lanthanide ions in acetyl-acetonato form, leading to Ln(tpyp)acac, where Ln = Sm, Eu, Gd and Tb, was carried out. The cationic monoporphyrinates, Ln(tmepyp)acac, were synthesized via the corresponding Ln(tpyp)acac. These complexes are freely soluble in aqueous and non-aqueous solutions, like MeOH, H₂O or N,N-dimethylformamide. Their spectroscopic properties in water and DMF solutions are reported. All the complexes were characterized on the basis of their UV-vis, IR and ESR data. No ESR spectra were obtained for cationic porphyrins in DMF for Sm, Eu and Tb, while the spectra of Gd(tmepyp)acac in DMF exhibits smaller ΔH_pp (103.1 G) among the spectra of Gd^III complexes. The unexpected broad signal of Eu(t-mepyp)acac, ΔH_pp = 126.9 G, in H₂O is discussed in terms of the formal oxidation state +2 for the central ion.     

Synthesis, structure, solid-state thermal decomposition and magnetic properties of binuclear Nd, Gd and Eu cymantrenecarboxylates

New rare-earth cymantrenecarboxylates [Nd₂(μ₂-OOCCym)₄(OOCCym)₂(THF)₄] (1) and [Ln₂(μ₂-OOCCym)₄(OOCCym)₂(THF)₄]·THF (Ln = Gd (2), Eu (3); Cym = (η⁵-C₅H₄)Mn(CO)₃) were synthesized starting from carboxycymantrene and lanthanide nitrates, and characterized by X-ray diffraction. The crystals of 1-3 consist of isolated binuclear molecules; the Ln atoms are eight-coordinate. The magnetic properties of 2 are indicative of antiferromagnetic coupling between the Gd atoms at liquid helium temperature. The thermal decomposition of complexes 1-3 was studied by differential scanning calorimetry (DSC) and thermogravimetry (TG). According to the X-ray powder diffraction patterns, the thermal decomposition of the complexes in air affords a mixture of LnMn₂O₅ and Mn₂O₃ as the final products.     

原子吸收光谱测定Sm-Eu-Gd富集物中Sm、Eu、Gd

本文制定了N_2O-C_2H_2焰原子吸收光谱直接测定Sm-Eu-Gd富集物中Sm、Eu和Gd的分析方法。采用氧化镧溶液作为缓冲剂消除干扰提高灵敏度。此法不需要复杂的分离过程。方法简便、快速、成本低、适合工厂采用。     

同位素稀释质谱法测定U3O8中痕量Sm,Eu,Gd和Dy

建立了分析U_3O_8中痕量Sm、Eu、Gd和Dy的IDMS法。在一条灯丝上一次涂样完成4个相对含量10~(-8)的元素测定。方法较简便,测定含Sm、Eu、Gd和Dy分别为8.90×10~(-8)、9.07×10~(-8)、8.65×10~(-8)和8.47×10~(-8)的U_3O_8试样,方法精密度分别为±4.2%、±3.5%、±4.8%和±4.1%。本法与其他方法相比结果相符。测Gd,~(176)〔~(160)Dy~(16)O〕~+与~(176)〔~(160)Gd~(16)O〕~+有叠加。通过测定~(160)Dy~+峰高计算出~(176)〔~(160)Dy~(16)O〕~+峰高,从而校正~(176)〔~(160)Gd~(16)O〕~+峰高。     

Synthesis and properties of the TTA/Gd2O3: Eu3+ luminescent system

Journal of Sol-Gel Science and Technology - Hybrid materials based on lanthanide ions or lanthanide-doped nanostructured particles have received a lot of recent attention because organic ligands...     

Structural and magnetic properties of Gd3N@C80

Using relativistic and on-site correlation-corrected density functional theory, we have investigated the structural and magnetic properties of recently synthesized Gd3N@C80. The most stable structure of Gd3N@C80 has the three magnetic Gd ions pointing to the centers of hexagons in C80. The magnetic ground state of this structure has the three coplanar spins (S = 7/2) offset by 120 degrees angles. At the same time, the state with the highest multiplicity, where all the spins are parallel aligned, is found only about 4.5 meV higher in energy. Therefore, at room temperature, we expect Gd3N@C80 to be paramagnetic with the spin fluctuating between different multiplicities. As a result, Gd3N@C80 may exhibit greater proton relaxivity than Gd@C60 and Gd@C82 and serve as a possible candidate for the next generation of commercially available magnetic resonance imaging contrast agents.     

Laser-induced breakdown spectroscopy for simultaneous determination of Sm, Eu and Gd in aqueous solution

This paper reports studies on the determination of trace levels of samarium, europium and gadolinium in aqueous samples by laser-induced breakdown spectroscopy (LIBS). In this work, a membrane-based filter paper was used as a sample support for the liquid samples. The laser-induced plasma was produced in air at atmospheric pressure, using a pulsed Nd:YAG laser. Calibration standards and synthetic mixtures of these lanthanides were prepared using solutions prepared from respective high purity oxides. Linear calibration was obtained for Sm, Eu and Gd by normalizing the intensities of lanthanides emission lines with respective to C(I) 193.029 nm emission line. The concentrations of Sm, Eu and Gd were then determined in a solution containing a mixture of these lanthanides. The concentrations of individual lanthanides were obtained within 5% of the expected values. Limits of detection were found to be 1.3 ppmw (Sm), 1.9 ppmw (Eu) and 2.3 ppmw (Gd).     

Judd-Ofelt intensity parameters and spectral properties of Gd2O3:Eu3+ nanocrystals

Three nonequivalent centers of Cs (A, B, and C) in monoclinic phase and C2 and S6 centers in cubic phase were identified in the Gd2O3:Eu3+ nanocrystals with spectral techniques. Size dependence in the spectra indicated that the excitations from both host and charge-transfer band (CTB) for the 5D0 --> 7F2 transition of Eu3+ ions were nearly equal for a larger size of 135 nm of the cubic phase; however, with decreasing the size to or less than 23 nm, the excitations by the CTB dominated. The variation of excitation leading to the symmetry and energy change in the C2 and S6 sites was also observed for larger particle sizes. The Judd-Ofelt intensity parameters Omega(lambda) (lambda = 2, 4) for Gd2O3:Eu3+ nanoparticles were experimentally determined. The parameters Omega(lambda) were found to significantly change with the sizes of Gd2O3:Eu3+ from nanoparticles to bulk material. With decreasing the size from 135 to 15 nm, the quantum efficiencies for 5D0 reduced from 23.6% to 4.6% due to the increasing ratio of surface to volume.