Crystal growth, structural transitions, and magnetic properties of the fluorite-related osmates: Sm3OsO7, Eu3OsO7, and Gd3OsO7

The Ln3OsO7 (Ln = Sm, Eu, Gd) compounds were grown as single crystals from molten hydroxide fluxes. At temperatures above 235, 330, and 430 K, respectively, the Ln3OsO7 (Ln = Sm, Eu, Gd) compounds exist in the orthorhombic space group Cmcm. When they are cooled below these temperatures, the compounds undergo a structural phase transition 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 Os-O chains, and a reduction in the coordination of one of the rare earth cations from 8-fold to 7-fold. Sm3OsO7 and Eu3OsO7 exhibit complex magnetic behavior below about 50 K, and Gd3OsO7 shows a ferromagnetic-like order at 34 K in applied fields of less than 10 kG.     

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.     

Novel mixed-valent (V/VI) triple perovskite ruthenates: observation of a complex low-temperature structural and magnetic transition

Two new mixed-valent triple perovskites, Ba(3)MRu(2)O(9) (M = Li, Na), were grown from reactive hydroxide fluxes. They crystallize in the hexagonal space group P6(3)/mmc, where Ru(V) and Ru(VI) are disordered on only one crystallographic site. Upon cooling, single crystals of Ba(3)NaRu(2)O(9) undergo a complex symmetry-breaking structural transition at ca. 225 K from room-temperature hexagonal symmetry to a low-temperature orthorhombic symmetry, space group Cmcm. Accompanying this structural transition is a rather abrupt decrease in the magnetic susceptibility at 210 K followed by a steady decrease in the susceptibility with decreasing temperature. Interestingly, the lithium analogue does not display any structural transition down to 100 K. The structural transition in Ba(3)NaRu(2)O(9) generates three crystallographically unique Ru sites in the low-temperature structure as compared to only one distinct site in the room-temperature structure. On the basis of an analysis of the Ru-Ru distances in the face-sharing bi-octahedra, the structural transition also appears to involve charge ordering of Ru(V) and Ru(VI), causing all Ru(V) to occupy one set of bi-octahedra and all Ru(VI) to occupy another set.     

Eu4OCl6 and Eu4OBr6: Crystal growth and structure

Faint yellow transparent single crystals of Eu₄OCl₆ (1) and Eu₄OBr₆ (2) grow from fluxes that emerge from reaction mixtures containing EuX₃ (X ? Cl, br), Eu₂O₃ and lithium metal in 6:1:8 molar ratios at elevated temperatures in tantalum ampoules. Both crystallize with the Ba₄OCl₆ type structure (hexagonal, P6₃mc, Z = 2, 1: a = 944.07(4), c = 715.60(4) pm and 2: a = 982.04(4), c = 749.69(5) pm) with ?isolated”? O^2? centered Eu₄ tetrahedra.     

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 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 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.     

Synthesis and study of RbSrR(MoO4)3 ternary molybdates (R = Nd, Sm, Eu, Gd) with scheelite-like structure

Phase relations in the subsolidus region of the Rb₂MoO₄-SrMoO₄-R₂(MoO₄)₃ systems (where R = Nd, Sm, Eu, Gd) were studied by IR spectroscopy, X-ray diffraction analysis, and differential thermal analysis. RbSrR(MoO₄)₃ ternary molybdates (where R = Nd, Sm, Eu, Gd) with scheelite-like structures belonging to the monoclinic crystal system (space group P21/n) were synthesized. Their unit cell parameters were determined; IR and Raman spectra were characterized.     

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.     

Crystal structure variations in the series SrLnCuS3 (Ln = La,Pr, Sm,Gd, Er and Lu)

The crystal structures of the complex sulfides SrLnCuS₃ (Ln = Sm, Gd, Er and Lu) have been determined and refined using powder X‐ray diffraction. The crystals are found to be orthorhombic, with the structure type changing consecutively in the order BaLaCuS₃ → Eu₂CuS₃ → KZrCuS₃ as the Ln³⁺ ionic radius decreases in the order La/Pr → Sm/Gd → Er/Lu. Variations of the structure parameters along the series of compounds studied are analyzed, and an effect caused by crystallochemical contraction on the stabilization of the respective structure types is demonstrated.     

Crystal structure and fluorescence spectrum of the complex [Eu(III)(TTA)3(phen)]

The title complex Eu(III)(TTA)₃(phen) (where TTA = thenoyltrifluoroacetone monoanion; phen = 1,10-phenanthroline) has been synthesized in mixed solvents of acetone and ethanol (1:1 volume ratio) and its crystal structure has been determined by X-ray diffraction. The complex crystals are triclinic, space group P 1 (# 2) with cell dimensions of a = 1.32.41 (2) nm, b = 1.5278(4) nm, c = 0.9755(3) nm, α = 92.49 (2)°, β = 102.57(2)°, γ = 91.62(2)°, V = 1.9268(8) nm³, Z = 2, μ (Mo Ka)= 18.77 cm^?1, D_x=1.720 g/cm³. The coordination geometry of Eu atom is a distorted square antiprism, and the encapsulated structure that can meet the structural requirement of the typical europium luminescent sensor. The fluorescence spectrum suggests that the complex is a strong photoluminescent material.     

Crystal structure and photoluminescence of 7-(N,N'-diethylamino)-coumarin-3-carboxylic acid

The structure of 7-(N,N'-diethylamino)-coumarin-3-carboxylic acid (DCCA) was verified by single crystal X-ray crystallography. The UV-vis absorption and fluorescence of DCCA were discussed. The compound exhibits strong blue emission under ultraviolet light excitation. The molecular structure of DCCA was optimized using density function theory (DFT) at B3LYP/6-31G level, showing that the optimized geometers parameters are in good agreement with experiment data. In addition, the HOMO and LUMO levels of DCCA were deduced.     

Crystal structure and triboluminescence of the [Eu(TTA)2(NO3)(TPPO)2] complex

The crystal structure of [Eu(TTA)₂(NO₃)(TPPO)₂] (I) (TTA = thenoyltrifluoroacetone, TPPO = triphenylphosphine oxide) possessing intense triboluminescence was established by X-ray crystallography. The crystals are triclinic, noncentrocymmetrical: a = 11.047(3) Å, b = 11.794(3) Å, c = 12.537(3) Å; α = 102.635 (4)°, β = 102.088(4)°,γ = 117.765(3)°; space group P1, Z = 1. The central Eu(III) atom coordinates two oxygen atoms of two TPPO molecules at distances of 2.271 Å and 2.282 Å, two oxygen atoms of the nitrate group at distances of 2.478 Å and 2.481 Å, four oxygen atoms of two TTA ions at distances of 2.365 Å, 2.381 Å, and 2.363 Å, 2.371 Å (coordination number is 8). The coordination polyhedron of the Eu(III) atom is a distorted dodecahedron. Possible reasons for spectral differences in the Stark structure of photo-and triboluminescence of I are discussed.     

Eu(DBM)3qp和Eu(DBM)3pp的晶体结构及荧光性质对比研究

两种新型铕配合物Eu(DBM)₃qp(DBM=二苯甲酰甲烷,qp=喹喔啉并[2,3-i]-1,10-邻二氮杂菲)和Eu(DBM)_3pp(DBM=二苯甲酰甲烷,pp=吡嗪并[2,3-i]-1,10-邻二氮杂菲)的晶体结构均属单斜晶系,P2(1)/c空间群.中心铕离子分别与DBM配体的六个氧原子及第二配体的两个鳌合氮原子配位,形成八配位的扭曲四方反棱柱构型.两种配合物晶体中,每四个配合物分子的第二配体共轭平面相互平行,形成一种特殊的"块"状π-π堆积单元.在紫外光激发下两种配合物均表现为Eu³⁺的特征发射,由于第二配体能级的不同,Eu(DBM)_3pp的发射强度比Eu(DBM)_3qp高十几倍.     

Photoluminescence characterization of Ca10Na(PO4)7:Eu3+ red-emitting phosphor

Eu3+-doped Ca10Na(PO4)7 phosphors were successfully synthesized by solid-state reaction techniques. Their structures and photoluminescence characteristics were carefully studied. An efficient red emission under near-ultraviolet excitation is observed. The maximum intensity of luminescence was observed at the Eu3+ concentration around 9 mol%. The quadrupole-quadrupole interaction between Eu3+ ions is the dominant mechanism for concentration quenching of fluorescence emission from Eu3+ ions in Ca10-xNa(PO4)7:xEu3+. Due to the excitation spectrum is well coupled with near UV light, Ca10-xNa(PO4)7:xEu3+ phosphors have potential application as red phosphors in near UV chip-based white light emitting diodes.     

Crystal structure of Bi(0.9)Sm(0.1)Fe(1-x)Mn(x)O3 multiferroics

Bi(0.9)Sm(0.1)Fe(1-x)Mn(x)O(3), with x=0.00, 0.15, 0.30 have been synthesised by solid-state reaction. The structures of the materials, characterised via Rietveld analysis of high resolution powder neutron diffraction data, reveal a structural transition from R3c to orthorhombic Imma symmetry is complete for the x=0.30 sample. The antiferromagnetic ordering temperature, magnitude of the ordered magnetic moment at the B-site, and the dielectric constant all decrease as a function of increasing Mn content.     

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,structure, and properties of manganese orthovanadate Mn3(VO4)2

Manganese orthovanadate Mn₃(VO₄)₂ single crystals were grown for the first time from a flux of MnO/V₂O₅/MoO₃. The flux and oxygen partial pressure used are the key factors for the crystal growth and prevention of the oxidation of Mn²⁺ and the reduction of V⁵⁺ during the crystallization process. The reduction and oxidation chemistry of Mn₃(VO₄)₂ was studied. Mn₃(VO₄)₂ is isostructural with magnesium orthovanadate Mg₃(VO₄)₂, orthorhombic, space group Cmca, a=6.247(1) Å, b=11.728(2) Å, c=8.491(2) Å and Z=4, as determined by single crystal X-ray diffraction. Because it is a Mn²⁺ deficient spinel structure there are two-dimensional sheets of Mn²⁺O₆ octahedra within the structure which show unusual ferrimagnetic properties.