Synthesis and structural study of the new rare earth magnesium borates LnMgB5O10 (Ln = La, …, Er)

To obtain rare earth luminescent materials with weak concentration quenching, the B₂O₃-rich portion of the ternary diagram Ln₂O₃MgOB₂O₃ (Ln = rare earth) has been investigated. A ternary phase of composition LnMgB₅O₁₀ has been found for Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er. These compounds all crystallize in the monoclinic space group $\text{P2}{}_1\text{c}$. The structure has been determined on a LaMgB₅O₁₀ crystal. A full-matrix least-squares refinement leads to R = 0.039. The structure can be described as being made of (B₅O₁₀^5?)_n two-dimensional layers linked together by the lanthanum and magnesium ions. The rare earth atom coordination polyhedra form isolated chains. These borates are isostructural with some rare earth cobalt borates.     

Magnetic properties of EuLn2O4 (Ln=rare earths)

Ternary rare earth oxides EuLn₂O₄ (Ln=Gd, Dy-Lu) were prepared. They crystallized in an orthorhombic CaFe₂O₄-type structure with space group Pnma. ¹⁵¹Eu Mössbauer spectroscopic measurements show that the Eu ions are in the divalent state. All these compounds show an antiferromagnetic transition at 4.2-6.3 K. From the positive Weiss constant and the saturation of magnetization for EuLu₂O₄, it is considered that ferromagnetic chains of Eu²⁺ are aligned along the b-axis of the orthorhombic unit cell, with neighboring Eu²⁺ chains antiparallel. When Ln=Gd-Tm, ferromagnetically aligned Eu²⁺ ions interact with the Ln³⁺ ions, which would overcome the magnetic frustration of triangularly aligned Ln³⁺ ions and the EuLn₂O₄ compounds show a simple antiferromagnetic behavior.     

Crystal growth, structure and magnetic properties of the double perovskites Ln2MgIrO6 (Ln=Pr, Nd, Sm-Gd)

Single crystals of double-perovskite type lanthanide magnesium iridium oxides, Ln₂MgIrO₆ (Ln=Pr, Nd, Sm-Gd) have been grown in a molten potassium hydroxide flux. The compounds crystallize in a distorted 1:1 rock salt lattice, space group P2₁/n, consisting of corner shared MO₆ (M=Mg²⁺ and Ir⁴⁺) octahedra, where the rare earth cations occupy the eight-fold coordination sites formed by the corner shared octahedra. Pr₂MgIrO₆, Nd₂MgIrO₆, Sm₂MgIrO₆, and Eu₂MgIrO₆ order antiferromagnetically around 10-15 K.     

Spectroscopic properties of Ln2MoO6:Eu3+

The spectroscopic properties of Ln₂MoO₆:Eu³⁺ (Ln = La, Gd, Y) compounds were investigated. The differences in the recorded fluorescence spectra are in accord with the different structures. For the La₂MoO₆:Eu³⁺ case, the spectrum is compatible with a C₂ point site symmetry. It appears that the energy level scheme is connected with the rare earth oxychloride one, so it is possible to determine accurately sets of crystal field parameters simulating the spectrum. For the other compounds, the Eu³⁺ ions occupy three different point sites. By using the site-selective excitation on the ⁵D₀ level it is possible to identify the energy level scheme characterizing each point site.     

Ln(GaM2+)O4 and Ln(AlMn2+)O4 compounds having a layer structure [Ln = Lu,Yb, Tm,Er, Ho,and Y,and M = Mg,Mn, Co,Cu, and Zn]

A series of new compounds Ln(GaM²⁺)O₄ and Ln(AlMn²⁺)O₄ having a layer structure were successfully prepared [Ln = Lu, Yb, Tm, Er, Ho, and Y, and M = Mg, Mn, Co, Cu, and Zn]. The synthesis conditions and the unit cell parameters for 23 compounds have been determined. These compounds are isostructural with YbFe₂O₄ (space group $\text{R}\text{3}\text{m, a = 3.455(1)}$ Å, and c = 25.109(2) Å).     

High-throughput and microwave investigation of rare earth phosphonatoethanesulfonates—Ln(O3P-C2H4-SO3) (Ln=Ho, Er, Tm, Yb, Lu, Y)

Following the strategy of using bifunctional phosphonic acids for the synthesis of new metal phosphonates, the flexible ligand 2-phosphonoethanesulfonic acid, H₂O₃P-C₂H₄-SO₃H (H₃L), was used in a high-throughput (HT) and microwave investigation of rare earth phosphonatoethanesulfonates. The HT-investigation led to six isotypic compounds Ln(O₃P-C₂H₄-SO₃) with Ln=Ho (1), Er (2), Tm (3), Yb (4), Lu (5) and Y (6). The syntheses were scaled-up in glass reactor tubes in order to obtain larger amounts for a detailed characterization. Based on these results all compounds could be also synthesized by microwave-assisted heating and the influence of reaction time and stirring rate during the synthesis was established. For compound 2 the crystal structure was determined by single-crystal X-ray diffraction. The compounds contain isolated slightly distorted LnO₆ octahedra that are connected by the phosphonate and sulfonate groups into a three-dimensional framework. Thermogravimetric investigations demonstrate the high thermal stability of the compounds up to 460 °C.     

Raman scattering study and electrical properties characterization of elpasolite perovskites Ln2(BB′)O6 (Ln=La, Sm…Gd and B,B′=Ni, Co, Mn)

Two series of elpasolite perovskites Ln₂CoMnO₆ and Ln₂NiMnO₆ (Ln=La, Pr, Nd, Sm, Gd) have been prepared. The electronic band gap and magnetic Curie temperature vary systematically as a function of the rare earth cation size within both series. Here we used Raman scattering spectroscopy along with the results of previous structural studies to show that there is little change in octahedral distortion but significant changes in the octahedral tilting angle upon decreasing lanthanide ionic radius. The data indicate differences in the orbital overlap and bond strengths between the two series of materials that allow us to understand variations in the magnetic and electrical properties within and between the two perovskite series.     

Synthesis and characterization of monodisperse spherical SiO2@RE2O3 (RE=rare earth elements) and SiO2@Gd2O3:Ln (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles with core-shell structure

Spherical SiO₂ particles have been coated with rare earth oxide layers by a Pechini sol-gel process, leading to the formation of core-shell structured SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence spectra as well as lifetimes were used to characterize the resulting SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺, Er³⁺, Ho³⁺) samples. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 380 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (40 nm for two deposition cycles). Under the excitation of ultraviolet, the Ln³⁺ ion mainly shows its characteristic emissions in the core-shell particles from Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Sm³⁺, Dy³⁺, Er³⁺, Ho³⁺) shells.     

Syntheses, crystal structures and vibrational spectra of KLn(SO4)2·H2O (Ln=La, Nd, Sm, Eu, Gd, Dy)

The potassium lanthanide double sulphates KLn(SO₄)₂·H₂O (Ln=La, Nd, Sm, Eu, Gd, Dy) were obtained by evaporation of aqueous reaction mixtures of rare earth (III) sulphates and potassium thiocyanate at 298 K. X-ray single-crystal investigations show that KLn(SO₄)₂·H₂O (Ln=Nd, Sm, Eu, Gd, Dy) crystallise monoclinically (Ln=Sm: P2₁/c, Z=4, a=10.047(1), b=8.4555(1), c=10.349(1) Å, wR2=0.060, R1=0.024, 945 reflections, 125 parameters) while KLa(SO₄)₂·H₂O adopts space group P3₂21 (Z=3, a=7.1490(5), c=13.2439(12) Å, wR2=0.038, R1=0.017, 695 reflections, 65 parameters). The coordination environment of the lanthanide ions in KLn(SO₄)₂·H₂O is different in the case of the Nd/Sm/Gd and the Eu/Dy compounds, respectively. In the first case the Ln atoms are nine-fold coordinated in contrast to the latter where the Ln ions are eight-fold coordinated by oxygen atoms. The vibrational spectra of KLn(SO₄)₂·H₂O and the UV-vis reflection spectra of KEu(SO₄)₂·H₂O and KNd(SO₄)₂·H₂O are also reported.     

Structures and magnetic properties of Ln3OsO7 (Ln=Pr,Nd,Sm)

Polycrystalline samples of Ln₃OsO₇ (Ln=Pr,Nd,Sm) have been prepared. The structures of these compounds were determined by X-ray powder diffraction. They crystallize in a superstructure of cubic fluorite (space group Cmcm, Z=4). The samples have been characterized by magnetometry. The compounds show complex magnetic behavior at low temperatures caused by competing magnetic interactions leading to frustration.     

Hexagonal perovskite-intergrowth manganates: Ln2Ca2MnO7 (Ln=La, Nd and Sm)

Two structures, all consisting of alternative stacking of hexagonal perovskite layer and graphite-like Ca₂O layer, were identified in Ln₂Ca₂MnO₇ systems (Ln=La, Nd and Sm). La₂Ca₂MnO₇ (1), crystallizing in the space group with the lattice constants a=5.62231(7)  Å and c=17.3192(4) Å, contains almost ideal close packed [LnO₃] arrays. While for the smaller rare earth cations, e.g., Nd₂Ca₂MnO₇ (2) and Sm₂Ca₂MnO₇ (3), the structure distorts to large unit cell (a′=2a and c′=c). Study of the substituted systems, LnLn′Ca₂MnO₇ (Ln or Ln′=La, Ce, Pr, Nd, Sm, Eu, Gd) and La_2−xSm_xCa₂MnO₇, shows a phase transformation from (1) to (2) at certain value of cation size. The MnO₆ octahedra in these compounds are isolated, thus the magnetic property is mainly paramagnetic.     

Magnetic Properties of LnMnO3 (Ln=Ho, Er, Tm, Yb, and Lu)

Magnetic data are presented for LnMnO₃ (Ln=Ho, Er, Tm, Yb, and Lu) having the hexagonal crystal structure of P6₃cm. DC magnetization measurements show that magnetic order is not clearly observed for Ln=Ho-Yb, while an antiferromagnetic transition of the Mn³⁺ moments is found at ∼90 K for LuMnO₃, where the Lu³⁺ ion has no 4f localized moment. This is ascribed to both the paramagnetism of Ln³⁺ and the suppression of magnetization in the Mn³⁺ sublattices arising from strong antiferromagnetic interactions between Mn³⁺. Deviation from the Curie-Weiss law at low temperatures indicates the onset of antiferromagnetism. Some magnetization data of Ca-substituted compounds, Ln_0.5Ca_0.5MnO₃, which have the different crystal structure of orthorhombic Pnma, are also discussed briefly.     

Magnetic properties of orthorhombic fluorite-related oxides Ln3SbO7 (Ln=rare earths)

Ternary rare earth antimonates Ln₃SbO₇ (Ln=rare earths) were prepared and their structures were determined by X-ray diffraction measurements. They crystallize in an orthorhombic superstructure of cubic fluorite (space group Cmcm for Ln=La, Pr, Nd; C222₁ for Ln=Nd-Lu), in which Ln³⁺ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). Their magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 1.8 to 400 K. The Ln₃SbO₇ (Ln=Nd, Gd-Ho) compounds show an antiferromagnetic transition at 2.2-3.2 K. Sm₃SbO₇ and Eu₃SbO₇ show van Vleck paramagnetism. Measurements of the specific heat down to 0.4 K for Gd₃SbO₇ and the analysis of the magnetic specific heat indicate that the antiferromagnetic ordering of the 8-coordinated Gd ions occur at 2.6 K, and the 7-coordinated Gd ions order at a furthermore low temperature.     

The crystal growth and magnetic properties of Ln2LiIrO6 (Ln=La, Pr, Nd, Sm, Eu)

Single crystals of a series of lanthanide lithium iridium oxides, Ln₂LiIrO₆ (Ln=La, Pr, Nd, Sm, Eu) with the double perovskite structure have been grown from molten LiOH/KOH fluxes. The compounds crystallize in a distorted 1:1 rock salt lattice of Li⁺ and Ir⁵⁺ cations in the monoclinic space group P2₁/n. The magnetic susceptibilities of Ln₂LiIrO₆ (Ln=Pr, Nd, Sm, Eu) are presented.     

Seven new rare-earth transition-metal oxychalcogenides: Syntheses and characterization of Ln4MnOSe6 (Ln=La, Ce, Nd), Ln4FeOSe6 (Ln=La, Ce, Sm), and La4MnOS6

The quaternary oxychalcogenides Ln₄MnOSe₆ (Ln=La, Ce, Nd), Ln₄FeOSe₆ (Ln=La, Ce, Sm), and La₄MnOS₆ have been synthesized by the reactions of Ln (Ln=La, Ce, Nd, Sm), M (M=Mn, Fe), Se, and SeO₂ at 1173 K for the selenides or by the reaction of La₂S₃ and MnO at 1173 K for the sulfide. Warning: These reactions frequently end in explosions. These isostructural compounds crystallize with two formula units in space group of the hexagonal system. The cell constants (a, c in Å) at 153 K are: La₄MnOSe₆, 9.7596(3), 7.0722(4); La₄FeOSe₆, 9.7388(4), 7.0512(5); Ce₄MnOSe₆, 9.6795(4), 7.0235(5); Ce₄FeOSe₆, 9.6405(6), 6.9888(4); Nd₄MnOSe₆, 9.5553(5), 6.9516(5); Sm₄FeOSe₆, 9.4489(5), 6.8784(5); and La₄MnOS₆, 9.4766(6), 6.8246(6). The structure of these Ln₄MOQ₆ compounds comprises a three-dimensional framework of interconnected LnOQ₇ bicapped trigonal prisms, MQ₆ octahedra, and the unusual LnOQ₆ tricapped tetrahedra.     

LnSrScO4 (Ln=La, Ce, Pr, Nd and Sm) systems and structure correlations for A2BO4 (K2NiF4) structure types

The compounds LnSrScO₄, where Ln=La, Ce, Pr, Nd and Sm, have been synthesized. Rietveld profile analysis of powder X-ray diffraction data collected at room temperature reveal that the compounds possess a modified K₂NiF₄-type structure with orthorhombic cell symmetry formed by tilting of the ScO₆ octahedra. Variable temperature (25-1200 °C) powder X-ray diffraction data show that at the highest temperatures the structures of LaSrScO₄ and PrSrScO₄ transform to the regular tetragonal K₂NiF₄-structure type but the degree of orthorhombicity (c/a) in the unit cells initially increases on heating for all materials, reaching a maximum near 300 °C. This structural behavior is analyzed in terms of relative ionic radii of the various lanthanides and scandium. A general structural model based on tolerance factors has been developed for the family of materials A₂BO₄ with various A and B cation sizes.     

Rare-earth cobalticyanides LnCo(CN)6·nH2O

Crystalline cobalticyanides LnCo^III(CN)₆·nH₂O with Ln = La,…, Lu, Y have been synthesized by a double-infusion technique. In analogy to the Cr and Fe compounds, the large rare-earth ions form a hexagonal modification while the smaller ions lead to the orthorhombic structure with 4H₂O. Experiments show that no magnetic ordering occurs down to 1°K. The Stark splitting of the J ground state due to the crystalline field is analyzed for the Ce and Sm compounds.     

Synthesis and magnetic properties of rare earth ruthenates, Ln5Ru2O12 (Ln=Pr, Nd, Sm-Tb)

Single crystals of Ln₅Ru₂O₁₂ (Ln=Pr, Nd, Sm-Tb) were grown out of either NaOH or KOH fluxes in sealed silver tubes. The crystals of all the phases were observed to be twinned as confirmed by TEM studies. The series crystallize in the C2/m monoclinic system with lattice parameters, a=12.4049(4)-12.7621(6) Å, b=5.8414(2)-5.9488(3) Å, c=7.3489(2)-7.6424(4) Å, β=107.425(3)-107.432(2)° and Z=2. The crystal structure is isotypic with the defect/disorder model of Ln₅Re₂O₁₂ (Ln = Y, Gd) and consists of one dimensional edge shared RuO₆ octahedral chains separated by a two dimensional LnO_x polyhedral framework. Magnetic measurements indicate paramagnetic and antiferromagnetic behavior for Ln=Nd, Sm-Gd and Ln=Tb, respectively.     

Crystal structures of lanthanide and zirconium phosphates with general formula Ln0.33Zr2(PO4)3, where Ln=Ce, Eu, Yb

Crystal structures of synthetic phosphates Ce_0.33Zr₂(PO₄)₃, Eu_0.33Zr₂(PO₄)₃ and Yb_0.33Zr₂(PO₄)₃ have been refined by Rietveld method using powder diffraction data. Unit cell parameters: a=8.7419 (4), c=23.128 (2) Å; a=8.7659 (1), c=22.822 (1) Å; a=8.8078 (4), c=22.485 (3) Å, respectively; Z=6. Values of final R-factors in isotropic approximation: R_wp=4.00, R_wp=3.33, R_wp=4.12%, respectively. New space group P3¯c has been established for the compounds with general formula Ln_0.33Zr₂(PO₄)₃, where Ln=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. It has been confirmed that the synthetic phosphates with general formula Ln_0.33Zr₂(PO₄)₃ belong to the NZP (sodium zirconium phosphate) structure type.