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.     

Synthesis, structural characterization, and magnetic properties of the antiferromagnetic double perovskites Ln2LiOsO6 (Ln=La, Pr, Nd, Sm)

A series of osmium double perovskite oxides, Ln₂LiOsO₆ (Ln=La, Pr, Nd, Sm), has been prepared as single crystals from acidic molten hydroxide. All four oxides crystallize in the monoclinic space group P2₁/n (Glazer tilt system #10, a⁻a⁻b⁺), forming a 1:1 ordered rock salt lattice of Li⁺ and Os⁵⁺ cations. Magnetic susceptibility measurements show that these compounds are antiferromagnetic at low temperature with ordering temperatures of 39, 35, 23, and 32 K for Ln₂LiOsO₆ (Ln=La, Pr, Nd, Sm), respectively.     

Structural and magnetic properties of the quaternary oxides Ba6Ln2Fe4O15 (Ln=Pr and Nd)

The crystal structures and magnetic properties of the quaternary lanthanide oxides Ba₆Ln₂Fe₄O₁₅ (Ln=Pr and Nd) are reported. They crystallize in a hexagonal structure with space group P6₃mc and have the “Fe₄O₁₅ cluster” consisting of one FeO₆ octahedron and three FeO₄ tetrahedra. Measurements of the magnetic susceptibility, specific heat, and powder neutron diffraction reveal that this cluster behaves as a spin tetramer with a ferrimagnetic ground state of S_T=5 even at room temperature. The cluster moments show a long-range antiferromagnetic ordering at 23.2 K (Ln=Pr) and 17.8 K (Nd), and the magnetic moments of the Ln³⁺ ions also order cooperatively. By applying the magnetic field (∼2 T), this antiferromagnetic ordering of the clusters changes to a ferromagnetic one. This result indicates that there exists a competition in the magnetic interaction between the clusters.     

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 growth and structural investigation of A2BReO6 (A=Sr, Ba; B=Li, Na)

Single crystals of the double perovskite rhenates A₂BReO₆ (A=Sr, Ba; B=Li, Na) were grown out of molten hydroxide fluxes. Single crystals of orange/yellow Ba₂LiReO₆, Ba₂NaReO₆ and Sr₂LiReO₆ were solved in the cubic, Fm-3m space group with a=8.1214(11) Å, 8.2975(3) Å, and 7.9071(15) Å, respectively, while Sr₂NaReO₆ was determined to be monoclinic P2₁/n with a=5.6737(6) Å, b=5.7988(6) Å, c=8.0431(8) Å, and β=90.02(6) °. The cubic structure consists of a rock salt lattice of corner-shared ReO₆ and MO₆ (M=Li, Na) octahedra which, in the monoclinic structure, are both tilted and rotated. A discrepancy exists between the symmetry of Sr₂LiReO₆ indicated by the single-crystal refinement of flux-grown crystals (cubic, Fm-3m) and the symmetry indicated by the powder diffraction data collected on polycrystalline samples prepared by the ceramic method (tetragonal, I4/m). It is possible that the cubic crystals are a kinetic product that forms in small quantities at low temperatures, while the powder represents the more stable polymorph that forms at higher reaction temperature.     

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 series of lithium garnets Ln3Li5Ta2O12 (Ln=La, Pr, Nd): Structural properties, Alexandrite effect and unusual ionic conductivity

We report the single crystal structures of a series of lanthanide containing tantalates, Ln₃Li₅Ta₂O₁₂ (Ln=La, Pr, Nd) that were obtained out of a reactive lithium hydroxide flux. The structures of Ln₃Li₅Ta₂O₁₂ were determined by single crystal X-ray diffraction, where the Li⁺ positions and Li⁺ site occupancies were fixed based on previously reported neutron diffraction data for isostructural compounds. All three oxides crystallize in the cubic space group (No. 230) with lattice parameters a=12.7735(1), 12.6527(1), and 12.5967(1) Å for La₃Li₅Ta₂O₁₂, Pr₃Li₅Ta₂O₁₂, and Nd₃Li₅Ta₂O₁₂, respectively. A UV-Vis diffuse reflectance spectrum of Nd₃Li₅Ta₂O₁₂ was collected to explain its unusual Alexandrite-like optical behavior. To evaluate the transport properties of Nd₃Li₅Ta₂O₁₂, the impedance data were collected in air in the temperature range 300?T(°C)?500.     

Structures, magnetic, and thermal properties of Ln3MoO7 (Ln=La, Pr, Nd, Sm, and Eu)

Ternary lanthanide-molybdenum oxides Ln₃MoO₇ (Ln=La, Pr, Nd, Sm, Eu) have been prepared. Their structures were determined by X-ray diffraction measurements. They crystallize in a superstructure of cubic fluorite and the space group is P2₁2₁2₁. The Mo ion is octahedrally coordinated by six oxygens and the slightly distorted octahedra share corners forming a zig-zag chain parallel to the b-axis. These compounds have been characterized by magnetic susceptibility and specific heat measurements. The La₃MoO₇ shows complex magnetic behavior at 150 and 380 K. Below these temperatures, there is a large difference in the temperature-dependence of the magnetic susceptibility measured under zero-field-cooled condition and under field-cooled condition. The Nd₃MoO₇ show a clear antiferromagnetic transition at 2.5 K. From the susceptibility measurements, both Pr₃MoO₇ and Sm₃MoO₇ show the existence of magnetic anomaly at 8.0 and 2.5 K, respectively. The results of the specific heat measurements also show anomalies at the corresponding magnetic transition temperatures. The differential scanning calorimetry measurements indicate that two phase-transitions occur for any Ln₃MoO₇ compound in the temperature range between 370 and 710 K.     

Mg2MTaO6 (M=Nd or La): a group of new pyrochlore oxides

Preparation of two novel mixed metal oxide ceramic materials, namely magnesium neodymium tantalum oxide (Mg₂NdTaO₆) and magnesium lanthanum tantalum oxide (Mg₂LaTaO₆) by conventional solid-state reaction method is reported in this paper. The crystal structure of these new compounds, were studied by indexing the X-ray diffraction patterns, powder pattern calculation and profile fitting. They were found to have a defective cubic pyrochlore structure, with the A site being randomly occupied by Mg and La/Nd, while, Ta and Mg are randomly distributed at the B site. The formula assigned were (MgNd)(MgTa)O₆ and (MgLa)(MgTa)O₆. The variation of dielectric constant, dielectric loss and conductivity of sintered pellets of these materials with applied frequencies in the range of 30 Hz-1 MHz were studied at room temperature. These room temperature studies at 1 MHz gave dielectric constant values of 24.8 and 25.35; conductivity values of 7.75×10⁻⁶ and 8.27×10⁻⁶ S/m as well as dielectric loss values of 0.0055 and 0.006 for Mg₂NdTaO₆ and Mg₂LaTaO₆, respectively. These new pyrochlore compounds were found to have dielectric constant, dielectric loss and conductivity values in the range suitable for possible electronic ceramic applications.     

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.     

Crystal growth, transport, and magnetic properties of Ln3Co4Sn13 (Ln=La, Ce) with a perovskite-like structure

Ln₃Co₄Sn₁₃ (Ln=La, Ce) have been synthesized by flux growth and characterized by single crystal X-ray diffraction. These compounds adopt the Yb₃Rh₄Sn₁₃-type structure and crystallize in the cubic space group (No. 223) with Z=2. Lattice parameters at 298 K are , , and , for the La and Ce analogues, respectively. The crystal structure consists of an Sn-centered icosahedron at the origin of the unit cell, which shares faces with eight Co trigonal prisms and 12 Ln-centered cuboctahedra. Magnetization data at 0.1 T show paramagnetic behavior down to 1.8 K for Ce₃Co₄Sn₁₃, with per Ce³⁺, while conventional type II superconductivity appears below 2.85 K in the La compound. Electrical resistivity and specific heat data for the La compound show a corresponding sharp superconducting transition at T_c∼2.85 K. The entropy and resistivity data for Ce₃Co₄Sn₁₃ show the existence of the Kondo effect with a complicated semiconducting-like behavior in the resistivity data. In addition, a large enhanced specific heat coefficient at low T with a low magnetic transition temperature suggests a heavy-fermionic character for the Ce compound. Herein, the structure and physical properties of Ln₃Co₄Sn₁₃ (Ln=La, Ce) are discussed.     

Synthesis and properties of the double perovskites La2NiVO6, La2CoVO6, and La2CoTiO6

The double perovskites La₂CoVO₆, La₂CoTiO₆, and La₂NiVO₆, are described. Rietveld fitting of neutron and powder X-ray diffraction data show La₂NiVO₆ and La₂CoVO₆ to have a disordered arrangement of B-cations whereas La₂CoTiO₆ shows ordering of the B-cations (with ∼5% Co/Ti inversion). Curie-Weiss fits to the linear region of the 1/χ plots reveal Weiss temperatures of −107, −34.8, and 16.3 K for La₂CoVO₆, La₂CoTiO₆, and La₂NiVO₆, respectively, and magnetic transitions are observed. La₂CoTiO₆ prepared by our method differs from material prepared by lower-temperature routes. A simple antiferromagnetic spin model is consistent with the data for La₂CoTiO₆. These compounds are semiconductors with bandgaps of 0.41 (La₂CoVO₆), 1.02 (La₂CoTiO₆) and 0.45 eV (La₂NiVO₆).     

Synthesis, structure and physical properties of LnNi(Sn,Sb)3 (Ln=Pr, Nd, Sm, Gd, Tb)

Five new analogues of the β-CeNiSb₃ family have been synthesized and found to be LnNi(Sn,Sb)₃ and isostructural to the previously reported β-CeNiSb₃. LnNi(Sn,Sb)₃ (Ln=Pr, Nd, Sm, Gd, or Tb) crystallizes in the orthorhombic space group, Pbcm, with lattice parameters of a∼12.9 Å, b∼6.1 Å, c∼12.0 Å. The structure consists of layers of nearly square nets of X (X=Sn/Sb) atoms and highly distorted NiX₆ octahedra. Lanthanide atoms are located between layers of X and NiX₆ octahedra. All analogues are metallic and experimental effective magnetic moments are in agreement with the respective Ln³⁺ calculated moments.     

A new promising phosphor, Na3La2(BO3)3:Ln (Ln=Eu, Tb)

We present an efficient way to search a host for ultraviolet (UV) phosphor from UV nonlinear optical (NLO) materials. With the guidance, Na₃La₂(BO₃)₃ (NLBO), as a promising NLO material with a broad transparency range and high damage threshold, was adopted as a host material for the first time. The lanthanide ions (Tb³⁺ and Eu³⁺)-doped NLBO phosphors have been synthesized by solid-state reaction. Luminescent properties of the Ln-doped (Ln=Tb³⁺, Eu³⁺) sodium lanthanum borate were investigated under UV ray excitation. The emission spectrum was employed to probe the local environments of Eu³⁺ ions in NLBO crystal. For red phosphor, NLBO:Eu, the measured dominating emission peak was at 613 nm, which is attributed to ⁵D₀-⁷F₂ transition of Eu³⁺. The luminescence indicates that the local symmetry of Eu³⁺ in NLBO crystal lattice has no inversion center. Optimum Eu³⁺ concentration of NLBO:Eu³⁺ under UV excitation with 395 nm wavelength is about 30 mol%. The green phosphor, NLBO:Tb, showed bright green emission at 543 with 252 nm excited light. The measured concentration quenching curve demonstrated that the maximum concentration of Tb³⁺ in NLBO was about 20%. The luminescence mechanism of Ln-doped NLBO (Tb³⁺ and Eu³⁺) was analyzed. The relative high quenching concentration was also discussed.     

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.     

Crystallographic and magnetic properties of CaLaMnMoO6 double perovskite

Powder neutron diffraction studies show that CaLaMnMoO₆ double perovskite crystallizes in monoclinic P2₁/n, with a=5.56961(9), b=5.71514(9), and β=90.043(1)°. Mn and Mo occupy the 2c and 2d positions, respectively, with 6.0(4)% Mn/Mo anti-site mixing. Temperature-dependent magnetic susceptibility measurements reveal that CaLaMnMoO₆ is ferrimagnetic, with T_N=92(3) K, below which large magnetic frustration is detected. The zero-field magnetic moment measured at 5 K is about 1.2 μ_B, comparable to that of ALaMnMoO₆ (A=Ba and Sr), but much lower than expected for antiparallel ordering of formally Mn²⁺ (d⁵) and Mo⁵⁺ (d¹). Moreover, no long-range magnetic ordering is observed in neutron diffraction data down to 4 K. The magnetic frustration is discussed in the framework of nearest-neighbors next-nearest-neighbors magnetic frustration.     

Synthesis and characterization of the rare-earth dicyanamides Ln[N(CN)2]3 with Ln=La, Ce, Pr, Nd, Sm, and Eu

The rare-earth dicyanamides Ln[N(CN)₂]₃ (Ln=La, Ce, Pr, Nd, Sm, Eu) were obtained via ion exchange in aqueous medium and subsequent drying: The crystal structures were solved and refined based on X-ray powder diffraction data and they were found to be isotypic: Ln[N(CN)₂]₃; Cmcm (no. 63), Z=4, Ln=La: , , ; Ce: , , ; Pr: , , ; Nd: , , ; Sm: , , ; Eu: , , ). The compounds represent the first dicyanamides with trivalent cations. The Ln³⁺ ions are coordinated by three bridging N atoms and six terminal N atoms of the dicyanamide ions forming a three capped trigonal prism. The structure type is related to that of PuBr₃. The novel compounds Ln[N(CN)₂]₃ have been characterized by IR and Raman spectroscopy (Ln=La) and the thermal behavior has been monitored by differential scanning calorimetry (Ln=Ce, Nd, Eu).     

Magnetic properties of lanthanide rhenium oxides Ln3ReO7 (Ln=Sm, Eu, Ho)

Ternary lanthanide rhenium oxides Ln₃ReO₇ (Ln=Sm, Eu, Ho) 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=Sm, Eu; C222₁ for Ln=Ho). The magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 1.8 to 400 K. The Sm₃ReO₇ shows an antiferromagnetic transition at 1.9 K. The Eu₃ReO₇ indicates a magnetic anomaly at 12 K. On the other hand, the results of the specific heat measurements indicate that both Sm₃ReO₇ and Eu₃ReO₇ undergo a structure transition at 270 and 350 K, respectively. The Ho₃ReO₇ is paramagnetic down to 1.8 K.     

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.     

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.