Syntheses, structure, and magnetic properties of several LnYbQ3 chalcogenides, Q=S, Se

The six LnYbQ₃ compounds β-LaYbS₃, LaYbSe₃, CeYbSe₃, PrYbSe₃, NdYbSe₃, and SmYbSe₃ have been synthesized from high-temperature solid-state reactions of the constituent elements at 1223 K. The compounds are isostructural to UFeS₃ and crystallize in the space group Cmcm of the orthorhombic system with four formula units in a cell. Cell constants (Å) at 153 K are: β-LaYbS₃, 3.9238(8), 12.632(3), 9.514(2); LaYbSe₃, 4.0616(8), 13.094(3), 9.932(2); CeYbSe₃, 4.0234(5), 13.065(2), 9.885(1); PrYbSe₃, 4.0152(5), 13.053(2), 9.868(1); NdYbSe₃, 4.0015(6), 13.047(2), 9.859(1); SmYbSe₃, 3.9780(9), 13.040(3), 9.860(2). The structure is composed of layers of YbQ₆ (Q=S or Se) octahedra that alternate with layers of LnQ₈ bicapped trigonal prisms along the b-axis. Because there are no Q-Q bonds in the structure the formal oxidation states of Ln/Yb/Q are 3+/3+/2−. Magnetic susceptibility measurements indicate that CeYbSe₃ and SmYbSe₃ are Curie-Weiss paramagnets over the temperature range 5-300 K.     

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.     

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.     

Syntheses, structure, magnetism, and optical properties of the partially ordered quaternary interlanthanide sulfides PrLnYb2S6 (Ln=Tb, Dy)

Dark red single crystals of PrLnYb₂S₆ (Ln=Pr/Yb, Tb, Dy) have been synthesized through the reactions of elemental rare earth metals and S using a Sb₂S₃ flux at 1000 °C. These isotypic compounds adopt the F-Ln₂S₃ three-dimensional open-channel structure type. Eight-coordinate Pr³⁺ ions sit in the channels that are constructed from three different edge-shared double chains running down the b-axis that contain Yb(1)S₆ octahedra, Yb(2)S₆ octahedra, and LnS₇ monocapped trigonal prisms. Each double chain connects to four other neighbors by sharing vertices and edges. Considerable disordering in Ln positions was observed in single X-ray diffraction experiments only in the case of Pr/Yb. Least-squares refinements gave rise to the formulas of Pr_1.34Yb_2.66S₆, of PrTbYb₂S₆, and PrDyYb₂S₆, which are confirmed by the elemental analysis and magnetic susceptibility measurements. Pr_1.34Yb_2.66S₆, PrTbYb₂S₆, and PrDyYb₂S₆ are paramagnetic down to 2 K, without any indications of long-range magnetic ordering. The optical transitions for Pr_1.34Yb_2.66S₆, PrTbYb₂S₆, and PrDyYb₂S₆ are at approximately 1.6 eV. Crystallographic data are listed as an example for PrTbYb₂S₆: monoclinic, space group P2₁/m, a=10.9496(10) Å, b=3.9429(4) Å, c=11.2206(10) Å, β=108.525(2)°, V=459.33(7) Å³, Z=2.     

Systems Ln-Fe-O (Ln=Eu, Gd): thermodynamic properties of ternary oxides using solid-state electrochemical cells

The standard molar Gibbs energies of formation of LnFeO₃(s) and Ln₃Fe₅O₁₂(s) where Ln=Eu and Gd have been determined using solid-state electrochemical technique employing different solid electrolytes. The reversible e.m.f.s of the following solid-state electrochemical cells have been measured in the temperature range from 1050 to 1255 K.Cell (I): (−)Pt / {LnFeO₃(s)+Ln₂O₃(s)+Fe(s)} // YDT/CSZ // {Fe(s)+Fe_0.95O(s)} / Pt(+);Cell (II): (−)Pt/{Fe(s)+Fe_0.95O(s)}//CSZ//{LnFeO₃(s)+Ln₃Fe₅O₁₂(s)+Fe₃O₄(s)}/Pt(+);Cell (III): (−)Pt/{LnFeO₃(s)+Ln₃Fe₅O₁₂(s)+Fe₃O₄(s)}//YSZ//{Ni(s)+NiO(s)}/Pt(+);andCell(IV):(−)Pt/{Fe(s)+Fe_0.95O(s)}//YDT/CSZ//{LnFeO₃(s)+Ln₃Fe₅O₁₂(s)+Fe₃O₄(s)}/Pt(+).The oxygen chemical potentials corresponding to the three-phase equilibria involving the ternary oxides have been computed from the e.m.f. data. The standard Gibbs energies of formation of solid EuFeO₃, Eu₃Fe₅O₁₂, GdFeO₃ and Gd₃Fe₅O₁₂ calculated by the least-squares regression analysis of the data obtained in the present study are given byΔ_fG°_m(EuFeO₃, s) /kJ mol⁻¹ (± 3.2)=−1265.5+0.2687(T/K)   (1050 ? T/K ? 1570),Δ_fG°_m(Eu₃Fe₅O₁₂, s)/kJ mol⁻¹ (± 3.5)=−4626.2+1.0474(T/K)   (1050 ? T/K ? 1255),Δ_fG°_m(GdFeO₃, s) /kJ mol⁻¹ (± 3.2)=−1342.5+0.2539(T/K)   (1050 ? T/K ? 1570),andΔ_fG°_m(Gd₃Fe₅O₁₂, s)/kJ·mol⁻¹ (± 3.5)=−4856.0+1.0021(T/K)   (1050 ? T/K ? 1255).The uncertainty estimates for Δ_fG°_m include the standard deviation in the e.m.f. and uncertainty in the data taken from the literature. Based on the thermodynamic information, oxygen potential diagrams for the systems Eu-Fe-O and Gd-Fe-O and chemical potential diagrams for the system Gd-Fe-O were computed at 1250 K.     

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.     

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.     

Structural change in a series of protonated layered perovskite compounds, HLnTiO4 (Ln=La, Nd and Y)

A deuterated n=1 Ruddlesden-Popper compound, DLnTiO₄ (HLnTiO₄, Ln=La, Nd and Y), was prepared by an ion-exchange reaction of Na⁺ ions in NaLnTiO₄ with D⁺ ions, and its structure was analyzed by Rietveld method using powder neutron diffraction data. The structure analyses showed that DLaTiO₄ and DNdTiO₄ crystallized in the space group P4/nmm with a=3.7232(1) and c=12.3088(1) Å, and a=3.7039(1) and c=12.0883(1) Å, respectively. On the other hand, DYTiO₄ crystallized in the space group P2₁/c with a=11.460(1), b=5.2920(4), c=5.3628(5) Å and β=90.441(9)°. The loaded protons were found to statistically occupy the sites around an apical oxygen of TiO₆ octahedron in the interlayer of these compounds, rather than Na atom sites in NaLnTiO₄.     

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.     

Lanthanide N,N′-piperazine-bis(methylenephosphonates) (Ln=La, Ce, Nd) that display flexible frameworks, reversible hydration and cation exchange

Hydrothermal syntheses of lanthanide bisphosphonate metal organic frameworks comprising the light lanthanides lanthanum, cerium and neodymium and N,N′-piperazine bis(methylenephosphonic acid) (H₂L(1) and its 2-methyl and 2,5-dimethyl derivatives (H₂L(2) and H₂L(3)) gives three new structure types. At elevated starting pH (ca. 5 and above) syntheses give ‘type I’ materials with all metals and acids of the study (MLnLxH₂O, M=Na, K, Cs; Ln=La, Ce, Nd; x≈4: KCeL(1)·4H₂O, C2/c, a=23.5864(2) Å, b=12.1186(2) Å, c=5.6613(2) Å, β=93.040(2)°). The framework of structure type I shows considerable flexibility as the ligand is changed, due mainly to rotation around the -N-CH₂- bond of the linker in response to steric considerations. Type I materials demonstrate cation exchange and dehydration and rehydration behaviour. Upon dehydration of KCeL·4H₂O, the space group changes to P2₁/n, a=21.8361(12) Å, b=9.3519(4) Å, c=5.5629(3) Å, β=96.560(4)°, as a result of a change of the piperazine ring from chair to boat configuration. When syntheses are performed at lower pH, two other structure types crystallise. With the ‘non-methyl’ ligand 1, type II materials result (LnL(1)H₂L(1)·4.5H₂O: Ln=La, P−1, a=5.7630(13) Å, b=10.213(2) Å, c=11.649(2) Å, α=84.242(2)°, β=89.051(2)°, γ=82.876(2)°) in which one half of the ligands coordinate via the piperazine nitrogen atoms. With the 2-methyl ligand, structure type III crystallises (LnHL(2)·4H₂O: Ln=Nd, Ce, P2₁/c, a=5.7540(9) Å, b=14.1259(18) Å, c=21.156(5) Å, β=90.14(2)°) due to unfavourable steric interactions of the methyl group in structure type II.     

Crystal structure, spectroscopic properties, and magnetic behavior of the fluoride-derivatized lanthanoid(III) ortho-oxomolybdates(VI) LnF[MoO4] (Ln=Sm-Tm)

The fluoride-derivatized lanthanoid(III) ortho-oxomolybdates(VI) LnF[MoO₄] (Ln=Sm-Tm) crystallize in the monoclinic space group P2₁/c with four formula units per unit cell (a=516-528 pm, b=1220-1248 pm, c=659-678 pm, β=112.5-113.1°). The structure contains one crystallographically unique Ln³⁺ cation surrounded by two fluoride and six oxide anions in a square antiprism (CN=8). The square antiprisms [LnF₂O₆] are interconnected via three edges to form layers parallel (010), which are cross-linked along [010] by Mo⁶⁺ in tetrahedral oxygen coordination to form the three-dimensional crystal structure. The fluoride anions within this arrangement exhibit a twofold coordination of Ln³⁺ cations in the shape of a boomerang, which is connected to another F⁻ anion to form planar [F₂Ln₂]⁴⁺ rhombuses. Magnetic measurements for GdF[MoO₄], TbF[MoO₄], and DyF[MoO₄] show Curie-Weiss behavior, despite the peculiar arrangement of the lanthanoid(III) cations in layers comparable with those of gray arsenic. Furthermore, Raman, infrared, and diffuse reflectance spectroscopy data for these compounds were recorded and interpreted.     

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.     

Solvothermal syntheses, and characterization of [Ln(en)4(SbSe4)] (Ln=Ce, Pr) and [Ln(en)4]SbSe4·0.5en (Ln=Eu, Gd, Er, Tm, Yb): The effect of lanthanide contraction on the crystal structures of lanthanide selenidoantimonates(V)

Two types of lanthanide selenidoantimonates [Ln(en)₄(SbSe₄)] (Ln=Ce(1a), Pr(1b)) and [Ln(en)₄]SbSe₄·0.5en (Ln=Eu(2a), Gd(2b), Er(2c), Tm(2d), Yb(2e); en=ethylenediamine) were solvothermally synthesized by reactions of LnCl₃, Sb and Se with the stoichiometric ratio in en solvent at 140 °C. The four-en coordinated lanthanide complex cation [Ln(en)₄]³⁺ formed in situ balances the charge of SbSe₄³⁻ anion. In compounds 1a and 1b, the SbSe₄³⁻ anion act as a monodentate ligand to coordinate complex [Ln(en)₄]³⁺ and the neutral compound [Ln(en)₄(SbSe₄)] is formed. The Ln³⁺ ion has a nine-coordinated environment involving eight N atoms and one Se atom forming a distorted monocapped square antiprism. In 2a-2e the lanthanide(III) ion exists as isolated complex [Ln(en)₄]³⁺, in which the Ln³⁺ ion is in a bicapped trigonal prism geometry. A systematic investigation of the crystal structures reveals that two types of structural features of these lanthanide selenidoantimonates are related with lanthanides contraction across the lanthanide series. TG curves show that compounds 1a-1b and 2a-2e remove their organic components in one and two steps, respectively.     

One-dimensional GdVO4:Ln (Ln=Eu, Dy, Sm) nanofibers: Electrospinning preparation and luminescence properties

One-dimensional GdVO₄:Ln³⁺ (Ln=Eu, Dy, Sm) nanofibers have been prepared by a combination method of sol-gel process and electrospinning technology. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL), quantum efficiency (QE), and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The XRD, FT-IR, and TG-DTA results show that GdVO₄:Ln³⁺ nanofibers samples crystallize at 700 °C. SEM images indicate that the as prepared precursor fibers are smooth. After being calcined at 700 °C for 4 h, the fibers still maintain their fiberlike morphology with rough surface. TEM image further manifests that the GdVO₄:Ln³⁺ nanofibers consist of nanoparticles. Under ultraviolet excitation and low-voltage electron beam excitation, GdVO₄:Ln³⁺ phosphors showed their strong characteristic emission due to an efficient energy transfer from vanadate groups to dopants. The optimum doping concentration of Ln³⁺ in the GdVO₄ nanofibers also has been investigated.     

An investigation of structural parameters and magnetic and optical properties of EuLn2Q4 (Ln=Tb-Lu, Q=S, Se)

EuLn₂Q₄ (Ln=Tb-Lu; Q=S, Se) has been synthesized using Sb₂Q₃ (Q=S, Se) fluxes at 1000 °C. These compounds crystallize in a CaFe₂O₄-type three-dimensional channel structure that is built from edge-shared double rutile chains of [LnQ₆] octahedra running down the b-axis. Each double chain is connected at the vertices to four other double chains to form open channels where bicapped trigonal prismatic Eu²⁺ ions reside. All of these compounds show antiferromagnetic ordering with Neel temperatures, T_N∼3-4 K. The optical band gaps for EuTb₂Se₄, EuDy₂Se₄, EuHo₂Se₄, EuEr₂Se₄, EuTm₂Se₄, EuYb₂Se₄ EuLu₂Se₄, and EuYb₂S₄ are found to be 2.0, 1.8, 1.8, 1.7, 1.8, 1.3, 1.7, and 1.6 eV, respectively.     

The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties

The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI₃ and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln₁₂(C₂)₃I₁₇-type compounds (C 2/c, a=19.610(1) and 19.574(4) Å, b=12.406(2) and 12.393(3) Å, c=19.062(5) and 19.003(5) Å, β=90.45(3)° and 90.41(3)°, for Pr₁₂(C₂)₃I₁₇ and Nd₁₂(C₂)₃I₁₇, respectively). All compounds contain infinite zigzag chains of C₂-centered metal atom octahedra condensed by edge-sharing into the [tcc]_∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd₁₂(C₂)₃I₁₇ sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln³⁺)₁₂(C₂^6-)₃(I⁻)₁₇(e⁻) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd₁₂(C₂)₃I₁₇, Gd₁₂(C₂)₃I₁₇ and Dy₁₂(C₂)₃I₁₇ indicate the coexistence of competing magnetic interactions leading to spin freezing at T_f=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at T_N=25 and 29 K, respectively. For Dy₁₂(C₂)₃I₁₇, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe.     

Magnetic properties and structural transitions of orthorhombic fluorite-related compounds Ln3MO7 (Ln=rare earths, M=transition metals)

Magnetic properties and structural transitions of ternary rare-earth transition-metal oxides Ln₃MO₇ (Ln=rare earths, M=transition metals) were investigated. In this study, we prepared a series of molybdates Ln₃MoO₇ (Ln=La-Gd). They crystallize in an orthorhombic superstructure of cubic fluorite with space group P2₁2₁2₁, in which Ln³⁺ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). All of these compounds show a phase transition from the space group P2₁2₁2₁ to Pnma in the temperature range between 370 and 710 K. Their magnetic properties were characterized by magnetic susceptibility measurements from 1.8 to 400 K and specific heat measurements from 0.4 to 400 K. Gd₃MoO₇ shows an antiferromagnetic transition at 1.9 K. Measurements of the specific heat for Sm₃MoO₇ and the analysis of the magnetic specific heat indicate a “two-step” antiferromagnetic transition due to the ordering of Sm magnetic moments in different crystallographic sites, i.e., with decreasing temperature, the antiferromagnetic ordering of the 7-coordinated Sm ions occur at 2.5 K, and then the 8-coordinated Sm ions order at 0.8 K. The results of Ln₃MoO₇ were compared with the magnetic properties and structural transitions of Ln₃MO₇ (M=Nb, Ru, Sb, Ta, Re, Os, or Ir).     

Synthesis, structure and magnetic properties of the pillared perovskites La5Re3MO16(M=Mg, Fe, Co, Ni)

Four new compounds La₅Re₃MgO₁₆ La₅Re₃FeO₁₆ La₅Re₃CoO₁₆ La₅Re₃NiO₁₆ have been prepared by solid-state reaction and characterized by X-ray and neutron powder diffraction and SQUID magnetometry. Rietveld refinement revealed that the four compounds are isostructural with La₅Re₃MnO₁₆ and crystallize in space group with cell parameters a=7.9370(3), 7.9553(5), 7.9694(7), and 7.9383(4) Å; b=7.9998(3), 7.9960(6), 8.0071(8), and 7.9983(5) Å; c=10.1729(4), 10.1895(7), 10.182(1), and 10.1732(6) Å; α=90.190(3)°, 90.270(3)°, 90.248(4) °, 90.287(3)°; β=94.886(2)°, 95.082(3)°, 94.980(4)°, 94.864(3)°; γ=89.971(4)°, 90.001(5)°, 89.983(6)°, 89.968(4)° for Mg, Fe, Co, and Ni, respectively. The structures are related to a layered perovskite. The layers of corner-sharing octahedra Re⁵⁺M²⁺O₆ (M²⁺=Mg, Fe, Co, Ni) are pillared by diamagnetic edge-sharing octahedra dimers, Re₂O₁₀, involving a Re=Re double bond. Three crystallographically independent lanthanum atoms occupy the three-dimensional interstices. All compounds obey the Curie-Weiss law at sufficiently high temperatures with Curie constants or effective magnetic moments near the expected values for the combination of Re⁵⁺(S=1) and M²⁺(S=0, 2, 3/2, 1 for Mg, Fe, Co, and Ni, respectively). Weiss constants, θ_C, are negative (−575, −84, −71, and −217 K for Mg, Fe, Co, and Ni, respectively) indicating the predominance of antiferromagnetic exchange coupling. The phases for M=Fe, Co and Ni show long-range order at 155, 33, 36 and 14 K, respectively. Neutron diffraction discloses a magnetic structure for the Fe series member consisting of ferrimagnetic perovskite layers coupled antiparallel along the stacking c-axis, direction which is consistent with the magnetic structure found recently for La₅Re₃MnO₁₆.     

Phase equilibria and crystal structure of the complex oxides in the Ln-Ba-Co-O (Ln=Nd, Sm) systems

The phase equilibria in the Ln-Ba-Co-O (Ln=Nd, Sm) systems were systematically studied at 1100 °C in air. The homogeneity ranges and crystal structure of the solid solutions: Ln_2−xBa_xO_3−δ (0<x≤0.1 for Ln=Nd and 0<x≤0.3 for Ln=Sm), Nd_3−yBa_yCo₂O₇ (0.70≤y≤0.80), BaCo_1−zSm_zO_3−δ (0.1≤z≤0.2) were determined by X-ray diffraction of quenched samples. The values of oxygen content (5+δ) for slowly cooled LnBaCo₂O_5+δ (Ln=Nd, Sm) samples were estimated as 5.73 for Ln=Nd, and 5.60 for Ln=Sm. The unit cell parameters were refined using Rietveld full-profile analysis. It was shown that NdBaCo₂O_5.73 possesses tetragonal structure and SmBaCo₂O_5.60 - orthorhombic structure. The projections of isothermal-isobaric phase diagrams for the Ln-Ba-Co-O (Ln=Nd, Sm) systems to the compositional triangle of metallic components were presented.     

Syntheses, structures, physical properties, and electronic structures of KLn2CuS4 (Ln=Y, Nd, Sm, Tb, Ho) and K2Ln4Cu4S9 (Ln=Dy, Ho)

Seven new quaternary metal sulfides, KY₂CuS₄, KNd₂CuS₄, KSm₂CuS₄, KTb₂CuS₄, KHo₂CuS₄, K₂Dy₄Cu₄S₉, and K₂Ho₄Cu₄S₉, were prepared by the reactive flux method. All crystallographic data were collected at 153 K. The isostructural compounds KLn₂CuS₄ (Ln=Y, Nd, Sm, Tb, Ho) crystallize in space group Cmcm of the orthorhombic system with four formula units in cells of dimensions (Ln, a, b, c (Å)): Y, 3.9475(9), 13.345(3), 13.668(3); Nd, 4.0577(3), 13.7442(10), 13.9265(10); Sm, 4.0218(4), 13.6074(14), 13.8264(14); Tb, 3.9679(5), 13.4243(17), 13.7102(18); Ho, 3.9378(3), 13.3330(11), 13.6487(11). The corresponding R₁ indices for the refined structures are 0.0197, 0.0153, 0.0158, 0.0181, and 0.0178. The isostructural compounds K₂Dy₄Cu₄S₉ and K₂Ho₄Cu₄S₉ crystallize in space group C2/m of the monoclinic system with two formula units in cells of dimensions (Ln, a, b, c (Å), β (°)): Dy, 13.7061(13), 3.9482(4), 15.8111(15), 109.723(1); Ho, 13.6760(14), 3.9360(4), 15.7950 (16), 109.666(2). The corresponding R₁ indices are 0.0312 and 0.0207. Both structure types are closely related three-dimensional tunnel structures. The tunnels are filled with bicapped trigonal-prismatically coordinated K atoms. Their anionic frameworks are built from LnS₆ octahedra and CuS₄ tetrahedra. KLn₂CuS₄ contains _∞¹[CuS₃⁵⁻] chains of vertex-sharing tetrahedra and K₂Ln₄Cu₄S₉ contains _∞¹[Cu₄S₈¹²⁻] chains of tetrahedra. K₂Ho₄Cu₄S₉ shows Curie-Weiss paramagnetic behavior between 5 and 300 K, and has an effective magnetic moment of 10.71 μ_B for Ho³⁺ at 293 K. Optical band gaps of 2.17 eV for KSm₂CuS₄ and 2.43 eV for K₂Ho₄Cu₄S₉ were deduced from diffuse reflectance spectra. A first-principles calculation of the density of states and the frequency-dependent optical conductivity was performed on KSm₂CuS₄. The calculated band gap of 2.1 eV is in good agreement with the experimental value.