Crystal structure, thermal and magnetic properties of Cr2V4O13

Cr₂V₄O₁₃, a tetravanadate of Cr³⁺ has been prepared by repeated heating of stoichiometric amounts of Cr₂O₃ and V₂O₅ and its crystal structure is refined by Rietveld refinement of the powder XRD data. This compound crystallizes in a monoclinic lattice with unit cell parameters: a=8.2651(3), b=9.2997(3), c=14.5215(5) Å, β=102.618(3)°, V=1089.21(6) Å³ and Z=4 (Space group: P2₁/c). The U shaped (V₄O₁₃)⁶⁻ formed by corner connected VO₄ tetrahedra links the Cr₂O₁₀ (dimers of two edge shared CrO₆ octahedra) forming a three dimensional network structure of Cr₂V₄O₁₃. This compound is stable up to 635 °C and peritectically decomposes to orthorhombic CrVO₄ and V₂O₅ above this temperature. A possible long range antiferromagnetic ordering below 10 K is suggested from the squid magnetometry and electron paramagnetic resonance (epr) spectroscopic studies of Cr₂V₄O₁₃.     

Synthesis, crystal structure and NLO property of a nonmetal pentaborate [C6H13N2][B5O6(OH)4]

A nonmetal pentaborate [C₆H₁₃N₂][B₅O₆(OH)₄] (1) has been synthesized by 1,4-diazabicyclo[2.2.2] octane (DABCO) and boric acid, and characterized by single-crystal X-ray diffraction, FTIR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic system with space group Cc (no. 9), a=10.205(2) Å, b=14.143(3) Å, c=11.003(2) Å, β=113.97(3)°, V=1451.1(5) Å³, Z=4. The anionic units, [B₅O₆(OH)₄]⁻, are interlinked via hydrogen bonding to form a three-dimensional (3D) supramolecular network containing large channels, in which the protonated [C₆H₁₃N₂]⁺ cations are located. Second-harmonic generation (SHG) measurements on the powder samples reveal that 1 exhibits SHG efficiency approximately 0.9 times that of potassium dihydrogen phosphate (KDP).     

Effects of doping Fe cations on crystal structure and thermal expansion property of Yb2Mo3O12

Crystal structures and thermal expansion properties of Yb_(2-x)Fe_xMo_3O_(12)(x=0.0,0.6,1.0,1.1,1.4) solid solutions have been studied by X-ray powder diffraction(XRPD) at different temperatures.Rietveld analysis of the XRPD data shows that Yb_(2-x)Fe_xMo_3O_(12) solid solutions adopt orthorhombic structure and have variable thermal expansion coefficients controlled by the ratio of Yb~(3+) to Fe~(3+).Yb_2Mo_3O_(12) shows anisotropic negative thermal expansion property,induced by the reductions in average Yb-O-Mo angle and average apparent Mo2-O bond length with increasing temperatures.As more Yb~(3+) substituted by Fe~(3+),the linear thermal expansion coefficients of Yb_(2-x)Fe_xMo_3O_(12) increase from negative to positive.A near-zero thermal expansion coefficient of 0.55×10~(-6)K~(-1) for Yb_(0.6)Fe_(1.4)Mo_3O_(12) is observed in the temperature range of 573-873 K     

Synthesis, structure, and magnetic behavior of a new gadolinium thiosilicate: Gd4[SiS4]3

Single crystals of the title compound were prepared from the elements by a solid state reaction in an iodine atmosphere. Data collection were carried out using a STOE image plate detector at 293 K. The compound crystallizes in the space group P2₁/n of the monoclinic system isotypically to Tb₄[SiS₄]₃ with four formular units in cells of dimensions: a=986.7(2) pm, b=1099.69(19) pm, c=1646.2(4) pm, β=102.67(3)°. The corresponding residual (all data) for the refined structure is 3.09%.The magnetic behavior of the compound was investigated on powdered samples in a temperature range between 1.7 and 300 K. The deviations from the Curie-behavior could be interpreted by the molecular field approach.     

Synthesis and structural characterization of Al4SiC4-homeotypic aluminum silicon oxycarbide, [Al4.4Si0.6][O1.0C2.0]C

A new quaternary layered oxycarbide, [Al_4.39(5)Si_0.61(5)]_Σ5[O_1.00(2)C_2.00(2)]_Σ3C, has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX). The title compound was found to be hexagonal with space group P6₃/mmc, Z=2, and unit-cell dimensions a=0.32783(1) nm, c=2.16674(7) nm and V=0.20167(1) nm³. The atom ratios Al:Si were determined by EDX, and the initial structural model was derived by the direct methods. The final structural model showed the positional disordering of one of the three types of Al/Si sites. The maximum-entropy methods-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R_wp=3.73% (S=1.20), R_p=2.94%, R_B=1.04% and R_F=0.81%. The crystal was an inversion twin. Each twin-related individual was isostructural with Al₄SiC₄ (space group P6₃mc, Z=2).     

Synthesis, crystal structure, and preliminary study of luminescent properties of InTbGe2O7

A new indium terbium germanate InTbGe₂O₇, which is a member of the thortveitite family, was prepared as a polycrystalline powder material by high-temperature solid-state reaction. This new compound crystallizes in the monoclinic system, space group C2/c (No. 15), with unit cell parameters a=6.8818(2) Å, b=8.8774(3) Å, c=9.7892(4) Å, β=101.401(1)°, V=586.25(4) ų and Z=4. Its structure was characterized by Rietveld refinement of powder laboratory X-ray diffraction data. It consists of octahedral sheets that are held together by sheets of isolated Ge₂O₇ diorthogroups composed of two tetrahedra sharing a common vertex. It contains only one octahedral site occupied by In³⁺ and Tb⁺³ cations. The characteristic mirror plane in the thortveitite (Sc₂Si₂O₇) space group (C2/m, No. 12) is not present in this new compound. Besides, in InTbGe₂O₇, the Ge–O–Ge angle bridging two diorthogroups is 156.8(2)° as compared to the one in thortveitite, which is 180°. On the other hand, luminescent properties were observed when it is excited with 376.5 nm wavelength. The luminescence spectrum shows typical transitions from the ⁵D₄ multiplet belonging to the trivalent terbium ion.     

Synthesis, crystal structure, and nonlinear optical properties of Bi2Cu5B4O14

Bi₂Cu₅B₄O₁₄ crystallizes in the noncentrosymmetric triclinic space group P1 (No. 1) with cell parameters a=10.1381(11) Å, b=9.3917(11) Å, c=3.4566(4) Å, α=105.570(2)°, β=92.275(2)°, γ=107.783(2)°, Z=1 and R₁=0.0401 and wR₂=0.0980. It is a layered structure that is built up from sheets of rectangular CuO₄ and trigonal BO₃ groups. The sheets are connected by infinite chains of edge shared BiO₆ polyhedra that intersect the bc plane at an angle slightly greater than 90°. The second-harmonic generation efficiency of Bi₂Cu₅B₄O₁₄, using 1064 nm radiation, is about one half times that of KH₂PO₄.     

Syntheses, crystal structures and Si solubilities of new layered carbides Zr2Al4C5 and Zr3Al4C6

Two types of new ternary carbides, Zr₂Al₄C₅ and Zr₃Al₄C₆, have been synthesized and characterized by X-ray powder diffraction. The crystal structures were refined from laboratory X-ray powder diffraction data (CuKα₁) using the Rietveld method. These carbides form a homologous series with the general formula (ZrC)_mAl₄C₃ (m=2 and 3). The crystal structures can be regarded as intergrowth structures where the Al₄C₃-type [Al₄C₄] layers are the same, while the NaCl-type [Zr_mC_m+1] layers increase in thickness with increasing m value. The new carbides are most probably the end members of continuous solid-solutions (ZrC)_m[Al_4−xSi_x]C₃ with 0?x?0.44.     

Li2Si3O7: Crystal structure and Raman spectroscopy

The crystal structure of metastable Li₂Si₃O₇ was determined from single crystal X-ray diffraction data. The orthorhombic crystals were found to adopt space group Pmca with unit cell parameters of , and . The content of the cell is Z=4. The obtained structural model was refined to a R-value of 0.035. The structure exhibits silicate sheets, which can be classified as [Si₆O₁₄] using the silicate nomenclature of Liebau. The layers are build up from zweier single chains running parallel to c. Raman spectra are presented and compared with other silicates. Furthermore, the structure is discussed versus Na₂Si₃O₇.     

Syntheses, crystal structures and spectroscopic properties of Ag2Nb[P2S6][S2] and KAg2[PS4]

Ag₂Nb[P₂S₆][S₂] (1) was obtained from the direct solid state reaction of Ag, Nb, P₂S₅ and S at 500 °C. KAg₂[PS₄] (2) was prepared from the reaction of K₂S₃, Ag, Nd, P₂S₅ and extra S powder at 700 °C. Compound 1 crystallizes in the orthorhombic space group Pnma with a=12.2188(11), b=26.3725(16), c=6.7517(4) Å, V=2175.7(3) Å³, Z=8. Compound 2 crystallizes in the non-centrosymmetric tetragonal space group with lattice parameters a=6.6471(7), c=8.1693(11) Å, V=360.95(7) Å³, Z=2. The structure of Ag₂Nb[P₂S₆][S₂] (1) consists of [Nb₂S₁₂], [P₂S₆] and new found puckered [Ag₂S₄] chains which are along [001] direction. The Nb atoms are located at the center of distorted bicapped trigonal prisms. Two prisms share square face of two [S₂²⁻] to form one [Nb₂S₁₂] unit, in which Nb-Nb bond is formed. The [Nb₂S₁₂] units share all S²⁻ corners with ethane-like [P₂S₆] units to form 14-membered rings. The novel puckered [Ag₂S₄] chains are composed of distorted [AgS₄] tetrahedra and [AgS₃] triangles that share corners with each other. These chains are connected with [P₂S₆] units and [Nb₂S₁₂] units to form three-dimensional frame work. The structural skeleton of 2 is built up from [AgS₄] and [PS₄] tetrahedra linked by corner-sharing. The three-dimensional anionic framework contains orthogonal, intersecting tunnels directed along [100] and [010]. This compound possesses a compressed chalcopyrite-like structure. The structure is compressed along [001] and results from eight coordination sphere for K⁺. Both compounds are characterized with UV/vis diffuse reflectance spectroscopy and compound 1 with IR and Raman spectra.     

Synthesis, crystal structure and optical properties of BiMgVO5

The new vanadate BiMgVO₅ has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P2₁/n, , , , β=107.38(5)°, wR₂=0.0447, R=0.0255. The structure consists of [Mg₂O₁₀] and [Bi₂O₁₀] dimers sharing their corners with [VO₄] tetrahedra. The ranges of bond lengths are 2.129-2.814 Å for Bi-O; 2.035-2.167 Å for Mg-O and 1.684-1.745 Å for V-O. V-O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747 Å. An emission band overlapping the entire visible region with a maximum around 650 nm is observed.     

Single-crystal growth, crystal and electronic structure of NaCoO2

Single crystals of NaCoO₂ have been successfully synthesized for the first time by a flux method at 1323 K. A single-crystal X-ray diffraction study confirmed the trigonal space group and the lattice parameters , . The crystal structure has been refined to the conventional values R=1.9% and wR=2.1% for 309 independent observed reflections. The electron density distribution of NaCoO₂ has been studied by the maximum entropy method (MEM) using single-crystal X-ray diffraction data obtained at 298 K. From the results of the MEM analysis, the strong covalent bonding was clearly observed between Co and O atoms, while no bonding was observed around Na atoms. We also calculated the electron density of NaCoO₂ by first principles calculations. The electron density obtained experimentally is in good agreement with the theoretical one.     

Synthesis, phase relationship and crystal structure of the new binary compound Ir13Al45

The new phase Ir₁₃Al₄₅ was synthesized in equilibrium with an aluminum-rich melt. Its crystal structure was established from single-crystal diffraction data. The compound crystallizes in the space group Pnma and represents a novel structure type (Pearson symbol oP232, a=16.760(2) Å, b=12.321(1) Å, c=17.425(2) Å). The structure can essentially be described as a simple hexagonal column packing of pseudopentagonal columns formed by irregular Al polyhedra centered by Ir atoms. Ir₁₃Al₄₅ forms peritectically at 895 °C and exists in equilibrium with the melt in a narrow temperature interval of 19 °C.     

Synthesis, crystal structure and magnetic properties of a new pillared perovskite La5Mo2.75V1.25O16

A new pillared perovskite compound La₅Mo_2.76(4)V_1.25(4)O₁₆, has been synthesized by solid-state reaction and its crystal structure has been characterized using powder X-ray and neutron diffraction. The magnetic properties of this compound have been investigated using SQUID magnetometry, and the magnetic structure has been studied using neutron diffraction data. A theoretical calculation of relative strengths of spin interactions among different magnetic ions and through different pathways has been performed using extended Hückel, spin dimer analysis. The crystal structure of this material contains perovskite-type layers that are connected through edge-sharing dimeric units of octahedra. The structure is described in space group C2/m with unit cell parameters a=7.931(2) Å, b=7.913(2) Å, c=10.346(5) Å and β=95.096(5)°. The material shows both short-range ferrimagnetic correlations from ∼200 to 110 K and long-range antiferromagnetic order below T_c∼100 K. The magnetic structure was investigated by neutron diffraction and is described by k=(0 0 ) as for other pillared perovskites. It consists of a ferrimagnetic arrangement of Mo and V within the layers that are coupled antiferromagnetically between layers. This is the first magnetic structure determination for any Mo-based pillared perovskite.     

Synthesis and structural characterization of a new aluminum oxycarbonitride, Al5(O, C, N)4

A new aluminum oxycarbonitride, Al₅(O_xC_yN_4−x−y) (x∼1.4 and y∼2.1), has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and electron energy loss spectroscopy (EELS). The title compound was found to be hexagonal with space group P6₃/mmc, Z=2, and unit-cell dimensions a=0.328455(6) nm, c=2.15998(3) nm and V=0.201805(6) nm³. The atom ratios O:C:N were determined by EELS. The final structural model, which is isomorphous with that of (Al_4.4Si_0.6)(O_1.0C_3.0), showed the positional disordering of one of the three types of Al sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R_wp=6.94% (S=1.22), R_p=5.34%, R_B=1.35% and R_F=0.76%. The crystal was an inversion twin. Each twin-related individual was isostructural with Al₅C₃N (space group P6₃mc, Z=2).     

Syntheses, crystal structures and spectroscopic properties of KEu[AsS4], K3Dy[AsS4]2 and Rb4Nd0.67[AsS4]2

Three rare earth compounds, KEu[AsS₄] (1), K₃Dy[AsS₄]₂ (2), and Rb₄Nd_0.67[AsS₄]₂ (3) have been synthesized employing the molten flux method. The reactions of A₂S₃ (A = K, Rb), Ln (Ln = Eu, Dy, Nd), As₂S₃, S were accomplished at 600 °C for 96 h in evacuated fused silica ampoules. Crystal data for these compounds are: 1, monoclinic, space group P2₁/m (no. 11), a = 6.7276(7) Å, b = 6.7190(5) Å, c = 8.6947(9) Å, β = 107.287(12)°, Z = 2; 2, monoclinic, space group C2/c (no. 15), a = 10.3381(7) Å, b = 18.7439(12) Å, c = 8.8185(6) Å, β = 117.060(7)°, Z = 4; 3, orthorhombic, space group Ibam (no. 72), a = 18.7333(15) Å, b = 9.1461(5) Å, c = 10.2060(6) Å, Z = 4. 1 is a two-dimensional structure with ²_∞[Eu(AsS₄)]⁻ layers separated by potassium cations. Within each layer, distorted bicapped trigonal [EuS₈] prisms are linked through distorted [AsS₄]³⁻ tetrahedra. Each Eu²⁺ cation is coordinated by two [AsS₄]³⁻ units by edge-sharing and bonded to further two [AsS₄]³⁻ units by corner-sharing. Compound 2 contains a one-dimensional structure with ¹_∞[Dy(AsS₄)₂]³⁻ chains separated by potassium cations. Within each chain, distorted bicapped trigonal prisms of [DyS₈] are linked by slightly distorted [AsS₄]³⁻ tetrahedra. Each Dy³⁺ ion is surrounded by four [AsS₄]³⁻ moieties in an edge-sharing fashion. For compound 3 also a one-dimensional structure with ¹_∞[Nd₀.₆₇(AsS₄)₂]⁴⁻ chains is observed. But the Nd position is only partially occupied and overall every third Nd atom is missing along the chain. This cuts the infinite chains into short dimers containing two bridging [As₄]³⁻ units and four terminal [AsS₄]³⁻ groups. 1 is characterized with UV/vis diffuse reflectance spectroscopy, IR, and Raman spectra.     

Structure and thermoelectric properties of the ordered skutterudite CoGe1.5Te1.5

The skutterudite-related material CoGe_1.5Te_1.5 has been synthesised and structurally characterised by powder neutron diffraction. Analysis of the high-resolution powder neutron diffraction data indicates that the structure of CoGe_1.5Te_1.5 retains the a⁺a⁺a⁺ tilt system of the ideal skutterudite structure, while the anions are ordered in layers perpendicular to the [111] direction of the skutterudite unit cell. This anion ordering results in a lowering of the symmetry from cubic to rhombohedral (space group , a=12.3270(5) and c=15.102(1) Å at 293 K). The electrical transport properties have been investigated using four-probe resistivity and Seebeck coefficient measurements. The temperature dependence of the electrical resistivity and the magnitude of the Seebeck coefficient indicate that CoGe_1.5Te_1.5 is an n-type semiconductor.     

Synthesis and reactivity of [N(C6H4Br)3][B(C6F5)4]: the X-ray crystal structure of [Fe(C5H5)2][B(C6F5)4]

A new chemical oxidant [N(4-C₆H₄Br)₃][B(C₆F₅)₄], was prepared and used to synthesize [Fe(C₅H₅)₂][B(C₆F₅)₄]. The crystal structure of [Fe(C₅H₅)₂][B(C₆F₅)₄] was determined.     

On the symmetry and crystal structures of Ba2LaIrO6

Accurate profile analysis of X-ray diffraction data was carried out to settle recent dispute on the symmetry and crystal structures of the double perovskite Ba₂LaIrO₆. Even through careful comparison of the full-width at half-maximum values, we found no evidence for Ba₂LaIrO₆ adopting either monoclinic (I2/m) or mixed rhombohedral and monoclinic (I2/m) structures at room temperature, becoming triclinic at below about 200 K. The correct space group is just at temperatures between 82 and 653 K. Furthermore, the phase transition does occur in Ba₂LaIrO₆, but the transition temperature is found to be much higher than the reported value.