Analysis of the radial and longitudinal effects of a planar sample in a single TE102 rectangular electron paramagnetic resonance (EPR) cavity

The response of the cavity to the rotation of a concentrically positioned planar sample of variable width, w ∈ 〈1 mm, 10 mm〉, around the common cavity-sample x-axis in a Bruker single TE₁₀₂ rectangular cavity (radial effect) has been analysed. The observed dependence of the EPR signal intensity, Ipp, on the rotation angle has a general ovaloid shape with an eccentricity, ?, which varies linearly with the width, w, of the sample, ? = 0.0246 + 0.0311 × w, correlation, R = 0.996, for samples with a width greater than 2 mm but shows a positive deviation from linearity for the 1 and 2 mm samples. The dependence of the Ipp value on the planar sample width, w, is non-linear for all polar-angle values investigated. These experimental observations are in a very good agreement with theoretical calculations in which the response is modelled using the Cassinian curves modified for planar sample geometry. Similar trends of the angular Ipp dependence were observed for any position of the planar sample as the centre was moved along the vertical x-axis of the cavity. In the longitudinal Ipp dependence for a planar sample whose length, L = 30 mm, is greater than that of the cavity, then (i) for the case where the whole cavity length is occupied by the sample a constant value for the Ipp (a plateau) is observed and (ii) for sample movement in and out of this plateau region the dependence varies according to the left and right halves of a modified “sine-squared” function. The variation in the signal amplitude along the cavity x-axis (longitudinal effect) can be calculated theoretically using a “sine-squared” curve, modified for an “over full-length cavity” planar sample. In general, the response of the cavity to a planar sample situated at any position on the common sample cavity x-axis can be represented as a product of a modified Cassinian curve and a modified “sine-squared” curve. The non-linear radial effect may give rise to serious sources of systematic error in quantitative EPR spectroscopy with planar sample geometry and shows that accurate and precise positioning of the sample in the microwave cavity is essential.     

Liquid-liquid phase equilibria for some polystyrene-methylcyclohexane mixtures

Liquid-liquid cloud point diagrams of solutions of nearly monodisperse samples of polystyrene (PS), and binary mixtures of nearly monodisperse PS’s, both in methylcyclohexane (MCH), were determined for several polymer molecular weights (M_w) at 0.1 MPa. The bimodal mixtures (PS[M_w(1),ρ(1)] + PS[M_w(2),ρ(2)], M_w(1)=90×10³ g/mol, M_w(2)=13×10³ g/mol, 5.78 × 10³ g/mol, and 2.2 × 10³ g/mol, ρ=1.06) were prepared constraining 〈M_w〉=38.6×10³ g/mol, ρ=M_w/M_n is the polydispersity index. In each case the cloud point curves (CPC’s) for the bimodal mixtures are strongly skewed, lying well above CPC for 〈M_w〉 when φ<φ_CRITICAL, and below CPC for 〈M_w〉 when φ>φ_CRITICAL; φ is volume fraction polymer in the polymer/solvent mixture. The experimental results are discussed in the context of empirical and mean-field representations.     

Phase relations in a barium-rich high-temperature region (25-45 mol% CuO, 900-1100 °C) of the BaO-CuOx system

The phase relations have been studied in the BaO-CuO_x system in the range of 25.0-45.0 mol% CuO at 900-1100 °C at P(O₂)=21 kPa (air) by visual polythermal analysis (VPA), powder X-ray diffraction (XRD), electron diffraction (ED) with simultaneous energy-dispersive X-ray (EDX) elemental analysis in a transmission electron microscope (TEM), and iodometric chemical analysis. The discrete deviations 2.02 (101:50), 2.04 (102:50), 2.10 (105:50) of Ba/Cu (Ba:Cu) composition from the stoichiometric ratio 2:1 have been found for the known Ba₂CuO_3+δ oxides in the subsolidus region 900-970 °C. Unit cell parameters of the 101:50 orthorhombic oxide, 102:50 tetragonal one, 105:50 orthorhombic one are, respectively, a=4.049, b=3.899, c=13.034 Å; a=3.985, c=12.968 Å; a=4.087, b=3.897 and c=12.950 Å. ED patterns of the 101:50, 102:50, 105:50 oxides show characteristic supercell reflections with the respective vector 1/60[5 4 0], ≈2/11〈1 1 0〉 and 1/6[2 0 0]. Oxides of the 2:1, 7:4, 5:3 and 23:20 compositions have been found in the crystallization region 970-1050 °C. Unit cell parameters of the 2:1 orthorhombic oxide are a=4.095, b=3.795, c=13.165 Å. Interplanar spacings and X-ray characteristic peak intensities of the 7:4, 5:3 and 23:20 oxides are given. Oxides 2:1 and 7:4 melt pseudocongruently at 1020 and 1005 °C, oxides 5:3 and 23:20 melt incongruently at 995 and 980 °C, respectively. A diagram of the phase relations in the studied region of the BaO-CuO_x system has been constructed, whose structure is considered as the total projection of phase states of the system existing for different x.     

Cu2Sc2Ge4O13, a novel germanate isotypic with the quasi-1D compound Cu2Fe2Ge4O13 between 100 and 298 K

The germanate compound Cu₂Sc₂Ge₄O₁₃ has been synthesized by solid-state ceramic sintering techniques between 1173 and 1423 K. The structure was solved from single-crystal data by Patterson methods. The title compound is monoclinic, a=12.336(2) Å, b=8.7034(9) Å, c=4.8883(8) Å, β=95.74(2), space group P2₁/m, Z=4. The compound is isotypic with Cu₂Fe₂Ge₄O₁₃, described very recently. The structure consists of crankshaft-like chains of edge-sharing ScO₆ octahedra running parallel to the crystallographic b-axis. These chains are linked laterally by [Cu₂O₆]⁸⁻ dimers forming a sheet of metal-oxygen-polyhedra within the a-b plane. These sheets are separated along the c-axis by [Ge₄O₁₃]¹⁰⁻ units. Cooling to 100 K does not alter the crystallographic symmetry of Cu₂Sc₂Ge₄O₁₃. While the b, c lattice parameter and the unit cell volume show a positive linear thermal expansion (α=6.4(2)×10⁻⁶, 5.0(2)×10⁻⁶ and 8.3(2)×10⁻⁶ K⁻¹ respectively), the a lattice parameter exhibits a negative thermal expansion (α=−3.0(2)×10⁻⁶ K⁻¹) for the complete T-range investigated. This negative thermal expansion of a is mainly due to the increase of the Cu-Cu interatomic distance, which is along the a-axis. Average bond lengths remain almost constant between 100 and 298 K, whereas individual ones partly show both significant shortages and lengthening.     

La(Li1/3Ti2/3)O3: a new 1:2 ordered perovskite

A new 1:2 ordered perovskite La(Li_1/3Ti_2/3)O₃ has been synthesized via solid-state techniques. At temperature >1185°C, Li and Ti are randomly distributed on the B-sites and the X-ray powder patterns can be indexed in a tilted (b⁻b⁻c⁺) Pbnm orthorhombic cell (a=a_c√2=5.545 Å, b=a_c√2=5.561 Å, c=2a_c=7.835 Å). However, for T?1175°C, a 1:2 layered ordering of Li and Ti along 〈111〉_c yields a structure with a P2₁/c monoclinic cell with a=a_c√6=9.604 Å, b=a_c√2=5.552 Å, c=a_c3√2=16.661 Å, β=125.12°. While this type of order is well known in the A²⁺(B²⁺_1/3B⁵⁺_2/3)O₃ family of niobates and tantalates, La(Li_1/3Ti_2/3)O₃ is the first example of a titanate perovskite with a 1:2 ordering of cations on the B-sites.     

The lanthanoid polyantimonides with the ideal compositions Pr5Sb12 and Nd5Sb12 crystallizing with a new structure type and Ho2Sb5 with Dy2Sb5-type structure

The title compounds were isolated in well-crystallized form from samples with a substantial excess of antimony, annealed at temperatures slightly below the melting point of that element. Their crystal structures were determined from single-crystal diffractometer data. Pr_9-xSb_21-y and Nd_9-xSb_21-y crystallize with a new monoclinic structure type, Pearson symbol mS(62-5.4), space group Cm, Z=2 with a=2859.1(4) pm, b=426.3(1) pm, c=1356.1(2) pm, β=95.52(1)°, R=0.034 for 4351 structure factors and 188 variable parameters for Pr_9-xSb_21-y and a=2845(2) pm, b=424.7(8) pm, c=1345.9(9) pm, β=95.42(7)°, R=0.069 for 2928 F values and 188 variables for Nd_9-xSb_21-y. Of the 30 atomic sites, three show fractional occupancy corresponding to the compositions Pr_8.303(5)Sb_20.03(1) and Nd_8.30(2)Sb_19.98(9), respectively. A model for the order of occupied atomic sites with a tripled b-axis is proposed resulting in the ideal compositions Pr₅Sb₁₂ and Nd₅Sb₁₂. The holmium compound Ho₂Sb₅ has a Dy₂Sb₅-type structure: mP28, P2₁/m, a=1301.8(3) pm, b=414.9(1) pm, c=1451.1(2) pm, β=102.14(1)°, R=0.028 for 2573 F values and 86 variables. In both structure types most rare earth atoms have nine antimony neighbors forming tricapped trigonal prisms. The coordination polyhedra of the antimony atoms show a great variety, with a trigonal prism of rare earth atoms as one extreme case. The other extreme coordination of an antimony atom is a distorted octahedron formed by six antimony atoms. The differences and similarities of both structures are discussed. Chemical bonding within the antimony polyanions is analyzed on the basis of an extended Zintl-Klemm concept using bond-length-bond-strength relationships.     

Crystal structure, thermal expansion and conductivity of anisotropic La1−xSrxGa1−2xMg2xO3−y (x=0.05, 0.1) single crystals

Crystal structure and anisotropy of the thermal expansion of single crystals of La_1−xSr_xGa_1−2xMg_2xO_3−y (x=0.05 and 0.1) were measured in the temperature range 300-1270 K. High-resolution X-ray powder diffraction data obtained by synchrotron experiments have been used to determine the crystal structure and thermal expansion. The room temperature structure of the crystal with x=0.05 was found to be orthorhombic (Imma, Z=4, a=7.79423(3) Å, b=5.49896(2) Å, c=5.53806(2) Å), whereas the symmetry of the x=0.1 crystal is monoclinic (I2/a, Z=4, a=7.82129(5) Å, b=5.54361(3) Å, c=5.51654(4) Å, β=90.040(1)°). The conductivity in two orthogonal directions of the crystals has been studied. Both, the conductivity and the structural data indicate three phase transitions in La_0.95Sr_0.05Ga_0.9Mg_0.1O_2.92 at 520-570 K (Imma-I2/a), 770 K (I2/a-R3c) and at 870 K (R3c-R-3c), respectively. Two transitions at 770 K (I2/a-R3c) and in the range 870-970 K (R3c-R-3c) occur in La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85.     

A novel open-framework with non-crossing channels in the uranyl vanadates A(UO2)4(VO4)3 (A=Li, Na)

A new sodium uranyl vanadate Na(UO₂)₄(VO₄)₃ has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the tetragonal symmetry with space group I4₁/amd and following cell parameters: a=7.2267(4) Å and c=34.079(4) Å, V=1779.8(2) Å³, Z=4 with ρ_mes=5.36(3) g/cm³ and ρ_cal=5.40(2) g/cm³. A full-matrix least-squares refinement on the basis of F² yielded R₁=0.028 and wR₂=0.056 for 52 parameters with 474 independent reflections with I?2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a CCD detector. The crystal structure is characterized by _∞²[(UO₂)₂(VO₄)] sheets parallel to (001) formed by corner-shared UO₆ distorted octahedra and V(2)O₄ tetrahedra, connected by V(1)O₄ tetrahedra to _∞¹[UO₅]⁴⁻ chains of edge-shared UO₇ pentagonal bipyramids alternately parallel to the a- and b-axis. The resulting three-dimensional framework creates mono-dimensional channels running down the a- and b-axis formed by face-shared oxygen octahedra half occupied by Na. The powder of Li analog compound Li(UO₂)₄(VO₄)₃ has been synthesized by solid-state reaction. The two compounds exhibit high mobility of the alkaline ions within the two-dimensional network of non-intersecting channels.     

Quaternary selenostannates Na2−xGa2−xSn1+xSe6 and AGaSnSe4 (A=K, Rb, and Cs) through rapid cooling of melts. Kinetics versus thermodynamics in the polymorphism of AGaSnSe4

The quaternary alkali-metal gallium selenostannates, Na_2−xGa_2−xSn_1+xSe₆ and AGaSnSe₄ (A=K, Rb, and Cs), were synthesized by reacting alkali-metal selenide, Ga, Sn, and Se with a flame melting-rapid cooling method. Na_2−xGa_2−xSn_1+xSe₆ crystallizes in the non-centrosymmetric space group C2 with cell constants a=13.308(3) Å, b=7.594(2) Å, c=13.842(3) Å, β=118.730(4)°, V=1226.7(5) Å³. α-KGaSnSe₄ crystallizes in the tetragonal space group I4/mcm with a=8.186(5) Å and c=6.403(5) Å, V=429.1(5) Å³. β-KGaSnSe₄ crystallizes in the space group P2₁/c with cell constants a=7.490(2) Å, b=12.578(3) Å, c=18.306(5) Å, β=98.653(5)°, V=1705.0(8) Å³. The unit cell of isostructural RbGaSnSe₄ is a=7.567(2) Å, b=12.656(3) Å, c=18.277(4) Å, β=95.924(4)°, V=1741.1(7) Å³. CsGaSnSe₄ crystallizes in the orthorhombic space group Pmcn with a=7.679(2) Å, b=12.655(3) Å, c=18.278(5) Å, V=1776.1(8) Å³. The structure of Na_2−xGa_2−xSn_1+xSe₆ consists of a polar three-dimensional network of trimeric (Sn,Ga)₃Se₉ units with Na atoms located in tunnels. The AGaSnSe₄ possess layered structures. The compounds show nearly the same Raman spectral features, except for Na_2−xGa_2−xSn_1+xSe₆. Optical band gaps, determined from UV-Vis spectroscopy, range from 1.50 eV in Na_2−xGa_2−xSn_1+xSe₆ to 1.97 eV in CsGaSnSe₄. Cooling of the melts of KGaSnSe₄ and RbGaSnSe₄ produces only kinetically stable products. The thermodynamically stable product is accessible under extended annealing, which leads to the so-called γ-form (BaGa₂S₄-type) of these compounds.     

Investigation of structural and hydrogen absorption properties in the LaNi5−xPtx-H2 system

The substitution of nickel by platinum in the binary LaNi₅ compound (CaCu₅ structure type, a=5.019(1) Å, c=3.981(1) Å, space group P6/mmm) and its effect on the hydrogenation properties was studied. The phase LaNi_5−xPt_x has a homogeneity domain ranging from x=0 to 5. For x<3, platinum substitutes almost exclusively on site 3g and also replaces nickel on site 2c for x>3. Contrary to what is observed in other systems, the hydrogen absorption plateau pressure was found to increase as a function of the cell volume. Powder neutron diffraction experiments were conducted for two deuterated compounds with x=0.25 and 0.75. Deuterium partial ordering occurs in the case of x=0.25 leading to a symmetry decrease to the space group P6mm (LaNi_4.75Pt_0.25D_5.23, a=4.225(1) Å, c=5.357(1) Å, Z=1, R_Bragg=3.3%). For x=0.75, an orthorhombic superstructure based on the CaCu₅-type lattice was found (LaNi_4.25Pt_0.75D_2.61, a_orth=√3a_hex=9.089(1) Å, b_orth=b_hex=5.272(1) Å, c_orth=2c_hex=8.145(1) Å, Z=4, SG Ibam, R_Bragg=6.1%).     

Crystal structures and magnetic properties of two-dimensional antiferromagnets Co1−xZnxTeMoO6

Crystal structures and magnetic properties of metal telluromolybdates Co_1−xZn_xTeMoO₆ (x=0.0, 0.1,…,0.9) are reported. All the compounds have an orthorhombic structure with space group P2₁2₁2 and a charge configuration of M²⁺Te⁴⁺Mo⁶⁺O₆. In this structure, M ions form a pseudo-two-dimensional lattice in the ab plane. Their magnetic susceptibility measurements have been performed in the temperature range between 1.8 and 300 K. The end member CoTeMoO₆ shows a magnetic transition at 24.4 K. The transition temperature for solid solutions rapidly decreases with increasing x and this transition disappears between x=0.4 and 0.5, which is corresponding to the percolation limit for the square-planer lattice. From the magnetization, specific heat, and powder neutron diffraction measurements, it is found that the magnetic transition observed in the CoTeMoO₆ is a canted antiferromagnetic ordering of Co²⁺ ions. The antiferromagnetic component of the ordered magnetic moment (3.12(3)μ_B at 10 K) is along the b-axis. In addition, there exists a small ferromagnetic component (0.28(3)μ_B) along the a-axis.     

Syntheses and crystal structures of RE3MnSn5−x (RE=Tm, Lu) with 3D Mn-Sn framework

Four new isostructural rare earth manganese stannides, namely RE₃MnSn_5−x (x=0.16(6), 0.29(1) for RE=Tm, x=0.05(8), 0.21(3) for RE=Lu), have been obtained by reacting the mixture of corresponding pure elements at high temperature. Single-crystal X-ray diffraction studies revealed that they crystallized in the orthorhombic space group Pnma (No. 62) with cell parameters of a=18.384(9)-18.495(6) Å, b=6.003(3)-6.062(2) Å, c=14.898(8)-14.976(4) Å, V=1644.3(14)-1679.0(9) Å³ and Z=8. Their structures belong to the Hf₃Cr₂Si₄ type and feature a 3D framework composed of 1D [Mn₂Sn₇] chains interconnected by [Sn₃] double chains via Sn-Sn bonds, forming 1D large channels based on [Mn₄Sn₁₆] 20-membered rings along the b-axis, which are occupied by the rare earth atoms. Electronic structure calculations based on density functional theory (DFT) for idealized “RE₃MnSn₅” model indicate that these compounds are metallic, which are in accordance with the results from temperature-dependent resistivity measurements.     

Flux growth of a new cobalt-zinc-tin ternary phase Co7+xZn3−xSn8 and its relationship to CoSn

The intermetallic compound Co_7+xZn_3−xSn₈ (−0.2<x<0.2) forms from the reaction of cobalt in zinc/tin eutectic flux. This phase has a new structure type in orthorhombic space group Cmcm, with unit cell parameters a=4.138(1) Å, b=12.593(4) Å, and c=11.639(4) Å (Z=2; R₁=0.0301). Varying the amount of cobalt in the synthesis leads to formation of a superstructure in space group Pnma, with lattice parameters a=12.5908(2) Å, b=11.6298(3) Å, and c=8.2704(2) Å (Z=4; R₁=0.0347). A Co/Zn mixed site and a partially occupied Co site in the Cmcm structure order to form the Pnma supercell. TGA/DSC studies indicate that the binary phase CoSn initially forms in the flux at 1173 K, and then reacts with the zinc in the cooling solution to form the ternary structure at 823 K. This phase exhibits Pauli paramagnetic behavior.     

Crystal structures and phase transitions of SrZr(PO4)2-BaZr(PO4)2 solid solutions

A complete series of solid solutions was prepared in the SrZr(PO₄)₂-BaZr(PO₄)₂ system and examined by conventional X-ray powder diffraction (XRPD). The crystals of Sr_xBa_1−xZr(PO₄)₂ with x?0.1 were isomorphous with yavapaiite (KFe(SO₄)₂, space group C2/m). The solid solution with 0.2?x?0.7 has been composed of a new phase, showing a superstructure along the a-axis (c-axis of the yavapaiite substructure). The crystals with 0.8?x?0.9 were composed of both the new phase and the triclinic phase, the latter being isostructural with SrZr(PO₄)₂ (x=1). The crystal structure of the new phase has been determined using direct methods, and it has been further refined by the Rietveld method. The crystal of Sr_0.7Ba_0.3Zr(PO₄)₂ (x=0.7) is monoclinic (space group P2/c, Z=4 and D_x/Mg m⁻³=3.73) with a=1.53370(8) nm, b=0.52991(3) nm, c=0.84132(4) nm, β=92.278(1)° and V=0.68321(6) nm³. Final reliability indices are R_wp=7.32%, R_p=5.60% and R_B=3.22%. The powder specimen was also examined by high-temperature XRPD and differential thermal analysis (DTA) to reveal the occurrence of two phase transitions during heating; the space group changed from P2/c to C2/m at ∼400 K, followed by the monoclinic-to-hexagonal (or trigonal) transition at 1060 K. The P2/c-to-C2/m transition has been, for the first time, described in the yavapaiite-type compounds.     

Modulated Structure of the Composite Crystal Ca0.83CuO2

We have determined the crystal structure of the quasi one-dimensional cuprate Ca_0.83CuO₂, known as Ca₄Cu₅O₁₀, etc., by a superspace group approach. The compound consists of two interpenetrating subsystems of CuO₂ chains and Ca atoms. Structural parameters were refined with a superspace group of F2/m(1+α 0 γ)0s using powder X-ray and neutron diffraction data. Lattice parameters were refined to be a₁=2.8043(2) Å, b=6.3179(2) Å, c₁=10.5744(5) Å, and β₁=90.10(1)° for the [CuO₂] subsystem and a₂=3.3652(2) Å, b=6.3179(2) Å, c₂=10.5893(5) Å, and β₂=93.04(1)° for the [Ca] subsystem. Remarkable displacive modulation of the O and Ca atom sites is observed parallel to the b-axis and the c-axis, respectively. On the other hand, the Cu atom sites deviate mainly in the a direction to yield a periodic fluctuation between the nearest Cu-Cu distances. The Ca atoms suitably sit in the center of the modulated O₆ octahedra.     

The crystal chemistry of Bi6TP2O15+x, T=Fe, Ni, Zn: Isomorphism and polymorphism, structural relationship to Bi6TiP2O16

The crystal structures of compounds with nominal compositions Bi₆FeP₂O_15+x (I), Bi₆NiP₂O_15+x (II) and Bi₆ZnP₂O_15+x (III) were determined from single-crystal X-ray diffraction data. They are monoclinic, space group I2, Z=2. The lattice parameters for (I) are a=11.2644(7), b=5.4380(3), c=11.1440(5) Å, β=96.154(4)°; for (II) a=11.259(7), b=5.461(4), c=11.109(7) Å, β=96.65(1)°; for (III) a=19.7271(5), b=5.4376(2), c=16.9730(6) Å, β=131.932(1)°. Least squares refinements on F² converged for (I) to R1=0.0554, wR₂=0.1408; for (II) R₁=0.0647, wR₂=0.1697; for (III) R₁=0.0385, wR₂=0.1023. The crystals are complexly twinned by 2-fold rotation about , by inversion and by mirror reflection. The structures consist of edge-sharing articulations of OBi₄ tetrahedra forming layers in the a-c plane that then continue by edge-sharing parallel to the b-axis. The three-dimensional networks are bridged by Fe and Ni octahedra in (I) and (II) and by Zn trigonal bipyramids in (III) as well as by oxygen atoms of the PO₄ moieties. Bi also randomly occupies the octahedral sites. Oxygen vacancies exist in the structures of the three compounds due to required charge balances and they occur in the octahedral coordination polyhedron of the transition metal. In compound (III), no positional disorder in atomic sites is present. The Bi-O coordination polyhedra are trigonal prisms with one, two or three faces capped. Magnetic susceptibility data for compound (I) were obtained between 4.2 and 350 K. Between 4.2 and 250 K it is paramagnetic, μ_eff=6.1 μ_B; a magnetic transition occurs above 250 K.     

Ab initio structure determination of new compound Li4CaB2O6

A new compound, Li₄CaB₂O₆, has been synthesized by solid-state reaction and its structure has been determined from powder X-ray diffraction data by direct methods. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=10.4%, R_wp=14.2%, R_exp=4.97%. This compound belongs to the orthorhombic space group Pnnm, with lattice parameters a=9.24036(9) Å, b=8.09482(7) Å, and c=3.48162(4) Å. Fundamental building units are isolated [BO₃]³⁻ anionic groups, which are all parallel to the a-b plane stacked along the c-axis. The Ca atoms are six-coordinated by the O atoms to form octahedral coordination polyhedra, which are joined together through edges along the c-axis, forming infinitely long three-dimensional chains. The Li atoms have a four-fold and a five-fold coordination with O atoms that lead to complex Li-O-Li chains that also extend along the c-axis. The infrared spectrum of Li₄CaB₂O₆ was also studied, which is consistent with the crystallographic study.     

Neutron diffraction studies of RSn1+xGe1−x (R=Tb-Er) compounds

The magnetic structures of RSn_1+xGe_1−x (R=Tb, Dy, Ho and Er, x≈0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn_1.12Ge_0.88 is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1) μ_B at 1.62 K. It lies in the b-c plane and form an angle θ=17.4(2)° with the c-axis. This structure is stable up to the Nèel temperature equal to 31 K. The magnetic structures of RSn_1+xGe_1−x, where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2, 0) with the sequence (++−+) of magnetic moments in the crystal unit cell. In DySn_1.09Ge_0.91 and HoSn_1.1Ge_0.9 magnetic moments equal 7.25(15) and 8.60(6) μ_B at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to T_N=10.7 K. For ErSn_1.08Ge_0.92, the Er magnetic moment equals 7.76(7) μ_B at T=1.5 K and it is parallel to the b-axis. At T_t=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of k_x component and a quick decrease of k_y component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b-c plane and form an angle 48(3)° with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Nèel temperature is observed.     

Hydrothermal synthesis of two layered indium oxalates with 12-membered apertures

Two layered indium oxalates, In(C₂O₄)_2.5(C₃N₂H₁₂)(H₂O)₃, I, and In(C₂O₄)_1.5(H₂O)₃, II, have been hydrothermally synthesized. In I, the linkage between indium and oxalate units gives rise to a sheet with a rectangular 12-membered aperture (six indium atoms and six oxalate units). Indium atom of II has an unusual pentagonal bipyramidal coordination arrangement. The connectivity between indium and oxalate units forms a neutral puckered layer with 12- (along a-axis) and eight-membered (along b-axis) apertures. Crystal data for these two indium oxalates are as follows: I, triclinic, space group: P-1 (No. 2), a=8.725(3) Å, b=9.170(3) Å, c=9.901(3) Å, α=98.101(4)°, β=97.068(4)°, γ=102.403(4)°, V=756.3(4) Å³, Z=2, M=463.0(5), ρ_calc=2.042 g/cm³, R₁=0.0377, wR₂=0.0834. II, monoclinic, space group: P2₁/c (No. 14), a=10.203(5) Å, b=6.638(1) Å, c=11.152(7) Å, β=95.649(4)°, V=751.7(4)ų, Z=4, M=300.9(0), ρ_calc=2.659 g/cm³, R₁=0.0229, wR₂=0.0488. TG analyses indicate the water molecules of I can be removed at 150°C. The dehydrated product retains structural integrity.     

Crystal structure of Mg0.65Sc0.35Dx deuterides studied by X-ray and neutron powder diffraction

The structural properties of the Mg_0.65Sc_0.35D_x deuterides have been investigated by X-ray and neutron powder diffraction at different deuterium content (0?x?2.2 D/f.u.). The metallic phase adopts a pseudo-CsCl structure (Pm-3m space group (SG); a=3.5921(2) Å) that transforms upon hydrogenation into a face centered cubic (FCC) phase involving an elongation of the c-axis, a shrinkage of the a-axis and a re-ordering of the metallic atoms. The fully hydrided compound (2.2 D/f.u.) adopts a cubic structure (Fm-3m SG; a=4.8087(7) Å) and deuterium is located in fully occupied tetrahedral sites and partially filled (24%) octahedral sites. Upon desorption, a two-phase domain appears with coexistence of a hydrogen-rich (1.55 D/f.u.) and a hydrogen-poor (0.85 D/f.u.) phase (Fm-3m SG; a=4.7598(3) and 4.6936(3) Å, respectively). All deuterium atoms are located in the tetrahedral sites with different occupancy factors: 77% for the H-rich phase and 43% for the H-poor phase. The appearance of a plateau in the pressure-composition-isotherm curve measured at 573 K confirms this two-phase behavior. The structural properties of the Mg_0.65Sc_0.35D_x system are discussed and compared with other body centered cubic (BCC) alloys adopting the same structure.