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1.
The magnetic structures of RSn1+xGe1−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 TbSn1.12Ge0.88 is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1) μB 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 RSn1+xGe1−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 DySn1.09Ge0.91 and HoSn1.1Ge0.9 magnetic moments equal 7.25(15) and 8.60(6) μB at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to TN=10.7 K. For ErSn1.08Ge0.92, the Er magnetic moment equals 7.76(7) μB at T=1.5 K and it is parallel to the b-axis. At Tt=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 kx component and a quick decrease of ky 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. 相似文献
2.
Crystals of Ba5Fe5−xPtxClO13 and Ba5Co5−yPtyClO13 were prepared for x=1.31, 1.51, 1.57, 1.59 and y=0, 0.97 and 1.08 in a BaCl2 flux and investigated by X-ray diffraction methods. These compounds adopt a 10H perovskite structure built from the stacking of BaO3 and BaOCl layers in the sequence (BaO3)4(BaOCl) with space group P63/mmc. The cation sites within the trimeric unit of face-sharing octahedra are occupied by Co or Fe and Pt ions, while the tetrahedral sites formed between BaO3 and BaOCl layers are only occupied by Fe or Co. Moreover, oxygen stoichiometry indicates an average oxidation state for Co and Fe higher than +III, indicating the stabilization of Co4+ and Fe4+. 相似文献
3.
F. Lindberg S.Ya. Istomin G. Svensson P. Svedlindh A. Wannberg E.V. Antipov 《Journal of solid state chemistry》2006,179(5):1434-1444
The effect of replacing Co3+ by Ga3+ and Fe3+ in the perovskite-related tetragonal phase Sr0.75Y0.25CoO2.625 with unit cell parameters: a=2ap, and c=4ap (314 phase) has been investigated. The 314 phase is formed by Sr0.75Y0.25Co1−xMxO2.625+δ, with x?0.375 for M=Ga and x?0.625 for M=Fe. High-resolution transmission electron microscopy and electron diffraction revealed frequent microtwinning in the iron-containing compounds, in contrast to the Ga-substituted 314 phases. Diffraction experiments and electron microscope images indicated that at higher Fe contents, 0.75?x?0.875, a disordered cubic perovskite structure forms. The crystal structures of Sr0.75Y0.25Co0.75Ga0.25O2.625 and Sr0.75Y0.25Co0.5Fe0.5O2.625+δ were refined using neutron powder diffraction data. It was found that the oxygen content of Sr0.75Y0.25Co0.5Fe0.5O2.625+δ is higher than in Fe-free 314 phase, so that δ corresponds to 0.076, whereas δ=0 in Sr0.75Y0.25Co0.75Ga0.25O2.625+δ. Magnetization measurements on the unsubstituted Sr0.7Y0.3CoO2.62 and Ga-substituted Sr0.75Y0.25Co0.75Ga0.25O2.625 compounds indicate the presence of a ferromagnetic-like contribution to the measured magnetization at 320 and 225 K, respectively, while replacing Co by Fe leads to the suppression of this contribution. A neutron diffraction study shows that the Sr0.75Y0.25Co0.5Fe0.5O2.625+δ compound is G-type antiferromagnetic at room temperature, whereas Sr0.75Y0.25Co0.75Ga0.25O2.625 does not exhibit magnetic ordering at room temperature. 相似文献
4.
Structures of the double perovskites Ba2M(II)M ′(VI)O6 (M=Ca, Sr, M′=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2/m (M′ =W) and (M′=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P21/n (M′=U) or cubic (M′=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba2SrTeO6 and Ba2CaUO6, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba2SrWO6 and Ba2CaWO6 in the temperature range between 80 and 723 K. It was found that the rhombohedral structure exists in Ba2SrWO6 above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba2CaWO6 undergoes a structural phase transition at low temperature to the tetragonal I4/m structure. 相似文献
5.
Structural and photoluminescence properties of undoped and Ce3+-doped novel silicon-oxynitride phosphors of Ba4−zMzSi8O20−3xN2x (M=Mg, Sr, Ca) are reported. Single-phase solid solutions of Ba4−zMzSi8O20−3xN2x oxynitride were synthesized by partial substitutions of 3O2−→2N3− and Ba→M (M=Mg, Ca, Sr) in orthorhombic Ba2Si4O10. The influences of the type of alkaline earth ions of M, the Ce3+ concentration on the photoluminescence properties and thermal quenching behaviors of Ba3MSi8O20−3xN2x (M=Mg, Ca, Sr, x=0.5) were investigated. Under excitation at about 330 nm, Ba3MSi8O20−3xN2x:Ce3+ (x=0.5) exhibits efficient blue emission centered at 400-450 nm in the range of 350-650 nm owing to the 5d→4f transition of Ce3+. The emission band of Ce3+ shifts to long wavelength by increasing the ionic size of M due to the modification of the crystal field, as well as the Ce3+ concentrations due to the Stokes shift and energy transfer or reabsorption of Ce3+ ions. Among the silicon-oxynitride phosphors of Ba3MSi8O18.5N:Ce3+, M=Sr0.6Ca0.4 possesses the best thermal stability probably related to its high onset of the absorption edge of Ce3+. 相似文献
6.
Peter D. Battle Siân E. Dutton Gary J. Long Sirikarn Wisetsuwannaphum 《Journal of solid state chemistry》2011,184(9):2580-2587
Nd18Li8Co3FeO39−y, Nd18Li8CoFe3O39−y and Nd18Li8Co3TiO39−y have been synthesised and characterised by neutron powder diffraction, magnetometry and Mössbauer spectroscopy. Their cubic structure (Pm3?n, a∼11.9 Å) is based on intersecting <1 1 1> chains comprised of alternating octahedral and trigonal-prismatic coordination sites. These chains lie within hexagonal-prismatic cavities formed by a Nd-O framework. Each compound has an incomplete oxide sublattice (y∼1), with vacancies located around the octahedral sites that lie at the points of chain intersection. These sites are fully occupied by a disordered arrangement of transition-metal cations but only 75% of the remaining octahedral sites are occupied. The trigonal-prismatic sites are fully occupied by lithium except in the case of Nd18Li8CoFe3O39−y where some iron is present. Antiferromagnetic interactions are present on the Nd sublattice in each composition, but a spin glass forms below 5 K when a high concentration of spins is also present on the octahedral sites. 相似文献
7.
L. Vasylechko V. Vashook A. Senyshyn M. Knapp M. Berkowski U. Bismayer 《Journal of solid state chemistry》2003,172(2):396-411
Crystal structure and anisotropy of the thermal expansion of single crystals of La1−xSrxGa1−2xMg2xO3−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 La0.95Sr0.05Ga0.9Mg0.1O2.92 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 La0.9Sr0.1Ga0.8Mg0.2O2.85. 相似文献
8.
J.J. Blanco 《Journal of solid state chemistry》2004,177(8):2749-2755
The double perovskites, Sr2FeReO6 and Sr2FeRe0.9M0.1O6 (M=Nb, Ta) have been obtained by soft synthesis methods which yield homogeneous particles of micrometric grain size. The materials have been studied by X-ray and neutron powder diffraction, scanning electron microscopy and magnetic measurements. Rietveld refinements show that the compounds adopt a tetragonal I4/mmm structure at high temperatures and monoclinic P21/n below the transition temperature. The magnetic structures were determined by neutron powder diffraction at 100 and 300 K for the Sr2FeReO6, Sr2FeRe0.9Nb0.1O6 and Sr2FeRe0.9Ta0.1O6 phases, respectively. Evidence for a ferrimagnetic coupling between the Fe3+ and Re5+ sublattices has been observed. Magnetic measurements yield magnetic moments lower than the theoretical ones being in accord with the antisite disorder of 25% in the B-B′ positions. 相似文献
9.
B. Dabrowski E.N. Caspi S. Kolesnik J. Mais 《Journal of solid state chemistry》2005,178(11):3453-3460
We report the synthesis of SrMn1−xGaxO3−δ perovskite compounds and describe the dependence of their phase stability and structural and physical properties over extended cation and oxygen composition ranges. Using special synthesis techniques derived from thermogravimetric measurements, we have extended the solubility limit of random substitution of Ga3+ for Mn in the cubic perovskite phase to x=0.5. In the cubic perovskite phase the maximum oxygen content is close to 3−x/2, which corresponds to 100% Mn4+. Maximally oxygenated solid solution compounds are found to order antiferromagnetically for x=0-0.4, with the transition temperature linearly decreasing as Ga content increases. Increasing the Ga content introduces frustration into the magnetic system and a spin-glass state is observed for SrMn0.5Ga0.5O2.67(3) below 12 K. These properties are markedly different from the long-range antiferromagnetic order below 180 K observed for the layer-ordered compound Sr2MnGaO5.50 with nominally identical chemical composition. 相似文献
10.
A novel ternary boron-rich scandium borocarbide Sc4.5−xB57−y+zC3.5−z (x=0.27, y=1.1, z=0.2) was found. Single crystals were obtained by the floating zone method by adding a small amount of Si. Single-crystal structure analysis revealed that the compound has an orthorhombic structure with lattice constants of a=1.73040(6), b=1.60738(6) and c=1.44829(6) nm and space group Pbam (No. 55). The crystal composition ScB13.3C0.78Si0.008 calculated from the structure analysis agreed with the measured composition of ScB12.9C0.72Si0.004. The orthorhombic crystal structure is a new structure type of boron-rich borides and there are six structurally independent B12 icosahedra I1—I6, one B8/B9 polyhedron and nine bridging sites all which interconnect each other to form a three-dimensional boron framework. The main structural feature of the boron framework structure can be understood as a layer structure where two kinds of boron icosahedron network layer L1 and L2 stack each other along the c-axis. There are seven structurally independent Sc sites in the open spaces between the boron icosahedron network layers. 相似文献
11.
Klaus W. Richter Hans FlandorferHugo F. Franzen 《Journal of solid state chemistry》2002,167(2):517-524
The title compounds MxTa11−xGe8 (M=Ti, Zr, Hf) were prepared from the pure elements by arc-melting and subsequent induction heating at temperatures between 1200°C and 1400°C. X-ray powder diffraction studies of the samples were performed using the Guinier technique and the respective powder patterns were refined with a structure model based on the orthorhombic Cr11Ge8-structure type (oP76, Pnma). The homogeneity ranges of the compounds were determined to be 0.9<x<1.3 (M=Ti), 0.7<x<1.3 (M=Zr) and 0.7<x<2.4> (M=Hf) by means of electron probe microanalysis. Chemical bonding, electronic structure and site preferences are discussed based on extended Hückel calculations performed on hypothetical binary Ta11Ge8. 相似文献
12.
The title compounds and their deuterides have been prepared by solid-state and solid-gas reactions from the elements and investigated by X-ray and neutron powder diffraction as a function of temperature. At room temperature they crystallize with an anion-deficient cubic K2PtCl6-type structure (space group ) in which five hydrogen (deuterium) atoms surround iridium randomly on six octahedral sites with average bond distances of Ir-D=169-171 pm. At low temperature they undergo a tetragonal deformation (space group I4/mmm) to the partially ordered Sr2IrD5 (T=4.2K)-type structure in which four hydrogen (deuterium) atoms occupy planar sites with full occupancy (Ir-D=166-170 pm) and two hydrogen (deuterium) atoms axial sites (Ir-D=174-181 pm) with ∼50% occupancy, i.e., the data are consistent with a mixture of square-pyramidal [IrD5]4− complexes pointing in two opposite directions. The transitions occur at ∼240 K (Eu0.5Ca1.5IrD5, Eu0.5Sr1.5IrD5), ∼210 K (EuSrIrD5), ∼200 K (EuCaIrD5, Eu2IrD5), and are presumably of first order. 相似文献
13.
S. Shafeie S.Ya. Istomin S.A. Chen J.M. Chen M. Karppinen G. Svensson 《Journal of solid state chemistry》2011,184(1):177-190
Perovskite-type cobaltates in the system La2Co1+z(MgxTi1−x)1−zO6 were studied for z=0≤x≤0.6 and 0≤x<0.9, using X-ray and neutron powder diffraction, electron diffraction (ED), magnetic susceptibility measurements and X-ray absorption near-edge structure (XANES) spectroscopy. The samples were synthesised using the citrate route in air at 1350 °C. The space group symmetry of the structure changes from P21/n via Pbnm to R3¯c with both increasing Mg content and increasing Co content. The La2Co(MgxTi1−x)O6 (z=0) compounds show anti-ferromagnetic couplings of the magnetic moments for the Co below 15 K for x=0, 0.1 and 0.2. XANES spectra show for the compositions 0≤x≤0.5 a linear decrease in the L3/(L3+L2) Co-L2,3 edge branching ratio with x, in agreement with a decrease of the average Co ion spin-state, from a high-spin to a lower-spin-state, with decreasing nominal Co2+ ion content. 相似文献
14.
Vladimir G. Zubkov Ivan I. Leonidov Alexander P. Tyutyunnik Ludmila L. Surat Marina A. Melkozerova Elena V. Zabolotskaya Dina G. Kellerman 《Journal of solid state chemistry》2010,183(5):1186-1346
The crystal structure of the promising optical materials Ln2M2+Ge4O12, where Ln=rare-earth element or Y; M=Ca, Mn, Zn and their solid solutions has been studied in detail. The tendency of rare-earth elements to occupy six- or eight-coordinated sites upon iso- and heterovalent substitution has been studied for the Y2−xErxCaGe4O12 (x=0-2), Y2−2xCexCa1+xGe4O12 (x=0-1), Y2Ca1−xMnxGe4O12 (x=0-1) and Y2−xPrxMnGe4O12 (x=0-0.5) solid solutions. A complex heterovalent state of Eu and Mn in Eu2MnGe4O12 has been found. 相似文献
15.
16.
Richard Clements James R. Hester Chris D. Ling 《Journal of solid state chemistry》2011,184(8):2108-2113
Twelve members of the Ho2−yNdyZr2O7 series, prepared using conventional solid state methods, have been characterised by neutron powder diffraction. Ho2Zr2O7 has a defect fluorite structure whereas Nd2Zr2O7 is found to adopt the ordered pyrochlore structure with the composition induced fluorite-pyrochlore transformation occurring near y=1. Rietveld analysis on the neutron data for all the compositions reveals an increase in lattice parameter as a function of y across the entire series, with a small discontinuity associated with the transformation. The neutron profile results suggest that domains of pyrochlore-type initially begin to form before crystallising into a separate phase, and therefore that anion and cation ordering processes are distinct. There is a strong correlation between the extent of disorder in the anion sublattice and the x-parameter of 48f oxygen. These results point the way to a better understanding of the stability observed in pyrochlore structures. 相似文献
17.
Y. TsuchiyaK. Oh-ishi 《Journal of solid state chemistry》2002,168(1):85-90
Solid solutions of Li-doped Mg0.857Cu2.143O3 (LixMg0.857−xCu2.143O3−y) were prepared at 950°C for 12 h in air by the solid-state method using Li2CO3, MgO and CuO powders. The solid solutions were obtained as the single α phase with the güggenite structure in 0≦x≦0.06 region. With the increasing of the Li content x, the lattice parameters a, b and unit cell volume V decreased, while c increased. On the basis of the charge neutrality, hole carrier estimated by the oxygen content increased with the Li substitution. The Seebeck coefficient at room temperature of x = 0.03 sample was +400 μV/K. The electrical resistivity ρ at room temperature drastically decreased with the increasing x. Temperature dependences of ρ for x = 0.01, 0.03 and 0.06 samples were semi-conductive behavior from room temperature to about 12 K. Interaction between Cu2+ and Cu2+ through O2− seems to be somewhat large antiferromagnetic one. Sperconducting transition was not detected in the temperature range. 相似文献
18.
Rainer Niewa Andreas Czulucki Gudrun Auffermann Martin Meven Frank Steglich 《Journal of solid state chemistry》2010,183(6):1309-1313
Large single crystals of ZrAsxSey (x>y, x+y≤2, PbFCl type of structure, space group P4/nmm) were grown by Chemical Transport. Structural details were studied by single crystal neutron diffraction techniques at various temperatures. One single crystal specimen with chemical composition ZrAs1.595(3)Se0.393(1) was studied at ambient temperature (R1=5.10 %, wR2=13.18 %), and a second crystal with composition ZrAs1.420(3)Se0.560(1) was investigated at 25 K (R1=2.70%, wR2=5.70 %) and 2.3 K (R1=2.30 %, wR2=4.70 %), respectively. The chemical compositions of the crystals under investigation were determined by wavelength dispersive X-ray spectroscopy. The quantification of trace elements was carried out by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry. According to the crystal structure refinements the crystallographic 2a site is occupied by As, together with a significant amount of vacancies. One of the 2c sites is fully occupied by As and Se (random distribution). With respect to the fractional coordinates of the atoms, the crystal structure determinations based on the data obtained at 25.0 K and 2.3 K did not show significant deviations from ambient temperature results. The temperature dependence of the displacement parameters indicates a static displacement of As on the 2a sites (located on the (0 0 1) planes) for all temperatures. No indications for any occupation of interstitial sites or the presence of vacancies on the Zr (2a) site were found. 相似文献
19.
Navida Nasir Nataliya Melnychenko-Koblyuk Ingeborg Bednar 《Journal of solid state chemistry》2010,183(10):2329-2342
Three series of vacancy-free quaternary clathrates of type I, Ba8ZnxGe46−x−ySiy, Ba8(Zn,Cu)xGe46−x, and Ba8(Zn,Pd)xGe46−x, have been prepared by reactions of elemental ingots in vacuum sealed quartz at 800 °C. In all cases cubic primitive symmetry (space group Pm3?n, a∼1.1 nm) was confirmed for the clathrate phase by X-ray powder diffraction and X-ray single crystal analyses. The lattice parameters show a linear increase with increase in Ge for Ba8ZnxGe46−x−ySiy. M atoms (Zn, Pd, Cu) preferably occupy the 6d site in random mixtures. No defects were observed for the 6d site. Site preference of Ge and Si in Ba8ZnxGe46−x−ySiy has been elucidated from X-ray refinement: Ge atoms linearly substitute Si in the 24k site whilst a significant deviation from linearity is observed for occupation of the 16i site. A connectivity scheme for the phase equilibria in the “Ba8Ge46” corner at 800 °C has been derived and a three-dimensional isothermal section at 800 °C is presented for the Ba-Pd-Zn-Ge system. Studies of transport properties carried out for Ba8{Cu,Pd,Zn}xGe46−x and Ba8ZnxSiyGe46−x−y evidenced predominantly electrons as charge carriers and the closeness of the systems to a metal-to-insulator transition, fine-tuned by substitution and mechanical processing of starting material Ba8Ge43. A promising figure of merit, ZT ∼0.45 at 750 K, has been derived for Ba8Zn7.4Ge19.8Si18.8, where pricey germanium is exchanged by reasonably cheap silicon. 相似文献
20.
V. Paul-Boncour S.M. Filipek R. Wierzbicki F. Porcher G. Wiesinger 《Journal of solid state chemistry》2011,184(2):463-469
RMn2−xFexD6 compounds were obtained by applying a deuterium pressure of several kbar to RMn2−xFex compounds for x≤0.2 and R=Y, Er. These compounds are isostructural to RMn2D6 compounds and crystallize in a K2PtCl6 type structure with a random substitution of R and half the Mn atoms in the same 8c site whereas the other Mn atoms are located on the 4a site and surrounded by six D atoms (24e site). According to neutron powder diffraction analysis the Fe atoms are preferentially substituted on the 4a site. YMn2−xFexD6 compounds are paramagnetic and their molar susceptibility follows a modified Curie-Weiss law. ErMn2−xFexD6 compounds display a ferromagnetic behavior at 2 K, but their saturation magnetization (MS∼4.0 μB/f.u.) is half that of their parent compounds (MS∼8.0 μB/f.u.). The neutron diffraction patterns of ErMn1.8Fe0.2D6 display below 13 K both ferromagnetic and antiferromagnetic short range order, which can be related to a disordered distribution of Er moments. The paramagnetic temperatures of ErMn2−xFexD6 compounds are negative and decrease versus the Fe content whereas they are positive and increase for their parent compounds. 相似文献