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1.
A new phase YMn2D6 was synthesized by submitting YMn2 to 1.7 kbar deuterium pressure at 473 K. According to X-ray and neutron powder diffraction experiments, YMn2D6 crystallizes in the space group with at 300 K. The Y and half of the Mn atoms occupy statistically the 8c site whereas the other Mn atoms are located in 4a site and surrounded by 6 D atoms (24 e). This corresponds to a K2PtCl6-type structure with a partially disordered substructure which can be written as [YMn]MnH6. No ordered magnetic moment is observed in the NPD patterns and the magnetization measurements display a paramagnetic behavior. The study of the thermal stability by Differential Scanning Calorimetry and XRD experiments indicates that this phase decomposes in YD2 and Mn at 625 K, and is more stable than YMn2H4.5.  相似文献   

2.
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   

3.
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   

4.
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   

5.
The structural, magnetic, and electrochemical properties of the LiNi1−xCoxO2 samples with x= 0, 0.05, 0.1, and 0.25 have been investigated by powder X-ray diffraction analyses, magnetic susceptibility (χ) measurements, and electrochemical charge and discharge test in non-aqueous lithium cell. According to the structural analyses using a Rietveld method, the occupancy of the Ni ions in the Li layer was estimated to be below 0.01 for all the samples and was eventually independent of x. The temperature (T) dependence of χ−1 obtained with the magnetic field H=10 kOe indicated that all the samples are a Curie-Weiss paramagnet down to . At low T, all the samples entered into a spin-glass-like phase below Tf. The magnitude of Tf was found to decrease almost linearly with x, as in the case for the x dependences of the lattice parameters of ah- and ch-axes, Weiss temperature, and effective magnetic moment. It is, therefore, found that the change of the magnetic properties with x is simply explained by a dilution effect due to the increase of the quantity of Co3+ ions. On the other hand, the electrochemical measurements demonstrated that the irreversible capacity at the initial cycle is drastically decreased by the small amount of Co ions. Furthermore, the discharge capacity (Qdis) for the x=0.05 and 0.1 samples are larger than that for the x=0 sample; namely, Qdis=180 mAh g−1 for x=0, Qdis=217 mAh g−1 for x=0.05, and Qdis=206 mAh g−1 for x=0.1. Comparing with the past results, the amount of Ni ions in the Li layer is found to play a significant role for determining the magnetic and electrochemical properties of LiNi1−xCoxO2.  相似文献   

6.
New phases which arise from partial substitution of Ti4+ by Cr3+ and Li+ of the compound La2/3TiO3 have been obtained, giving rise to the series La1.33LixCrxTi2−xO6 (x=0.66, 0.55 and 0.44). These phases adopt a perovskite-type structure as deduced from their structural characterization. Rietveld's analyses of neutron diffraction data show that it is orthorhombic (S.G. Pbnm) with ordered domains. Conductivity has been examined by complex impedance spectroscopy and it increases with increasing lithium and chromium content. These materials behave as mixed conductors with low activation energies. Magnetic susceptibility variation with temperature shows antiferromagnetic interactions at the lowest temperatures.  相似文献   

7.
B-site disordered RFe0.5V0.5O3 compounds, with R=La, Nd, Eu and Y, have been prepared by solid-state reaction technique and their structures and magnetic properties have been investigated through X-ray powder diffraction, time-of-flight neutron powder diffraction and magnetization measurements at temperatures ranging from 5 to 700 K. The four compounds can be described as distorted perovskites with space group symmetry Pbnm and a+bb tilt system. The studied compounds also show antiferromagnetic ordering with Neel temperatures of 299, 304, 304, and 335 K respectively. The magnetic structures of R=La, Nd and Y compounds were determined from the neutron powder diffraction as Gz with observed magnetic moments of 2.55, 2.54 and 2.69μB at 30, 40 and 40 K, respectively.  相似文献   

8.
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 Rc 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   

9.
The magnetic structure of the Fe2P-type R6CoTe2 phases (R=Gd-Er, space group P6¯2m) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: TC=220 K and TCN=180 K for Gd6CoTe2, TC=174 K and TCN=52 K for Tb6CoTe2, TC=125 K and TCN=26 K for Dy6CoTe2, TCN=60 K and TN=22 K for Ho6CoTe2 and TCN∼30 K and TN∼14 K for Er6CoTe2.Between 174 and 52 K Tb6CoTe2 has a collinear magnetic structure with K0=[0, 0, 0] and with magnetic moments along the c-axis, whereas below 52 K it adopts a non-collinear ferromagnetic one.Below 60 K the magnetic structure of Ho6CoTe2 is that of a non-collinear ferromagnet. The holmium magnetic components with a K0=[0, 0, 0] wave vector are aligned ferromagneticaly along the c-axis, whereas the magnetic component with a K1=[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22 K coincides with the reorientation of the Ho magnetic component with the K0 vector from the collinear to the non-collinear state.Below 30 K Er6CoTe2 shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K0=[0, 0, 0] and K1=[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14 K corresponds to the variation in the magnitudes of the MErK0 and MErK1 magnetic components.In these phases, no local moment was detected on the cobalt site.The magnetic entropy of Gd6CoTe2 increases from ΔSmag=−4.5 J/kg K at 220 K up to ΔSmag=−6.5 J/kg K at 180 K for the field change Δμ0H=0-5 T.  相似文献   

10.
A polycrystalline sample of Pr18Li8Fe4RuO39 has been synthesized by a solid state method and characterized by neutron powder diffraction, magnetometry and Mössbauer spectroscopy; samples of Pr18Li8Fe5−xMnxO39 and Pr18Li8Fe5−xCoxO39 (x=1, 2) have been studied by magnetometry. All these compounds adopt a cubic structure (space group , a0∼11.97 Å) based on intersecting 〈111〉 chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Pr-O framework. The trigonal-prismatic site in Pr18Li8Fe4RuO39 is occupied by Li+ and high-spin Fe3+. The remaining transition-metal cations occupy the two crystallographically-distinct octahedral sites in a disordered manner. All five compositions adopt a spin-glass-like state at 7 K (Pr18Li8Fe4RuO39) or below.  相似文献   

11.
The magnetic and transport properties of ternary rare-earth chromium germanides RCr0.3Ge2 (R=Y and Tb-Er) have been determined. X-ray and neutron diffraction studies indicate that these compounds have the CeNiSi2-type structure (space group Cmcm) [1]. Magnetic measurements reveal the antiferromagnetic ordering below TN equal to 18.5 K (R=Tb), 11.8 K (Dy), 5.8 K (Ho) and 3.4 K (Er). From the neutron diffraction data the magnetic structures have been determined. For TbCr0.3Ge2 and DyCr0.3Ge2 at low temperatures the magnetic ordering can be described by two vectors k1=(,0,0) and k2=(,0,), and k1=(,0,0) and k2=(,0,), respectively. In HoCr0.3Ge2 and ErCr0.3Ge2 the ordering can be described by one propagation vector equal to (,,0) and (0,0,0.4187(2)), respectively. In DyCr0.3Ge2 some change in the magnetic ordering is observed at Tt=5.1 K. In temperature range from Tt to TN the magnetic ordering is given by one propagation vector k=(,0,0). YCr0.3Ge2 is a Pauli paramagnet down to 1.72 K which suggests that in the entire RCr0.3Ge2 series the Cr atoms do not carry magnetic moments. All compounds studied exhibit metallic character of the electrical conductivity. The temperature dependencies of the lattice parameters reveal strong magnetostriction effect at the respective Nèel temperatures.  相似文献   

12.
The effect of Fe doping on the ferromagnetic Nd0.7Pb0.3Mn1−xFexO3 (x=0, 0.025, 0.05, 0.075, 0.1) phases has been studied in order to analyze the double-exchange interaction. The structural and magnetic study has been carried out by neutron powder diffraction and susceptibility measurements between 1.7 and 300 K. The substitution of Fe at the Mn site results in reductions in both the Curie temperature Tc and the magnetic moment per Mn ion without appreciable differences in the crystal structures. All the compounds crystallize in Pnma space group. The thermal evolution of the lattice parameters of the Nd0.7Pb0.3Mn1−xFexO3 (x=0.025, 0.05, 0.075) compounds shows discontinuities in volume and lattice parameters close to the magnetic transition temperature. Increasing amounts of Fe3+ reduces the double exchange interactions and no magnetic contribution for x=0.1 is observed. The magnetic structures of Nd0.7Pb0.3Mn1−xFexO3 (x=0, 0.025, 0.05, 0.075) compounds show that the Nd and Mn ions are ferromagnetically ordered.  相似文献   

13.
The valence state of Pr in the B-site ordered double perovskites Ba2PrRu1−xIrxO6 is shown to be sensitive to both the precise Ru:Ir content and temperature. Pr LIII XANES measurements show that at room temperature the Pr is trivalent in the Ru-rich compounds with x<0.25. At higher Ir contents the Pr is tetravalent. High-resolution powder synchrotron X-ray and neutron diffraction methods have been used to study the composition and temperature dependence of the crystal structures of these oxides. The Ru and Ir are statistically distributed on one of the two available B-sites. The oxides undergo an apparently first-order monoclinic P21/n to tetragonal P4/mnc phase transition in response to the change on the Pr and Ru/Ir valence. High temperatures and Ru contents favor the lower symmetry monoclinic structure, that is arises from the presence of the larger PrIII cations. The variations in the observed metal-oxygen bond distances are consistent with a simultaneous change in the valence of the Ru/Ir accompanying the PrIII-PrIV valence transition.  相似文献   

14.
New niobium oxynitrides containing either magnesium or silicon were prepared at 1000 °C by ammonia nitridation of oxide precursors obtained via the citrate route. The products had rock-salt type crystal structures. Crystallinity was improved by annealing in 0.5 MPa N2 and the final compositions were (Nb0.95Mg0.05)(N0.92O0.08) at 1500 °C and (Nb0.87Si0.090.04)(N0.87O0.13) at 1200 °C. The magnesium and oxide ions partially co-substitute the niobium and nitride ions in the octahedral sites of the δ-NbN lattice, respectively. Silicon ions were also successfully doped together with oxide ions into the rock-salt type NbN lattice. The Si doped product exhibited relatively large displacement at the octahedral sites and was accompanied by a small amount of cation vacancies. Superconductivity was improved by annealing to obtain critical temperatures/volume fractions of Tc=17.6 K/100% for Mg- and Tc=16.2 K/95% for the Si-doped niobium oxynitrides.  相似文献   

15.
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   

16.
The title compounds have been prepared as polycrystalline powders by thermal treatments of stoichiometric mixtures of R2O3 and MoO3 in air. The room-temperature crystal structure for all the series has been refined from high-resolution neutron powder diffraction data. All the phases are isostructural (space group C2/c, Z=8) with the polymorph α-R2MoO6, typified by Sm2MoO6. The structure contains four zigzag, one-dimensional MoO5 polyhedral rows per unit cell, running through the RO8 polyhedral framework along the [001] direction. MoO5 form discrete units (i.e. do not share common oxygen), with Mo-O distances ranging from 1.77 to 2.24 Å, although the oxygen coordination can be extended to distances of about 3.1 Å, giving rise to strongly distorted MoO8 scalenohedra. Thus, MoO8 and RO8 polyhedra are fully ordered in R2MoO6 compounds, which in fact can be considered as superstructures of fluorite (M3O6), containing 24 MO2 fluorite units per unit cell, with unit-cell parameters related to that of cubic fluorite ( Å). A bond valence study demonstrates that the present crystal structure is especially stable for small rare-earth cations, and becomes more unstable when the R3+ size increases, thus explaining the observed preference of the large rare-earth molybdates for polymorphs β and γ with the same stoichiometry.  相似文献   

17.
The crystal structure and magnetism of Ca2−xLaxFeReO6 (0≤x≤0.8) double perovskites have been investigated. The samples with low doping (x≤0.4) are found to crystallize with the monoclinic P21/n superstructure, while those in the high doping ones (x≥0.6) have orthorhombic Pbnm superstructure. With the increase of an La doping, the anti-site defects increases, giving rise to highly disordered samples at the Fe and Re positions. At the low doping region (x≤0.4), the compounds undergo a simultaneous structural and magnetic transition accompanying a slight increase of the Curie temperature. The increase of Curie temperature is discussed in terms of the structural change with doping.  相似文献   

18.
We have synthesized samples in the system BaTi1−xFexO3−x/2 with x=0.1−0.6 at temperatures of 1200-1300°C under reducing conditions of oxygen fugacity. After drop quenching, samples were characterized using the electron microprobe, X-ray diffraction and Mössbauer spectroscopy. All samples were hexagonal with a 6H-BaTiO3 type structure. Mössbauer spectroscopy showed all iron to be present as Fe3+, occurring in octahedral and pentahedral sites. Analysis of area ratios indicates that oxygen vacancies are distributed randomly over O1 sites, and that a random distribution of Fe and Ti cations over M1 and M2 sites is consistent with the data. No evidence for ordering of oxygen vacancies was found. Results are consistent with conductivity results, which show generally increasing ionic conductivity with increasing oxygen vacancy concentration.  相似文献   

19.
Mössbauer and magnetic measurements were carried out on the compositions Mn4.5Fe0.5Ge3, Mn4FeGe3, and Mn3.5Fe1.5Ge3. Data were obtained from liquid N2 to about 600°K. The iron substitution takes place initially in the 4(d) sites of the D88 structure of Mn5Ge3 until one half of manganese is replaced; additional iron, then, may substitute in 6(g) sites. The postulated magnetic structure for Mn5Ge3 consists of ferromagnetic alignment of spins within the two sublattices and parallel alignment between them. When the Fe concentration exceeds 0.5, canting of spins occurs either between, or within, the sublattices. The limit of solubility of Fe in the structure appears to occur at, or slightly beyond, the Mn4FeGe3 composition.  相似文献   

20.
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.  相似文献   

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