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1.
The structure, magnetization and magnetostriction of Laves phase compound TbCo2 are investigated by temperature dependent high resolution neutron powder diffraction. The compound crystallizes in the cubic Laves phase C15 structure above its Curie temperature TC and exhibits a rhombohedral distortion (space group ) below TC. By an appropriate extrapolation of the temperature factor of Co atom above TC, the Rietveld refinement of the neutron powder diffraction data of the rhombohedral structure converges satisfactorily and reveals that the moments of Co1(3b) and Co2(9e) are almost equal. Tb moment follows well the Brillouin function. The total magnetic moment of TbCo2 is about 5.8μB/f.u., the anisotropic magnetostriction constant λ111 is about 4.6 × 10−3 and the volume magnetostriction ωs is about 8.7 × 10−3 at 14 K.  相似文献   

2.
Powder samples of cubic HoMn2Hx hydrides, with 0 ≤ x ≤ 4.3, have been investigated by X-ray diffraction and AC/DC magnetometry as a function of temperature and external magnetic field. Hydrogen is demonstrated to strongly modify structural and magnetic properties. X-ray studies revealed many structural transformations placed at low temperatures. In particular, a transformation from the cubic to the monoclinic structure was detected, which so far has not been reported for other cubic RMn2Hx (R - rare earth or Yttrium) compounds. The structural transformations are reflected in the magnetic behavior. The change in ordering temperatures implies a very strong relationship between the magnetic interactions and the Mn-Mn distance modified at hydrogen absorption. Tentative magnetic and structural phase diagrams are proposed. The presented results are compared with the properties of other cubic and hexagonal RMn2Hx hydrides.  相似文献   

3.
Half-Heusler compounds of Sn-doped TiCoSb “TiCoSnxSb1−x (x = 0.0, 0.01, and 0.05)” were prepared and their thermoelectric properties were measured above room temperature. From the EDX analysis, all the samples have three phases: the TiCoSnxSb1−x, Co-rich, and Ti-rich phases. The values of the thermoelectric power increase with Sn doping, and a positive thermoelectric power is obtained in the sample of TiCoSn0.05Sb0.95. The thermal conductivity decreases both with increasing temperature and with Sn content. The maximum value of ZT for p-type material is 0.030 at 988 K in the sample of TiCoSn0.05Sb0.95.  相似文献   

4.
The subsolidus phase relation of the system ZnO–Li2O–MoO3 has been investigated by X-ray diffraction (XRD) analyses. The phase diagram has been constructed. There are six binary compounds and one ternary compound in this system. The phase diagram comprises nine three-phase regions. The ternary compound Li2Zn2(MoO4)3 is refined by the Rietveld method. It belongs to an orthorhombic system with space group Pnma and lattice constants a = 5.1114 Å, b = 10.4906 Å, c = 17.6172 Å.  相似文献   

5.
The crystal structure of the ternary compound Ag2SiS3 was determined on the basis of X-ray powder diffraction. The compound belongs to a new structure type, space group P21/c, a = 0.66709(1), b = 0.66567(2), c = 1.31748(3) nm, and β = 118.658(1)°. Ag2SiS3 contains isolated [Si2S6] anionic units consisting of pairs of edge-shared tetrahedra. The Ag atoms are situated in the interstices formed by these fragments.  相似文献   

6.
The crystal structure of the ternary Laves phase ZrTiCu2 with unusual stoichiometry has been determined from combined refinement of X-ray powder, X-ray single crystal and neutron powder intensity data. The derived structure is of type MgZn2 (space group P63/mmc) with lattice parameters a = 0.51491(3) nm, c = 0.82421(8) nm. Crystal symmetry and composition reveal a high degree of atomic disorder, because Ti and Zr atoms share the 4f sites, whereas Ti and Cu atoms are found at the 6h sites. The 2a sites, however, are exclusively occupied by Cu. Lattice parameters for alloys Zr1−xTi1−xCu2+2x (annealed at 800 °C) as a function of the concentration of Cu for a constant ratio of Zr/Ti = 1 vary in a nonlinear way, which is consistent with the described complex atomic substitution mechanism. At a load of 2 N the micro-hardness was measured to be 7.5 ± 0.3 GPa, which is significantly larger than for most of the binary Ti–Cu or Zr–Cu phases. By a density functional theory ab initio approach the site preferences of Zr, Ti and Cu were calculated indicating that a random mixture of Ti and Cu atoms at the 6h lattice sites is a key factor to stabilize the proposed structure, which is unique for a Laves phase. Lattice parameters, elastic constants and shear moduli for polycrystalline ZrTiCu2 were also derived. The Vickers hardness of 6.2 GPa was estimated by applying a correlation between shear modulus and hardness. Data as calculated by the ab initio approach are in good agreement with the experimental findings.  相似文献   

7.
The crystal structures of the Ag4HgGe2S7 and Ag4CdGe2S7 compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.74546(8), b=0.68093(2), c=1.05342(3) nm, β=93.398(3)° for Ag4HgGe2S7 and a=1.74364(8), b=0.68334(3), c=1.05350(4) nm, β=93.589(3)° for Ag4CdGe2S7. Atomic parameters were refined in the isotropic approximation (RI=0.0761 and RI=0.0727, respectively).  相似文献   

8.
The structural and magnetic properties of doubly substituted Nd2Fe17−xyTixGay (0  x  1.0, 0  y  3) compounds have been investigated by a combined technique of X-ray diffraction, neutron diffraction and magnetic measurements. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th2Zn17-type structure. For a given Ti content (x), the lattice parameters a and c, and unit cell volume V of Nd2Fe17−xyTixGay all increase linearly with increasing Ga content. The addition of Ti initially has a considerably positive effect on the increasing rates of a, c, and unit cell volume V, but later the effect becomes very slight and even negative with the further increase of Ti content. The site occupancies of Ti and Ga in the crystallographic sites change a little compared to what is observed in the corresponding singly substituted compounds. The effects of Ti and Ga on the bond lengths of the doubly substituted compounds are quite different from that of the singly substituted compounds. Magnetic measurements show the TC of Nd2Fe17−xyTixGay increases with increasing Ti content for a low Ga content while it behaves conversely for a higher Ga content. The TC of Nd2Fe17−xyTixGay increases with increasing Ga content for a particular Ti content, while the addition of Ti results in a slower increase of TC on the Ga content (y  3). For a given Ti content, the Ms of Nd2Fe17−xyTixGay first increases a little and then decreases with the increase of Ga content, while for a given Ga content the Ms of Nd2Fe17−xyTixGay decreases with the increase of Ti content.  相似文献   

9.
We report the crystal structure and magnetic properties of new ternary actinide compounds UPd5Al2 and NpPd5Al2. Both compounds crystallize in the body-centered tetragonal ZrNi2Al5-type tetragonal structure (I 4/mmm). Although the magnetic susceptibility of both compounds follows the Curie–Weiss behavior at high temperature, no magnetic phase transition was observed. UPd5Al2 has a nonmagnetic ground state where the magnetic susceptibility saturates at low temperature, while NpPd5Al2 superconducts below 4.9 K as reported recently.  相似文献   

10.
We present structural and magnetic data on ZnV2O4 single crystals. Single crystal X-ray diffraction shows the measured crystals to be of very high quality, especially with respect to atomic order. The measured magnetic susceptibility resembles to that of a spin glass system, surprising for a translational invariant structure. The results are discussed in the framework of disorder in a magnetically frustrated lattice.  相似文献   

11.
The system (1−x)FeIn2S4xFeIn2Se4 has been investigated by X-ray powder methods. The subsolidus phase diagram is constructed in the temperature interval 600–1000°C. The spinel type FeIn2S4 exhibits a phase width up to the composition FeIn2S3Se and the layered FeIn2Se4 is formed for 1≥x≥0.65. A new layered compound is formed for 0.55≥x≥0.4 which crystallizes at temperatures below 850°C in an -FeGa2S4 structure with a=363.6 pm and c=1207.1 pm (x=0.5) for the hexagonal cell and at higher temperatures in the MgAl2S4-type with a=393.9 pm and c=3843.2 pm (x=0.5) for the hexagonal cell. Both structures have been refined by the Rietveld-method. All phase boundaries are nearly independent from temperature.  相似文献   

12.
CaLi2−xMgx (0 ≤ x ≤ 2) which has the C14-type Laves phase structure has been successfully synthesized and hydrogenated. The C14-type Laves phase structure was kept after hydrogenation of CaLi2−xMgx (x = 0.2, 0.5, 1). After hydrogenation of CaLi2 and CaMg2, the Laves phase disappeared. The CaH2 and LiH phases were formed from CaLi2 and the CaH2 and Mg phases from CaMg2, respectively. CaLi2−xMgx (0 < x < 2) ternary alloys formed stable hydride phases with the C14-type Laves phase structure in contrast to CaLi2 and CaMg2 binary alloys.  相似文献   

13.
We have studied, by means of neutron powder diffraction, the temperature evolution of the hydrogen solid solutions ZrV2Dx in the intermediate range, 2.18≤x≤2.73, separating two hydrogen-ordered phases, ZrV2D≤2 with k=(1/2, 1/2, 1/2) and ZrV2D≥2.8 with k=(0, 0, 1−δ). Instead of ordinary phase separation, we have found an uncommon phase. This phase is a kind of a disordered one and, simultaneously, it keeps a modulation of hydrogen density with the same k as for the ordered phase, one or another. Under favourable conditions this modulation transforms into the regular ordered phase.  相似文献   

14.
A new ternary compound Al0.32ErGe2 has been synthesized and studied from 298 K to 773 K using X-ray powder diffraction technique. Its structure has been determined at room temperature by Rietveld refinement of X-ray powder diffraction data. The ternary compound Al0.32ErGe2 crystallizes in the orthorhombic with the defect CeNiSi2 structure type (space group Cmcm, a = 0.40701(2) nm, b = 1.60401(9) nm, c = 0.39240(2) nm, Z = 4 and Dcalc = 8.326 g/cm3). The average thermal expansion coefficients , and of Al0.32ErGe2 are 1.72 × 10−5 K−1, 1.11 × 10−5 K−1 and 1.52 × 10−5 K−1, respectively. The bulk thermal expansion coefficient is 4.35 × 10−5 K−1. Electrical resistivity of Al0.32ErGe2 was measured between 5 K and 300 K.  相似文献   

15.
The crystal structure of new ternary R3Si1.25Se7 (R = Pr, Nd and Sm) compounds (Dy3Ge1.25S7 structure type, Pearson symbol hP22.5, space group P63, a = 1.05268 (3) nm, c = 0.60396 (3) nm, RI = 0.0897 for Pr3Si1.25Se7; a = 1.04760 (3) nm, c = 0.60268 (3) nm, RI = 0.0891 for Nd3Si1.25Se7; a = 1.04166 (6) nm, c = 0.59828 (6) nm for Sm3Si1.25Se7) was determined using X-ray powder diffraction. The nearest neighbours of the R and Si atoms are exclusively Se atoms. The latter form distorted trigonal prisms around the R atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbours surround every Se2 atom.  相似文献   

16.
A comparative survey is given on the variety of magnetic structures of the series of RCoC2 and RNiC2 with R=Pr, Nd, Tb, Dy, Ho, Er and Tm, which have been analysed by neutron diffraction. Rare earth structure relevant features are summarized. All compounds, except those with Pr, order magnetically at low temperatures. Magnetic order is confined to the rare earths; Co and Ni sites remain non-magnetic. RCoC2 become ferromagnets; RNiC2 order antiferromagnetically in different spin configurations. The type of order and R dependent moment configurations are explained by RKKY exchange and additional crystal field interactions.  相似文献   

17.
The crystal structure of the monoclinic phase η-Al11Cr2 of the space group C2/c, a ≈ 1.76 nm, b ≈ 3.05 nm, c ≈ 1.76 nm, β ≈ 90° [L.A. Bendersky, R.S. Roth, J.T. Ramon, D. Shechtman, Metall. Trans. A 22A (1991) 5] has been determined by single-crystal X-ray diffraction. The structure model, refined to a final R value of 0.0441, has the composition of Al83.8Cr16.2. a = 1.77348(10) nm, b = 3.04555(17) nm, c = 1.77344(10) nm, monoclinic angle β = 91.0520(12)°. There are 80 (66Al + 14Cr) independent atomic positions in a unit cell, of which all Cr atom sites and 8 Al atom sites have icosahedral coordination. These icosahedra are interconnected forming icosahedral chains along , (1 0 1) icosahedral layer blocks as well as a three-dimensional icosahedral structure.  相似文献   

18.
Zr(Mn0.45-xNi0.55Vx)2(x=0.05~0.40)Laves相储氢合金中的Zr-Ni相类型主要有ZrNi和Zr9Ni11相。ZrNi11相在整个研究的成分范围内出现,而 ZrNi相仅在x=0.20-0.40范围内出现。Zr9Ni11相的含量与合金中的 Mn、V含量关系不大,而ZrNi相的含量随合金中的Mn、V含量变化呈增加趋势。Zr9Ni11和ZrNi相的晶格常数随合金中的Mn、V含量变化而出现波动。Zr9Ni11相为长程有序结构,有序堆垛方向为[100]和[010],同时ZrNi11相基本上被包围在C15相中间,并与C15相存在一定取向关系,Zr9Ni11相的<111>晶向与C15相的<110>晶向基本平行,两者的差值在2°~3°之间。  相似文献   

19.
Response surface methodology was employed to study the effect of three factors, namely as milling time, milling speed and ball to powder weight ratio, on the mechanical activation of polymorphic phase transformation in nanocrystalline TiO2 powder and identify the probable interactions between these factors. The response was the rutile percentage after annealing the samples. Based on the statistical analysis, ball to powder weight ratio was found as the most effective factor and just one statistically significant interaction was found between milling speed and ball to powder ratio. It was also shown that increasing the milling time has no significant effect on the phase transformation since the required activation energy for the phase transformation is unattainable under these conditions. The rutile percentage was calculated from X-ray diffraction patterns of the samples via Rietveld refinement method. Raman spectroscopy was employed to verify the phase composition analysis based on X-ray diffraction results.  相似文献   

20.
Sn(II)1.2(Nb(V)1.6Sn(IV)0.4)O6 pyrochlore precursor was oxidized at temperature of the range 573–973 K in 1% O2/Ar and O2 gases for various periods of time. Two kinds of novel metastable phases with a composition of Sn(IV)0.6(Nb(V)0.8Sn(IV)0.2)O3.6 could be synthesized. Further, the other novel metastable phase with the same composition was found as a phase contained. One of the metastable phases was the cubic κ-CeZrO4 related-type possessing the fluorite-related structure, which was formed by the cation diffusionless insertion of the oxygen atom into original oxygen vacant site of the pyrochlore-type structure. Another was an orthorhombic α-PbO2 related-type possessing a cation ordered arrangement unlike a well known NiWO4 structure. The other was the rutile related-type possessing a cation ordered arrangement. Appearance of the two latter metastable phases could be attributed to the displacement of the oxygen stacking in the κ-CeZrO4 related-type phase without cation redistributions. The appearance mechanisms were analogous to the well known transformations for AX2 compounds among rutile-type, α-PbO2-type, and fluorite-type phases under high pressure and its release. The dependence of the appearance of these novel metastable phases on oxygen partial pressure and temperature has been discussed in terms of the driving forces and energy barriers for reactions.  相似文献   

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