首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
The crystal structures of three new intermetallic ternary compounds in the LnNiSb3 (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb3, NdNiSb3 and SmNiSb3 all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb6 octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb3), 4.6 K (NdNiSb3), and 2.9 K (SmNiSb3). Effective moments of 3.62 μB, 3.90 μB and 0.80 μB are found for PrNiSb3, NdNiSb3 and SmNiSb3, respectively, and are consistent with Pr3+ (f 2), Nd3+ (f 3), and Sm3+ (f 4).  相似文献   

2.
The luminescence hosts K3YF6 and K3GdF6 were obtained in a single-crystal form. Their crystal structure was determined from single-crystal X-ray diffraction data. Both crystals adopt monoclinic system with space group P21/n, Z=2. Lattice parameters for K3YF6 are refined to the following values , , , β=90.65(3) and for K3GdF6, , , β=90.80(3). The vibrational analysis, IR and Raman spectroscopy at room temperature, was applied to these compounds in order to study the site symmetry of Y3+ and Gd3+ ions.  相似文献   

3.
The crystal structure of Nb22O54 is reported for the first time, and the structure of orthorhombic Nb12O29 is reexamined, resolving previous ambiguities. Single crystal X-ray and electron diffraction were employed. These compounds were found to crystallize in the space groups P2/m (, , , β=102.029(3)°) and Cmcm (, , ), respectively and share a common structural unit, a 4×3 block of corner sharing NbO6 octahedra. Despite different constraints imposed by symmetry these blocks are very similar in both compounds. Within a block, it is found that the niobium atoms are not located in the centers of the oxygen octahedra, but rather are displaced inward toward the center of the block forming an apparent antiferroelectric state. Bond valence sums and bond lengths do not show the presence of charge ordering, suggesting that all 4d electrons are delocalized in these compounds at the temperature studied, T=200 K.  相似文献   

4.
The novel compound Ca2Co1.6Ga0.4O5 with brownmillerite (BM) structure has been prepared from citrates at 950 °C. The crystal structure of Ca2Co1.6Ga0.4O5 was refined, from neutron powder diffraction (NPD) data, in space group Pnma, , , , χ2=1.798, , Rwp=0.0378 and Rp=0.0292. On the basis of the NPD refinement the compound was found to be a G-type antiferromagnet (space group Pnma) at room temperature, with the magnetic moments of cobalt atoms directed along chains of tetrahedra in the BM structure. Electron diffraction and electron microscopy studies revealed disorder in the crystallites, which can be interpreted as the presence of slabs with BM-type structure of Pnma and I2mb symmetry.  相似文献   

5.
6.
A new compound, CePdGa6, and its isostructural analog, LaPdGa6 have been synthesized by flux growth and characterized by single-crystal X-ray diffraction. The compounds adopt a tetragonal structure with P4/mmm space group, Z=1. The lattice parameters for CePdGa6 are and and and for LaPdGa6. Magnetic and thermal measurement have revealed that CePdGa6 is a heavy-fermion with the specific heat coefficient and Ce f moments order antiferromagnetically along c-axis at . Reconfiguration of spin occurs at to induce a ferromagnetic component only in the a-b plane. This strong anisotropy in the magnetism might be related to its unique layered structure.  相似文献   

7.
The rare-earth dicyanamides Ln[N(CN)2]3 (Ln=La, Ce, Pr, Nd, Sm, Eu) were obtained via ion exchange in aqueous medium and subsequent drying: The crystal structures were solved and refined based on X-ray powder diffraction data and they were found to be isotypic: Ln[N(CN)2]3; Cmcm (no. 63), Z=4, Ln=La: , , ; Ce: , , ; Pr: , , ; Nd: , , ; Sm: , , ; Eu: , , ). The compounds represent the first dicyanamides with trivalent cations. The Ln3+ ions are coordinated by three bridging N atoms and six terminal N atoms of the dicyanamide ions forming a three capped trigonal prism. The structure type is related to that of PuBr3. The novel compounds Ln[N(CN)2]3 have been characterized by IR and Raman spectroscopy (Ln=La) and the thermal behavior has been monitored by differential scanning calorimetry (Ln=Ce, Nd, Eu).  相似文献   

8.
The copper vanadium oxide bronze Cu2.33−xV4O11 exhibits a three part composite structure refined on the basis of XRD low-temperature studies. It crystallizes in the triclinic system with the non-centric superspace group X1 and cell parameters ; ; ; α=90.0°; β=101.95(3)°; γ=90.0° with a modulation q-vector equal to (0,0.11,0). The three different parts of this composite structure differ by their b-unit cell repeat defined as b1 ; () and (). These parts are respectively associated to the V4O11 substructure and to each of the two different copper sites. Such refinement allows us to describe the structure using only one and fully occupied crystallographic site for each of the Cu ions. The maximum composition (x=0) is then achieved. Bond valence sum calculations on the basis of such composite structure is in agreement with electronic structure calculation made using the average one and allows us to attribute the proper valence state to each Cu ions. Then, the calculated ratio appears, contrary to the average structure, in prefect agreement with the one deduced from XPS experiment.  相似文献   

9.
10.
A new ternary compound, Ce2PdGa10, has been synthesized using Ga flux and characterized by single-crystal X-ray diffraction. Ce2PdGa10 adopts a tetragonal structure in the I4/mmm space group and is isostructural to Ce2NiGa10. Lattice parameters are , , , and Z=2. The compound is metallic (dρ/dT>0), with the resistance decreasing roughly linearly with temperature from 300 to 175 K. The magnetic susceptibility of Ce2PdGa10 is consistent with local-moment paramagnetism and no long-range magnetic ordering occurs down to 2 K. A large positive magnetoresistance over 200% is observed at 2 K for fields of 9 T. In this paper, we present the structure and physical properties of Ce2PdGa10 and compared them to CePdGa6.  相似文献   

11.
A novel ternary borate oxide, lead bismuth boron tetraoxide, PbBiBO4, has been prepared by solid-state reaction at temperature below 800 °C. The single-crystal X-ray structural analysis showed that PbBiBO4 crystallizes in the monoclinic space group P21/n with , , , β=91.48(1), Z=4. It represents a new structure type in which distorted BiO69− octahedra are connected to each other in corner- and edge-sharing manner to form two-dimensional layers that are bridged by B atoms of BO3 triangles giving rise to a three-dimensional framework, with channels parallel to the [0 1 0] direction accommodating the pyramidally coordinated Pb2+ cations.  相似文献   

12.
A ferroelectric crystal (C3N2H5)5Sb2Br11 has been synthesized. The single crystal X-ray diffraction studies (at 300, 155, 138 and 121 K) show that it is built up of discrete corner-sharing bioctahedra and highly disordered imidazolium cations. The room temperature crystal structure has been determined as monoclinic, space group, P21/n with: , and and β=96.19°. The crystal undergoes three solid-solid phase transitions: ) discontinuous, continuous and discontinuous. The dielectric and pyroelectric measurements allow us to characterize the low temperature phases III and IV as ferroelectric with the Curie point at 145 K and the saturated spontaneous polarization value of the order of along the a-axis (135 K). The ferroelectric phase transition mechanism at 145 K is due to the dynamics of imidazolium cations.  相似文献   

13.
Ln3Co4Sn13 (Ln=La, Ce) have been synthesized by flux growth and characterized by single crystal X-ray diffraction. These compounds adopt the Yb3Rh4Sn13-type structure and crystallize in the cubic space group (No. 223) with Z=2. Lattice parameters at 298 K are , , and , for the La and Ce analogues, respectively. The crystal structure consists of an Sn-centered icosahedron at the origin of the unit cell, which shares faces with eight Co trigonal prisms and 12 Ln-centered cuboctahedra. Magnetization data at 0.1 T show paramagnetic behavior down to 1.8 K for Ce3Co4Sn13, with per Ce3+, while conventional type II superconductivity appears below 2.85 K in the La compound. Electrical resistivity and specific heat data for the La compound show a corresponding sharp superconducting transition at Tc∼2.85 K. The entropy and resistivity data for Ce3Co4Sn13 show the existence of the Kondo effect with a complicated semiconducting-like behavior in the resistivity data. In addition, a large enhanced specific heat coefficient at low T with a low magnetic transition temperature suggests a heavy-fermionic character for the Ce compound. Herein, the structure and physical properties of Ln3Co4Sn13 (Ln=La, Ce) are discussed.  相似文献   

14.
15.
Single crystals of a new form of L-Ta2O5 with a 19×b superstructure have been synthesised by flux growth. The phase is most likely stabilised by the incorporation of a small amount of lithium (0.14 wt% Li) from the flux. The phase has C-centred monoclinic symmetry with , (), , γ=90.00(1)°. The structure was refined in space group C112/m to R1=0.044 for 814 unique reflections with F>4σ(F). The structure can be described as comprising chains of edge-shared TaO7 pentagonal bipyramids that are regularly folded at (010) planes to give sinusoidal chains along [010]. These chains are interconnected along [100] and [001] by corner sharing, creating inter-chain regions that are occupied by isolated TaO6 octahedra and pairs of corner-shared octahedra. A comparison with published data for high-quality refinements of related structures has led to the development of a general model that can explain the structural chemistry variations in the known L-Ta2O5-related structures. A shorthand notation is presented for representing the structures, based on the sequence along [010] of the interchain octahedra.  相似文献   

16.
Single crystals of a new sodium manganese oxide, NaMn2O4, were synthesized for the first time using a high-temperature and high-pressure technique. The NaMn2O4 single crystal is black, has a needle shape, and crystallizes in the orthorhombic calcium ferrite-type structure, space group Pnam with , , , , and Z=4. The structure was determined from a single-crystal X-ray study and refined to the conventional values R=0.041 and wR=0.034 for 1190 observed reflections. The framework structure is built up from edge-sharing chains of MnO6 octahedra that condense to form one-dimensional tunnels in which the sodium atoms are located. The Mn-O bond distance and bond valence analyses revealed the manganese valence Mn3+/Mn4+ ordering in the two “double rutile” chains of NaMn2O4.  相似文献   

17.
18.
Three manganese oxalates have been hydrothermally synthesized, and their structures determined by single-crystal X-ray diffraction. MnC2O4·2H2O (I) is orthorhombic, P212121, , , , , Z=4, final R, Rw=0.0832, 0.1017 for 561 observed data (I>3σ(I)). The one-dimensional structure consists of chains of oxalate-bridged manganese centers. [C4H8(NH2)2][Mn2(C2O4)3] (II) is triclinic, , , , , α=81.489(2)°, β=81.045(2)°, γ=86.076(2)°, , Z=1, final R, Rw=0.0467, 0.0596 for 1773 observed data (I > 3σ (I)). The three-dimensional framework is constructed from seven coordinate manganese and oxalate anions. The material contains extra-framework diprotonated piperazine cations. Mn2(C2O4)(OH)2 (III) is monoclinic, P21/c, , , , β=91.10(3)°, , Z=1, final R1, wR2=0.0710, 0.1378 for 268 observed data (I>2σ (I)). The structure is also three dimensional, with layers of MnO6 octahedra pillared by oxalate anions. The hydroxide group is found bonded to three manganese centers resulting in a four coordinate oxygen.  相似文献   

19.
We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of , , , α=76.617°, β=84.188°, γ=74.510° and space group . The crystal structure suggests the chemical formula CoMoO4·3/4H2O. The structure consists of MoO4 tetrahedra and CoO6 octahedra, confirming the earlier X-ray absorption near-edge spectroscopic (XANES) investigation on the hydrate. The comparison of the crystal structures of the hydrate and the α-,β-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the β-phase, but had arrangements of CoO6 and MoOn polyhedra similar to those of the hp-phase.  相似文献   

20.
Structural phase transitions in LiTaOGeO4 (LTGO) and LiTaOSiO4 (LTSO) have been observed using differential scanning calorimetry, X-ray diffraction and MAS NMR spectroscopy. LTGO transforms from P21/c to C2/c space group symmetry at , while the isomorphic transition occurs at in LTSO. An analogous phase transition is known to occur in the structurally related mineral titanite, CaTiOSiO4. Spontaneous strain accompanying this phase transition in LTSO is significantly stronger than in titanite. As in titanite non-vanishing strain components are observable for Tc<T<Ti, with a similar ratio Ti/Tc. MAS NMR spectroscopy in combination with computation of the electric field gradient by first principle methods confirms that the tetrahedral Li coordination environment is retained during the phase transitions in LTGO and in LTSO. In LTSO substantial motional narrowing is observed, indicating increased mobility of the Li cation above . The narrowing of the spinning sidebands is significantly modified immediately above and below the critical temperature.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号