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 62 毫秒
1.
The strontium chromium oxide [Sr2O2][CrO2]1.85 misfit layer compound has been synthesised at high-pressure and high-temperature conditions. Electron diffraction patterns and high-resolution transmission electron microscopy images along [001] show the misfit character of the different layers composing the structure with a supercell along the incommensurate parameter b≈7b1≈13b2. The modulated crystal structure has been refined within the superspace formalism against single-crystal X-ray diffraction data, employing the (3+1)-dimensional superspace group Cnmb(0σ20)0 0 s. The compound has a composite structure with lattice parameters a1=5.182(1) Å, b1=5.411(1) Å, c1=18.194(3) Å for the first, SrO, subsystem and the same a and c, but with b2=2.925(1) Å for the second, CrO2, subsystem. The layer stacking is similar to that of orthorhombic PbS(TiS2)1.18, but with a much stronger intersubsytem bonding in the case of the oxide. The intersubsystem lattice mismatch is mainly handled by displacement modulations of the Sr atoms, correlated with modulations of the valence, the coordination and the anisotropic displacement parameters.  相似文献   

2.
The ferromagnetic shape memory (MSM) alloy Ni2MnGa undergoes a martensitic transformation (MT) at T=220 K on cooling. The structure of this phase is studied by powder X-ray diffraction experiment. The analysis of the experimental data combined with the huge information reported in literature allowed to conclude that the Ni2MnGa martensite shows an incommensurate modulated structure closely related to a five-fold layered superstructure. The symmetry of the basic structure is found to be orthorhombic. The structure is refined by Rietveld method with superspace group Immm(00γ)s00 having a=4.2187(1) Å, b=5.5534(1) Å and c=4.1899(1) Å and modulation vector q=0.4248(3)c*. The results show that the modulation is mainly related to the periodic shuffling of the atomic layers perpendicular to the c-axis of the orthorhombic basic structure.  相似文献   

3.
4.
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 Rp=10.4%, Rwp=14.2%, Rexp=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.  相似文献   

5.
The crystal chemistry and crystallography of the compounds SrR2CuO5 (Sr-121, R=lanthanides) were investigated using the powder X-ray Rietveld refinement technique. Among the 11 compositions studied, only R=Dy and Ho formed the stable SrR2CuO5 phase. SrR2CuO5 was found to be isostructural with the “green phase”, BaR2CuO5. The basic structure is orthorhombic with space group Pnma. The lattice parameters for SrDyCuO5 are a=12.08080(6) Å, b=5.60421(2) Å, c=7.12971(3) Å, V=482.705(4) Å3, and Z=8; and for the Ho analog are a=12.03727(12) Å, b=5.58947(7) Å, c=7.10169(7) Å, V=477.816(9) Å3, and Z=8. In the SrR2CuO5 structure, each R is surrounded by seven oxygen atoms, forming a monocapped trigonal prism (RO7). The isolated CuO5 group forms a distorted square pyramid. Consecutive layers of prisms are stacked in the b-direction. Bond valence calculations imply that residual strain is largely responsible for the narrow stability of the SrR2CuO5 phases with R=Dy and Ho only. X-ray powder reference diffraction patterns for SrDy2CuO5 and SrHo2CuO5 were determined.  相似文献   

6.
New weberite-type Ca2Ta2O7 and zirconolite-type CaZrTi2O7 polytypes have been prepared by doping with Nd/Zr and Th/Al, respectively, and their structures have been refined using single-crystal X-ray diffraction intensity data. The 3T zirconolite polytype, Ca0.8Ti1.35Zr1.3Th0.15Al0.4O7, has a=7.228(1), c=16.805(1) Å. The 3T weberite-type polytype, Ca1.92Ta1.92Nd0.08Zr0.08O7, has a=7.356(1), c=18.116(1) Å. Both 3T polytypes have space group P3121, Z=6. The 4M Ca2Ta2O7 polytype has the same composition, from electron microprobe analyses, as the 3T polytype, and has cell parameters: a=12.761(1), b=7.358(1), c=24.565(1) Å, β=100.17(1)°, space group C2, Z=16. The structural relationships between the different zirconolite and weberite polytypes are discussed. A consideration of the structures from the viewpoint of anion-centered tetrahedral arrays shows that zirconolite can be considered as an anion-deficient fluorite derivative phase. However, the fluorite-type topology of edge-shared OM4 tetrahedra is not maintained in the Ca2Ta2O7 weberite-type polytypes, even though they have a fluorite-like fcc packing of metal atoms. One of the oxygen atoms moves from a tetrahedral Ta3Ca interstice to an adjacent Ta2Ca4 octahedral interstice in the weberite polytypes.  相似文献   

7.
The crystal structure of La0.63(Ti0.92,Nb0.08)O3 has been refined by the Rietveld analysis of Cu X-ray powder diffraction data collected at 23°C. This material was confirmed to have an A-site deficient orthorhombic perovskite-type structure with double ideal perovskite ABO3 units along the c-axis (space group Pmmm, Z=2, a=3.86036(5) Å, b=3.87222(5) Å, c=7.82609(9) Å). Lattice parameters of the same sample have been investigated in situ in the temperature range from 25°C to 496°C by 1.37873(3) Å synchrotron X-ray powder diffraction. The synchrotron X-ray powder diffraction technique was found to be very powerful to determine precise lattice parameters around a phase transition temperature. This compound exhibited a reversible phase transition between the orthorhombic and tetragonal phases at around 370°C. (1) The lattice parameters increased continuously with temperature, while the b/a ratio decreased continuously with temperature and became unity at the orthorhombic-tetragonal transition point. (2) No hysteresis was observed in the lattice parameter values between heating and cooling. These results of (1) and (2) suggest that the orthorhombic-tetragonal phase transition is continuous.  相似文献   

8.
NaPd3O4, Na2PdO3 and K3Pd2O4 have been prepared by solid-state reaction of Na2O2 or KO2 and PdO in sealed silica tubes. Crystal structures of the synthesized phases were refined by the Rietveld method from X-ray powder diffraction data. NaPd3O4 (space group Pmn, a=5.64979(6) Å, Z=2) is isostructural to NaPt3O4. It consists of NaO8 cubes and PdO4 squares, corner linked into a three-dimensional framework where the planes of neighboring PdO4 squares are perpendicular to each other. Na2PdO3 (space group C2/c, a=5.3857(1) Å, b=9.3297(1) Å, c=10.8136(2) Å, β=99.437(2)°, Z=8) belongs to the Li2RuO3-structure type, being the layered variant of the NaCl structure, where the layers of octahedral interstices filled with Na+ and Pd4+ cations alternate with Na3 layers along the c-axis. Na2PdO3 exhibits a stacking disorder, detected by electron diffraction and Rietveld refinement. K3Pd2O4, prepared for the first time, crystallizes in the orthorhombic space group Cmcm (a=6.1751(6) Å, b=9.1772(12) Å, c=11.3402(12) Å, Z=4). Its structure is composed of planar PdO4 units connected via common edges to form parallel staggered PdO2 strips, where potassium atoms are located between them. Magnetic susceptibility measurements of K3Pd2O4 reveal a Curie-Weiss behavior in the temperature range above 80 K.  相似文献   

9.
Two new compounds Ca0.5Bi3V2O10 and Sr0.5Bi3V2O10 have been synthesized in the ternary system: MO-Bi2O3-V2O5 system (M=M2+). The crystal structure of Sr0.5Bi3V2O10 has been determined from single crystal X-ray diffraction data, space group and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å3. Ca0.5Bi3V2O10 is isostructural with Sr0.5Bi3V2O10, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å3 and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi2O2) along c-axis formed by linkage of BiO8 and BiO6 polyhedra interconnected by MO8 polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10−5 and 3.63×10−5 S cm−1 for Ca0.5Bi3V2O10 and Sr0.5Bi3V2O10, respectively at 725 °C.  相似文献   

10.
Three new compounds Ca(HF2)2, Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6) were obtained in the system metal(II) fluoride and anhydrous HF (aHF) acidified with excessive PF5. The obtained polymeric solids are slightly soluble in aHF and they crystallize out of their aHF solutions. Ca(HF2)2 was prepared by simply dissolving CaF2 in a neutral aHF. It represents the second known compound with homoleptic HF environment of the central atom besides Ba(H3F4)2. The compounds Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6) represent two additional examples of the formation of a polymeric zigzag ladder or ribbon composed of metal cation and fluoride anion (MF+)n besides PbF(AsF6), the first isolated compound with such zigzag ladder. The obtained new compounds were characterized by X-ray single crystal diffraction method and partly by Raman spectroscopy. Ba4F4(HF2)(PF6)3 crystallizes in a triclinic space group P1¯ with a=4.5870(2) Å, b=8.8327(3) Å, c=11.2489(3) Å, α=67.758(9)°, β=84.722(12), γ=78.283(12)°, V=413.00(3) Å3 at 200 K, Z=1 and R=0.0588. Pb2F2(HF2)(PF6) at 200 K: space group P1¯, a=4.5722(19) Å, b=4.763(2) Å, c=8.818(4) Å, α=86.967(10)°, β=76.774(10)°, γ=83.230(12)°, V=185.55(14) Å3, Z=1 and R=0.0937. Pb2F2(HF2)(PF6) at 293 K: space group P1¯, a=4.586(2) Å, b=4.781(3) Å, c=8.831(5) Å, α=87.106(13)°, β=76.830(13)°, γ=83.531(11)°, V=187.27(18) Å3, Z=1 and R=0.072. Ca(HF2)2 crystallizes in an orthorhombic Fddd space group with a=5.5709(6) Å, b=10.1111(9) Å, c=10.5945(10) Å, V=596.77(10) Å3 at 200 K, Z=8 and R=0.028.  相似文献   

11.
Single crystals of Ca3CuRhO6, Ca3Co1.34Rh0.66O6 and Ca3FeRhO6 were synthesized by high temperature flux growth in molten K2CO3 and structurally characterized by single crystal X-ray diffraction. While Ca3Co1.34Rh0.66O6 and Ca3FeRhO6 crystallize with trigonal (rhombohedral) symmetry in the space group , Z=6: Ca3Co1.34Rh0.66O6a=9.161(1) Å, c=10.601(2) Å; Ca3FeRhO6a=9.1884(3) Å, c=10.7750(4) Å; Ca3CuRhO6 adopts a monoclinic distortion of the K4CdCl6 structure in the space group C2/c, Z=4: a=9.004(2) Å, b=9.218(2) Å, c=6.453(1) Å, β=91.672(5). All crystals of Ca3CuRhO6 examined were twinned by pseudo-merohedry. Ca3CuRhO6, Ca3Co1.34Rh0.66O6, and Ca3FeRhO6 are structurally related and contain infinite one-dimensional chains of alternating face-sharing RhO6 octahedra and MO6 trigonal prisms. In the monoclinic modification, the copper atoms are displaced from the center of the trigonal prism toward one of the rectangular faces adopting a pseudo-square planar configuration. The magnetic properties of Ca3CuRhO6, Ca3Co1.34Rh0.66O6, and Ca3FeRhO6 are discussed.  相似文献   

12.
The subsolidus phase relations in the B-rich part of the ternary system, Na2O-SrO-B2O3, are investigated by the powder X-ray diffraction method. Four ternary compounds: NaSrBO3, NaSr4B3O9, Na3SrB5O10 and NaSrB5O9 were found in it, the two lasts are new. NaSrB5O9 crystallizes in the monoclinic space group P21/c, with the lattice parameters a=6.4963(1) Å, b=13.9703(2) Å, c=8.0515(1) Å, β=106.900(1)°. Na3SrB5O9 is also monoclinic, space group C2, a=7.290(1) Å, b=13.442(2) Å, c=9.792(1) Å, β=109.60(1). NaSrB5O9 is isostructural with another pentaborate NaCaB5O9, and its structure was refined by Rietveld method based on the structural model of NaCaB5O9. The fundamental building units are [B5O9]3− anionic groups, forming complex thick anionic sheets, extending parallel to the ac plane. The Na and Sr atoms are all eight-coordinated with O atoms, forming trigonal dodecahedra. The [NaO8] polyhedra are distributed between the B-O sheets, while the [SrO8] polyhedra located in the sheets and connect with each other by edges to form infinite chains along the c-axis.  相似文献   

13.
Two polymorphs of Li2CuZrO4 have been synthesized and their structures characterized by X-ray, neutron and electron diffraction. Both have novel types of ordered rock salt structure. β-Li2CuZrO4 is tetragonal, a=4.165(1) Å, c=9.418(1) Å, I-4m2, Z=4, RI=5.9%; the four sets of octahedral sites contain Zr, Li and partially ordered Li/Cu (two sets). γ-Li2CuZrO4 is orthorhombic, a=9.383(1) Å, b=5.894(1) Å, c=5.862(1) Å, Cccm, Z=8, RI=6.3%: in this case, the four sets of octahedral cation sites are fully ordered. Both structures show Jahn-Teller cooperative elongation of CuO6 octahedra. The transition from the low-temperature γ polymorph to the high-temperature β phase is first order as indicated by the presence of a transition enthalpy at an onset temperature of 1047°C on heating.  相似文献   

14.
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.  相似文献   

15.
The ternary nitrides, Ca4TiN4 and Ca5NbN5, were synthesized in sealed niobium tubes using lithium nitride as a flux at 900 and 1050 °C, respectively. The structures of both compounds were solved from single-crystal X-ray diffraction data. Ca4TiN4 is the first example of a calcium group IV nitride; it crystallizes in the triclinic space group (No. 2) with cell parameters a=5.9757(5) Å, b=6.0129(5) Å, c=6.0116(12) Å, α=71.565(4)°, β=79.471(4)°, γ=68.258(4)° and Z=2. Ca4TiN4 is isostructural with Na4TiO4 and contains tetrahedral TiN4 units connected through edges and corners to CaN4 tetrahedra and CaN5 square pyramids. Ca5NbN5 crystallizes in the monoclinic space group C2/m (No. 12) with cell parameters a=11.922(7) Å, b=6.878(5) Å, c=8.936(7) Å, β=101.22(3)° and Z=4. Ca5NbN5 is isostructural with Ba5NbN5; the structure contains NbN4 tetrahedra that share vertices with CaN5 trigonal bipyramids.  相似文献   

16.
The high-temperature polymorphs of two photocatalytic materials, BiNbO4 and BiTaO4 were synthesized by the ceramic method. The crystal structures of these materials were determined by single-crystal X-ray diffraction. BiNbO4 and BiTaO4 crystallize into the triclinic system P1¯ (No. 2), with a=5.5376(4) Å, b=7.6184(3) Å, c=7.9324(36) Å, α=102.565(3)°, β=90.143(2)°, γ=92.788 (4)°, V=326.21 (5) Å3, Z=4 and a=5.931 (1) Å, b=7.672 (2) Å, c=7.786 (2) Å, α=102.94 (3)°, β=90.04 (3)° γ=93.53 (3)°, V=344.59 (1) Å3 and Z=4, respectively. The structures along the c-axis, consist of layers of [Bi2O2] units separated by puckered sheets of (Nb/Ta)O6 octahedra. Photocatalytic studies on the degradation of dyes indicate selectivity of BiNbO4 towards aromatics containing quinonic and azo functional groups.  相似文献   

17.
Two new ternary ytterbium transition metal stannides, namely, Yb3CoSn6 and Yb4Mn2Sn5, have been obtained by solid-state reactions of the corresponding pure elements in welded tantalum tubes at high temperature. Their crystal structures have been established by single-crystal X-ray diffraction studies. Yb3CoSn6 crystallizes in the orthorhombic space group Cmcm (no. 63) with cell parameters of a=4.662(2), b=15.964(6), c=13.140(5) Å, V=978.0(6) Å3, and Z=4. Its structure features a three-dimensional (3D) open-framework composed of unusual [CoSn3] layers interconnected by zigzag Sn chains, forming large tunnels along the c-axis which are occupied by the ytterbium cations. Yb4Mn2Sn5 is monoclinic space group C2/m (no. 12) with cell parameters of a=16.937(2), b=4.5949(3), c=7.6489(7) Å, β=106.176(4)°, V=571.70(8) Å3, and Z=2. It belongs to the Mg5Si6 structure type and its anionic substructure is composed of parallel [Mn2Sn2] ladders interconnected by unusual zigzag [Sn3] chains, forming large tunnels along the c-axis, which are filled by the ytterbium cations. Band structure calculations based on density function theory methods were also made for both compounds.  相似文献   

18.
Crystal structure of BaMg2Si2O7 was determined and refined by a combined powder X-ray and neutron Rietveld method (monoclinic, C2/c, no. 15, Z=8, a=7.24553(8) Å, b=12.71376(14) Å, c=13.74813(15) Å, β=90.2107(8)°, V=1266.44(2) Å3; Rp/Rwp=3.38%/4.77%). The structure contains a single crystallographic type of Ba atom coordinated to eight O atoms with C1 (1) site symmetry. Under 325-nm excitation Ba0.98Eu0.02Mg2Si2O7 exhibits an asymmetric emission band around 402 nm. The asymmetric shape of the emission band is likely associated with a small electron-phonon coupling in BaMg2Si2O7. The integrated intensity of the emission band was observed to remain constant over the temperature range 4.2-300 K.  相似文献   

19.
A new 1:2 ordered perovskite La(Li1/3Ti2/3)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 (bbc+) Pbnm orthorhombic cell (a=ac√2=5.545 Å, b=ac√2=5.561 Å, c=2ac=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=ac√6=9.604 Å, b=ac√2=5.552 Å, c=ac3√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(Li1/3Ti2/3)O3 is the first example of a titanate perovskite with a 1:2 ordering of cations on the B-sites.  相似文献   

20.
Two new vanadium squarates have been synthesized, characterized by infrared and thermal behavior and their structures determined by single crystal X-ray diffraction. Both structures are made of discrete, binuclear vanadium entity but in 1, [V(OH)(H2O)2(C4O4)]2·2H2O the vanadium atom is trivalent and the entity is neutral while in 2, (NH4)[(VO)2(OH)(C4O4)2(H2O)3]·3H2O, the vanadium atom is tetravalent and the entity is negatively charged, balanced by the presence of one ammonium ion. Both molecular anions are bridged by two terminal μ2 squarate ligands. 1 crystallizes in the triclinic system, space group P-1, with lattice constants a=7.5112(10) Å, b=7.5603(8) Å, c=8.2185(8) Å, α=106.904(8)°, β=94.510(10)°, γ=113.984(9)° while 2 crystallizes in the monoclinic system, space group C2/c, with a=14.9340(15) Å, b=6.4900(9) Å, c=17.9590(19) Å and β=97.927(12)°. From the magnetic point of view, V(III) binuclear species show ferromagnetic interactions at low temperatures. However, no anomalies pointing to magnetic ordering are observed down to 2 K.  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