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1.
Sr2Co2O5 with the perovskite-related brownmillerite structure has been synthesised via quenching, with the orthorhombic unit cell parameters a=5.4639(3) Å, b=15.6486(8) Å and c=5.5667(3) Å based on refinement of neutron powder diffraction data collected at 4 K. Electron microscopy revealed L-R-L-R-intralayer ordering of chain orientations, which require a doubling of the unit cell along the c-parameter, consistent with the assignment of the space group Pcmb. However, on the length scale pertinent to NPD, no long-range order is observed and the disordered space group Imma appears more appropriate. The magnetic structure corresponds to G-type order with a moment of 3.00(4) μB directed along [1 0 0]. 相似文献
2.
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 Pn′m′a) 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
3.
The new mixed oxide having composition close to Ca7Co3Ga5O18 was synthesized from CaCO3, Co3O4 and Ga2O3 at 1150 °C in air and studied by neutron and synchrotron X-ray powder diffraction, selected-area electron diffraction and high-resolution electron microscopy. The structure was refined, using time-of-flight (TOF) neutron powder diffraction data, in space group F432, with and Z=8, to RF=0.7%. It is considerably disordered, with four different tetrahedral sites randomly occupied by Co and Ga atoms at a ratio of 1:2. The tetrahedra form a disordered (Co1/3Ga2/3)O2 3D-framework inside which isolated CoO6 octahedra, surrounded by 8 Ca atoms, are located. The structure is related to the ordered structure of Ca14Al10Zn6O35. Electron diffraction patterns confirmed the symmetry and unit cell and revealed no diffuse scattering. High-resolution electron microscopy images showed the absence of extended structural defects. 相似文献
4.
M. Retuerto M.J. Martínez-Lope M.T. Fernández-Díaz 《Journal of solid state chemistry》2011,184(9):2428-2433
The title compounds have been synthesized by a citrate technique followed by thermal treatments in air (BiFe0.5Mn1.5O5) or under high oxygen pressure conditions (BiFeMnO5), and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization measurements. The crystal structures have been refined from NPD data in the space group Pbam at 295 K. These phases are isostructural with RMn2O5 oxides (R=rare earths) and contain infinite chains of Mn4+O6 octahedra sharing edges, linked together by (Fe,Mn)3+O5 pyramids and BiO8 units. These units are strongly distorted with respect to those observed in other RFeMnO5 compounds, due to the presence of the electronic lone pair on Bi3+. It is noteworthy the certain level of antisite disorder exhibited in both samples, where the octahedral positions are partially occupied by Fe cations, and vice versa. BiFexMn2−xO5 (x=0.5, 1.0) are short-range magnetically ordered below 20 K for x=0.5 and at 40 K for x=1.0. The main magnetic interactions seem to be antiferromagnetic (AFM); however, the presence of a small hysteresis in the magnetization cycles indicates the presence of some weak ferromagnetic (FM) interactions. 相似文献
5.
Matthew J. Davis 《Journal of solid state chemistry》2003,173(1):122-129
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
6.
Magnetic susceptibility of Ca2F2-xMnxO5 members crystallizing in two different structures, one having octahedral (O), tetrahedral (T) and square-pyramidal (SP) coordination
of transition metal atoms (OTSP structure) and the other having octahedral and tetrahedral coordination (OT structure), has
been investigated. Susceptibility behaviour of the oxides with OTSP structure is different from that of the oxides with OT
structure. Ca2Fe1-33Mn0-67O5 with OTSP structure shows an antiferromagnetic ordering while the corresponding oxide with OT structure shows weak ferromagnetism.
Contribution No. 398 from the Solid State and Structural Chemistry Unit 相似文献
7.
Günther J. Redhammer Georg Roth Werner Treutmann Markus Hoelzel Werner Paulus Gilles Andr Clemens Pietzonka Georg Amthauer 《Journal of solid state chemistry》2009,182(9):2374-2384
The clinopyroxene compounds LiFeSi2O6 and LiFeGe2O6 have been investigated by constant wavelength neutron diffraction at low temperatures and by bulk magnetic measurements. Both compounds are monoclinic, space group P21/c and do not exhibit a change in nuclear symmetry down to 1.4 and 5 K respective. However, they transform to a magnetically ordered state below 20 K. LiFeSi2O6 shows a simple magnetic structure with no indication of an incommensurate modulation. The magnetic space group is P21/c′ and the structure is described by a ferromagnetic coupling of spins within the infinite M1 chains of edge-sharing octahedra, while the coupling between these M1 chains is antiferromagnetic. The magnetic phase transition is accompanied by magnetostriction of the lattice when passing through the magnetic phase transition. The magnetic structure of LiFeGe2O6 is different to the silicate: the space group is and the magnetic unit cell doubled along the a-direction. Within the M1 chains spins are coupled antiferromagnetically, while the chain to chain coupling is antiferromagnetic when coupling goes via the GeB tetrahedron and ferromagnetic when it goes via the GeA tetrahedron. 相似文献
8.
Farshid Ramezanipour Shahab Derakhshan John E. Greedan Lachlan M.D. Cranswick 《Journal of solid state chemistry》2008,181(12):3366-3373
A new pillared perovskite compound La5Mo2.76(4)V1.25(4)O16, has been synthesized by solid-state reaction and its crystal structure has been characterized using powder X-ray and neutron diffraction. The magnetic properties of this compound have been investigated using SQUID magnetometry, and the magnetic structure has been studied using neutron diffraction data. A theoretical calculation of relative strengths of spin interactions among different magnetic ions and through different pathways has been performed using extended Hückel, spin dimer analysis. The crystal structure of this material contains perovskite-type layers that are connected through edge-sharing dimeric units of octahedra. The structure is described in space group C2/m with unit cell parameters a=7.931(2) Å, b=7.913(2) Å, c=10.346(5) Å and β=95.096(5)°. The material shows both short-range ferrimagnetic correlations from ∼200 to 110 K and long-range antiferromagnetic order below Tc∼100 K. The magnetic structure was investigated by neutron diffraction and is described by k=(0 0 ) as for other pillared perovskites. It consists of a ferrimagnetic arrangement of Mo and V within the layers that are coupled antiferromagnetically between layers. This is the first magnetic structure determination for any Mo-based pillared perovskite. 相似文献
9.
Janet L. Hunting Marta M. Szymanski Philip E. Johnson C. Brenhin Kellar Francis J. DiSalvo 《Journal of solid state chemistry》2007,180(1):31-40
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
10.
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
11.
A.-K. Larsson R.L. Withers J.D. Fitz Gerald B.J. Kennedy 《Journal of solid state chemistry》2008,181(8):1816-1823
The P63 (a=2ap, b=2bp, c=cp) crystal structure reported for BaAl2O4 at room temperature has been carefully re-investigated by a combined transmission electron microscopy and neutron powder diffraction study. It is shown that the poor fit of this P63 (a=2ap, b=2bp, c=cp) structure model for BaAl2O4 to neutron powder diffraction data is primarily due to the failure to take into account coherent scattering between different domains related by enantiomorphic twinning of the P6322 parent sub-structure. Fast Fourier transformation of [0 0 1] lattice images from small localized real space regions (∼10 nm in diameter) are used to show that the P63 (a=2ap, b=2bp, c=cp) crystal structure reported for BaAl2O4 is not correct on the local scale. The correct local symmetry of the very small nano-domains is most likely orthorhombic or monoclinic. 相似文献
12.
Emily Asenath-Smith 《Journal of solid state chemistry》2010,183(7):1670-14
Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion αL) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma-Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α2σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of ∼2 W/mK and their similarity to Ruddlesden-Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (∼14×10−6 K−1) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers. 相似文献
13.
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
14.
A complex perovskite with composition Ca3Fe2WO9 has been synthesised, and the temperature evolution of nuclear and magnetic structures investigated by neutron powder diffraction. It was shown that at room temperature this compound adopts a monoclinic perovskite structure belonging to space group P121/n1 (, , ), β=90.04(2)°). The partial B-site ordering, of the Fe+3 and W+6 cations, at (2c) and (2d) sites was determined. At low temperatures the magnetic diffraction peaks were registered and a possible model for the magnetic structure was proposed in accordance with the ferrimagnetic properties of the title compound. The magnetic structure is defined by a propagation vector k=(1/2,1/2,0) and can be described as an array of ferromagnetic (20−1) layers, which couple antiferromagnetically to each other. All the Fe moments within a layer are aligned parallel (or anti-parallel) to the c-axis. The structural and magnetic features of this compound are discussed and compared with those of some other quaternary oxides A3Fe2WO9 (A=Ba, Sr, Pb). 相似文献
15.
The homogeneity range of the Ca3Co2-vMnvO6 solid-solution phase covers the entire composition interval from v=0 to 1. A systematic powder X-ray and neutron diffraction, magnetic susceptibility, and magnetization study has been carried out to investigate effects of the Mn-for-Co substitution on structural and magnetic properties. The Mn substitution concerns primarily only the octahedral Co1 site of the Ca3Co1Co2O6 crystal structure, whereas the trigonal-prismatic Co2 site structurally is left essentially unaffected. The Ca3Co2-vMnvO6 crystal structure belongs to space group with unit-cell dimensions (in hexagonal setting) 9.084?a?9.134 Å and 10.448?c?10.583 Å. A cut through the magnetic phase diagram at 10 K shows a ferrimagnetic domain for 0?v<∼0.3 and an antiferromagnetic domain for ∼0.50<v<∼1. The magnetic ordering temperatures are quite low (<∼25/18 K), and even so further magnetic transitions appear to take place at still lower temperature. The legitimity and reliability of the different indicators used to establish the magnetic transitions, their individual accuracy, and mutual consistency are briefly discussed. Variable parameters of the crystal and magnetic structures of Ca3Co11-vMnvCo2O6 are determined and their variation with v is briefly discussed in relation to chemical bonding. The magnetic structure in the ferrimagnetic region is essentially the same as that of the pristine v=0 phase, but since the moments at the Co2 site decrease and those at the (Co1,Mn) site increase with increasing v; characteristic traits of ferrimagnetism in magnetic susceptibility and magnetization gradually disappear. The magnetic arrangement in the antiferromagnetic region is characterized by differently sized moments at the (Co1,Mn) and Co2 sites, moments at adjacent sites in each of these sublattices being oppositely oriented along [001]. 相似文献
16.
Hamdi Ben Yahia Etienne Gaudin Cédric Feral-Martin Jacques Darriet 《Journal of solid state chemistry》2010,183(4):776-783
The NaCdVO4-Cd3V2O8 and CdO-V2O5 sections of the ternary system Na2O-CdO-V2O5 have been studied and the crystal structures of Cd3V2O8 and Cd18V8O38 compounds were determined from single-crystal X-ray diffraction data. Cd3V2O8 crystallizes with the maricite-type structure in space group Pnma, a=9.8133(10) Å, b=6.9882(10) Å, c=5.3251(10) Å and Z=4, whereas Cd18V8O38 crystallizes in space group P1 with a new-type structure, a=8.5761(14), b=8.607(3), c=12.896(2) Å, α=95.64(1), β=102.45(1), γ=108.42(1)° and Z=1. The Cd3V2O8 structure is made up of Cd1O4 infinite chains of edge-sharing Cd1O6 octahedra which are parallel to the b direction. The Cd1O4 chains are linked together by VO4 tetrahedra and strongly distorted Cd2O4 tetrahedra. The structure of Cd18V8O38 is based on an ordered three-dimensional framework of cadmium and vanadium polyhedra that share corners. The distorted CdO6 octahedra, CdO5 trigonal bipyramids and CdO5 square pyramids share corners, edges or faces. 相似文献
17.
新型固体氧化物燃料电池阴极材料Ca2-xSrxFe2O5的电化学性能研究 总被引:2,自引:2,他引:0
采用固相法合成了固体氧化物燃料电池(SOFC)阴极材料2-xSrxFe2O5(x=0.00,0.05,0.10,0.15,0.20),利用XRD和SEM对其结构和微观形貌进行了表征.结果表明该阴极材料与固体电解质Sm0.8Ce0.2O1.9(SDC)在1000℃烧结时不发生化学反应,且烧结4 h后,二者之间可形成良好的接触界面.利用交流阻抗谱技术对阴极材料的电化学性能进行研究,结果显示,阴极上的反应过程主要为电荷的迁移反应,其中Ca1.95Sr0.05Fe2O5电极在空气中700℃下具有最小的极化电阻为0.95Ω·cm2.当测试温度为700℃时,阴极电流密度为74mA·cm-2时,阴极过电位为100mV. 相似文献
18.
A new vanadate PbCo2V2O8 was obtained through the study of PbO-CoO-V2O5 ternary system. The crystal structure was determined by Rietveld method, indicating that PbCo2V2O8 has a tetragonal structure of space group I41cd with a spiral chain along the c-axis. Magnetic properties of the titled compound were investigated by means of susceptibility, magnetization, and heat capacity measurements. The results show that PbCo2V2O8 is a quasi-one-dimensional canted antiferromagnet with Neel temperature of ∼4 K, being consistent with its crystal structure. 相似文献
19.
The crystal structure of Ca5Te3O14 at room temperature was studied by the Rietveld method using combined X-ray and neutron powder diffraction data. The compound crystallizes in the space group Cmca with the lattice parameters a=10.4268(2) Å, b=10.3908(2) Å and c=10.4702(2) Å. The structure of Ca5Te3O14 is chiolite-like and consists of a framework of corner-linked TeO6 octahedral layers in which a linear TeO2 group of every fourth octahedron is substituted by a Ca atom. This type of structure was previously observed in BaSr4U3O14. The relationship between the chiolite-like structure and the fluorite structure is discussed. 相似文献
20.
Alexei A. Belik Qingzhen Huang Jeffrey W. Lynn 《Journal of solid state chemistry》2008,181(9):2292-2297
The crystal and magnetic structures of SrFe2+2(PO4)2 have been determined by neutron powder diffraction data at low temperatures (space group P21/c (no. 14); Z=4; a=9.35417(13) Å, b=6.83808(10) Å, c=10.51899(15) Å, and β=109.5147(7)° at 15 K). Two magnetic phase transitions were found at T1=7.4 K (first-order phase transition) and T2=11.4 K (second-order phase transition). The transition at T2 was hardly detectable by dc and ac magnetization measurements, and a small anomaly was observed by specific heat measurements. At T1, strong anomalies were found by dc and ac magnetization and specific heat. The structure of SrFe2(PO4)2 consists of linear four-spin cluster units, Fe2-Fe1-Fe1-Fe2. Below T1, the propagation vector of the magnetic structure is k=[0,0,0]. The magnetic moments of the inner Fe1-Fe1 atoms of the four-spin cluster unit are ferromagnetically coupled. The magnetic moment of the outer Fe2 atom is also ferromagnetically coupled with that of the Fe1 atom but with spin canting. The four-spin cluster units form ferromagnetic layers parallel to the [−101] plane, while these layers are stacked antiferromagnetically in the [−101] direction. Spin canting of the outer Fe2 atoms provides a weak ferromagnetic moment of about 1 μB along the b-axis. The refined magnetic moments at 3.5 K are 4.09 μB for Fe1 and 4.07 μB for Fe2. Between T1 and T2, a few weak magnetic reflections were observed probably due to incommensurate magnetic order. 相似文献