共查询到20条相似文献,搜索用时 31 毫秒
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L. Ortega‐San Martín J. P. Chapman G. Cuello J. Gonzlez‐Calbet M. I. Arriortua T. Rojo 《无机化学与普通化学杂志》2005,631(11):2127-2130
The crystal structure of the ordered double perovskite Sr2MnTeO6 has been refined at ambient temperature from high resolution neutron and X‐ray powder diffraction data in the monoclinic space group I 1 2/m 1 with a = 5.6166(1) Å, b = 5.5807(1) Å, c = 7.8797(1) Å and β = 90.048(2)°. The structure is the result of out‐of‐phase (–) rotations of virtually undistorted NiO6 and TeO6 octahedra in the (0 – –) sense about two of the axes of the ideal cubic perovskite. Electron diffraction measurements have been used to confirm the proposed space group and structure. 相似文献
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Elizabeth Castillo-Martínez J. Paul Attfield 《Journal of solid state chemistry》2006,179(11):3505-3510
The miscibility of TbBaMn2O5+x and TbBaMn2O5.5−y has been investigated at 100-600 °C using in situ powder neutron diffraction. No miscibility is observed, and the two phases remain oxygen stoichiometric (x,y=0) at 600 °C. Structure refinement results show that neither material undergoes a phase transition in this temperature range. TbBaMn2O5 is Mn2+/Mn3+ charge ordered and any charge melting transition is >600 °C. This symmetry-broken charge ordering is remarkably robust in comparison to that in other oxides. 相似文献
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S. Shafeie S.Ya. Istomin S.A. Chen J.M. Chen M. Karppinen G. Svensson 《Journal of solid state chemistry》2011,184(1):177-190
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 R3¯c 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
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利用电子衍射、X射线衍射和荧光光谱等方法研究了 L n Ba B9O16(L n=L a,Y)的结构特性 .L n Ba B9O16为单斜晶系 ,其中 L a Ba B9O16的晶胞参数 a=1.36 6 0 nm,b=0 .7882 nm,c=1.6 2 53nm,β=10 6 .15°;YBa B9O16的晶胞参数 a=1.3476 nm,b=0 .7776 nm,c=1.6 0 4 0 nm,β=10 6 .38°.荧光光谱研究表明 ,这两种化合物结构不同 ,Y3 +在 YBa B9O16结构中处于中心对称格位 ,而 L a Ba B9O16中 L a3 +的格位则无中心对称性 .Gd3 +部分取代 L a Ba B9O16∶ Eu3 +中的 L a3 +可改善 Eu3 +离子的发光性质 .L a Ba B9O16∶ Eu3 +在真空紫外区的吸收比较弱 ,这可能与硼氧比较小有关 . 相似文献
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R.K.B GoverN.D. Withers S. AllenR.L. Withers J.S.O. Evans 《Journal of solid state chemistry》2002,166(1):42-48
SnP2O7 is a member of the ZrP2O7 family of materials, several of which show unusual thermal expansion behavior over certain temperature ranges and which show a number of displacive phase transitions on cooling from high temperature. Here we describe the structural properties of SnP2O7 from 100 to 1243 K as determined by X-ray and neutron powder diffraction. These studies reveal that SnP2O7 shows two phase transitions in this temperature range. At room temperature the material has a pseudo-cubic 3×3×3× superstructure. Electron diffraction studies show that the symmetry of this structure is P213 or lower. On warming to ∼560 K it undergoes a phase transition to a structure in which the subcell reflections show a triclinic distortion; above 830 K the subcell reflections show a rhombohedral distortion. Significant hysteresis in cell parameters is observed between heating and cooling. The structure of SnP2O7 is discussed with references to other members of the AM2O7 family of materials. 相似文献
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LnBaB9O16:Eu3+(Ln=La,Y)的结构与荧光性质 总被引:6,自引:0,他引:6
利用电子衍射、X射线衍射和荧光光谱等方法研究了LnBaB9O16(Ln=La,Y)的结构特性.LnBaB9O16为单斜晶系,其中LaBaB9O16的晶胞参数a=1.3660nm,b=0.7882nm,c=1.6253nm,β=106.15°;YBaB9O16的晶胞参数a=1.3476nm,b=0.7776nm,c=1.6040nm,β=106.38°.荧光光谱研究表明,这两种化合物结构不同,Y3+在YBaB9O16结构中处于中心对称格位,而LaBaB9O16中La3+的格位则无中心对称性.Gd3+部分取代LaBaB9O16:Eu3+中的La3+可改善Eu3+离子的发光性质.LaBaB9O16:Eu3+在真空紫外区的吸收比较弱,这可能与硼氧比较小有关. 相似文献
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Maxim Avdeev Sergey Yakovlev Aleksey A. Yaremchenko Vladislav V. Kharton 《Journal of solid state chemistry》2007,180(12):3535-3544
The results of in situ high-temperature X-ray and neutron powder diffraction experiments reconcile inconsistencies in previous reports on the symmetry of high-temperature phases of SrAl2O4. The material undergoes two reversible phase transitions and at 680 and 860 °C, respectively, and the latter one is experimentally observed and characterized for the first time. The higher symmetry above the transition is gained by disordering off-center split site of oxygen atoms around trigonal axis rather than by unbending Al–O–Al angle to the ideal value 180°. The analysis of the literature suggests that it is a common feature of the P6322 phases of stuffed tridymites. 相似文献
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Philip Coppens 《Angewandte Chemie (International ed. in English)》1977,16(1):32-40
Some recent results of charge density analysis by X-ray and neutron diffraction are discussed. Problems that have been studied in a number of laboratories include the nature of single, double, and triple bonds, lone-pair hybridization, bonding in some metals, alloys, and organometallic compounds, and the derivation of physical properties from X-ray diffraction densities. At the present stage of development of methods studies of series of related compounds are feasible and expected to find widespread application. 相似文献
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F. Lindberg S.Ya. Istomin G. Svensson P. Svedlindh A. Wannberg E.V. Antipov 《Journal of solid state chemistry》2006,179(5):1434-1444
The effect of replacing Co3+ by Ga3+ and Fe3+ in the perovskite-related tetragonal phase Sr0.75Y0.25CoO2.625 with unit cell parameters: a=2ap, and c=4ap (314 phase) has been investigated. The 314 phase is formed by Sr0.75Y0.25Co1−xMxO2.625+δ, with x?0.375 for M=Ga and x?0.625 for M=Fe. High-resolution transmission electron microscopy and electron diffraction revealed frequent microtwinning in the iron-containing compounds, in contrast to the Ga-substituted 314 phases. Diffraction experiments and electron microscope images indicated that at higher Fe contents, 0.75?x?0.875, a disordered cubic perovskite structure forms. The crystal structures of Sr0.75Y0.25Co0.75Ga0.25O2.625 and Sr0.75Y0.25Co0.5Fe0.5O2.625+δ were refined using neutron powder diffraction data. It was found that the oxygen content of Sr0.75Y0.25Co0.5Fe0.5O2.625+δ is higher than in Fe-free 314 phase, so that δ corresponds to 0.076, whereas δ=0 in Sr0.75Y0.25Co0.75Ga0.25O2.625+δ. Magnetization measurements on the unsubstituted Sr0.7Y0.3CoO2.62 and Ga-substituted Sr0.75Y0.25Co0.75Ga0.25O2.625 compounds indicate the presence of a ferromagnetic-like contribution to the measured magnetization at 320 and 225 K, respectively, while replacing Co by Fe leads to the suppression of this contribution. A neutron diffraction study shows that the Sr0.75Y0.25Co0.5Fe0.5O2.625+δ compound is G-type antiferromagnetic at room temperature, whereas Sr0.75Y0.25Co0.75Ga0.25O2.625 does not exhibit magnetic ordering at room temperature. 相似文献
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Single crystals of NASICON-type material Li1+xTi2−xAlx(PO4)3 (LATP) with 0 ≤ x ≤ 0.5 were successfully grown using long-term sintering techniques. Sample material was studied by chemical analysis, single crystal X-ray and neutron diffraction. The Ti4+ replacement scales very well with the Al3+ and Li+ incorporation. The additional Li+ thereby enters the M3 cavity of the NASICON framework at x, y, z ∼ (0.07, 0.34, 0.09) and is regarded to be responsible for the enhanced Li+ conduction of LATP as compared to Al-free LTP. Variations in structural parameters, associated with the Ti4+ substitution with Al3+ + Li+ will be discussed in detail in this paper. 相似文献
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Dr. Tilman A. Grünewald Dr. Harald Rennhofer Pieter Tack Dr. Jan Garrevoet Dr. Didier Wermeille Paul Thompson Dr. Wim Bras Prof. Laszlo Vincze Prof. Helga C. Lichtenegger 《Angewandte Chemie (International ed. in English)》2016,55(40):12190-12194
Conventional analysis of the preferred orientation of crystallites (crystallographic texture) involves X‐ray diffraction with area detectors and 2D data output. True 3D, spatially resolved information requires sample rotation in the beam, thus changing the probed volume, which introduces signal smearing and precludes the scanning of complex structures. This obstacle has been overcome by energy‐dispersive Laue diffraction. A method has been devised to reach a large portion of reciprocal space and translate the X‐ray photon energy into the missing third dimension of space. Carbon fibers and lobster exoskeleton as examples of biomineralized tissue have been analyzed. The major potential of this method lies in its “one‐shot” nature and the direct 3D information requiring no previous knowledge of the sample. It allows the texture of large samples with complex substructures to be scanned and opens up the conceptual possibility of following texture changes in situ, for example, during crystallization. 相似文献
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La3NbO7 and Nd3NbO7 are insulating compounds that have an orthorhombic weberite-type crystal structure and undergo a phase transition at about 360 and 450 K, respectively. The nature of the phase transitions was investigated via heat capacity measurements, synchrotron X-ray and neutron diffraction experiments. It is here shown that above the phase transition temperature, the compounds possess a weberite-type structure described by space group Cmcm (No. 63). Below the phase transition, the high temperature phase transforms into a weberite-type structure with space group Pmcn (No. 62). The phase transformation primarily involves the off-center shifting of Nb5+ ions inside the NbO6 octahedra, combined with shifts of one third of the Ln3+ (Ln3+=La3+ and Nd3+) ions at the center of the LnO8 polyhedra towards off-center positions. The phase transition was also proven to have great impacts on the dielectric properties. 相似文献
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Junji Awaka Norihito Kijima Hiroshi Hayakawa Junji Akimoto 《Journal of solid state chemistry》2009,182(8):2046-2052
We have successfully synthesized a high-purity polycrystalline sample of tetragonal Li7La3Zr2O12. Single crystals have been also grown by a flux method. The single-crystal X-ray diffraction analysis verifies that tetragonal Li7La3Zr2O12 has the garnet-related type structure with a space group of I41/acd (no. 142). The lattice constants are a=13.134(4) Å and c=12.663(8) Å. The garnet-type framework structure is composed of two types of dodecahedral LaO8 and octahedral ZrO6. Li atoms occupy three crystallographic sites in the interstices of this framework structure, where Li(1), Li(2), and Li(3) atoms are located at the tetrahedral 8a site and the distorted octahedral 16f and 32g sites, respectively. The structure is also investigated by the Rietveld method with X-ray and neutron powder diffraction data. These diffraction patterns are identified as the tetragonal Li7La3Zr2O12 structure determined from the single-crystal data. The present tetragonal Li7La3Zr2O12 sample exhibits a bulk Li-ion conductivity of σb=1.63×10−6 S cm−1 and grain-boundary Li-ion conductivity of σgb=5.59×10−7 S cm−1 at 300 K. The activation energy is estimated to be Ea=0.54 eV in the temperature range of 300–560 K. 相似文献
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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