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1.
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
2.
The first member of the Ruddlesden-Popper family, Ca2MnO4, has been revisited. Coexistence of two structures has been shown from electron microscopy at room temperature and neutron diffraction data have evidenced two antiferromagnetic structures at low temperature. Two forms, with an orthorhombic Aba2 ( and c≈12 Å) and a tetragonal I41/cad ( and c≈24 Å) symmetries, were found to coexist coherently within the same matrix. 相似文献
3.
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
4.
The crystal structures of Ba2LnSbO6 (Ln=La, Pr, Nd and Sm) at room temperature have been investigated by profile analysis of the Rietveld method using either combined X-ray and neutron powder diffraction data or X-ray powder diffraction data. It has been shown that the structure of Ba2LnSbO6 with Ln =La, Pr and Nd are neither monoclinic nor cubic as were previously reported. They are rhombohedral with the space group . The distortion from cubic symmetry is due to the rotation of the LnO6/SbO6 octahedra about the primitive cubic [111]p-axis. On the other hand, the structure of Ba2SmSbO6 is found to be cubic. All compounds contain an ordered arrangement of LnO6 and SbO6 octahedra. 相似文献
5.
Jeroen Spooren 《Journal of solid state chemistry》2005,178(5):1683-1691
We report the synthesis of the perovskite manganites Pr0.5Sr0.5MnO3 and Nd0.5Sr0.5MnO3 using mild hydrothermal conditions. Both are formed as polycrystalline powders from solutions of metal salts in aqueous potassium hydroxide at 240 °C, and crystallise as a tetragonal polymorph (space group I4/mcm). Scanning electron microscopy shows both materials to contain cuboid-shaped crystallites several microns in dimension, and the average particle size is verified by light scattering measurements. We also report the first hydrothermal synthesis of 2H-BaMnO3 and 4H-SrMnO3, and the first subcritical hydrothermal synthesis of CaMn2O4 (marokite). Despite the formation of these alkali-earth manganese oxides at 240 °C, we have been unable to isolate rare-earth manganese oxides LnMnO3 using similar conditions. We discuss the formation of perovskite manganites in hydrothermal reactions by relating our new results to those manganites already reported to form under hydrothermal conditions, and rationalise the trends seen by considering tolerance factor of the perovskite and the variance of the A-site metal radius. 相似文献
6.
C. AutretC. Martin A. MaignanM. Hervieu B. RaveauG. André F. Bourée 《Journal of solid state chemistry》2002,165(1):65-73
The Ho0.5Sr0.5MnO3 perovskite, synthesized in air, has been studied by combining neutron powder and electron diffraction techniques. The Pnma-type structure exhibits a strong tilting of the MnO6 octahedra. This octahedra tilting and microtwinning involve a complex strained structure. No structural transition is observed down to 1.4 K, but short-range A-type antiferromagnetism running over only a few perovskite subcells is evidenced below ≈90 K. The different behavior of this perovskite compared to other Ln0.5Sr0.5MnO3 perovskites is discussed in terms of A-site cationic mismatch. 相似文献
7.
Alexandre I. Rykov Yutaka Ueda Kiyoshi Nomura 《Journal of solid state chemistry》2009,182(8):2157-2166
The layered manganese oxides LnBaMn1.96Fe0.04Oy (Ln=Y, Gd, Sm, Nd, Pr, La) have been synthesized for y=5,5.5 and 6. In the oxygen-saturated state (y=6) they exhibit the charge and orbital order at ambient temperature for Ln=Y, Gd, Sm, but unordered eg-electronic system for Ln=La, Pr, Nd. Fourfold increase of quadrupole splitting was observed owing to the charge and orbital ordering. This is in agreement with the jumplike increase in distortion of the reduced perovskite-like cell for the charge and orbitally ordered manganites compared to the unordered ones. Substitution of 2% of Mn by Fe suppresses the temperatures of structural and magnetic transitions by 20–50 K. Parameters of the crystal lattices and the room-temperature Mössbauer spectra were studied on 40 samples whose structures were refined within five symmetry groups: P4/mmm, P4/nmm, Pm-3m, Icma and P2/m. Overwhelming majority of the Fe species are undifferentiated in the Mössbauer spectra for most of the samples. Such the single-component spectra in the two-site structures are explained by the preference of Fe towards the site of Mn(III) and by the segmentation of the charge and orbitally ordered domains. 相似文献
8.
Neutron powder diffraction has been used to determine the magnetic structure of the quasi-one-dimensional compound Ba2CoS3, which contains linear [001] chains of vertex-sharing CoS4 tetrahedra, spaced apart by Ba2+ cations. At 1.5 K the Co2+ cations in the chains are antiferromagnetically ordered with an ordered magnetic moment of 1.97(4) μB per cation aligned along [100]. Each Co2+ cation is ferromagnetically aligned with four cation in neighbouring chains and antiferromagnetically aligned with two others. 相似文献
9.
Brendan J. Kennedy Qingdi Zhou Maxim Avdeev 《Journal of solid state chemistry》2011,184(11):2987-2993
The synthesis of bulk samples of polycrystalline CdTiO3 in both the rhombohedral ilmenite and orthorhombic perovskite forms is described and the structures of these have been refined using powder neutron diffraction data. This involved the preparation of samples enriched in 114Cd. Cooling perovskite-type CdTiO3 to 4 K induces a ferroelectric phase transition, with the neutron data suggesting the low temperature structure is in Pna21. Mode analysis shows the polar mode to be dominant at low temperatures. The ilmenite-structure of CdTiO3 is compared with that of ZnTiO3. The refined scattering length of the 114Cd is estimated to be 5.56 fm. Attempts to dope CdTiO3 with Ca and Sr are described. 相似文献
10.
Junji Awaka Norihito Kijima Hiroshi Hayakawa Junji Akimoto 《Journal of solid state chemistry》2010,183(1):180-1434
We have successfully synthesized a polycrystalline sample of tetragonal garnet-related Li-ion conductor Li7La3Hf2O12 by solid state reaction. The crystal structure is analyzed by the Rietveld method using neutron powder diffraction data. The structure analysis identifies that tetragonal Li7La3Hf2O12 has the garnet-related type structure with a space group of I41/acd (no. 142). The lattice constants are a=13.106(2) Å and c=12.630(2) Å with a cell ratio of c/a=0.9637. The crystal structure of tetragonal Li7La3Hf2O12 has the garnet-type framework structure composed of dodecahedral La(1)O8, La(2)O8 and octahedral HfO6. Li atoms occupy three types of crystallographic site in the interstices of this framework structure, where Li(1) atom is located at the tetrahedral 8a site, and Li(2) and Li(3) atoms are located at the distorted octahedral 16f and 32g sites, respectively. These Li sites are filled with the Li atom. The present tetragonal Li7La3Hf2O12 sample exhibits bulk Li-ion conductivity of σb=9.85×10−7 S cm−1 and grain-boundary Li-ion conductivity of σgb=4.45×10−7 S cm−1 at 300 K. The activation energy is estimated to be Ea=0.53 eV in the temperature range of 300-580 K. 相似文献
11.
M Latroche V Paul-Boncour A Percheron-Guégan 《Journal of solid state chemistry》2004,177(7):2542-2549
The crystal structure of two deuterides RY2Ni9Dx (R=La; x=12.8 and R=Ce; x=7.7) have been investigated by means of neutron powder diffraction and X-ray absorption spectroscopy. The structures are best described in the space group . The deuterium location has been determined for both compounds. The nature and the occupancy factors of the different D sites are presented. Comparisons are made between the La-based deuteride and the Ce-one in relation with the crystal structure of the intermetallic compounds. Differences in site occupancies within the RM2 and RM5 building units of the PuNi3-type structure are discussed and heterogeneous mixed valence state is reported for the cerium compound. 相似文献
12.
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
13.
It was found that the manganese perovskite oxides Ln0.5Ca0.5MnO3 (Ln=Ho, Er, Tm, Yb and Lu) have an orthorhombic structure (space group Pnma). The Mn-O-Mn angles were calculated to be ∼148-150°, revealing an existence of a large crystallographic distortion in these oxides. Electrical resistivity measurements indicated both an insulating nature and a small magnetoresistance effect, both of which are owing to narrow bandwidths of the Mn-3d electrons arising from the crystallographic distortion. DC magnetization measurements showed the three characteristic temperatures, which could be assigned to charge-order, antiferromagnetism of Mn moments, and possible glassy states. All of these temperatures were decreased for the heavier Ln ions, which is explained in connection with both a difference of ionic radii of Ln3+ and Ca2+, and a lowering of electron transfer. The charge-ordering transition was not clearly observed only for Lu0.5Ca0.5MnO3 containing the smallest lanthanide ion, plausibly due to a large randomness of magnetic interactions arising from the ionic radii difference of Lu3+ and Ca2+. In addition, preliminary measurements of AC dielectric response suggested that these manganites belong to a so-called multiferroic system. 相似文献
14.
Paul J. Saines Brendan J. Kennedy Maxim Avdeev 《Journal of solid state chemistry》2007,180(11):2991-3000
The structure of 14 compounds in the series Ba2LnTaO6 have been examined using synchrotron X-ray diffraction and found to undergo a sequence of phase transitions from I2/m monoclinic to I4/m tetragonal to cubic symmetry with decreasing ionic radii of the lanthanides. Ba2LaTaO6 is an exception to this with variable temperature neutron diffraction being used to establish that the full series of phases adopted over the range of 15-500 K is P21/n monoclinic to I2/m monoclinic to rhombohedral. The chemical environments of these compounds have also been investigated and the overbonding to the lanthanide cations is due to the unusually large size for the B-site in these perovskites. 相似文献
15.
A new bismuth tellurium oxychloride was obtained by reaction of BiOCl and TeO2 in air. According to energy dispersive X-ray spectroscopy and neutron powder diffraction refinement the composition of the substance was determined as Bi0.87Te2O4.9Cl0.87. The new compound crystallizes in the trigonal system space group R 3¯ (#148), Z=6, a=4.10793(4), c=31.1273(4) Å, χ2=3.20, wRp=0.0369. Bi0.87Te2O4.9Cl0.87 has a new type of layered structure constructed by Bi-Te-O layers separated by chloride ions. The Te atoms in Bi0.87Te2O4.9Cl0.87 show an unusual umbrella-like environment. A comparison with known related structures has been made. 相似文献
16.
The room temperature structure of perovskite CeAlO3 has been reinvestigated by X-ray powder diffraction. The Rietveld refinement has confirmed the tetragonal symmetry; but revealed a super cell, a=5.32489(6) Å and c=7.58976(10) Å, with the space group I4/mcm. In CeAlO3, the distortion from the ideal cubic perovskite is caused by the cooperative tilting of the AlO6 octahedra around the primitive cubic [001]p-axis. 相似文献
17.
Neutron powder diffraction study of the crystal and magnetic structures of BiNiO3 at low temperature
Sandra J.E. Carlsson Yuichi Shimakawa Alan Hewat 《Journal of solid state chemistry》2008,181(3):611-615
The crystal and magnetic structures of the charge ordered perovskite BiNiO3 have been studied at temperatures from 5 to 300 K using neutron diffraction. Rietveld analysis of the data shows that the structure remains triclinic (space group ) throughout the whole temperature range. Bond-valence sum calculations based on the Bi-O and Ni-O bond distances confirm that the charge distribution is Bi3+0.5Bi5+0.5Ni2+O3 down to 5 K. The magnetic cell is identical to that of the triclinic superstructure and a G-type antiferromagnetic model gives a good fit to the magnetic intensities, with an ordered Ni2+ moment of 1.76(3) μB at 5 K. However, BiNiO3 is ferrimagnetic due to the inexact cancellation of opposing, inequivalent moments in the low symmetry cell. 相似文献
18.
Bi2O3-MoO3 system shows a large panoply of phases depending on Bi/Mo ratio, among them, the low temperature phases of the homologous series Bi2(n+2)MonO6(n+1) with n=3, 4, 5 and 6. They exhibit, alike most of the phases of this system, strong fluorite sub-network. Nevertheless, a multitechnique approach has been followed in order to solve the crystal structure of the n=3 member, i.e. Bi10Mo3O24. From ab initio indexing X-ray powder pattern cell parameters were derived. It belongs to the monoclinic system, space group C2, with cell parameters: a=23.7282(2) Å, b=5.64906(6) Å, c=8.68173(9) Å, β=95.8668(7)° with Z=2. The matrix relating this cell with the fluorite one is 4 0 1/0 1 0/ 0 and a cationic localization was derived. HRTEM allowed the cationic Bi and Mo order to be modified and specified, as well as to build up a full structural ab initio model on the basis of crystal chemistry considerations. Simultaneous Rietveld refinement of multipattern X-ray and neutron powder diffraction data taking advantage of the neutron scattering length for O location have been performed. The goodness of the model was ascertained by low reliability factors, weighted Rb=4.97% and Rf=3.21%. This complex Bi10Mo3O24 structure, with 5Bi, 2Mo and 13O in different crystallographic positions of the asymmetric unit, shows good agreement between observed and calculated patterns within the data resolution. Moreover, the determination of this structure sets the basis for the crystallographic characterization of the complete family Bi2(n+2)MonO6(n+1), whose guidelines are also evidenced in this paper. 相似文献
19.
High-resolution synchrotron and neutron powder diffraction techniques were used to determine precise structures for the series of perovskite oxides A2−xSrxCoWO6 (ACa, or Ba, 0?x?2). The studies demonstrated that the symmetry decreases as the average size of the A-site cation decreases with a sequential introduction of in-phase and out-of-phase tilting of the BO6 octahedra. A cubic structure in Fm3¯m with rock-salt like ordering of the Co and W cations was formed for Ba2−xSrxCoWO6 with x∼<1.4. As the Sr content was increased, the materials became tetragonal in I4/m and ultimately monoclinic in P21/n. A mixture of monoclinic and tetragonal phases occurs in Sr2CoWO6 at room temperature but this was purely monoclinic at 20 K. 相似文献
20.
Phase transitions that occurred in perovskite BaPbO3 have been investigated using high-resolution time-of-flight neutron powder diffraction. The structure at room temperature is orthorhombic (space group Imma), which is derived from the cubic aristotype by tilting the PbO6 octahedra around the two-fold axis (tilt system a0b−b−). The orthorhombic structure shows anisotropic line broadening attributed to the presence of micro twins. At above about 573 K, BaPbO3 undergoes a discontinuous phase transition to a tetragonal structure (space group I4/mcm) with the tilting of the PbO6 octahedra being about the four-fold axis of the cubic aristotype (tilt system a0a0c−). With further increasing the temperature, BaPbO3 experiences a continuous phase transition to a simple cubic structure (space group Pm3¯m) at above about 673 K. The later phase transition is characterised by a critical exponent of β=0.36, depicted by the three-dimensional Heisenberg universality class. The earlier reported Imma→I2/m phase transition above room temperature has not been observed. 相似文献