Octahedral Network Research Articles

The electronic structure and the O 1s x-ray absorption cross section of the perovskite-derived compound SrNbO3.4

We present the results of self-consistent LMTO-ASA band structure calculations for SrNbO3.4 based on the LDA. Eight bands per spin cut the Fermi surface. In accordance with experiment, we obtain a low density of states at the Fermi level, rising steeply with increasing energy. This explains qualitatively the low susceptibility found in this material. Similar to the simple perovskite structure SrNbO3, the conduction band complex is separated from the 5.6 eV wide valence band region by a gap of 1.7 eV. The spatial charge distribution shows that the bonding between the niobium and the oxygen atoms within the two-dimensional octahedral network is of primarily ionic character. A band complex of width 3.45 eV found at 17 eV below EF is due to the O 2s states. The reasonable agreement between our calculated XAS cross sections for different light polarizations with recent experimental results suggest that an LDA treatment of this class of substances is appropriate, whereas Coulomb correlations play a minor role.

Structural reasons for the high dielectric anisotropy of tungsten bronze-like dielectrics

Single crystal x-ray analyses of Ba6-3XR8+2xTi18O54 were performed for the La, Pr, and Sm analogues. Calculations based on refined atomic fractional coordinates showed that 53% of [100], 100% of [010], and 67% of [001] direction tilt angles increase with a reduction in the ionic radius of ions occupying pentagonal or tetragonal channels. This shows a significant anisotropy in the flexibility of the lattice. High flexibility in the [010] direction is also reflected in the anisotropy of the thermal expansion and in variations of the cell parameters across particular solid solubility regions. Variations in the dielectric properties are correlated to modifications of the octahedral network indicating that the high dielectric anisotropy is related to the high anisotropy in the network flexibility.

Structural Study of PbZn1/3Nb2/3O3 by Single Crystal X-ray Diffraction and EXAFS.

The structure of PbZn1/3Nb2/3O3 ferroelectric relaxor was investigated by the single crystal X-ray diffraction and the extended X-ray absorption fine structure (EXAFS) techniques at room temperature. The crystal has a rhombohedral R3m symmetry with a=0.40620(4)nm and α=89.93 (1)°. The metal atoms are displaced from the cubic prototype positions by 0.035(1)nm for Pb, and 0.012(2)nm for Zn and Nb. The Pb atoms are statistically distributed at the 9b positions in the hexagonal setting. EXAFS analysis gave mean bond distances of 0.235(1)nm for Pb-O, 0.204(1)nm for Zn-O, and 0.194(1)nm for Nb-O. The coordination number of Pb was estimated to be 3.8 (2). Single crystal X-ray diffraction and EXAFS data suggested a pyramidal coordination for the local structure around Pb, which is similar to PbO4 in PbO. The different bond distances of Zn-O and Nb-O imply a concurrent constriction of NbO6 and expansion of ZnO6 octahedra in the crystal, leading to an aperiodic distortion of the corner-shared octahedral network.

Synthesis and structure determination of the new Sm2Ti2O5S2 compound

Abstract Sm 2 Ti 2 O 5 S 2 was obtained in an attempt to prepare an oxysulfide of samarium and titanium in a way similar to the obtention of the quaternary Sm 3 NbO 4 Se 3 compound. The structure was determined by single-crystal X-ray diffraction. The following crystal data were obtained: M r = 540.6 g mol −1 , tetragonal symmetry with unit cell parameters a = 3.819(1) A, c = 22.964(5) A, space group I4/ mmm (139). Refinement for 127 unique reflections with I > 3σ(1), and 11 variables, converged to the reliability factor R = 1.77 %. The structure can be described as a stacking, along the c -direction, of [Sm 2 S 2 ] slabs of a rock-salt type (two-atom-thick-layers) separated by a 2D network of corner-sharing octahedra [= Ti 2 O 5 ] of a ReO 3 structure type.

A hybrid open‐framework structure: synthesis and structure of an iron phosphate oxalate, [C10N4H28][Fe2(HPO4)3(C2O4)

A new inorganic–organic hybrid structure has been synthesized hydrothermally in the iron phosphate oxalate family using 1,4-bis(3-aminopropyl)piperazine as the structure-directing agent. Crystal data for I, [C10N4H28][Fe2(HPO4)3(C2O4)]2: M = 589.8, monoclinic, space group = P21/n (no. 14), a = 10.829(1), b = 12.747(1), c = 12.397(1) A, β = 95.1(1)°, V = 1704.4(3) A3, Z = 4, R = 0.036 and Rw = 0.083 [1860 observed reflections with I > 2σ(I)]. The structure comprises a network of FeO6 octahedra and PO4 tetrahedra forming inorganic layers which are bridged by the oxalate units forming 8-membered channels in which the amine molecule resides. Magnetic susceptibility studies indicate an antiferromagnetic behavior with TN = ≈40 K, the highest known in an open-framework material.

Phase Transition and Structure of a K1−xLixMnF3Single Crystal in the Range 100–298 K

The cubic-to-tetragonal phase transition in the mixed perovskite K1−xLixMnF3(x<0.036) was investigated by single-crystal X-ray diffraction. Results of the structure refinement at 298 and 145 K are discussed. They confirm the cubic symmetry, the space groupPm3m, of the room temperature phase with strongly anisotropic thermal vibration amplitudes of the F atoms, which were also observed in the parent KMnF3. Substitutional lattice imperfections at the K+sites shift the ferrodistortive phase transition to higher temperatureTc1=191 K, compared to 186.5 K in KMnF3. The structural changes in the tetragonal phase (I4/mcm) are characterized by the displacements of the F atoms from the positions they occupy aboveTc1. However, the Li+ion dopants do not affect the octahedral network, the MnF6octahedra remain regular, and no displacements of K+/Li+cations along the tetragonalcaxis are observed. The thermodynamic character of the transition is illustrated with the critical behavior of the unit cell parameters and the temperature-dependent evolution of the tetragonal deformation and the macroscopic strain. A variation of the integrated intensity of superstructure reflections close toTc1has been assumed to describe the behavior of the order parameter. As far as the precision of the present experiment allows, all these observations show that 3.6% Li+substitution at the K+site does not radically change the nature of the transition in KMnF3atTc1.

Zur Kristallchemie der Kupfer(II)-ZinkteIlurate Cu5Zn4Te3O18 und Cu1,5Zn1,5TeO6, mit einer Notiz über Cu1,5Co1,5TeO6 / On the Crystal Chemistry of the Copper(II) Zinc Tellurates Cu5Zn4Te3O18 and Cu1,5Zn1,5TeO6 with a Note on Cu1,5Co1,5TeO6

Single crystals of Cu5Zn4Te3O18 (I), Cu1.5Zn1.5TeO6 (II) and Cu1.5Co1.5TeO6 (III) have been prepared and investigated by X-ray work. The structure of (I) was solved in the monoclinic space group C3 2-C2, a = 14.834(2), b = 8.801(1), c = 10.375(2) Å, β = 93.27(2)°, Z = 4. (II) and (III) crystallize with cubic symmetry, space group Th 7-Ia3̄, a(II) = 9.557(1), a(III) = 9.570(1) Å, Z = 8. (I) shows a complicated structure formed by TeO6 octahedra isolated from each other, Zn2O6 double tetrahedra and Zn2O8 double square pyramids. These polyhedra are incorporated into a network of edge and corner connected stretched CuO6 octahedra. (II) and (III) are isotypic to Cu3TeO6 and have a (Cu/M)3O6 octahedra network, statistically occupied by Cu2+ and Zn2+ or Cu2+ and Co2+.

(C6H5CH2CH2NH3)2[CdCl4

The title compound, bis(β-phenylethylammonium) tetrachlorocadmate, (C8H12N)2[CdCl4] crystallizes as a layer structure; the heavy atoms form a two-dimensional network of corner-connected octahedra, the organic cation being connected to the network through hydrogen bonding.

On the non-local screening mechanisms in the 2 p photoelectron spectra of NiO and La 2NiO 4

An unresolved question in solid state physics concerns the nature of charge transfer mechanisms in the late transition metal compounds. This paper shows that a structure similar to the doubly peaked feature detected in the Ni 2 p X-ray photoelectron spectra of NiO and attributed to non-local screening is observed also in the Ni 3 s spectrum. However, in this case the spectrum is fully accounted for on the basis of charge transfer, near degeneracy, and exchange mechanisms and neglecting non-local screening. In addition, it is demonstrated that non-local screening mechanisms are not observed in La 2NiO 4 where such an effect, on the basis of the NiO octahedra network, is expected. Finally, the significant differences among the Ni 2 p XPS spectra in NiO, Ni 0.1Mg 0.9O and La 2NiO 4 suggest that core line spectra in nickel oxide based compounds cannot be evaluated simply on the basis of the NiO cluster network but it is necessary to consider the long range crystal structure effects.

Über die Kristallstrukturen der Tellurate Pb3Fe2Te2O12 und Pb2CoTeO6 / On the Crystal Structures of the Tellurates Pb3Fe2Te2O12 and Pb2CoTeO6

Pb3Fe2Te2O12 (I) and Pb2CoTeO6 (II) have been prepared by crystallization from melts. Single crystal X-ray investigations led to monoclinic (I) and tetragonal (II) symmetry, space groups C4 s-Cc and D17 4h-14/mmm. Lattice constants I: a = 9.866(3), b = 15.332(4), c = 7.172(2) Å, β = 111.34(3)°, Z = 4. II: a = 5.661(5), c = 8.004(7) Å, Z = 2. (I) represents a new crystal structure, characterized by a network of octahedra occupied by Fe3+ and Te6+ in a disordered manner. The centres of negative charge of the lone pairs of Pb2+ in I are estimated by Coulomb term calculations. II belongs to the elpasolithe type

Local Structure of the Amorphous Precursor to Ba-Hexaferrite Thin Films: An Anisotropic Octahedral Fe-O Glass Network.

Anisotropic local structure has been observed around both the Fe and Ba ions in the amorphous precursor to Ba-hexaferrite thin films, using polarization-dependent extended x-ray-absorption fine structure. This anisotropic local structure, consisting mainly of a network of Fe-O octahedra, determines the orientation of the fast-growing basal planes during crystallization, and thus the directions of the c axes and the resulting magnetic anisotropy.

Zr9Co2P4 and Zr9Ni2P4: A New 3D Structure Type, Consisting of Edge- and Vertex-Condensed Zr6 Octahedra

The isostructural title compounds were synthesized by arc-melting of stoichiometric ratios of ZrP, Zr, and Co and Ni, respectively, and subsequent annealing at 1450 °C. Their crystal structure (space group P4/mbm; Zr9Co2P4, a = 12.1200(6) A, c = 3.6158(4) A, V = 531.37(7) A3, Z = 2; Zr9Ni2P4, a = 12.0862(2) A, c = 3.6435(3) A, V = 532.23(5) A3, Z = 2) is derived from a three-dimensional network of Zr6 octahedra. These octahedra are connected via common vertices to form chains parallel to the c axis and via common edges and vertices in the ab plane, resulting in one double chain and one single chain. Both kinds of the interstitial atoms, the iron-group-metal atom and the phosphorus, are situated in trigonal prismatic holes between these chains, forming short M−P and M−M‘ bonds. These octahedra can be described as being of the M6X8 cluster type as is also observed in the chalcogenide Chevrel phases. Due to the electronically nonsaturated character of the Zr octahedra and their three-dimensional connectivity...

Cationic Distribution in α-MZr3F15 Series (M = Y, In, Ln, Tl)

A series of fluorozirconates MZr3F15 was prepared by direct reaction of the binary fluorides, involving trivalent cations with a wide range of sizes: In, Tl, Lu, Yb, Y, Gd, Eu, and Pr (0.80 Å < Rion < 1.13 Å). The samples were synthesized in sealed Pt tubes and heated between 700 and 1000°C, except for TlZr3F15, which was heated at 500°C under F2 flow. Their crystal structure was solved by X-ray diffraction for single crystals of Y and Gd and for powders using the Rietveld method for the other phases. The structure is isotypic with that of BiZr3F15 and corresponds to a three-dimensional network of corner-sharing octahedra and dodecahedra, in a 1:3 proportion (cationic sites 6a and 18e of the R3̄c space group). The cationic distribution in these two sites depends on the size of the M3+ cation:—Large cations, such as Y3+ and Ln3+, are localized in the 18e site, with Zr4+ distributed on both sites;—a small cation, such as In3+, is perfectly ordered in an octahedral site, with Zr4+ in a dodecahedral coordination;—a cation of medium size, such as Tl3+, presents an average distribution, with Zr4+ on both sites.Structural relationships with anion-excess ReO3-type and with the low-temperature polymorph β-PrZr3F15 are discussed.

Kristallstrukturuntersuchung an einem bismuthaltigen Hollandit: Bi1.9CU4V4O16 / Crystal Structure Investigation of the Bismuth Containing Hollandite: Bi1.9Cu4V4O16

Single crystals of Bi1.9Cu4V4O16 have been prepared by quenching of CO2-LASER heated samples. They were investigated by X-ray techniques. The compound crystallizes with tetragonal symmetry, space group C5 4h-I4 /m , a = 9.945(2) Å , c = 2.915(3) Å, Z = 1, and is isotypic to the mineral Hollandite. Bi1.9Cu4V4O16 is the first Hollandite with a statistical distribution of vanadium and copper in the network of octahedra. Calculations of the Coulomb terms of lattice energy led to a distance of bismuth to the lone pair of 1.07 Å. Considering the lone pair as part of the coordination sphere of Bi3+ a square pyramidal polyhedron is obtained.

Awaxs study of amorphous WO3 and WO3 · nH2O

Anomalous Wide Angle X-Ray Scattering (AWAXS) has been applied to glassy bulk WO3. In this system the partial distribution of pairs WW and WO may be reliably extracted. Glasses have been prepared by non-reactive grinding from both the metastable pyrochlore type structure and from the hydrates WO3· nH2O. A weighted differential analysis has been developed, leading to the knowledge of the oxygen surrounding and to the extraction of the partial WW first correlations. The influence of water content on the octahedra's network in the amorphous states is analyzed and the medium range order are considered in the framework of hexagonal, pyrochlore and ReO3 type structures.

Synthesis, Crystal Structure, and Magnetic Study of Na7Sr2Fe7F32

Na7Sr2Fe7F32 is orthorhombic (space group Fddd) with a = 10.372(3) Å, b = 10.805(3) Å, c = 44.98(2) Å, and Z = 8. The structure was determined from single-crystal data using 1261 independent X-ray reflections, with reliability R = 0.036 (RW = 0.029). Corner-sharing iron octahedra give rise to a three-dimensional network |:Fe7F32|11n-n, where linear trans connected |FeF5|2n-n chains and |Fe5F26| octahedra pentamers can be distinguished. Na7Sr2Fe7F32 clearly exhibits an atypic magnetic behavior evidenced from Mössbauer and magnetic measurements (Tc ≈ 35 K). A competition between ferromagnetic and antiferromagnetic couplings is suggested in relation to a frustrated octahedra network.

ChemInform Abstract: Crystal Structure of NaBa, an Interpenetrating Network of Sodium Tetrahedra and Barium Octahedra.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Zur kristallstruktur von SrAl 8Ti 3O 19

Single crystals of SrAl 8Ti 3O 19 were prepared by high temperature reactions and investigated by X-ray techniques. SrAl 8Ti 3O 19 crystallizes with monoclinic symmetry, space group C 2h 6-C2/c, a = 22.736 A ̊ , b = 11.069 A ̊ , c = 9.759 A ̊ , β = 98.56°, Z = 8 . The crystal structure is characterized by an octahedral network of oxygen around Ti 4+ and Al 3+ filled by AlO 4 tetrahedra and Sr 2+ ions within 12-fold coordination.

Structural and magnetic studies on PrBa 2Cu 2NbO 8− y

We have investigated structural and magnetic properties of PrBa 2Cu 2NbO 8− y (PrBCNO) which is related to PrBa 2Cu 3O 7− y (PrBCO). Neutron diffraction measurements on PrBCNO are consistent with Cu(1)−O(1) chains of PrBCO being replaced by NbO 6 octahedra. Magnetic susceptibility measurements show that PrBCNO orders antiferromagnetically with Néel temperature, T N , of about 10 K - somewhat smaller than the T N of 17 K for PrBCO. The effective paramagnetic moment of Pr is found to be 2.85 μ B - a value intermediate between that of Pr 3+ and Pr 4+. The observation of magnetic ordering in PrBCNO suggests the presence of chain site Cu is not essential for the magnetic ordering of Pr moments. The effect of the NbO 6 octahedral network on the Pr-containing block, CuO 2-Pr-CuO 2, is to alter the Cu(2)-Cu(2) interlayer distance, d, from 3.5226 Å in PrBCO to 3.413 Å in PrBCNO. The lowering of T N in PrBCNO may be due to the reduction in this interlayer distance.

The crystal structure of a mineral related to paulkerrite

Abstract An apparently new phosphate mineral (named “benyacarite”) showing evident relationships with paulkerrite and mantienneite, but richer in Mn+2, was found in granitic pegmatites in Argentina (Cerro Blanco, Tanti, Còrdoba) where it is associated with other phosphates such as triplite etc., and fluorides such as pachnolite. The unit-cell parameters are: a o = 10.561(5) Å, b o = 20.585(8) Å, c o = 12.516(2) Å, orthorhombic, space group Pbca, Z = 4, Dx = 2.37 gcm−3. The crystal structure has been refined to R(unweighted) = 0.034 and R(weighted) = 0.040 using 1023 independent reflections. It contains layers perpendicular to [010] of two kinds of octahedra, M(2)O5(O,F) and TiO5(O,F), the first essentially centered by Fe+3 atoms, with some Ti+4; the fluorine atom shares vertices of both octahedra. On both sides of these layers there are PO4 tetrahedra, with one face approximately parallel to the layers; the three corners of this face are shared with octahedra centered on Ti and M(2), whereas the remaining one is shared with another M(1)O6 octahedron centered by Mn+2 atoms (in part replaced by Fe+2). This network of octahedra and tetrahedra leaves cavities occupied by K+ and water molecules. According to these data, and to microprobe analysis the chemical formula corresponds to (H2O0.78K0.16Na0.03)2Ti(Mn0.75 +2Fe0.21 +2Mg0.04)2(Fe0.68 +3Ti0.28 +4Al0.07)2(PO4)4-(O0.6F0.4)2 · 14H2O. On the basis of the knowledge of the structure of “benyacarite” and the strong similarities of its crystal chemistry with those of paulkerrite and mantienneite, a better characterization of these minerals is obtained. These species imply substitution of Mn+2 by Mg or Fe+2, and of Fe+3 by Ti+4, or Al, respectively.