Space Group Pbam Research Articles

Ternary Magnesium Rhodium Boride Mg2Rh1-xB6+2x with a Modified Y2ReB6-Type Crystal Structure

The new ternary magnesium rhodium boride Mg2Rh1-xB6+2x has been prepared by the reaction of the mixture of Mg powder, RhB, and crystalline boron in a Ta container sealed under argon. The crystal structure of Mg2Rh0.75(1)B6.50(4) is determined using single-crystal X-ray diffraction, electron diffraction, and high-resolution electron microscopy (space group Pbam, a=8.795(2) A, b=11.060(2) A, c=3.5279(5) A, Z=4, 630 reflections, RF=0.045). It represents a modified Y2ReB6 structure type with an unusual replacement of part of the Rh atoms by boron pairs located in the pentagonal channels parallel to the c axis. The pairs interconnect the neighboring planar boron nets into the 3D framework. The variation of the lattice parameters reveals a homogeneity range Mg2Rh1-xB6+2x. The random distribution of the Rh atoms and boron pairs and the stabilizing effect of the boron pairs on the Y2ReB6 type structure motif are discussed using electronic band structure calculations and chemical bonding analysis with the electron localization function (ELF).

Evolution of the structure, microstructure and physical properties of RuSr2GdCu2O8 as a function of the thermal treatment

The crystal structure of RuSr2GdCu2O8 was successfully refined in the orthorhombic system (Pbam space group) using synchrotron powder diffraction data collected on a high purity and low defect containing sample. The microstructures of selected samples submitted to different thermal treatments were investigated by means of TEM analysis: the progressive annealing in an O2 atmos phere suppresses the formation of nano-domains and extended planar defects, whereas annealing under vacuum favours the formation of extended planar defects and nano-domains as well. Lattice parameters increase with the anneling time, whereas an abrupt decrease of the c parameter occurs after de-oxygenation. A dependence of magnetization and superconductivity on the thermal treatment was evidenced and related to the structural and microstructural changes.

Interplay between Size and Electronic Effects in Determining the Homogeneity Range of the A9Zn4+xPn9 and A9Cd4+xPn9 Phases (0 ≤ x ≤ 0.5), A = Ca, Sr, Yb, Eu; Pn = Sb, Bi

Seven cadmium- and zinc-containing Zintl phases, A9Zn(4+x)Pn9 and A9Cd(4+x)Pn9 (0 < or = x < or = 0.5), A = Ca, Sr, Yb, Eu; Pn = Sb, Bi, have been synthesized, and their structures have been determined by single-crystal X-ray diffraction. All compounds are isostructural and crystallize in the centrosymmetric orthorhombic space group Pbam (no. 55, Z = 2), and their structures feature tetrahedra of the pnicogens, centered by the transition metal. The tetrahedra are not isolated but are connected through corner sharing to form ribbons, which are separated by the divalent cations. The occurrence of a small phase width and its variation across this family of compounds has been systematically studied by variable temperature crystallography, resistivity, and magnetic susceptibility measurements, and these results have been reconciled with electronic structure calculations performed using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method. These analyses of the crystal and electronic structure indicate that the polyanionic subnetwork requires 19 additional electrons, whereas only 18 electrons are provided by the cations. Such apparent "electron deficiency" necessitates the presence of an interstitial atom in order for an optimal bonding to be achieved; however, an interplay between the sizes of the cations and anions and the total valence electron concentration (governed by the stoichiometry breadth) is suggested as a possible mechanism for achieving structure stability. The structural relationship between these and some known structures with two-dimensional layers are discussed as well.

X-Ray Diffraction Study of Ba 6-3x (Eu 1/2 Nd 1/2) 8+2x Ti 18O 54 Microwave Dielectric Ceramics Prepared by Sol-Gel Method

Perfectly-sintered Ba 6-3x (Eu 1/2 Nd 1/2) 8+2x Ti 18O 54 ( x = 2/3) (BENT) microwave dielectric ceramics was fabricated successfully with BENT powders prepared by Sol-Gel process. The lattice parameters of BENT ceramic powders were determined by method of X-ray diffraction in ordinary temperature. Orthorhombic lattice type (space group Pbam) of BENT in ordinary temperature was determined, its pattern was indexed and its polycrystalline X-ray diffraction data were listed. By analysis of its X-ray diffraction data, it could be concluded that Eu and Nd coexisted in the single phase and could not be distinguished in BENT ceramics. The increasing dielectric losses of BENT could be explained basically by the disorder of Eu ions and Nd ions occupied in Al-sites.

Microporous titanosilicates Synthesis and structural characterization of a new orthorhombic-type labuntsovite

The crystal structure of a new orthorhombic-type labuntsovite with composition Na 5.36 Ti 4 (Si 4 O 12 ) 2 (O 0.34 OH 0.66 ) 4 · 10.31H 2 O, obtained as side product of hydrothermal runs devoted to the synthesis of rhodesite-type microporous silicates, has been solved and refined in the space group Cmmm ( a = 7.278, b = 14.134, c = 7.118 A; Z = 1) with X-ray single-crystal diffraction data collected by a Bruker-AXS Smart Apex diffractometer equipped with a CCD area detector. The crystal structure shows the overall features known for the heteropolyhedral framework (tetrahedral/octahedral) structures of the labuntsovite-group minerals, like systems of channels and disorder. The simpler chemical composition of the synthetic compound, which does not show isomorphous replacements, allows a detailed discussion of the zeolite-like disorder in the channels, which is related to the charge of the framework [Ti 4 (Si 4 O 12 ) 2 (OH 4−x O x )] (4+x)− and to the system of hydrogen bonding. The different space group Pbam shown by the two known natural labuntsovites (nenadkevichite and korobitsynite) is attributed to the presence in the natural samples of the Nb → Ti substitution.

Synthesis and Study of the Crystallographic and Magnetic Structure of HoFeMnO5

AbstractA new oxide of stoichiometry HoFeMnO5 has been obtained by replacing Mn3+ cations by Fe3+ in the parent oxide HoMn2O5. The crystallographic and magnetic structures have been analyzed by neutron powder diffraction (NPD), which complements susceptibility and magnetization measurements. HoFeMnO5 is orthorhombic, belonging to the Pbam space group like the parent compound. The crystal structure contains infinite chains of edge‐sharing Mn4+O6 octahedra, interconnected by dimer units of Fe3+O5 square pyramids. In comparison with HoMn2O5, containing elongated Mn3+O6 pyramids, the Fe3+O5 units are flattened. The magnetization measurements show that HoFeMnO5 presents a long‐range magnetic order below TC ≈ 153 K. An NPD study shows that HoFeMnO5 adopts a collinear ferrimagnetic structure: each of the Mn4+ and Fe3+ sublattices are ferromagnetically coupled, and the coupling between the two sublattices is antiferromagnetic; the magnetic moments are oriented along the c direction. The Ho3+ cations also order below TC, but with a very small magnetic moment; the Ho3+ moments are parallel to the Fe3+ magnetic sublattice. At T = 2.7 K, the ordered magnetic moments for the Mn4+, Fe3+ and Ho3+ ions are 1.31(6), 3.20(10) and 0.36(7) μB, respectively. In comparison with ErFeMnO5, where Er3+ cations are fully ordered at low temperatures, in HoFeMnO5 there is a frustration concerning the long‐range order of the Ho3+ cations, which remain virtually paramagnetic over the whole temperature range.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Crystal Structure and Physical Properties of Polymorphs of LnAlB4 (Ln = Yb, Lu)

Single crystals of YbAlB4 were grown in excess Al flux. Plate- and needle-shaped crystals were found. The plates are found to be s-YbAlB4, which crystallizes with the ThMoB4 structure type in space group Cmmm (No. 65), Z = 4, with lattice parameters of a = 7.3080(4), b = 9.3150(5), and c = 3.4980(2) A. The needle-shaped crystals were identified as the first form of YbAlB4 which crystallizes with the YCrB4 structure type in space group Pbam (No. 55), Z = 4, with lattice parameters of a = 5.9220(2), b = 11.4730(3), and c = 3.5060(5) A. While both compounds have heavy fermion ground states with Isinglike magnetic anisotropy, the electronic specific heat coefficients (γ) differ. The s-phase has a γ value near 300 mJ mol -1 K-2, more than twice that of the α-phase, γ = 130 mJ mol-1 K-2. A comparison of the structures and physical properties of both polymorphs is presented. © 2007 American Chemical Society.

Synthesis, structure and properties of Li 2Rh 3B 2

Li 2Rh 3B 2 has been synthesized at 1000 °C from a stoichiometric mix of rhodium and boron and an excess of lithium. Li 2Rh 3B 2 crystallizes in the orthorhombic space group Pbam (no. 55, Z=2) with room temperature lattice constants a=5.7712(1) Å, b=9.4377(2) Å, c=2.8301(1) Å and cell volume 154.149(6) Å 3. The structure was solved from single crystal X-ray diffraction yielding the final R indices (all data) R1=2.8% and w R2=4.7%. The structure is a distortion of the CeCo 3B 2 structure type, containing a network of Rh 6B trigonal prisms and short Li–Li contacts of 2.28(2) Å. Li 2Rh 3B 2 is a diamagnetic metal with a room temperature resistivity of 19 μΩ cm, as determined by magnetic susceptibility and single crystal transport measurements. The measured diamagnetism and electronic structure calculations show that Li 2Rh 3B 2 contains rhodium in a d 10 configuration.

Hydrothermal synthesis and magnetic properties of RMn 2O 5 ( R=La, Pr, Nd, Tb, Bi) and LaMn 2O 5+δ

RMn 2O 5 ( R=La, Pr, Nd, Tb, Bi) crystallites were prepared by a mild hydrothermal method and characterized by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and magnetic measurement. The formation of manganates was sensitive to the alkalinities and Mn-containing precursors of the reaction mixtures. This family of manganates is isostructural and has a space group of Pbam. The magnetic measurements for RMn 2O 5 showed an antiferromagnetic transition. The strong irreversibility between the ZFC and FC curves indicated a helicoidally magnetic structure below 40 K. The max d.c. susceptibilities of LaMn 2O 5+ δ ( δ=0.01, 0.06, 0.08, 0.16, 0.17) were found to be variable and the excess oxygen ( δ) in the compounds was influenced by the alkalinity used in the hydrothermal synthesis.

Thermal expansion between 480 and 940 C of Cr-doped mullites derived from single-phase precursors

The lattice parameters were determined by in situ X-ray powder diffraction between room temperature (RT) and 940 ^oC for the Cr-doped mullite derived from single-phase precursors containing up to 9.60 wt% Cr_2O_3. Mullites were orthorhombic, space group Pbam. Chromium doping caused the increase in unit-cell parameters. Strongest expansion caused by Cr incorporation into mullite was noticed along the c-axis followed by a and b. In temperature region from 480 to 940 ^oC the lattice parameters a, b, and c expanded almost linearly, and the linear coefficients of thermal expansion along crystallographic axes were calculated for this region. Strongest expansion caused by the thermal treatment was noticed along the b-axis followed by c and a. The linear thermal expansion coefficients were also dependent on the chromium content in mullite. All thermal expansion coefficients, alpha(a), alpha(b) and alpha(c), exhibited minima for 6.97 wt% Cr_2O_3.

A new high-pressure CaGe2O5 polymorph with 5- and 6-coordinated germanium

We discovered a new CaGe 2 O 5 polymorph in high-pressure experiments (above 8 GPa). The phase is orthorhombic, space group Pbam , with a = 7.306(2), b = 8.268(2), c = 5.714(1) A, V = 345.2(1) A 3 , and Z = 4. The new phase, which we call post-titanite CaGe 2 O 5 , is the high-pressure polymorph of titanite CaGe 2 O 5 . The structure of this new polymorph is based on a network of 5- and 6-coordinated Ge polyhedra and 8-coordinated Ca atoms. Following the germanate analog to silicate, post-titanite CaSi 2 O 5 could be expected to form at high-pressure conditions and thus might exist in Earth’s mantle.

Magnetic properties and magnetic structure of [formula omitted

HoMnFeO 5 obtained from HoMn 2 O 5 by replacing Mn 3 + by Fe 3 + . The study of the crystallographic structure indicates that HoMnFeO 5 is orthorhombic, Pbam space group. The magnetic measurements and the neutron diffraction experiments show that HoMnFeO 5 is ferrimagnetic, with T C ≈ 153 K . The Ho 3 + ions seem to present a frustrated magnetic order.

Effect of iron doping on the magnetic properties of TbMn 2O 5

We synthesized a series of TbFe xMn 2−xO 5 (0⩽ x⩽0.2) samples and studied the effect of the Fe-doping on their magnetic properties. X-ray diffraction patterns indicate a pure orthorhombic structure with space group Pbam for all the samples. Based on the data of temperature- and field-dependent magnetization, M( T) and M( H) curves, it is found that the magnetic moment enhances with increase in the Fe-content in TbMn 2O 5. With increase in the Fe-content from 0 to 0.2, the magnetic moment increases progressively from 0.014 to 0.030 μ Bohr p.f.u. at room temperature (RT). Particularly for the TbFe 0.2Mn 1.8O 5 sample, a current–voltage curve displays a nonlinear behavior at RT. If a strong coupling between magnetic moment and electric polarization exists, the Fe-doped sample may have a higher polarization/ferroelectric effect, which should be a great advantage for the future application of the spintronics devices.

Investigation of the R 2Se 3–Cu 2Se–In 2Se 3 (R = La, Pr, Y and Er) systems at 870 K and crystal structure of the R 2CuInSe 5 (R = La, Ce and Pr) compounds

Phase equilibria in R 2Se 3–Cu 2Se–In 2Se 3 (R = La, Pr, Y and Er) systems at 870 K were determined using X-ray powder diffraction. The existence of the RCuSe 2 (LaCuS 2 structure type, space group P2 1/ c) and La 5Cu 13Se 14 (unknown structure) compounds was confirmed in the R 2Se 3–Cu 2Se (R = La, Pr) sections. The formation of the solid solutions R (2+ x)/3 Cu 2− x Se 2 (0 ≤ x ≤ 1) (Er 2/3Cu 2S 2 structure type, space group P 3 ¯ ) and the ErCu 5Se 4 compound with unknown structure was confirmed in the R 2Se 3–Cu 2Se (R = Y, Er) sections. The existence of the La 3In 1.67Se 7 (Ce 3Al 1.67S 7 structure type, space group P6 3) and La 4In 4.67Se 13 (La 4In 4.72Se 13 structure type, space group Pbam) compounds in the La 2Se 3–In 2Se 3 system and the Pr 3InSe 6 (Pr 3InSe 6 structure type, space group Pnnm) compound in the Pr 2Se 3–In 2Se 3 system was confirmed. No ternary compounds exist in the Er 2Se 3–In 2Se 3 and Y 2Se 3–In 2Se 3 sections. The formation of the CuInSe 2, CuIn 3Se 5, CuIn 5Se 8, CuIn 7Se 11 and CuIn 11Se 17 compounds in the Cu 2Se–In 2Se 3 section was observed. The crystal structure of new quaternary R 2CuInSe 5 (R = La, Ce and Pr) compounds (space group Pnma, a = 1.20382(6) nm, b = 0.41185(2) nm, c = 1.7556(1) nm (for La 2CuInSe 5), a = 1.19997(7) nm, b = 0.40855(2) nm, c = 1.7464(1) nm (for Ce 2CuInSe 5) and a = 1.1973(3) nm, b = 0.40649(9) nm, c = 1.7408(4) nm (for Pr 2CuInSe 5)) was determined.

Synthesis, Crystal Structure, and Magnetic Studies of One-Dimensional Cyano-Bridged Ln3+−Cr3+Complexes with bpy as a Blocking Ligand

The reaction of Ln(NO3)3.aq with K3[Cr(CN)6] and 2,2'-bipyridine (bpy) in a water/ethanol solution led to two families of complexes: 4 one-dimensional (1D) complexes of the formula trans-[Cr(CN)4(mu-CN)2Ln(H2O)3(bpy)2]n.4nH2O.3.5nbpy (Ln3+ = La, Ce, Pr, and Nd) and 10 1D complexes of the formula trans-[Cr(CN)4(mu-CN)2Ln(H2O)4(bpy)]n.3.5nH2O.1.5nbpy (Ln3+ = Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The structures for the fourteen complexes [LaCr]n (1), [CeCr]n (2), [PrCr]n (3), [NdCr]n (4), [NdCr]n (4'), [SmCr]n (5), [EuCr]n (6), [TbCr]n (7), [DyCr]n (8), [HoCr]n (9), [ErCr]n (10), [TmCr]n (11), [YbCr]n (12), and [LuCr]n (13) have been solved. Complexes 1-4 crystallize in the orthorhombic space group Pbam and are isomorphous; complexes 4'-13 crystallize in the triclinic space group PI and are isomorphous. The X-ray structural characterization of complexes 1-4 shows the presence of a discrete decameric water cluster built around a cyclic hexameric core stabilized by the solid-state structure, which represents another new mode of association of water molecules. The Ln3+-Cr3+ magnetic interaction is negligible in 6 and 12, antiferromagnetic in 2, 4', 7, 8, 9, 10, and 11, and unresolved for 3. The complex 5 is a ferrimagnet because its magnetic studies suggest the onset of a very weak ferromagnetic three-dimensional ordering.

Syntheses, crystal structures and thermal properties of 3D coordination polymers assembled from 1,4,5,8-naphthalenetetracarboxylic acid

Two new coordination polymers based on 1,4,5,8-naphthalenetetracarboxylate (ntc) has been prepared by hydrothermal methods. Their crystal structures have been determined from synchrotron powder X-ray diffraction data. Ca 2(C 14H 4O 8)(H 2O) 2, CPO-13, is built around infinite chains of seven coordinated calcium atoms. Zn 2(C 14H 4O 8)(H 2O) 2, CPO-14, is isostructural with Mn 2(C 14H 4O 8)(H 2O) 2, and is built around infinite chains of corner sharing Zn octahedra. Crystal data for CPO-13: Triclinic space group P-1, with a = 5.820 , b = 6.759 , c = 10.168 Å , α = 72.32 ° , β = 86.09 ° , γ = 107.74 ° , V = 357.310 Å 3 and Z = 1 . Crystal data for CPO-14: Orthorhombic space group Pbam, with a = 9.773 , b = 7.060 , c = 9.879 Å , V = 681.729 Å 3 and Z = 2 . The thermal properties were investigated for both compounds. An unusual anisotropic thermal expansion for CPO-14 is caused by the carboxylate groups of the ntc anions gradually bending away from each other.

Synthesis and Crystal Structures of Four New Bromo‐Chalcogenides: MnSbS2Br, MnBiSe2Br and Two Allotropic Forms of MnSbSe2Br. Crystal Chemistry of the MnPnQ2X Family (Pn: Sb, Bi; Q: S, Se; X: Cl, Br, I).

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Cadaverinium dichloride: a case of centro–non-centrosymmetric ambiguity

In the title salt, also known as pentane-1,5-diammonium dichloride, C(5)H(16)N(2)(2+)x2Cl(-), the cation exists in an ideal fully extended conformation and lies on a mirror plane in the space group Pbam. In the crystal structure, layers of cations are hydrogen bonded with Cl(-) anions, which occupy the space between the layers. This kind of packing leads to a short unit-cell parameter of 4.463 (1) Angstrom. This structure is another case of centro-non-centrosymmetric ambiguity; the best results were obtained in a centrosymmetric space group, with the disordered NH(3) groups accounting for the non-centrosymmetric 'component'.

Crystal-structure refinement, thermal expansion, and chemical distortion of Bi2Ga4O9

Single crystals of Bi 2 Ga 4 O 9 are grown from a solution in a bismuth oxide melt. The structure (orthorhombic, space group Pbam , a = 7.918(2) A, b = 8.299(2) A, c = 5.894(2) A, Z = 2) is refined to R = 0.052 in the anisotropic approximation based on single-crystal X-ray diffraction data. The structure is a framework. The bismuth(III) atoms are sixfold coordinated; gallium(III) exists in both tetrahedral and octahedral coordina- tions. The thermal expansion of Bi 2 Ga 4 O 9 is studied by high-temperature X-ray powder diffraction method and is found to be sharply anisotropic. A structural interpretation of the anisotropy is proposed. Chemical distortion in the Bi 2 M 4O9 compounds with M = Fe(III), Al, or Ga is analyzed and compared with the thermal expansion of Bi2Ga4O9.

Crystal structures of the R 4In 4.72Se 13 (R = La and Ce) compounds

The crystal structures of the R 4In 4.72Se 13 (R = La and Ce) compounds (space group Pbam, Pearson symbol oP43.44) were determined by means of X-ray single crystal diffraction ( a = 1.2442(3) nm, b = 2.2146(4) nm, c = 0.41969(8) nm, R 1 = 0.0426 for La 4In 4.72Se 13) and X-ray powder diffraction ( a = 1.23725(6) nm, b = 2.2144(1) nm, c = 0.41463(2) nm, R I = 0.0984 for Ce 4In 4.72Se 13). The R atoms are surrounded by trigonal prisms with two additional atoms, the In1 atoms by tetrahedra, the In2–In5 atoms by octahedra. The R-centered trigonal prisms form columns along z-axis. The chains of the In1-centered tetrahedra and In2–In5-centered octahedra are also located along z-axis.