Monoclinic Structure In Space Group Research Articles

(Ca0.5Mn0.5)2MnTeO6 - An Anomalously Stable High-Pressure Double Perovskite.

High pressure high temperature treatments of the composition CaMnMnTeO6 are found to yield only an A2BB'O6-type double perovskite (Ca0.5Mn0.5)2MnTeO6, rather than a AA'BB'O6 double double perovskite with A- and B- site cation order as found in analogs CaMnMnReO6 and CaMnMnWO6 with similar cation sizes. Double perovskite (Ca0.5Mn0.5)2MnTeO6 adopts a monoclinic structure in space group P21/n with a framework of highly tilted MnO6 and TeO6 octahedra enclosing disordered Ca2+ and Mn2+ cations. Magnetic measurements show that (Ca0.5Mn0.5)2MnTeO6 is a highly frustrated spin glass with a freezing transition at 5 K, and no long-range spin order is apparent by neutron diffraction at 1.6 K.

Multifunctional continuous solid solution Na0.9Mg0.45Ti3.55O8-Na2Fe2Ti6O16: Preparation, characterization, magnetism, dual absorption, adsorption, and photocatalysis

Multifunctional continuous solid solutions Na0.9Mg0.45Ti3.55O8-Na2Fe2Ti6O16 (NFMTO-x) were synthesized via a one-step hydrothermal method by controlling the ratio of Mg and Fe. The NFMTO-x continuous solid solutions share same monoclinic structure of space group C2/m and same morphology of long hexagonal nanosheets with Na0.9Mg0.45Ti3.55O8 (NMTO) and Na2Fe2Ti6O16 (NFTO). XPS and EDX results reveal five elements Na, Mg, Fe, Ti, and O in the continuous solid solutions to confirm the change in Mg and Fe contents. The NFMTO-x continuous solid solutions enjoy dual absorption, significantly expanding their visible light response in comparison with pure NMTO. The organic pollutant methylene blue (MB) was effectively degraded through the NFMTO-x adsorption and photocatalysis, which exhibits higher performances than the pure NMTO and NFTO. Effective adsorption towards dyes is an important prerequisite to promote photocatalytic effectivity. LC-MS and TOC tests at different times reveal that MB dye was effectively mineralized to some degradation intermediates. NFMTO-x samples also have a certain capacity for CO2 methanation, converting CO2 to CO and CH4. The magnetic properties let us easily collect the powders from water after photodegradation for recycling utilization. The electron spin resonance identified O2− as the important active group in photocatalytic degradation. This research provides a significant multifunctional material used in water purification.

Lost horses on the frontier: K2BiCl5 and K3Bi2Br9

Two missing members, K3Bi2Cl9 and K3Bi2Br9, within the series of Bi-containing defect perovskite halides A3Bi2X9 were sought. K3Bi2Cl9 could not be obtained, but the previously identified but uncharacterized compound K2BiCl5 was prepared. K3Bi2Br9 was successfully prepared. K2BiCl5 and K3Bi2Br9 were synthesized by reactions of binary halides at 450–500 ​°C and their structures were determined by single-crystal X-ray diffraction methods. K2BiCl5 adopts the K2PrCl5-type structure in orthorhombic space group Pnma with Z ​= ​4 and cell parameters of a ​= ​12.5461(7) Å, b ​= ​8.7630(5) Å, and c ​= ​7.9865(5) Å. This structure features one-dimensional columns of edge-sharing BiCl7 capped octahedra. K3Bi2Br9 adopts the Tl3Bi2Br9-type structure in monoclinic space group P21/c with Z ​= ​4 and cell parameters of a ​= ​18.718(3) Å, b ​= ​8.1148(13) Å, c ​= ​13.154(2) Å, and β ​= ​91.329(2)°. In this defect perovskite variant, Bi atoms occupy two-thirds of the octahedral sites formed by close-packed arrays of the K and Br atoms, and the BiBr6 octahedra are connected by corner-sharing within slabs. Among defect perovskite halides A3Bi2X9 containing corner-sharing octahedra, K3Bi2Br9 exhibits the greatest degree of distortion from the ideal cubic perovskite structure observed so far. The band gaps, as measured from optical diffuse reflectance spectra, are 2.8 ​eV for K2BiCl5 and 2.2 ​eV for K3Bi2Br9. Electronic structure calculations indicate an indirect gap for K2BiCl5 and a direct gap with rather flat bands for K3Bi2Br9.

LaHf2Ni5−xAs4: A filled version of monoclinic LaZr2Ni4−xAs4

The quaternary arsenide LaHf2Ni5−xAs4 was prepared by reaction of the elements in a tube furnace, followed by heating in an induction furnace. LaHf2Ni5−xAs4 (x ​= ​0.25(1)) crystallizes in a new monoclinic structure in space group P21/m (with cell parameters of a ​= ​9.6766(16) Å, b ​= ​3.9280(7) Å, c ​= ​9.8605(17) Å, β ​= ​93.339°) and can be regarded as a filled variant of the monoclinic LaZr2Ni4−xAs4-type structure. The structure of LaHf2Ni5−xAs4 contains As-centred trigonal prisms arranged in propeller-shaped units, which are linked together by single trigonal prisms. The Hf atoms occupy square pyramidal sites (CN5), while the Ni atoms occupy tetrahedral sites (CN4). Band structure calculations and bonding analysis suggest that this compound is a metallic conductor, the origin of the conductivity being largely attributed to Hf–Hf and Hf–Ni interactions.

Insights into the Structural Chemistry of Anhydrous and Hydrous Hexavalent Uranium and Neptunium Dinitrato, Trinitrato, and Tetranitrato Complexes.

A systematic investigation is presented which examines the structural chemistry of anhydrous and hydrous ternary hexavalent uranium and neptunium dinitrato, trinitrato, and tetranitrato complexes. Using slow evaporation methods under acidic conditions the uranium and neptunium nitrate complexes γ-K[UO2(NO3)3], K2[UO2-cis-(NO3)4], [NpO2(NO3)2(H2O)2]·4H2O, and Cs[NpO2(NO3)3] have been synthesized and their structures refined using single-crystal X-ray diffraction data. γ-K[UO2(NO3)3] adopts an orthorhombic structure in space group Pbca consisting of antiparallel aligned [UO2(NO3)3]- moieties. K2[UO2-cis-(NO3)4] adopts a monoclinic structure in space group P21/c consisting of [UO2(NO3)4]2- moieties with two monodentate and two bidentate nitrate ligands that are arranged in a cis configuration about the uranyl, UO22+, center. Previous investigations have only identified trans variants of this monoclinic structure, and this is the first report of the cis form and also the occurrence of geometric isomerism in uranyl nitrates. [NpO2(NO3)2(H2O)2]·4H2O adopts an orthorhombic structure in space group Cmc21 consisting of parallel aligned [NpO2(NO3)2(H2O)2] moieties that are in a trans configuration with respect to the bidentate nitrate ligands. Cs[NpO2(NO3)3] adopts a hexagonal structure in space group R3c consisting of parallel aligned [NpO2(NO3)3]- moieties. It was found that despite using a Np(V) nitrate solution as the starting reagent, Np(VI) nitrate structures were consistently recovered under acidic conditions. These observations are discussed and rationalized with respect to standard reduction potentials, particularly how redox conditions and acidity affect the oxidation state of Np and subsequent structure formation. The structures uncovered in this investigation are discussed comparatively and systematically in detail with other reported anhydrous and hydrous ternary hexavalent uranium and neptunium dinitrato, trinitrato, and tetranitrato complexes, particularly with respect to how synthesis conditions, including pH and geometric isomerism, affect the structural chemistry.

Near-ultraviolet excited Eu3+ doped KSrY(BO3)2 phosphors for solid-state lighting: synthesis, structure and photoluminescent properties

A series of KSrY(BO3)2: Eu3+ phosphors have been prepared by the conventional solid-state reaction method for the first time and characterized using X-ray diffraction, UV–Vis absorbance, as well as Photoluminescence techniques. The XRD results indicated that all prepared samples could be attributable to the monoclinic structure in space group P21/m. The combination of first-principles calculations with UV–Vis absorption spectra confirmed the direct band gap characteristic of the phosphors. Upon 394 nm excitation, the 5D0→7F1 transition of the emission spectra dominated when the Eu3+ ions concentration was low, but the 5D0→7F2 transition rapidly increased and dominated with the doping concentration increasing. When the concentration of Eu3+ ions was 40%, the phosphors has the best luminescence and its CIE chromaticity coordinates were located at (0.6399, 0.3584), the color purity was as high as 99.9%. In addition, correlated color temperature, decay properties and Judd–Ofelt (J–O) theory were discussed in detail.

Theoretical and Experimental Exploration of a Novel In-Plane Chemically Ordered (Cr2/3M1/3)2AlC i-MAX Phase with M = Sc and Y

We have uncovered two inherently laminated transition metal carbides, (Cr2/3Sc1/3)2AlC and (Cr2/3Y1/3)2AlC, which display in-plane chemical order in carbide sheet and Kagome pattern in Al layer. The phases belong to the most recently discovered family of so called i-MAX phases. The materials were synthesized and the crystal structures evaluated by means of analytical high resolution scanning transmission electron microscopy, selected area electron diffraction, and X-ray diffraction Rietveld refinement. An orthorhombic structure of space group Cmcm (#63) and a monoclinic structure of space group C2/c (#15) are solved. The compounds were investigated by first principles calculations based on density functional theory, suggesting close to degenerate antiferro- and ferromagnetic spin states, dynamical and mechanical stability, and a Voigt bulk modulus in the range 134-152 GPa.

Pressure induced Ag2Te polymorphs in conjunction with topological non trivial to metal transition

Silver telluride (Ag2Te) is well known as superionic conductor and topological insulator with polymorphs. Pressure induced three phase transitions in Ag2Te have been reported in previous. Here, we experimentally identified high pressure phase above 13 GPa of Ag2Te by using high pressure synchrotron x ray diffraction method in combination with evolutionary crystal structure prediction, showing it crystallizes into a monoclinic structure of space group C2/m with lattice parameters a = 6.081Å, b = 5.744Å, c = 6.797 Å, β = 105.53°. The electronic properties measurements of Ag2Te reveal that the topologically non-trivial semiconducting phase I and semimetallic phase II previously predicated by theory transformed into bulk metals for high pressure phases in consistent with the first principles calculations.

Crystal Growth, Structures, and Properties of the Complex Borides, LaOs2Al2B and La2Os2AlB2.

Single crystals of two novel quaternary metal borides, LaOs2Al2B and La2Os2AlB2, have been grown from La/Ni eutectic fluxes. LaOs2Al2B crystallizes in tetragonal space group P4/mmm with the CeCr2Si2C-type structure, and lattice parameters a = 4.2075(6) Å and c = 5.634(1) Å. La2Os2AlB2 exhibits a new crystal structure in monoclinic space group C2/c with lattice parameters a = 16.629(3) Å, b = 6.048(1) Å, c = 10.393(2) Å, and β = 113.96(3)°. Both structures are three-dimensional frameworks with unusual coordination (for solid-state compounds) of the boron atoms by transition metal atoms. The boron atom is square planar in LaOs2Al2B, whereas it exhibits linear and T-shaped geometries in La2Os2AlB2. Electrical resistivity measurements reveal poor metal behavior (ρ300K ∼ 900 μΩ cm) for La2Os2AlB2, consistent with the electronic band structure calculations, which also predict a metallic character for LaOs2Al2B.

Room Temperature Ferromagnetism in Fe-Doped CuO Nanoparticles

The pure and Fe-doped CuO nanoparticles of the series Cu(1-x)Fe(x)O (x = 0.00, 0.02, 0.04, 0.06 and 0.08) were successfully prepared by a simple low temperature sol-gel method using metal nitrates and citric acid. Rietveld refinement of the X-ray diffraction data showed that all the samples were single phase crystallized in monoclinic structure of space group C2/c with average crystallite size of about 25 nm and unit cell volume decreases with increasing iron doping concentration. TEM micrograph showed nearly spherical shaped agglomerated particles of 4% Fe-doped CuO with average diameter 26 nm. Pure CuO showed weak ferromagnetic behavior at room temperature with coercive field of 67 Oe. The ferromagnetic properties were greatly enhanced with Fe-doping in the CuO matrix. All the doped samples showed ferromagnetism at room temperature with a noticeable coercive field. Saturation magnetization increases with increasing Fe-doping, becomes highest for 4% doping then decreases for further doping which confirms that the ferromagnetism in these nanoparticles are intrinsic and are not resulting from any impurity phases. The ZFC and FC branches of the temperature dependent magnetization (measured in the range of 10-350 K by SQUID magnetometer) look like typical ferromagnetic nanoparticles and indicates that the ferromagnetic Curie temperature is above 350 K.

Crystal structures and phase transitions in Sr2InTaO6 perovskite

The preparation and crystal structure of the double perovskite oxide Sr2InTaO6 are reported. This oxide has a monoclinic structure in space group P21/n at room temperature, where In and Ta display a rock-salt type ordering with a = 5.73356(10), b = 5.74052(10), c = 8.10905(14) A and β = 90.022(6)°. Variable temperature neutron diffraction measurements demonstrate this displays the sequence of phase transitions \( P2_{1} /n\mathop{\longrightarrow}\limits^{{605\,^\circ {\text{C}}}}I2/m\mathop{\longrightarrow}\limits^{{705\,^\circ {\text{C}}}}I4/m\mathop{\longrightarrow}\limits^{{930\,^\circ {\text{C}}}}Fm\bar{3}m \) as a consequence of the sequential loss of tilting of the corner shared octahedra upon heating. The evolution of Sr2InTaO6 crystal structure upon heating is analysed and described in terms of symmetry-adapted distortion modes. The GM4+ and X3+, that are responsible for anti-phase and in-phase tilting, respectively, are highly temperature dependent, with the GM4+ mode having the largest amplitude at room temperature.

Crystal structure and phase transitions in the uranium perovskite, Ba2SrUO6

The structure of one of the oxides proposed to be present in the grey phase of irradiated mixed oxide fuel, the double perovskite Ba2SrUO6 has been investigated from room temperature to 1300K using synchrotron X-ray powder diffraction methods. The divalent strontium and hexavalent uranium are found to be fully ordered in the double-perovskite arrangement of alternating octahedra sharing corner oxygen atoms. At room temperature Ba2SrUO6 adopts a monoclinic structure in space group P21/n. Heating to above 900K induces a first order transition to a rhombohedral structure, and further heating to above 1200K results in a continuous transition to a cubic structure. The sequence of structures is associated with the progressive loss of cooperative tilting of the corner sharing SrO6 and UO6 octahedra.

Crystal structures and thermal behavior of bis[dibenzyldimethylammonium]CuBr 4, bis[dibenzyldimethylammonium]CuCl 4 and bis[dimethyldi(2-phenylethyl)ammonium]CuBr 4 crystallized from acetonitrile and dilute HX (X=Cl or Br) solutions

Bis[dibenzyldimethylammonium]CuBr 4, bis[dibenzyldimethylammonium]CuCl 4 and bis[dimethyldi(2-phenylethyl)ammonium]CuBr 4 were crystallized from acetonitrile and/or dilute HX solutions. Five different kinds of single crystals were obtained. In the case of bis[dibenzyldimethylammonium]CuX 4 (X=Br or Cl), the acetonitrile molecules cocrystallized into the crystal structure when acetonitrile solution was used. As a result, the isomorphic structures of Bis[dibenzyldimethylammonium]CuX 4·0.5 CH 3CN (X=Br or Cl) in monoclinic space group P2 1/ n were obtained. When a dilute HX solution was used, the bis[dibenzyldimethylammonium]CuX 4 (X=Br or Cl) crystallized without solvent molecules. The formed crystals were not isomorphous with each other as the tetrabromocuprate structure crystallized in triclinic space group and the tetrachlorocuprate structure in monoclinic space group. The third compound, bis[di(2-phenylethyl)dimethylammonium]CuBr 4, crystallized without solvent molecules from an acetonitrile solution and no measurable single crystals were obtained from a dilute HX solution. Elemental analysis and powder diffraction analysis were performed to verify the structural similarities of all formed single crystals. The powder diffraction measurements also showed that the compounds have the same structure at room temperature and at a temperature of −100 °C. The thermal behaviour of the compounds was studied by using TG/DTA and DSC measurements; the compounds decomposed in two stages. No phase transitions were observed between room temperature and the melting point. In addition, these crystals showed to be very stable in the air at room temperature as they could be kept in the air for several weeks without any marks of the decomposition.

Structural refinement of Eu doped CaMgSi 2O 6 using X-ray powder diffraction data

Blue-color emitting material, CaMgSi 2O 6:Eu 2+ (CMS:Eu 2+), was synthesized by a normal solid state reaction using CaCO 3, MgO, SiO 2 and EuF 3 as starting materials. The Rietveld method was employed to quantitatively determine the structural parameters of synthesized CMS:Eu 2+. The structural parameters for CMS:Eu 2+ were successfully determined by Rietveld refinement using X-ray powder diffraction data. The final weighted R-factor, R wp, was 9.22% and the goodness-of-fit indicator, S ( = R wp / R e ) , was 1.45. The synthesized sample consisted of CMS:Eu 2+ and SiO 2 (cristobalite) phases with refined phase fractions of 89.18(1)% and 10.82(2)%, respectively. Doped Eu 2+ ions occupied the Ca sites (4 e) and replaced 1.0% of the Ca 2+ ions. The refined model of CMS:Eu 2+ describes a structure in monoclinic space group C 2/ c with Z = 4 , a = 9.7474 (2) Å, b = 8.9384 (2) Å, c = 5.2490 (1) Å and β = 105.87 (1)°.

Hydrogen‐Induced Phase Decomposition of Ba7Al13 and the Crystal Structure of Ba2AlH7.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The crystal structure of Zr2NiD4

The crystal structure of Zr2NiD4 at room temperature has been investigated by high resolution neutron powder diffraction. The diffraction pattern has been successfully fitted on the basis of a monoclinic structure in space group I2/c with cell parameters a = 0.6789 nm, b = 0.6758 nm, c = 0.5675 nm, β = 91.04° relative to the neutron wavelength of 0.1893(1) nm. The site occupancies of the deuterium atoms are compared with model calculations and results from previous X-ray and neutron data from Zr2Ni hydrides and deuterides of similar compositions based on the similar tetragonal CuAl2-type structure of Zr2Ni.