Crystallographic shear in the Nb2O5WO3 and Ta2O5WO3 systems

Crystallographic shear (CS) phases occurring in the Nb₂O₅WO₃ and Ta₂O₅WO₃ systems near to WO₃ were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The Nb₂O₅WO₃ samples were heated at 1600K. They contained ordered {104} and {001} CS planes and wavy CS which were composed of intergrowths of {104} and {001} CS segments. The composition range over which the {104} CS series extended was from (Nb,W)O_2.954 i.e., (Nb,W)₆₅O₁₉₂, to (Nb,W)O_2.942, i.e., (Nb,W)₅₂O₁₅₃. The composition range over which the {001} CS series extended was from (Nb,W)O_2.9375, i.e., (Nb,W)₁₆O₄₇ to (Nb,W)O_2.875, i.e., (Nb,W)₈O₂₃. The Ta₂O₅WO₃ samples were prepared at 1593, 1623, and 1672K. At lower temperatures ordered {103} CS phases were found, with a composition range extending between (Ta,W)O_2.960, i.e., (Ta,W)₅₀O₁₄₈, to (Ta,W)O_2.944, i.e., (Ta,W)₃₆O₁₀₆. At 1673K ordered {103} CS phases occurred, as did wavy CS composed of intergrowths of {103} and {104} CS segments.     

Structured diffuse scattering and polar nano-regions in the Ba(Ti1−xSnx)O3 relaxor ferroelectric system

The observation via electron diffraction of relatively sharp G±{001}* sheets of diffuse intensity arising from the large amplitude excitation of inherently polar, transverse optical modes of distortion in Ba(Ti_1−xSn_x)O₃ (BTS), 0.1?x?0.5, samples, both at room temperature as well as liquid nitrogen temperature, shows that the polar nano-regions (PNRs) in these relaxor ferroelectric materials correspond to the same highly anisotropic 〈001〉 chain dipoles as are characteristic of the normal ferroelectric end member BaTiO₃ itself. The correlation length along the chain of these 1-d PNRs can, in principle, be determined from the width of the observed {001}* diffuse sheets in reciprocal space and is estimated to be at least 5 nm even for the higher x samples. The distribution of the substitutional Sn ions thus appears to have only a minor effect upon the correlation length along the 〈001〉 chain dipole directions. It is suggested that the role of the dopant Sn ions is not to directly induce PNRs but rather to set up random local strain fields preventing the condensation of long wavelength homogeneous strain distortions of the unit cell thereby suppressing transverse correlations of the 〈001〉 chain dipoles and the development of long-range ordered ferroelectric state/s.     

High temperature crystal structures and superionic properties of SrCl2, SrBr2, BaCl2 and BaBr2

The structural properties of the binary alkaline-earth halides SrCl₂, SrBr₂, BaCl₂ and BaBr₂ have been investigated from ambient temperature up to close to their melting points, using the neutron powder diffraction technique. Fluorite-structured SrCl₂ undergoes a gradual transition to a superionic phase at 900–1100 K, characterised by an increasing concentration of anion Frenkel defects. At a temperature of 920(3) K, the tetragonal phase of SrBr₂ undergoes a first-order transition to a cubic fluorite phase. This high temperature phase shows the presence of extensive disorder within the anion sublattice, which differs from that found in superionic SrCl₂. BaCl₂ and BaBr₂ both adopt the cotunnite crystal structure under ambient conditions. BaCl₂ undergoes a first-order structural transition at 917(5) K to a disordered fluorite-structured phase. The relationship between the (disordered) crystal structures and the ionic conductivity behaviour is discussed and the influence of the size of the mobile anion on the superionic behaviour is explored.     

Phase separation, cation ordering and nano-structural complexities in Nd2/3−xLi3xTiO3 with x=0.14

Transmission electron microscopy (TEM) investigations on Nd_2/3−xLi_3xTiO₃ with x=0.14 reveal a rich variety of structural features in the samples prepared under different conditions, such as superstructures, anti-phase domains, and nano-chessboard structures. Our careful analysis shows that these structural phenomena can be fundamentally understood as the combination of structural effects of (Nd, Li)-ordering along the 〈001〉_p direction and the spinodal decomposition along the 〈100〉_p/〈010〉_p direction. The coexistence of phase separation and cation ordering can lead to visible nano-structural complexities in many crystals, as the typical results, the regular lamella structure, nano-chessboard structures and anti-phase boundaries have been extensively studied.     

The dehydration of CuSr2(HCOO)6 · 8H2O: A crystallographic study

The isothermal dehydration of CuSr₂(HCOO)₆ · 8H₂O single crystals as well as powdered material has been followed by several techniques, mainly X-ray diffraction and optical microscopy. Evidence was found of a two-stage process, with an early appearance of an amorphous state (attributed to internal dissolution) and further recrystallization of the stable phases. One of these (CuSr(HCOO)₄, monoclinic, P_c, Z = 2, a = 7.345(10) Å, b = 8.692(15) Å, c = 6.702(10)Å, β = 97.25(5)°) has not been reported so far in the literature. When dehydration takes place near room temperature, the remaining product (Sr(HCOO)₂) bears a topotactic relationship to the parent matrix ((hk0)//(hk0)′; 〈0k0〉//〈0k0〉′). A striking metric match between both (hk0) sections, as well as the absence of any common structural motive, suggest an inner epitactic growth as the most probable mechanism for the transformation.     

Local crystal chemistry, structured diffuse scattering and the dielectric properties of (Bi1−xYx)2(MNb)O7 (M=Fe, In) Bi-pyrochlores

Electron diffraction is used to investigate the large amplitude displacive disorder characteristic of the Bi₂(M^IIINb^V)O₇ Bi-pyrochlores, Bi₂InNbO₇ and Bi₂FeNbO₇, as well as of their A site substituted Bi_1.5Y_0.5InNbO₇ and Bi_1.5Y_0.5FeNbO₇ variants. Highly structured diffuse distributions in the form of {110}* sheets of diffuse intensity perpendicular to the six 〈110〉 directions of real space along with 〈111〉* rods of diffuse intensity perpendicular to the four {111} real space planes are observed. The existence of this structured diffuse scattering is interpreted in terms of large amplitude, β-cristobalite-type tetrahedral rotations of the O′A₂ tetrahedral framework sub-structure of the ideal pyrochlore structure type. Bond valence sum calculations are used to understand the local crystal chemistry responsible for such displacive disorder. The frequency-dependent dielectric properties of Bi₂InNbO₇ and Bi₂FeNbO₇ are also investigated along with the effect upon them of A site doping with Y.     

Composition-dependent microhardness and its relationship to bonding in sodium tungsten bronzes

The technique of microhardness measurements using diamond indenters is outlined and assessed for its potential use in quantifying bonding changes and studying reactions in nonstoichiometric crystals. Results are presented for both Vickers and Knoop hardness values on {001} and {011} crystal planes of cubic sodium tungsten bronzes, Na_xWO₃, with x in the range 0.5 to 0.75. The Knoop data show that in only one direction, 〈110〉 on {001}, is the hardness sensitive to changes in composition. Hardness in the 〈110〉 directions and the degree of anisotropy increase as the sodium content of the bronze increases. All the crystal faces examined showed marked anisotropic behavior, with 〈110〉 being about 50% harder than 〈100〉 on {001} faces, while on {011} planes hardness increases in the sequence $\text{〈100〉:〈21}\text{1}\text{〉:〈11}\text{1}\text{〉 ≈ 〈01}\text{1}\text{〉}$. Hardness results from isomorphous and isoelectronic ReO₃ are considered with the Na_xWO₃ data to show the dominant role played by Na⁺WO₃ matrix interactions in determining the properties of these materials. The results are discussed in terms of current bonding theories for bronzes.     

Pd(PBu 3 t ) Adducts of Os3(CO)12. Synthesis and Structures of Pd2Os3(CO)12(PBu 3 t )2 and Pd3Os3(CO)12 (PBu 3 t )3

Two new compounds Pd₂Os₃(CO)₁₂ , 13 and Pd₃Os₃(CO)₁₂ , 14 have been obtained from the reaction of with Os₃(CO)₁₂ at room temperature. The products were formed by the addition of two and three groups to the Os–Os bonds of Os₃(CO)₁₂. Compounds 13 and 14 interconvert between themselves by intermolecular exchange of the groups in solution. Compounds 13 and 14 have been characterized by single crystal X-ray diffraction analyses.Dedicated to Professor Brian F. G. Johnson on the occasion of his retirement – 2005.     

Phase and structural characterization of Sr2Nb2O7 and SrNbO3 thin films grown via pulsed laser ablation in O2 or N2 atmospheres

The influence of substrate temperature, process gas, deposition pressure, and substrate type on the phase selection, orientation/epitaxy, and growth morphology of thin films in the SrNbO_y (y≈3.0 or 3.5) family was investigated. Pulsed laser deposited films (from a Sr₂Nb₂O₇ target) obtained in both oxygen and nitrogen atmospheres upon various substrates were characterized with X-ray diffraction, energy dispersive spectroscopy, atomic force microscopy, and transmission electron microscopy. In oxygen atmospheres, films adopted the (110)-layered perovskite structure of the target. Higher temperatures, lower pressures of oxygen, and use of (110)-oriented SrTiO₃ substrates lead to highly crystalline, epitaxial films of Sr₂Nb₂O₇. The use of nitrogen atmospheres resulted in cubic perovskite SrNbO₃ formation: epitaxial, textured, or polycrystalline films were obtained depending on the substrate; no nitrogen incorporation could be observed on the anion sublattice. On SrTiO₃, the cubic perovskite films followed a cube-on-cube epitaxy and planar defects were observed to occur on the (110) perovskite planes.     

LiNbO_3不同晶面的光催化产氢性能

研究了LiNbO3(001)、(100)和(110)晶面的光催化产氢性能。(001)、(100)和(110)3个晶面光催化产氢性能之比为7.8∶1.3∶1.0。LiNbO3[001]晶向存在电偶极矩和自发极化,有利于增加光生电子和空穴的分离效率,减少光生电子和空穴的复合,提高LiNbO3(001)面的光催化活性。LiNbO3(001)面的空穴有效质量最小,有利于光生空穴的迁移,从而减少光生电子和空穴的复合,也有利于光催化性能的提高。     

Synthesis and characterisation of HRuRh3(CO)12. Crystal structures of HRuRh3(CO)12, HRuRh3(CO)10(PPh3)2 and HRuCo3(CO)10(PPh3)2

A new ruthenium-rhodium mixed-metal cluster HRuRh₃(CO)₁₂ and its derivatives HRuRh₃(CO)₁₀(PPh₃)₂ and HRuCo₃(CO)₁₀(PPh₃)₂ have been synthesized and characterized. The following crystal and molecular structures are reported: HRuRh₃(CO)₁₂: monoclinic, space group P2₁/c, a 9.230(4), b 11.790(5), c 17.124(9) Å, β 91.29(4)°, Z = 4; HRuRh₃(CO)₁₀(PPh₃)₂·C₆H₁₄: triclinic, space group P$\text{1}$, a 11.777(2), b 14.079(2), c 17.010(2) Å, α 86.99(1), β 76.91(1), γ 72.49(1)°, Z = 2; HRuCo₃(CO)₁₀(PPh₃)₂·CH₂Cl₂: triclinic, space group P$\text{1}$, a 11.577(7), b 13.729(7), c 16.777(10) Å, α 81.39(4), β 77.84(5), γ 65.56°, Z = 2. The reaction between Rh(CO)₄^? and (Ru(CO)₃Cl₂)₂ tetrahydrofuran followed by acid treatment yields HRuRh₃(CO)₁₂ in high yield. Its structural analysis was complicated by a 80–20% packing disorder. More detailed structural data were obtained from the fully ordered structure of HRuRh₃(CO)₁₀(PPh₃)₂, which is closely related to HRuCo₃(CO)₁₀(PPh₃)₂ and HFeCo₃(CO)₁₀(PPh₃)₂. The phosphines are axially coordinated.     

LiNbO3不同晶面的光催化产氢性能

研究了LiNbO₃（001）、（100）和（110）晶面的光催化产氢性能。（001）、（100）和（110）3个晶面光催化产氢性能之比为7.8：1.3：1.0。LiNbO₃[001]晶向存在电偶极矩和自发极化,有利于增加光生电子和空穴的分离效率,减少光生电子和空穴的复合,提高LiNbO₃（001）面的光催化活性。LiNbO₃（001）面的空穴有效质量最小,有利于光生空穴的迁移,从而减少光生电子和空穴的复合,也有利于光催化性能的提高。     

Synthesis, crystal structure and properties of a new organic-inorganic hybrid Dawson-like polyoxotungstate [Co(2,2''''-bpy)3]2[Co(2,2''''-bpy)2Cl][Co(2,2''''-bpy)2]H2-[SbW18O60]·4H2O

A new organic-inorganic hybrid polyoxometalate based on Dawson-like polyoxotungstate anion [SbW18O60]9-, formulated [Co(2,2'-bpy)3]2[Co(2,2'-bpy)2Cl][Co(2,2'-bpy)2]H2[SbW18O60]·4H2O (2,2'-bpy= 2,2(-bipyridine) has been synthesized from Sb2O3, Na2WO4, CoCl2, and 2,2'-bipyridine materials by hydrothermal method, and which was characterized by elemental analyses, IR, XPS, EPR, TG, and X-ray single crystal diffraction. Structure analysis shows that the polyoxoanion self-assembled under hydrothermal conditions consists of a Dawson-like polyoxotungstate cluster anion [SbW18O60]9- encapsulating a pyramidal {SbO3} group within the {W18} cluster cage. EPR spectra show that the high-spin octahedral CoⅡ and low-spin CoⅡ ions coexist in the title compound. Magnetic properties indicate that the compound is antiferromagnetic.     

Reductively induced homolytic carbon-carbon bond cleavage in Co(CO)3(PPh3)(COCF3)

The chemical or electrochemical reduction of the trifluoroacetyl complex Co(CO)₃(PPh₃)(COCF₃) involves a single electron transfer yielding trifluoromethyl radical and an anionic cobalt carbonyl complex. The mechanism is proposed to involve electron transfer followed by initial dissociation of either a carbonyl or phosphine ligand from the 19-electron [Co(CO)₃(PPh₃)(COCF₃)]⁻ anion. The resulting 17-electron intermediate undergoes subsequent one-electron reductive elimination of trifluoromethyl radical by homolytic cleavage of the carbon-carbon bond of the trifluoroacetyl group. The radical can be trapped by either benzophenone anion, forming the anion of α-(trifluoromethyl)benzhydrol, or Bu₃SnH, yielding CF₃H. The ultimate organometallic product is an 18-electron anion, either [Co(CO)₄]⁻ or [Co(CO)₃(PPh₃)]⁻, depending upon which ligand is initially lost. Fluorine-containing products were identified and quantitated by ¹⁹F NMR while cobalt-containing products were determined by IR.     

Crystal structure of [Cu(NH3)4](ReO4)2

At T = 150 K, the crystal structure of [Cu(NH₃)₄](ReO₄)₂ is studied: a = 6.5167(3) ?, b = 6.7790(3) ?, c = 7.4627(3) ?, α = 67.336(1)°, β = 80.004(1)°, γ = 70.687(1)°, V = 286.70(2) ?³, P-1 space group, Z = 1, d _x = 3.661 g/cm³. We analyze the packing of ions using the translation sublattice isolation technique.     

La(Li1/3Ti2/3)O3: a new 1:2 ordered perovskite

A new 1:2 ordered perovskite La(Li_1/3Ti_2/3)O₃ has been synthesized via solid-state techniques. At temperature >1185°C, Li and Ti are randomly distributed on the B-sites and the X-ray powder patterns can be indexed in a tilted (b⁻b⁻c⁺) Pbnm orthorhombic cell (a=a_c√2=5.545 Å, b=a_c√2=5.561 Å, c=2a_c=7.835 Å). However, for T?1175°C, a 1:2 layered ordering of Li and Ti along 〈111〉_c yields a structure with a P2₁/c monoclinic cell with a=a_c√6=9.604 Å, b=a_c√2=5.552 Å, c=a_c3√2=16.661 Å, β=125.12°. While this type of order is well known in the A²⁺(B²⁺_1/3B⁵⁺_2/3)O₃ family of niobates and tantalates, La(Li_1/3Ti_2/3)O₃ is the first example of a titanate perovskite with a 1:2 ordering of cations on the B-sites.     

Ordered perovskites in the A(Li1/4Nb3/4)O3-A(Li2/5W3/5)O3 (A=Sr, Ca) systems

Single-phase 1:2 B-site ordered perovskites are formed in the (1−x)A²⁺(Li_1/4Nb_3/4)O₃-(x)A²⁺(Li_2/5W_3/5)O₃ systems, A²⁺=Sr and Ca, within the range 0.238?x?0.333. The X-ray and electron diffraction patterns are consistent with a P2₁/c monoclinic supercell, , , , β≈125°, where the 1:2 order is combined with b⁻b⁻c⁺ octahedral tilting. Rietveld refinements of the ordered A(B^I_1/3B^II_2/3)O₃ structures give a good fit to a model with B^I occupied by Li and Nb, B^II by W and Nb, and a general stoichiometry (Sr,Ca)(Li_3/4+y/2Nb_1/4−y/2)_1/3(Nb_1−yW_y)_2/3O₃, y=0.9x=0.21-0.30. The Sr system also includes regions of stability of a 1:3 ordered phase for 0.0?x?0.111, and a 1:1 ordered double perovskite for 0.833?x?1.0. The formation of the non-stoichiometric 1:2 ordered phases is associated with the large site charge/size differences that can be accessed in these systems, and restricted by local charge imbalances at the A-sites for W-rich compositions. These concepts are used to generate stability maps to rationalize the formation of the known 1:2 ordered oxide perovskites.     

Layered metal phosphonates containing pyridyl groups: Syntheses and characterization of Mn2(2-C5H4NPO3)2(H2O) and Zn(6-Me-2-C5H4NPO3)

This paper reports the syntheses and characterization of two phosphonate compounds with layered structures, namely, Mn₂(2-C₅H₄NPO₃)₂(H₂O) (1) and Zn(6-Me-2-C₅H₄NPO₃) (2). In compound 1, double chains are found in which the {Mn₂O₂} dimers are linked by both aqua and O-P-O bridges. These double chains are connected through corner-sharing of {MnO₅N} octahedra and {CPO₃} tetrahedra, forming an inorganic layer. The pyridyl groups fill the inter-layer spaces. In compound 2, each {ZnO₃N} tetrahedron is vertex-shared with three {CPO₃} tetrahedra and vice versa, hence forming an inorganic honeycomb layer. The pyridyl groups reside between the layers. Magnetic studies show that weak antiferromagnetic interactions are mediated between the manganese ions in compound 1. Crystal data for 1: monoclinic, space group C2/c, , , , β=107.3(1)°. For 2: orthorhombic, space group Pbca, , , .     

Syntheses and Characterization of One-Dimensional Antimony(III) Diphosphonates: [NH3(CH2)nNH3][Sb{CH3C(O)(PO3)2}] (n=4, 5)

This paper describes the hydrothermal syntheses and characterization of two antimony(III) diphosphonates: [NH₃(CH₂)_nNH₃]Sb{CH₃C(O)(PO₃)₂} [n=4 (1), 5 (2)]. The two compounds are isostructural based on their XRD measurements. Single-crystal structure determination of compound 1 revealed a one-dimensional linear chain structure where the distorted {SbO₅E} octahedra (E is the lone pair electrons occupying an axial position) are corner-shared by {CPO₃} tetrahedra. The protonated diamines are located between the chains, with their nitrogen atoms locked by the hydrogen bonds with the phosphonate oxygens. Crystal data for 1: orthorhombic, space group Pnma, a=13.426(4), b=17.149(4), c5.4496(14) Å, V=1254.7(6) Aų, Z=4.     

A Novel Dimeric Polyoxotungstate Decorated by 3d-4f atoms: K4LaH[As2W20CuO67 (H2O)3]Cl2· 22.5H2O

A novel dimeric polyoxotungstate K₄LaH[As₂W₂₀CuO₆₇(H₂O)₃ ]Cl₂·22.5H₂O has been synthesized and characterized by IR, element analysis TG and cyclic voltammogram. The anion K₄LaH[As₂W₂₀CuO₆₇(H₂O) ₃]Cl₂·22.5H₂O can be characterized as two {As^IIIW₉O₃₃}⁹⁻ moieties linked via a {Cu(OH)}, a {W(H₂O)} and a {WO(H₂O)} group which total coordination numbers are respectively 5, 5, 6. An additional lanthanide atom connects the dimeric cluster via a W-O-La bond. The X-ray single crystal diffraction shows that it is in the triclinic system, space group P-1, with a = 12.287(6) ?, b = 20.197(1) ?,c=21.483(1)?,α = 62.584(8)°,β = 74.659(8)°,γ = 75.273(9)°,V = 4509(4)?³, Z = 2. To our known, the polyoxotungstate is the novel sandwich-type polyoxoanion, which is decorated by transition-metal and lanthanide atoms at the same time.