Electronic polarizability and crystallization of K2O-TiO2-GeO2 glasses with high TiO2 contents

Some K₂O-TiO₂-GeO₂ glasses with a large amount of TiO₂ contents (15-25 mol%) such as 25K₂O-25TiO₂-50GeO₂ have been prepared, and their electronic polarizability, Raman scattering spectra, and crystallization behavior are examined to clarify thermal properties and structure of the glasses and to develop new nonlinear optical crystallized glasses. It is proposed that the glasses consist of the network of TiO₆ and GeO₄ polyhedra. The glasses show large optical basicities of Λ=0.88-0.92, indicating the high polarizabity of TiO_n (n=4-6) polyhedra in the glasses. K₂TiGe₃O₉ crystals are formed through crystallization in all glasses prepared in the present study. In particular, 20K₂O-20TiO₂-60GeO₂ glass shows bulk crystallization and 18K₂O-18TiO₂-64GeO₂ glass exhibits surface crystallization giving the c-axis orientation. The crystallized glasses show second harmonic generations (SHGs), and it is suggested that the distortion of TiO₆ octahedra in K₂TiGe₃O₉ crystals induces SHGs.     

Phase equilibria and glass formation in the As2S3-TlAs2S2Se2 section of the As2S3-As2Se3-TlS system

Alloys in the As₂S₃-TlAs₂S₂Se₂ section of the As₂S₃-As₂Se₃-TlS ternary system were studied and a phase diagram was constructed using physicochemical methods (differential thermal analysis, microstructural analysis, X-ray powder diffraction, also microhardness and density measurements). The diagram in the As₂S₃-TlAs₂S₂Se₂ section is a non-quasi-binary diagonal section of the As₂S₃-As₂Se₃-TlSe quasi-ternary system. It was found that all the alloys in the section under ordinary conditions are obtained in the vitreous state. At low As₂S₃ concentrations in the section, solid solutions form up to 2.5 mol %, and at low TlAs₂S₂Se₂ concentrations, their extent is 3 mol %.     

Structure de La2Fe2S5 et de La2Fe1.87S5

The compound La₂Fe₂S₅ is orthorhombic. Cell parameters are: a = 3.997(2)Å; b = 16.485(5)Å; c = 11.394(4)Å. Space group is Cmc2₁ (Z = 4. In the cell, chains of polyedra comprised of sulfur atoms tetrahedrally or octahedrally coordinating centrally located iron atoms give a monodimensional character to the structure. This one is refined to R = 0.037. To complete the study of these chains, in the La₂Fe_2?xS₅ system, vacancies are introduced on iron atom sites. The ordered compound, La₂Fe_1.87S₅, having such vacancies, is an orthorhombic superstructure of the stoechiometric compound. Cell parameters are: a = 3.9996(5)Å; b = 49.508(3)Å; c = 11.308(3)Å. Space group is Cmc2₁ and Z = 12. The structure is refined to R = 0.068. Only two iron atom sites have vacancies. One is tetrahedral, the other octahedral. In this last case the chain deformations are the more important. The chain becomes a sort of tunnel made of atoms of sulfur, with in its center the short iron-iron separation of 2.82 Å.     

Li2O-TiO2-SiO2-P2O5和Li2O-TiO2-Al2O3-P2O5体系锂离子固体电解质的制备及性能研究

一些具有NASICON型网格结构的固体电解质具有高的电导率和好的稳定性,NASICON的意思是Na Super Ionic Conductor[1]。当NaZr2(PO4)3中P5 被Si4 部分取代时便可以得到具有NASICON结构的Na1 xZr2SixP3-xO12体系,其具有高的钠离子电导率。然而有相同结构的Li1 xZr2SixP3-xO12体系的离子电导率却很低,这是因为Li 半径太小,而NASICON三维网格结构的离子通道太大,两者不匹配而使电导率下降[2]。但当LiZr2(PO4)3中Zr4 被离子半径小些的Ti4 取代,所得LiTi2(PO4)3的通道就与Li 半径相匹配,适合于锂离子的迁移,从而使其电导率…     

Polymorphism in the Sc2Si2O7-Y2Si2O7 system

This paper examines the structural changes with temperature and composition in the Sc₂Si₂O₇-Y₂Si₂O₇ system; members of this system are expected to form in the intergranular region of Si₃N₄ and SiC structural ceramics when sintered with the aid of Y₂O₃ and Sc₂O₃ mixtures. A set of different compositions have been synthesized using the sol-gel method to obtain a xerogel, which has been calcined at temperatures between 1300 and 1750 °C during different times. The temperature-composition diagram of the system, obtained from powder XRD data, is dominated by the β-RE₂Si₂O₇ polymorph, with γ-RE₂Si₂O₇ and δ-RE₂Si₂O₇ showing very reduced stability fields. Isotherms at 1300 and 1600 °C have been analysed in detail to evaluate the solid solubility of the components. Although, the XRD data show a complete solid solubility of β-Sc₂Si₂O₇ in β-Y₂Si₂O₇ at 1300 °C, the ²⁹Si MAS-NMR spectra indicate a local structural change at x ca. 1.15 (Sc_2−xY_xSi₂O₇) related to the configuration of the Si tetrahedron, which does not affect the long-range order of the β-RE₂Si₂O₇ structure. Finally, it is interesting to note that, although Sc₂Si₂O₇ shows a unique stable polymorph (β), Sc³⁺ is able to replace Y³⁺ in γ-Y₂Si₂O₇ in the compositional range 1.86?x?2 (where x is Sc_2−xY_xSi₂O₇) as well as in δ-Y₂Si₂O₇ for compositions much closer to the pure Y₂Si₂O₇.     

Ag2Se-Tl2Se-Bi2Se3 quasi-ternary system

The Ag₂Se-Tl₂Se-Bi₂Se₃ quasi-ternary system (system A) was studied using DTA, X-ray powder diffraction, microstructure examination, and microhardness measurements. TlBiSe₂-AgBiSe₂, AgTlSe-AgBiSe₂, AgTlSe-Bi₂Se₃, and Tl₂Se-AgBiSe₂ polytherms, isothermal sections at 500 and 800 K, and liquidus surface projection of system A were constructed. System A is congruently triangulated into the following subordinate triangles: Tl₂Se-AgTlSe-Tl₉BiSe₆ (I), AgTlSe-Tl₉BiSe₆-TlBiSe₂ (II), Ag₂Se-AgTlSe-TlBiSe₂ (III), Ag₂Se-AgBiSe₂-TlBiSe₂ (IV), and AgBiSe₂-TlBiSe₂-Bi₂Se₃ (V). Subsystems I, III, and V are ternary systems with three-phase eutectic equilibrium; system II has a three-phase eutectic, and system IV is characterized by several invariant and monovariant peritectic and eutectic equilibria. Primary crystallization and homogeneity fields were outlined, and the types and coordinates of invariant and monovariant equilibria in system A were determined. A characteristic feature of the title system is an extensive field of solid solutions between high-temperature cubic AgBiSe₂ and TlBiSe₂ phases; this field lies as a continuous belt along the AgBiSe₂-TlBiSe₂ quasibinary section and covers about one-fourth of the surface area of the triangular diagram of system A.     

Phase diagram and infrared-spectral investigation of the 2TeO2 · V2O5-Na2O · V2O5 · 2TeO2 system

The phase diagram of the 2TeO₂ · V₂O₅-Na₂O · V₂O₅ · 2TeO₂ system is studied by X-ray diffraction, ir spectroscopy, and DTA. A new compound with a composition of Na₂O · 3V₂O₅ · 6TeO₂ is established. The ir spectra of the alkaline trivanadates are interpreted. They are considered as structural analogs of the new phase. As a result of this comparison, the postulate is made that the main structural units in the Na₂O · 3V₂O₅ · 6TeO₂ compound are V₂O₈ groups, while tellurium is present both in the TeO₃ and TeO₄ groups. Contrary to the crystal phases, in glasses the transition from VO₅ toward VO₄ does not proceed through the formation of new structural units of vanadium; but rather a gradual transition of the structure is observed with a change in the composition from 2TeO₂ · V₂O₅ to Na₂O · V₂O₅ · 2TeO₂.     

Photodissociation of the dimer ions Ar+2, Ne+2, and (CO2)+2

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of Ar⁺₂, Ne⁺₂, and (CO₂)⁺₂. The cross sections for photodissociation of Ar⁺₂ exhibited a strong dependence on ion source pressure, varying from 2 × 10 ^?18cm² at 0.1 torr to 6 × 10^?19cm² at 0.5 torr. A large photodissociation cross section (2 × 10^?17cm² for the reaction (CO₂)⁺₂ → CO⁺₂+ CO₂ was observed at the red end of the visible spectrum (580–620 nm) suggesting that this may be an important reaction in CO₂ rich planetary ionspheres such as that of Mars.     

Syntheses and characterizations of complex perovskite oxynitrides LaMg1/3Ta2/3O2N, LaMg1/2Ta1/2O5/2N1/2, and BaSc0.05Ta0.95O2.1N0.9

The following complex oxynitride perovskites have been prepared: LaMg_1/3Ta_2/3O₂N, LaMg_1/2Ta_1/2O_5/2N_1/2, and BaSc_0.05Ta_0.95O_2.1N_0.9. Synchrotron X-ray powder diffraction analyses show that LaMg_1/3Ta_2/3O₂N and LaMg_1/2Ta_1/2O_5/2N_1/2 are isostructural to the oxide La₂Mg(Mg_1/3Ta_2/3)O₆ (space group P2₁/n), whereas BaSc_0.05Ta_0.95O_2.1N_0.9 has a simple cubic symmetry similarly to BaTaO₂N. The orderings of octahedral cations are markedly diminished in the above oxynitrides, as compared with the related oxides such as La₂Mg(Mg_1/3Ta_2/3)O₆ and Ba₂ScTaO₆. The optical band gaps are similar for the homologous compositions, LaMg_1/3Ta_2/3O₂N, LaMg_1/2Ta_1/2O_5/2N_1/2 and LaTaON₂ (1.9 eV), and BaSc_0.05Ta_0.95O_2.1N_0.9 and BaTaO₂N (1.8 eV), while the absorption edges become broader for the complex derivatives. As revealed from the impedance spectroscopic analysis, the oxynitrides have clearly different dielectric components from those of comparable oxides containing Ta⁵⁺. Impedance spectroscopy reveals interesting capacitor geometry in BaSc_0.05Ta_0.95O_2.1N_0.9 in which the semiconducting oxynitride grains are separated by insulating secondary phases. Most notably BaSc_0.05Ta_0.95O_2.1N_0.9 has a bulk component with a high relative permittivity (κ=7300) and the grain boundary component with an even higher κ.     

The reaction of MgCl2·4H2O with CCl2F2

A new reaction of MgCl₂·4H₂O with CCl₂F₂ is investigated by DTA and TG from room temperature to 350 °C. It is observed that MgF₂ was obtained between 252 and 350 °C, Below the temperature, MgCl₂·4H₂O dehydrates and hydrolyzes to MgCl₂ and Mg(OH)Cl, which are the real reactants of the reaction with CCl₂F₂. The formation of MgF₂ is ascribed to the reaction of MgCl₂ and Mg(OH)Cl with HF, which forms by decomposition of CCl₂F₂ with the taking part in of H₂O released from dehydration of hydrated magnesium chloride on the surface of MgCl₂ and Mg(OH)Cl, which catalyzes the decomposition of CCl₂F₂ in this case. Consequently, the reactions are tested in the fluid-bed condition. It is found that MgF₂ formed at temperatures down to 200 °C in a fluid-bed reactor. This reaction may be used as a method of disposing of the environmentally sensitive CCl₂F₂ (rather than release into the atmosphere). It is also a method for the preparation of MgF₂.     

The preparation of NbH5(Me2PCH2CH2Me2)2 and NbHL2(Me2PCH2CH2PMe2)2 (L = CO or C2H4)

MMe₅(dmpe) (M = Nb or Ta, dmpe = Me₂PCH₂CH₂PMe₂) reacts with H₂ (500 atm) and dmpe in THF at 60°C to give MH₅(dmpe)_2? NbH₅(dmpe)₂ readily reacts with two mol of CO or ethylene (L) to give NbHL₂(dmpe)₂. The exchange of the hydride ligand with the ethylene protons in NbH(C₂H₄)₂(dmpe)₂ is not rapid on the ¹H NMR time scale (60 MHz) at 95°C.     

Reduction reactions of the metallocene complex (η-C5H4CMe2C9H7)2ZrCl2

The preparation and characterization of the substituted bis(cyclopentadienyl) zirconium dichloride complexes (η⁵-C₅H₄CMe₂C₉H₇)₂ZrCl₂ (1a, b) is reported. The isomer mixture of 1a, b was treated with different reducing agents such as sodium and n-butyllithium under various reaction conditions. In these reactions CC and CH activation and cleavage reactions were observed. In combination with methylaluminoxane (MAO) 1a, b and 3 showed low activities as homogeneous ethylene polymerization catalysts and no activities towards propylene. Compounds 2 and 3 were characterized by NMR spectroscopy and X-ray crystallography.     

Hydrothermal synthesis and characterization of the first 1-D indiumphosphate chain In2(HPO4)2(H2PO4)2F2·C4N2H12, a precursor for high dimensional structures

The first one-dimensional (1-D) indiumphosphate chain, In₂(HPO₄)₂(H₂PO₄)₂F₂·C₄N₂H₁₂ (1), has been hydrothermally prepared using piperazine (PIP) as a template. The structure consists of infinite chains of trans,trans-corners-sharing InO₄F₂ octahedra with the adjacent octahedra being bridged by tetrahedral PO₃(OH) and PO₂(OH)₂ units, which are H-bonded with amine groups of the organic cations. Interestingly, this macroanionic chain InP₂O₈H₃F⁻ is similar to that found in the mineral tancoite-like chains and has potential to further set up higher-dimensional networks. On heating 1 in the presence of additional phosphoric acid at 180 °C under hydrothermal condition, compound 2, In₂(OH)(H₂O)(PO₄)₂·H₃O·H₂O, possessed a 3-D structure building from the repetition of a secondary building unit is obtained. When 1 is heated with additional PIP, an unknown phase, compound 3 is formed. Finally, on treatment with another amine, such as diethylenetriamine or 1,4-diaminobutane, at 180 °C, 1, as a precursor, can convert into a previously known 3-D framework structure with 16-membered ring compound 4. Compounds 1 and 2 are determined by single-crystal X-ray diffraction. Furthermore, 1 is characterized by X-ray powder diffraction, IR spectroscopy, inductively coupled plasma analysis, thermogravimetric analysis and differential thermal analysis.     

KCl-KBO2-K2CO3, K2MoO4-KBO2-K2CO3, and K2WO4-KBO2-K2CO3 ternary systems

phase diagrams of KCl-KBO₂-K₂CO₃, K₂MoO₄-KBO₂-K₂CO₃, and K₂WO₄-KBO₂-K₂CO₃ ternary systems were studied by a calculation-experimental method and differential thermal analysis (DTA). The coordinates of ternary eutectics were determined to be E ₁: 622°C, 8.5 mol % KBO₂, 56.5 mol % KCl, and 35 mol % K₂CO₃; E ₂: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂MoO₄; E ₃: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂WO₄. The specific heats of melting of the eutectics were determined.     

Structure and basic magnetic properties of the honeycomb lattice compounds Na2Co2TeO6 and Na3Co2SbO6

The synthesis, structure, and basic magnetic properties of Na₂Co₂TeO₆ and Na₃Co₂SbO₆ are reported. The crystal structures were determined by neutron powder diffraction. Na₂Co₂TeO₆ has a two-layer hexagonal structure (space group P6₃22) while Na₃Co₂SbO₆ has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co²⁺ and Te⁶⁺/Sb⁵⁺ ions in the ab plane such that the Co²⁺ ions form a honeycomb array. The stacking of the honeycomb arrays differ in the two compounds. Both Na₂Co₂TeO₆ and Na₃Co₂SbO₆ display magnetic ordering at low temperatures, with what appears to be a spin-flop transition found in Na₃Co₂SbO₆.     

Ionogenic equilibria of (φ3CCl + HgCl2) and ((pClC6H4)3CCl + HgCl2) in CH2Cl2

Binary ionogenic equilibria (RX + MtX_x ? R⁺MtX_{n + l}^? ? R⁺ + MtX_{n + 1}^?, R = φ₃C, (pClC₆H₄)₃C; X = Cl; Mt = Hg) are studied in CH₂Cl₂ by conductivity and u.v. spectroscopy. The importance of such studies to cationic polymerisation is emphasised. The equilibrium constants, the thermodynamic parameters and the molar conductivities of the individual ions are given and the results discussed both in terms of a comparison between the two systems studied and in terms of a comparison with similar data in the literature.     

Revisiting Y2Si2O7 and Y2SiO5 polymorphic structures by Y MAS-NMR spectroscopy

This paper describes the ⁸⁹Y MAS-NMR spectra for all the established polymorphs of Y₂Si₂O₇ (y, α, β, γ and δ) and Y₂SiO₅ (X1 and X2). The combination of our spectroscopic data with the structural information published up to now from diffraction data permits the revision and correction of mistakes which appear in the literature. Finally, the influence of different structural factors, such as yttrium coordination number and Y-O distances on the ⁸⁹Y NMR isotropic chemical shift is analyzed.     

(H2NC4H8NCH2CH2NH2)(HNCH2CH2NH2)3Zn2Ge2Se8: A new,templated one-dimensional ternary semiconductor stabilized by mixed organic cations

The novel, 1D semiconductor (H₂NC₄H₈NCH₂CH₂NH₂)(HNCH₂CH₂NH₂)₃Zn₂Ge₂Se₈ has been synthesized under solvothermal conditions using N-(2-aminoethyl)piperazine as solvent and templating agent at 200 °C. The material was characterized by single crystal and powder X-ray diffraction, IR and Raman spectroscopy and thermogravimetric analysis. The compound consists of 1D anionic [Zn₂Ge₂Se₈]⁴⁻ chains made of alternating edge-shared [ZnSe₄] and [GeSe₄] tetrahedra that charged balanced by one N-(2-aminoethyl)piperazinium and three piperazinium cations. The optical properties were investigated with solid state UV–Vis/near IR spectroscopy and the results show that the solid is a medium gap semiconductor with an absorption edge at 1.8 eV.     

Synthesis and characterization of inorganic solid electrolytes of Li2O-SiO2-P2O5 and Li2O-TiO2-SiO2-P2O5 systems

The lithium-ion-conducting inorganic solid electrolytes in the oxide systems Li₂O-SiO₂-P₂O₅ and Li₂O-TiO₂-SiO₂-P₂O₅ were prepared by the solid-state reaction, and the electrolyte pellet made by cold-pressing method had diameter of 13 mm and was about 1 mm thick. Phase identification and surface morphology of the products were carried out by X-ray diffraction and scanning electron microscopy. Ionic conductivity of the pellets was investigated through ac impedance. The results show that the adding of other cations can improve the ionic conductivity of the solid electrolyte, and the sintering temperature and duration can influence the ionic conductivity. The maximum ionic conductivity in the samples is 9.9 × 10⁻⁴ S/cm in the Li₂O-TiO₂-SiO₂-P₂O₅ system. Original Russian Text ? W. Li, M. Wang, Z.H. Li, X.F. Shang, H. Wang, Y.W. Wang, Y.B. Xu, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 11, pp. 1341–1345.