一种新型共生沸石(T-L)的合成与表征

在Na₂O-K₂O-Al₂O₃-SiO₂-H₂O体系中水热合成了一种新型的共生沸石, 它由L型沸石生长在T型沸石的一端而形成, 称之为T-L型沸石. 通过XRD, SEM, TEM, EDX, IR等手段对其进行了初步的表征. SEM相片表明这种沸石具有特殊的铆钉状外形; 在TEM相片上可以清楚地看到L型沸石的大孔道, 此孔道与L型沸石的表面垂直. 通过EDX的数据计算发现共生沸石的两相有不同的骨架硅铝比: T型沸石部分Si/Al＝3.71, L型沸石部分Si/Al＝3.41. 在该样品中B酸大于L酸.     

Intergrowth between V2O5 and TiO2 (anatase): High resolution electron microscopy evidence

V₂O₅/TiO₂ (anatase) with 5 and 20 wt.% loadings of V₂O₅ have been studied using high resolution electron microscopy. This has provided the first direct evidence for the formation of a coherent interfacial boundary between two crystalline TiO₂ and V₂O₅ phases. The type of the interfacial stacking was found to be similar for all the samples, whereas the length of the boundary formed depended on the V₂O₅ loading. A model for the atomic arrangement of this boundary based on a comparison of structural positions of oxygen and metal atoms in the crystal lattices of both phases is proposed.     

New metal-rich mixed chalcogenides with an intergrowth structure: Ni<Subscript>5.68</Subscript>SiSe<Subscript>2</Subscript>, Ni<Subscript>5.46</Subscript>GeSe<Subscript>2</Subscript>, and Ni<Subscript>5.42</Subscript>GeTe<Subscript>2</Subscript>

New metal-rich mixed nickel-silicon and nickel-germanium chalcogenides, Ni_5.68SiSe₂, Ni_5.46GeSe₂, and Ni_5.42GeTe₂, were synthesized by high-temperature ceramic techniques. The X-ray diffraction study of single crystals grown from a molten flux revealed that the compounds are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2). These compounds are the first members of the family of M_7−δEX₂-type (M = Ni or Pd; E = Sn or Sb; X is chalcogen) intergrowth structures containing “light” p elements E. Resistivity measurements on pressed textured pellets showed that both selenides are anisotropic metallic conductors in the directions parallel and perpendicular to the heterometallic bond systems. The geometric criteria of stability of the intergrowth structure type under consideration are discussed. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1632–1638, September, 2007.     

On the Rotational Intergrowth of Hierarchical FAU/EMT Zeolites

A structural study of a hierarchical zeolite X, which is similar to the one first synthesized by Inayat et al., 12 was performed using transmission electron microscopy imaging and diffraction. Evidence is provided, by comparison to simulations, that this material is an intergrowth of FAU and EMT and a conceptual model is presented for the growth of the FAU material with a small fraction of EMT in an atypical morphology of assembled sheets with well‐defined intersection angles.     

Toward a Unified Approach to the Crystal Chemistry of Aurivillius-Type Compounds.: I. The Structural Model

A generalized structural model of Aurivillius-type compounds is presented using a 4D superspace group analysis where Aurivillius structures are considered as cation-deficient perovskites with the general formula AB_1−xO₃. Being essentially composition independent, the model is valid for any Aurivillius-type compounds where x is the only composition-dependent parameter. The atomic domains representing the atoms in superspace are described by means of crenel functions. For any composition, the conventional space groups can be easily derived from a unique superspace group. This work is supported by a TEM investigation where the continuously variable character of the diffraction diagram indicates that the various stacking sequences can be interpreted in terms of a structural modulation over a common average structure.     

Solution‐Based Synthesis of Layered Intergrowth Compounds of the Homologous PbmBi2nTe3n+m Series as Nanosheets

Layered intergrowth compounds in the homologous Pb_mBi_2nTe_3n+m family are interesting because they are examples of natural heterostructures. We present a simple solution‐based synthesis of two‐dimensional nanosheets of PbBi₂Te₄, Pb₂Bi₂Te₅, and PbBi₆Te₁₀ layered intergrowth compounds, which are members of the Pb_mBi_2nTe_3n+m [that is, (PbTe)_m(Bi₂Te₃)_n] homologous series. Few‐layer nanosheets exhibit narrow optical band gaps (0.25–0.7 eV) with semiconducting electronic‐transport properties.     

Structural Characterization of Y2Pd14B5

Y₂Pd₁₄B₅ is the major phase in as‐cast and annealed multiphase alloys with nominal compositions near YPd₅B₃C_0.3. Its crystal structure determined the first time here by single crystal X‐ray diffraction is body‐centered tetragonal (space group I4₁/amd). Transmission electron microscopy (TEM) reveals that in as‐cast specimens the tetragonal phase has a modulated structure and is oriented intergrown with a face‐centered cubic phase of similar composition, namely YPd₇B₂. According to Rietveld analyses of the multiphase system the structure of this phase can be well‐described by space group Fm m. Annealing the sample for 150 hrs at 973 K results in a coarsening and enrichment of the tetragonal phase as well as a disappearance of the modulations allowing a detailed structure analysis by single crystal diffractometry.     

A Hierarchical MFI Zeolite with a Two‐Dimensional Square Mesostructure

A conceptual design and synthesis of ordered mesoporous zeolites is a challenging research subject in material science. Several seminal articles report that one‐dimensional (1D) mesostructured lamellar zeolites are possibly directed by sheet‐assembly of surfactants, which collapse after removal of intercalated surfactants. However, except for one example of two‐dimensional (2D) hexagonal mesoporous zeolite, no other zeolites with ordered 2D or three‐dimensional (3D) mesostructures have been reported. An ordered 2D mesoporous zeolite can be templated by a cylindrical assembly unit with specific interactions in the hydrophobic part. A template molecule with azobenzene in the hydrophobic tail and diquaternary ammonium in the hydrophilic head group directs hierarchical MFI zeolite with a 2D square mesostructure. The material has an elongated octahedral morphology, and quaternary, ordered, straight, square channels framed by MFI thin sheets expanded along the a–c planes and joined with 90° rotations. The structural matching between the cylindrical assembly unit and zeolite framework is crucial for mesostructure construction.     

Structural Study of Li1+x−yNb1−x−3yTix+4yO3 Solid Solutions

The structures of Li_1+x−yNb_1−x−3yTi_x+4yO₃ solid solutions within the so-called M-phase field in the Li₂O-Nb₂O₅-TiO₂ system were investigated using high-resolution transmission electron, microscope (HRTEM) and single-crystal X-ray diffraction. The results demonstrated that the phase field is not a solid solution but rather a homologous series of commensurate intergrowth structures with LiNbO₃-type (LN) slabs separated by single [Ti₂O₃]²⁺ corundum-type layers. The thickness of the LN slab decreases with increasing Ti-content from ∼55 to 3 atomic layers in the metastable H-Li₂Ti₃O₇ end-member. The LN slabs accommodate a wide range of Ti⁴⁺/Nb⁵⁺ substitution, and for a given homolog the distribution of Ti and Nb is not uniform across the slab. A single-crystal X-ray diffraction study of a structure composed of nine-layer LN slabs revealed preferential segregation of Ti to the slab surfaces which apparently provides partial compensation for the charge on the adjacent [Ti₂O₃]²⁺ corundum layers. The extra cations in phases with x>0 are accommodated through the formation of Li-rich Li₂MO₃-type layers in the middle of the LN slabs. The fraction of layers with extra cations increases with increasing Ti-content in the structure.     

The low‐temperature form of calcium gold stannide,CaAuSn

The EuAuGe‐type CaAuSn phase has been synthesized and single‐crystal X‐ray diffraction analysis reveals that it has an orthorhombic symmetry (space group Imm2), with a = 4.5261 (7) Å, b = 7.1356 (11) Å and c = 7.8147 (11) Å. The structure features puckered layers that are connected by homoatomic Au—Au and Sn—Sn interlayer bonds. This structure is one of the two parent structures of its high‐temperature polymorph (ca 873 K), which is an intergrowth structure of the EuAuGe‐ and SrMgSi‐type structures in a 2:3 ratio.