Typical Layered Structure Research Articles

Four Flexible Bis(Thiabendazole)-Based Cd(II) Coordination Polymers with Various Aromatic Carboxylates: Syntheses, Structures and Properties

Four Cd(II) coordination polymers (CPs) including [Cd(btbb)0.5(L1)]n (1), [Cd(btbb)(L2)·(H2O)1.5]n (2), [Cd(btbb)(L3)]n (3), and [Cd(btbb)(HL4)]n (4) (btbb = 1,4-bis(thiabendazole)butane, H2L1 = 5-hydroxyisophthalic acid, H2L2 = 4,4′-biphenyldicarboxylic acid, H2L3 = tetrabromoterephthalic acid, H3L4 = 5-nitro-1,2,3-benzenetricarboxylic acid) were prepared under hydrothermal conditions based on flexible bis(thiabendazole) ligand and different co-carboxylates. Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectra, X-ray powder diffraction, and thermogravimetric analyses. CP 1 exhibits a 3D 2-nodal (3,4)-connected framework with the 3,4T10 topology. CP 2 and 3 feature typical hcb layer structure, and 3 is further combined into a 3D supramolecular architecture through C–H⋯O hydrogen bonds. CP 4 possesses an infinite chain and further extended into 2D supramolecular network by O–H⋯O hydrogen-bonding interactions. The effects of the aromatic polycarboxylate co-ligands on the CPs framework have been discussed and the catalytic activities of CPs 1–4 for degradation of methyl orange in Fenton-like process are also investigated.

Study on structure and fluorescence of Tb-doped CaAl LDHs prepared in ethanol/water system

An important material applied in biological fluorescent detector and medical treatment is highly desired in view of the biocompatibility and fluorescent property. Here, Tb-doped CaAl-layered double hydroxides with Ca2+/(Al3+ + Tb3+) molar ratio of 1.0, 2.0, 3.0, and 4.0 have been successfully prepared in a mixed solution of ethanol and water in a reasonable proportion. Chemical compositional analyses revealed that the experimental value of Ca2+/(Al3+ + Tb3+) molar ratio present in the samples was close to the initial value of Ca2+/(Al3+ + Tb3+) molar ratio of raw reactants. In the X-ray diffraction results, it was found that the typical layered double hydroxides structure can be kept between the Ca2+/(Al3++Tb3+) molar ratio of 1.0 and 4.0. The structural type of the Tb-doped CaAl-layered double hydroxides was monoclinic form when the Tb content was less than of 3.0 %, while rhombohedral form appeared and retained as the content of Tb3+ is kept between 3.0 and 5.28 wt%. Photoluminescence shows strong green emissions attributed to 5D4-7FJ (J = 3, 4, 5, 6) transition of Tb3+ ions incorporated in the Tb-doped CaAl-layered double hydroxides. A series of Tb-doped CaAl-LDHs with different molar ratio of Ca2+/(Al3+ + Tb3+) have been synthesized by co-precipitation in a mixed ethanol/water system. Strong green emission appeared in the Tb-doped CaAl-LDH. The Tb–CaAl-LDHs may be a promising biological fluorescent material because of the biocompatibility of Ca2+ ions as well as the fluorescent property of Tb3+ ions.

Calcium-Ion Intercalation Chemistry of the Hewettite for Rechargeable Calcium-Ion Batteries

Calcium-based battery is a very attractive alternative to Li-ion batteries due to theabundance of calcium. The hewettite (CaV6O16·xH2O) has recevied an attention due to its typical two-dimensional layered structure consisting of V3O8 layers and the hydrated calcium ions occupied between those layers (Fig1.a). The hewettite was known to be synthesized by sol-gel, hydrothermal or ion-exchange methods with a high yield, but taking a long reaction time (several days) to synthesize. In this work, we have developed a quick synthetic method to prepare CaV6O16·xH2O from Na1.2V3O8, utilizing a relatively simple electrochemical reaction. The electrodes of Na1.2V3O8 was first prepared, consisting of the active material (Na1.2V3O8), conducting carbon (super P) and binder (PVdF) with the weight ratio of 8:1:1, coated on stainless foil. Activated carbon (AC) was served as the counter and reference electrodes. The electrode was oxidized electrochemically by holding the voltage at 0.7V vs. AC for 24hr in 1M Ca(NO3)2 aqueous electrolyte, which resulted in formation of the hewettite (CaV6O16·xH2O) that was confirmed by powder XRD and elemental analyses (ICP, EDAX). The electrochemical properties of the obtained CaV6O16·xH2O electrodes were characterized with potentiostatic cyclic voltammogram (CV) (Fig1.b), galvanostatic discharge/charge cycles, powder XRD and elemental analyses. Reversible redox reactions were observed in CVs as well as the discharge/charge curves, which were responsible for the calcium-ion intercalation and evidenced by EQCM, elemental and structural analyses. The bond valence sum mapping (Fig1.c) showed the calcium-ion pathways in the crystal structure. Figure 1

NaCrO2 Cathode for High-Rate Sodium-Ionbatteries

Layered lithium intercalation compounds LiMeO2 (where Me is transition element) materials have been widely studied and applied as cathode materials for practical lithium ion batteries. Cost of lithium resource, however, has doubled since commercialization in 1991, and tight supply is expected due to the ever increasing demands of electric vehicles and energy storage systems. Indeed, the lithium resource is unevenly distributed in Southern America. Meanwhile, sodium resources are abundant and unlimited everywhere. Recently, layered NaMeO2 materials are being intensively studied because of reversible Na+ insertion/extraction, in particular, NaCrO2 (R-3m) in Na cell. Here, we report physical and electrochemical properties of NaCrO2. The NaCrO2 powder was synthesized by solid-state method. Stoichiometric mixture of Na2CO3 and Cr2O3 powders were pelletized, and the pellet was heated at 900 oC in Ar. All chemicals and products were handled in an Ar-filled gloved box to avoid air exposure. Phase identification of the products was made using X-ray diffraction (XRD) with Cu Kα radiation and the collected XRD data were analyzed by the Rietveld refinement. Electrochemical test were carried out in coin type sodium cells. Galvanostatic electrochemical charge and discharge tests in 1M NaClO4 in PC solution were carried out at room temperature. XRD pattern of the produced NaCrO2 demonstrated a phase-pure product and it was crystallized to O3 type layer structure with space group of R-3m. The delivered capacity was approximately 110 mAh (gNaCrO2) -1 in voltage range of 2 – 3.6 V and 97 % of the capacity was retained during 50 cycles. Also, the Na/NaCrO2 cell exhibited surprising high rate properties, namely, 84 % of capacity retention at 100 C-rates. Details will be discussed in the conference site. Figure 1

Magnetic and magnetoresistance studies of nanometric electrodeposited Co films and Co/Cu layered structures: Influence of magnetic layer thickness

The magnetic properties and the magnetoresistance behavior were investigated for electrodeposited nanoscale Co films, Co/Cu/Co sandwiches and Co/Cu multilayers with individual Co layer thicknesses ranging from 1nm to 20nm. The measured saturation magnetization values confirmed that the nominal and actual layer thicknesses are in fairly good agreement. All three types of layered structure exhibited anisotropic magnetoresistance for thick magnetic layers whereas the Co/Cu/Co sandwiches and Co/Cu multilayers with thinner magnetic layers exhibited giant magnetoresistance (GMR), the GMR magnitude being the largest for the thinnest Co layers. The decreasing values of the relative remanence and the coercive field when reducing the Co layer thickness down to below about 3nm indicated the presence of superparamagnetic (SPM) regions in the magnetic layers which could be more firmly evidenced for these samples by a decomposition of the magnetoresistance vs. field curves into a ferromagnetic and an SPM contribution. For thicker magnetic layers, the dependence of the coercivity (Hc) on magnetic layer thickness (d) could be described for each of the layered structure types by the usual equation Hc=Hco+a/dn with an exponent around n=1. The common value of n suggests a similar mechanism for the magnetization reversal by domain wall motion in all three structure types and hints also at the absence of coupling between magnetic layers in the Co/Cu/Co sandwiches and Co/Cu multilayers.

YB2C2: A machinable layered ternary ceramic with excellent damage tolerance

High purity bulk YB2C2, a member of ternary rare earth metal diborodicarbides, was synthesized by an in situ hot-pressing method using YH2, B4C, and graphite as initial materials. Physical and mechanical properties of YB2C2, such as Young's modulus (207GPa), shear modulus (87GPa), bulk modulus (116GPa), Vickers hardness (4.2±0.3GPa), three-point flexural strength (460±10MPa), and fracture toughness (4.6±0.1MPa·m1/2) were characterized. The as-received YB2C2 ceramic possesses typical layered structure, excellent damage tolerance and easy machinability.

Effect of Polymer/Solid and Polymer/Vapor Instantaneous Interfaces on the Interfacial Structure and Dynamics of Polymer Melt Systems.

Polymers are used in a wide range of applications that involve chemical and physical processes taking place at surfaces or interfaces which influence the interaction between the polymer material and the substance that comes into contact with it. Polymer surfaces are usually modified either chemically or physically for specific applications such as facilitating wetting, reducing friction, and enhancing adhesion. The variety and complexity of surface and interfacial processes requires a molecular-level understanding of the structural and dynamical properties of the surface/interface layer to help in the design of materials with desired functional properties. Using molecular dynamics (MD) simulations, we investigate the structure and dynamics at the surface of polymer films. We find that the density profiles of the films as a function of distance relative to an instantaneous surface have a structure indicative of a layering at the polymer/vapor interface similar to the typical layered structure observed at the polymer/substrate interface. However, the interfacial molecules at the polymer/vapor interface have a higher mobility compared to that in the bulk while the mobility of the molecules is lower at the polymer/substrate interface. Time correlation of the instantaneous polymer/vapor interface shows that surface fluctuations are strongly temperature dependent and are directly related to the mobility of polymer chains near the interface.

ChemInform Abstract: Layer Like Porous Materials with Hierarchical Structure

AbstractReview: 324 refs.

NaxVxTi1-XO2 (x = 0.6 - 1.0) Phases for Na-Ion Battery Electrode Materials

Introduction Due to the high cost of lithium-ion batteries and potential limited accessibility of lithium reserves, sodium-ion batteries have emerged as an alternate battery chemistry [1]. Sodium-ion batteries trade lithium ions for sodium ions while retaining the rocking chair like mechanism for electrochemical transport. The advantage of using sodium instead of lithium is its low cost, which is largely due to its widespread availability. Titanates have been investigated for use as anode materials in Na and Li cells. Recently and new family of titanates, NaxMyTi1-yO2 (M = Li, Ni, Co, or Cr), have been reported. These materials show remarkable low voltage cycling stability [2-5]. Herein another member of this family, namely the NaxVxTi1-xO2 (0.6 ≤ x ≤ 1) series, was studied for use as an anode material in sodium-ion batteries. Experimental Samples were synthesized via high energy ball milling of Na2CO3, V2O3, and TiO2 then heating pellets to 950 °C for 6 hours in an argon/H2:95/5 atmosphere. A 10 % Na excess was added due to the volatility of Na at these elevated temperatures. Samples for X-ray diffraction measurement were loaded under argon into an air-tight sample holder with an aluminized Mylar window. Electrodes comprising NaxVxTi1-xO2, carbon black and PVDF binder were cast using NMP as a solvent and dried at 120°C. Electrodes were cycled in 2325 coin type cells at a rate of C/10 (assuming a 100 mAh/g capacity) using Na metal counter/reference electrodes and 1M NaPF6 in PC electrolyte. Results and Discussion Figure 1 shows the XRD patterns of the as synthesized NaxVxTi1-xO2 (0.6 ≤ x ≤ 1) materials. They all have layered type structures. Electrochemical measurements showed that these materials can intercalate Na in bulk particles at low voltages and with very low hysteresis. Figure 2 shows the voltage profile of the x = 0.66 material for the first cycle and a half. These materials have substantial low voltage capacity and remarkably low hysteresis, as shown in Figure 2. As such they are promising candidates for Na-ion battery negative electrodes. Structural changes and stability during cycling, for different cut-off voltages, will be discussed.

Investigation of Structural Changes in Layered NaxNi0.5Mn0.5O2 Cathode Materials (0.5≤ x ≤1.2) and Their Electrochemical Performance

Compared to lithium, sodium is a highly abundant and cheap element. Although it has obvious weakness on gravimetric energy density due to the higher weight (M(Li)= 6.941 g/mol vs. M(Na)= 22.989 g/mol) (Hollemann et al.) and redox potential (the standard redox potential of sodium is 0.3 V above that of lithium), this cost benefit still makes it attractive to employ sodium ion batteries for large scale applications (Ellis und Nazar 2012). Such an application is for instance stationary energy storage for fluctuating renewable energy sources (e.g. solar energy or wind energy) (Barpanda et al. 2014) (Palomares et al. 2012). To keep the costs low, it is also necessary not to employ expensive and toxic transition metals, such as cobalt. Layered transition metal oxides, having the formula AMO2 (A- alkali metal, M- transition metals, O-oxygen), have already gained a lot of success in lithium-ion technology. There material are commonly crystallize in a O3-type layered structure, such as LiCoO2 and LiNiO2, which means that Li+ ions are located between sheets of transition metal oxides and are octahedrally coordinated by oxygen anions. Sodium based materials, which structure in the similar order, may also be the proper cathode candidate for sodium ion batteries. Several layered sodium oxides with different compositions have been synthesized. A promising one is the compound Na1.0Ni0.5Mn0.5O2, offering a high theoretical capacity of around 240 mAh/g when being desodiated completely. Practically, it can deliver a reversible capacity of around 185 mAh/g in the voltage range of 2.2V – 4.5V against Na/Na+ (Komaba et al. 2012). Starting from the initial O3 layered structure, many phase transitions are reported to take place during desodiation in the charge process and sodiation process, leading to a complex voltage profile. However, the final structure of the compound strongly depends on the sodium content as well as on the transition metal ratio. Beside O3 layered type structures, P2 and P3 layered type structures are reported as well for varied molar ratios between Na, Mn and Ni. In this work, NaxNi0.5Mn0.5O2 cathode material was synthesized with varying sodium content, ranging from 0.5≤ x ≤1.2. Half cells were cycled to examine the influence of sodium content on structural changes and electrochemical performance. The electrodes and active materials were examined by x-ray diffraction and scanning electron microscopy. Since best electrochemical performance as well as highest phase purity was found for a sodium content of x=0.9, this material was chosen for further investigations. In detail, in situ x-ray diffraction was conducted to observe structural changes during charging / discharging, the influence of different cut off potentials on cycling stability were tested and corresponding electrode surfaces were examined via scanning electron microscopy and x-ray photoelectron spectroscopy (XPS). Literature Barpanda, Prabeer; Oyama, Gosuke; Nishimura, Shin-ichi; Chung, Sai-Cheong; Yamada, Atsuo (2014): A 3.8-V earth-abundant sodium battery electrode. In: Nat Comms 5. DOI: 10.1038/ncomms5358. Ellis, Brian L.; Nazar, Linda F. (2012): Sodium and sodium-ion energy storage batteries. In: Current Opinion in Solid State and Materials Science 16 (4), S. 168–177. DOI: 10.1016/j.cossms.2012.04.002. Hollemann, A. F.; Wiberg, E.; Wiberg, N.: Lehrbuch der anorganischen Chemie. In: de Gruyter, zuletzt geprüft am 11.11.2014. Komaba, Shinichi; Yabuuchi, Naoaki; Nakayama, Tetsuri; Ogata, Atsushi; Ishikawa, Toru; Nakai, Izumi (2012): Study on the Reversible Electrode Reaction of Na 1– x Ni 0.5 Mn 0.5 O 2 for a Rechargeable Sodium-Ion Battery. In: Inorg. Chem. 51 (11), S. 6211–6220. DOI: 10.1021/ic300357d. Palomares, Verónica; Serras, Paula; Villaluenga, Irune; Hueso, Karina B.; Carretero-González, Javier; Rojo, Teófilo (2012): Na-ion batteries, recent advances and present challenges to become low cost energy storage systems. In: Energy Environ. Sci. 5 (3), S. 5884. DOI: 10.1039/c2ee02781j.

Facile Redox Synthesis of Layered LiNi1/3Co1/3Mn1/3O2 for Rechargeable Li-Ion Batteries

The increasing demand for energy storage devices has motivated the need to find environmentally friendly, high energy density, and cost-effective materials for energy storage and suitable synthesis techniques. In this work, we report a simple and cost-effective chemical route, in which intermediate Ni1/3Co1/3Mn1/3(OH)2 product was primarily prepared using a simple redox synthesis technique at ambient temperature. Lithiation reactions were then performed at higher temperatures to develop the final layered Lix(Ni1/3Co1/3Mn1/3)O2 structure (where x= 1.0 and 1.05). The lithium content was varied in order to analyze the effect of excess lithiation on the structural and electrochemical properties of the layered-type Li(Ni1/3Co1/3Mn1/3)O2 cathode. The XRD studies clearly confirmed the formation of layered-type structures corresponding to hexagonal α-NaFeO2 (space group R-3m). The ICP studies confirmed the stoichiometric chemical composition (Li(Ni0.32Co0.33Mn0.31)O2) of the prepared samples. FE-SEM images revealed that the particle growth occurred when the particles were heated at elevated temperatures of 950°C, and the average particle diameter was around a few micrometers. The electrochemical tests performed versus lithium indicated that competitive specific capacity values were registered for all the prepared cathodes and the capacity retention was impressive on repeated charge/discharge cycling within the potential range of 3.0 – 4.3 V and a current density of 14 mA/g. In particular, the Li(Ni0.32Co0.33Mn0.31)O2 sample demonstrated the highest capacity retention value (~ 99%) after 50 cycles and better rate performances of 104, 91, 76, and 67 mAh/g at higher current densities of 229, 457, 914, and 1429 mA/g respectively.

Potassium humate based reduced graphite oxide materials for supercapacitor applications

Reduced graphite oxide material (RGOM) has been prepared from potassium humate via a straightforward carbonization process at 700°C for an hour. Potassium humate consists of a skeleton of alkyl/aromatic units cross-linked by a wide variety of oxygen-containing functional groups, and is considered as functionalized graphene platelets. The as-prepared RGOM possesses a specific surface area of 463m2g−1 and typical layered structure with a carbon/oxygen atomic ratio of 6.3, similar to the reduced graphite oxide (RGO) reported in literatures. The RGOM based electrode delivers high volumetric capacitance of 144Fcm−3at a current density of 0.05Ag−1, as well as novel cycle performance. Its volumetric capacitance increases gradually during repeated galvanostatic charge-discharge (GC) in 3M KOH electrolyte, and reaches to be (∼150% of the initial cycle) after 2000 cycles at a high current density of 2.5Ag−1. The novel cycle performance is mainly attributed to the intercalation of OH− and K+ into the interlayer of RGOM during charge-discharge process, and the increase of the available surface area for charge storage.

Dielectric properties of a highly polar liquid crystalline material showing various types of layered structures

ABSTRACTLiquid crystal compound N-(4-n-pentyloxybenzalidene) 4′-n-pentylaniline is very interesting because of its rich phase variant, i.e. nematic, smectic A, smectic C, smectic F and smectic G phases. In the present work, temperature- and frequency-dependent dielectric studies on this compound in the homeotropic and planar orientation of molecules have been carried out in the frequency range of 1 Hz–10 MHz. The compound shows negative dielectric anisotropy (i.e.Δε < 0). Dielectric studies have shown three relaxation modes of different origin in various phases of the material. Relaxation frequencies of the observed modes follow Arrhenius behaviour. The relaxation due to interfacial polarisation, i.e. Maxwell–Wagner–Sillars effect has been observed in the nematic and isotropic phases. A relaxation mode due to the fluctuation of molecular tilt resembling the soft mode has been detected in the smectic A phase with pre- and post-transitional effects. Another mode due to the fluctuation of molecules about their short axes has been detected in the nematic and smectic A, C, F and G phases. Activation energies and ionic conductivity of these phases have also been determined.

Li-Rich Layered Cathode Material Li[Li0.157Ni0.138Co0.134Mn0.571]O2 Synthesized with Solid-State Coordination Method

Lithium-rich layered material Li[Li0.157Ni0.138Co0.134Mn0.571]O2 was prepared with the solid-state coordination method. Lithium nitrate, nickel acetate, cobalt acetate, and manganese acetate were used as raw materials, and citric acid as solid complexing agent. The lithium-rich layered material was prepared by heat-treating the precursors of the solid-phase complex compound. The prepared materials exhibited typical layer structure, nanosize distribution, and excellent electrochemical performance, and the preparation process has the advantages of low cost and simplicity. The initial discharge capacity of the prepared material reached as high as 270 mAh/g, and the charge-transfer resistance of the electrode was about 165 Ω at 4.0 V.

Microstructure and Electrical Properties of Cerium-Doped Bismuth-Layer 0.9Bi4Ti3O12-0.1K0.5Na0.5NbO3 Piezoelectric Ceramics

The cerium doped 0.9Bi4Ti3O12-0.1K0.5Na0.5NbO3 (BTO-KNN) piezoelectric ceramics were synthesized using conventional solid state processing. The effects of CeO2 doping on the microstructure and the electrical properties of BTO-KNN ceramics were investigated. It is found that the ceramics possess a pure phase of bismuth oxide layer-type structure. The piezoelectric properties of BTO-KNN-based ceramics are significantly improved after cerium doping. The piezoelectric constant d33, dielectric loss tan δ, mechanical quality factor Qm and remanent polarization Pr for the BTO-KNN ceramics with 0.75 wt% CeO2 dopant are found to be 28 pC/N, 0.29%, 2897, 11.83 µC/cm2, respectively, and with high Curie temperature TC (∼615 °C) and stable piezoelectric properties, demonstrating that the cerium doped BTO-KNN piezoelectric ceramics are the promising candidates for high-temperature applications.

Transforming growth factor-β3 promotes facial nerve injury repair in rabbits.

The present study investigated the effects of transforming growth factor (TGF)-β3 on the regeneration of facial nerves in rabbits. A total of 20 adult rabbits were randomly divided into three equal groups: Normal control (n=10), surgical control (n=10) and TGF-β3 treatment (n=10). The total number and diameter of the regenerated nerve fibers was significantly increased in the TGF-β3 treatment group, as compared with in the surgical control group (P<0.01). Furthermore, in the TGF-β3 treatment group, the epineurial repair of the facial nerves was intact and the nerve fibers, which were arranged in neat rows, were morphologically intact with visible myelin swelling. However, in the surgical control group, the epineurial repair was incomplete, as demonstrated by: Atrophic nerve fibers, partially disappeared axons and myelin of uneven thickness with fuzzy borders. Electron microscopy demonstrated that the regenerated fibers in the TGF-β3 treatment group were predominantly myelinated, with clear-layered myelin sheath structures and axoplasms rich in organelles. Although typical layered myelin sheath structures were observed in the surgical control group, the myelin sheaths of the myelinated nerve fibers were poorly developed and few organelles were detected in the axoplasms. Neuro-electrophysiological examination demonstrated that, as compared with the surgical control group, the latency period of the action potentials in the TGF-β3 treatment group were shorter, whereas the stimulus amplitudes of the action potentials were significantly increased (P<0.01). The results of the present study suggest that TGF-β3 may improve the regeneration of facial nerves following trauma or injury.

Enhancement of HPO&lt;sub&gt;4&lt;/sub&gt;&amp;ndash;OH layered structure in octacalcium phosphate and its morphological evolution by acetic acid

We show that acetic acid enhances the HPO4–OH layer structure of octacalcium phosphate (OCP) and hypothesize that the presence of acetic acid is essential for obtaining large-sized highly crystalline OCP with relatively high-temperature (∼65°C) aqueous-solution synthesis methods. The OCP crystal consists of three types of layer structures (apatite-like, transition, and HPO4–OH). X-ray diffraction (XRD) analysis indicates that increasing acetic acid concentration leads to the development of their greater structure. Infrared (IR) and nuclear magnetic resonance (NMR) spectroscopic measurements indicated development of the highly HPO4–OH layer-structure. The enhanced layer structure development caused by acetic acid is in contrast to the generally observed decrease in HPO4–OH layer structure in the presence of –COOH-containing molecules such as citrate and succinate.

Stable Dispersed MoS2 Nanosheets in Liquid Lubricant with Enhanced Rate of Penetration for Directional Well

MoS2 nanosheets of approx. 100 nm were synthesized by a reverse microemulsion route firstly, then were annealed under nitrogen atmosphere, and were finally modified with 1-dodecanethiol. The prepared MoS2 nanosheets were characterized by XRD, TEM, FTIR, and so forth. Experimental results show that MoS2 nanosheets with the typical layer structure can be easily dispersed in oil lubricant for rate of penetration (ROP) increasing in directional well. The ROP of directional well with the prepared liquid lubricant was 52.9% higher than that of the similar directional wells at least, and the drilling velocity was increased 20% while the total proportion of lubricant in drilling fluid was 1.5%.

The chemical bond properties and ferroelectricity studies of SrBi4Ti4O15

Spontaneous polarization as the most immediate parameter in ferroelectricity is always an emphasis in ferroelectric research. Some ferroelectric microscopic theory such as Berry-phase method and first principles calculation are used to study the spontaneous polarization of perovskite type ferroelectrics. SrBi4Ti4O15 is a typical bismuth layered structure ferroelectric, the complexity of its crystal structure makes the ferroelectric research more difficult. This study, from the perspective of chemical bond, analyzes the relationship between the chemical bond properties and the spontaneous polarization, and further explores the atomic bonding state in ferroelectric crystal and its impact on ferroelectricity.By starting from the crystal structure data of SrBi4Ti4O15, the atomic local cluster structure including bond length, atomic coordination situation and the number of atoms in a crystal structure unit are obtained by the atomic environment calculation (AEC). Calculation results show that there are 13 atomic local cluster structures in SrBi4Ti4O15. Then combined with the crystal decomposition method, the SrBi4Ti4O15crystal is decomposed into 38 pseudo-binary crystals, and each pseudo-binary crystal corresponds to a chemical bond. Accordding to the dielectric theory of chemical bond that used in binary crystal, chemical bond properties such as the number of effective valence electron, the effective valence electron density and the bond ionicity are calculated. Through improvement of the bond dipole moment model, the relationship among bond dipole moment, bond properties, and bond parameter is established, and the bond dipole moment of each bond in SrBi4Ti4O15 is calculated.The spontaneous polarization of an ferroelectric can be approximated as the superposition of the spontaneous polarization of various chemical bonds in the crystal, where the spontaneous polarization of chemical bond is due to the bond dipole moment. Based on the traditional polarization theory, the spontaneous polarization can be expressed as the average bond dipole moment per unit volume, and considering the number of molecules in unit cell (Z) and the atomic site occupation factor (SOF), the correlation between bond dipole moment and spontaneous polarization of the bismuth layered ferroelectrics is established. On the basis of this, the calculated spontaneous polarization along a axis in the ferroelectric SrBi4Ti4O15 is 28.03 C/cm2.This study simplifies the complex crystal research by AEC and crystal decomposition method, and studies the ferroelectricity of the bismuth layered ferroelectrics from the viewpoint of chemical bond. The bond dipole moment as the bridge in this study for connecting spontaneous polarization with chemical bond properties, which is a new micro study method in macro-properties of bismuth layered ferroelectrics. Based on this method, the spontaneous polarization of other relevant ferroelectrics such as orthogonal SrBi2Ta2O9, orthogonal Bi4Ti3O12, and tetragonal SrBi4Ti4O15 are calculated, all the results are in good agreement with the experimental values and other theoretically calculated values.

Communication—Formation of Porous Cu3Sn by High-Temperature Current Stressing

Cu3Sn is a compound commonly formed in solder joints on Cu. In this study, two different Cu3Sn structures were observed at different stages of current stressing. A normal layer-type and pore-less Cu3Sn structure was obtained at the current density of 2.27 × 104 A/cm2 at 222°C after 12 h. However, a porous Cu3Sn structure was formed under the same current stressing conditions after 22 h. The formation of porous Cu3Sn is explained by the mechanisms of phase transformation and reaction. The porous Cu3Sn structure is frequently observed in Cu/solder/Cu microbumps with a reduced solder height after electromigration tests.