A2 Structure Research Articles

Benzothiazole derivatives containing different electron acceptors exhibiting totally different data-storage performances

Two small conjugated molecules BTVCz–NO2 and BTVCz, each incorporating an electron-donating carbazole group and a medium electron-withdrawing benzothiazole group, were both successfully designed and synthesized. Molecule BTVCz–NO2 is an A1–D–A2 structure while BTVCz is a single D–A structure. Both molecules were made into thin films by spin-coating. The two films differentiated over their optical, electrochemical and morphological properties. And the fabricated device with BTVCz–NO2 as an active material showed non-volatile ternary WORM data-storage behavior with its switching threshold voltages at −1.5 V and −2.5 V in tandom when an electrical field was applied, whereas its “counterpart” device with BTVCz as an active material exhibited volatile binary DRAM data-storage behavior with its switching threshold voltage at −1.3 V. Combined with theoretical calculation of each molecule, we conclude that different data-storage behaviors can be achieved by introducing different electron acceptors and that molecule BTVCz–NO2, as an A1–D–A2 structure, is more likely to achieve ternary data-storage performance.

Structural Characterization of Co Thin Film with bcc-Based A2 Structure Epitaxially Grown on GaAs(100) Single-Crystal Substrate

Structural Characterization of Co Thin Film with bcc-Based A2 Structure Epitaxially Grown on GaAs(100) Single-Crystal Substrate

Microstructure and magnetostrictive properties of Tb doped Fe–Ga bulk alloys prepared by melt quenching

The microstructure and magnetostrictive properties were investigated in the Tb doped Fe83Ga17−xTbx (x = 0.05, 0.10, 0.20, 0.30, 0.40, 0.50) bulk rods prepared by melt rapidly quenching. The partial solid solubility of Tb in the Fe–Ga matrix was preliminary detected by the lattice parameters and SEM observation. The matrix keeps A2 structure and the second phase appears surround the grain boundary as x ≥ 0.1. \( \left\langle {100} \right\rangle \) preferred orientation is also observed for x = 0.1 sample along the axis of the quenched rod. The saturation magnetostriction first increases and maximum value reaches at x = 0.1, and then decreases with Tb addition increasing. The initial increase of the magnetostriction should be associated with the partial solution of Tb in the matrix, the maximum value at x = 0.1 should be attributed to the \( \left\langle {100} \right\rangle \) preferred orientation, and the decrease of the magnetostriction is correlated with the appearance of the second phase along the grain boundary.

Many-atom interactions in the theory of higher order elastic moduli: A general theory

The total potential energy of a crystal U({rik}) as a function of the vectors rik connecting centers of equilibrium positions of the ith and kth atoms is assumed to be represented as a sum of irreducible interaction energies in clusters containing pairs, triples, and quadruples of atoms located in sites of the crystal lattice A2: U({rik}) ≡ ΣN=14EN({rik}). The curly brackets denote the “entire set.” A complete set of invariants {Ij({rik})}N, which determine the energy of each individual cluster as a function of the vectors connecting centers of equilibrium positions of atoms in the cluster EN({rik}) ≡ EN({Ij({rik})}N), is obtained from symmetry considerations. The vectors rik are represented in the form of an expansion in the basis of the Bravais lattice. This makes it possible to represent the invariants {Ij({rik})}N in the form of polynomials of integers multiplied by τ2m. Here, τ2 is one-half of the edge of the unit cell in the A2 structure and m is a constant determined by the model of interaction energy in pairs, triples, and quadruples of atoms. The model interaction potential between atoms in the form of a sum of the Lennard-Jones interaction potential and similarly constructed interaction potentials of triples and quadruples of atoms is considered as an example. Within this model, analytical expressions for second-order and third-order elastic moduli of crystals with the A2 structure are obtained.

Mössbauer spectroscopy study of the disordering process of Fe-rich FeAlSi alloys

In this work we study systematically the influence of different Al/Si ratios on the magnetic and structural properties of mechanically disordered powder Fe75Al25−xSix, Fe70Al30−xSix and Fe60Al40−xSix alloys by means of Mossbauer spectroscopy and X-ray diffraction measurements. In order to obtain different stages of disorder the alloys were deformed by ball milling annealed (ordered) alloys during different number of hours. X-ray and Mossbauer data show that mechanical deformation induces the disordered A2 structure in these alloys. The results indicate that addition of Si to binary Fe–Al alloys makes the disordering more difficult. The study of the hyperfine fields indicates that depending on the Fe content the magnetic behaviour of these ternary alloys varies. For Fe75Al25−xSix series, the alloys have different magnetic behaviours with deformation depending on the Si content. The magnetization of the alloys with high Si content decreases with deformation, as it happens to binary Fe75Si25 and the magnetization of the alloys with low Si content increases with deformation, as it happens to binary Fe75Al25. For Fe70Al30−xSix series the mean hyperfine fields show that there are two different stages with the disordering, in a first stage the mean hyperfine fields decrease and in the second stage they increase. Finally, for Fe60Al40−xSix alloys there is a magnetic transition, from a paramagnetic ordered state to a magneticdisordered state.

Use of Half Metallic Heusler Alloys in CoFeB/MgO/Heusler Alloy Tunnel Junctions

Heusler Alloys Co2FeSi and Co2MnSi were deposited on both single crystal MgO (100) and polycrystalline SiO2 silicon thermal oxide substrates and characterized by x-ray diffraction before and after thermal annealing at various temperatures. Co2FeSi and Co2MnSi deposited on MgO (100) grow as L21 or B2 structures but grow as an A2 structure on the SiO2 substrate. Co2FeSi and Co2MnSi were also deposited in a magnetic tunnel junction (MTJ) stack as the free and reference layers above and below the MgO barrier layer respectively, thereby replacing Co20Fe60B20 as those layers in the more common MTJ stack. The tunneling magnetoresistance (TMR) ratio is higher if Co2FeSi is the free layer, but lower when Co2FeSi is the reference layer.

Fabrication of highly oriented D03-Fe3Si nanocrystals by solid-state dewetting of Si ultrathin layer

In this paper, highly oriented nanocrystals of Fe3Si with a D03 structure are fabricated on SiO2 using ultrathin Si on insulator substrate. First, (001) oriented Si nanocrystals are formed on the SiO2 layer by solid state dewetting of the top Si layer. Then, Fe addition to the Si nanocrystals is performed by reactive deposition epitaxy and post-deposition annealing at 500°C. The structures of the Fe–Si nanocrystals are analyzed by cross-sectional transmission electron microscopy and nanobeam electron diffraction. We observe that Fe3Si nanocrystals with D03, B2, and A2 structures coexist on the 1-h post-annealed samples. Prolonged annealing at 500°C is effective in obtaining Fe3Si nanocrystals with a D03 single phase, thereby promoting structural ordering in the nanocrystals. We discuss the formation process of the highly oriented D03-Fe3Si nanocrystals on the basis of the atomistic structural information.

Annexin A2 Heterotetramer: Structure and Function

Annexin A2 is a pleiotropic calcium- and anionic phospholipid-binding protein that exists as a monomer and as a heterotetrameric complex with the plasminogen receptor protein, S100A10. Annexin A2 has been proposed to play a key role in many processes including exocytosis, endocytosis, membrane organization, ion channel conductance, and also to link F-actin cytoskeleton to the plasma membrane. Despite an impressive list of potential binding partners and regulatory activities, it was somewhat unexpected that the annexin A2-null mouse should show a relatively benign phenotype. Studies with the annexin A2-null mouse have suggested important functions for annexin A2 and the heterotetramer in fibrinolysis, in the regulation of the LDL receptor and in cellular redox regulation. However, the demonstration that depletion of annexin A2 causes the depletion of several other proteins including S100A10, fascin and affects the expression of at least sixty-one genes has confounded the reports of its function. In this review we will discuss the annexin A2 structure and function and its proposed physiological and pathological roles.

Annexin A2: The Importance of Being Redox Sensitive

Hydrogen peroxide (H2O2) is an important second messenger in cellular signal transduction. H2O2-dependent signalling regulates many cellular processes, such as proliferation, differentiation, migration and apoptosis. Nevertheless, H2O2 is an oxidant and a major contributor to DNA damage, protein oxidation and lipid peroxidation, which can ultimately result in cell death and/or tumourigenesis. For this reason, cells have developed complex antioxidant systems to scavenge ROS. Recently, our laboratory identified the protein, annexin A2, as a novel cellular redox regulatory protein. Annexin A2 possesses a reactive cysteine residue (Cys-8) that is readily oxidized by H2O2 and subsequently reduced by the thioredoxin system, thereby enabling annexin A2 to participate in multiple redox cycles. Thus, a single molecule of annexin A2 can inactivate several molecules of H2O2. In this report, we will review the studies detailing the reactivity of annexin A2 thiols and the importance of these reactive cysteine(s) in regulating annexin A2 structure and function. We will also focus on the recent reports that establish novel functions for annexin A2, namely as a protein reductase and as a cellular redox regulatory protein. We will further discuss the importance of annexin A2 redox regulatory function in disease, with a particular focus on tumour progression.

Local ferromagnetic structure in Heusler alloy Mn2CoGa and Mn2CoAl doped by Cr, Fe and Co

The crystal structures and magnetic properties of Mn2CoMxGa1-x and Mn2CoMxAl1-x (M=Cr, Fe, Co) alloys are investigated through experiment and calculation. Due to the covalent effect, the doped Fe and Co atoms preferentially occupy the A sites. It causes that some MnA (-2.1 B) atoms become MnD (3.2 B) and a local ferromagnetic structure of MnB-CoC-MnD is generated in the ferrimagnetic matrix, showing that an increment of molecular moment is as high as 6.18 B. The achievement of the ferromagnetic structure consumes the exchange interaction energy, consequently, reducing the TC in Fe doping alloys. It is found that the toleration for doping Co in Mn2CoAl reaches up to x=0.64, much more than that in Mn2CoGa (x=0.36), and the change from ordered B2 to A2 structures along with the decrease of Al content. These observations reveal the importance of the covalent effect in these intermetallic compounds. The Cr doping shows an abnormal increment of molecular moment of 3.65 B and increases the TC rapidly, which implies that Cr atoms may take an atomic configuration thereby disobeying to the occupation rule.

Structure determination of thin CoFe films by anomalous x-ray diffraction

This work reports on the investigation of structure-property relationships in thin CoFe films grown on MgO. Because of the very similar scattering factors of Fe and Co, it is not possible to distinguish the random A2 (W-type) structure from the ordered B2 (CsCl-type) structure with commonly used x-ray sources. Synchrotron radiation based anomalous x-ray diffraction overcomes this problem. It is shown that as grown thin films and 300 K post annealed films exhibit the A2 structure with a random distribution of Co and Fe. In contrast, films annealed at 400 K adopt the ordered B2 structure.

Impact of Late-Accumulated Mantle-Derived CO2 on Quality of Paleogene Clastic Reservoir at Actic Area, Qin Nan Sag

In this paper, the origin and accumulation time of CO2, and the transformation of clastic reservoir bed by CO2 in the A2 structure at the actic area of Qin Nan Sag were studied. The elevated δ13CCO2, R/Ra values and 40Ar/36Ar values showed that CO2 was mantle derived. CO2-bearing inclusions were associated with hydrocarbon inclusions, and CO2-bearing inclusions included hydrocarbon components, showing migration and filling of CO2 and hydrocarbon at the same stage. Basin modeling and homogenization temperature of inclusions indicated that the time of hydrocarbon and CO2 accumulation was mainly less than 3 Ma. CO2 late filling resulted in strong dissolution of feldspar and carbonate cement, with a high content of intragranular dissolution pores and a high proportion of intergranular primary pores, mostly from carbonate cement dissolution. Acidic environment inhibited illite growth, and dissolution of feldspar and acidic environment promoted formation of kaolinite. CO2 late filling brought out obvious thermal fluctuation, which was in favor of redistribution of dissolved matter, and top strong cementation was found at rock cores. Because of late accumulation of CO2, acidic environment of reservoir bed lasting for a long time, reservoir bed at a high temperature, undergrown dawsonite showed weak influence on reservoir bed quality. Dissolution of feldspar and carbonate cement, inhibition of illite growth, a high content of authigenic kaolinite, a low content of dawsonite, and redistribution of dissolved matter played a decisive role in improving reservoir quality, with rarely seen high permeability.

Annealing temperature dependence of crystal structures and magnetic properties of Fe2CrAl and Fe2CrGa Heusler alloys

The crystal structures, spontaneous magnetic moment, Is, and the Curie temperature, TC, of Fe2CrAl and Fe2CrGa Heusler alloys were investigated. Single phases of A2, B2 and L21-type structures were obtainable in Fe2CrAl alloy by controlling the annealing temperature. The values of the Is and TC of the A2-type phase were 2.2μB/f.u. and 316K and those of the B2-type phase were 2.0μB/f.u. and 274K, larger than those of the L21-type phase of 1.6μB/f.u. and 210K, respectively. A single phase of the A2-type phase in Fe2CrGa alloy was obtained and the Is and TC were about 2.8μB/f.u. and 353K, respectively. The B2 or L21-type single phases of Fe2CrGa alloy could not be obtained because of the inevitable precipitants.

Toward a theory of the third-order elastic modulus of crystals with A2 structure: The case of α-Fe

The third-order elastic modulus of α-Fe were calculated based on the computation of lattice sums. The lattice sums were determined using an integer rational basis of invariants composed by vectors connecting equilibrium atomic positions in the crystal lattice. Irreducible interactions within clusters consisting of atomic pairs and triplets were taken into account in performing the calculations. Comparison with experimental data showed that the potential can be written in the form of \(\varepsilon _9 = - \sum\nolimits_{i,k} {A_{19} r_{ik}^{ - 6} } + \sum\nolimits_{i,k} {A_{29} r_{ik}^{ - 12} + \sum\nolimits_{i,k,l} {Q_9 I_9^{ - 1} } }\), where \(I_9 = \vec r_{ik}^2 \left[ {\left( {\vec r_{ik} \vec r_{kl} } \right)^2 + \left( {\vec r_{li} \vec r_{ik} } \right)^2 } \right] + \vec r_{kl}^2 \left[ {\left( {\vec r_{ik} \vec r_{kl} } \right)^2 + \left( {\vec r_{kl} \vec r_{li} } \right)^2 } \right] + \vec r_{li}^2 \left[ {\left( {\vec r_{li} \vec r_{ik} } \right)^2 + \left( {\vec r_{kl} \vec r_{li} } \right)^2 } \right]\). If the values of \(\vec r_{ik}\) are scaled in half-lattice constant units, then \(A_{19} = 1.22\left\lfloor {\tau ^9 } \right\rfloor GPa, A_{29} = 5.07 \times 10^2 \left\lfloor {\tau ^{15} } \right\rfloor GPa, Q_9 = 5.31\left\lfloor {\tau ^9 } \right\rfloor GPa\), and τ = 1.26 A. It is shown that the condition of thermodynamic stability of a crystal requires that we allow for irreducible interactions in atom triplets in at least four coordination spheres. The analytical expressions for the lattice sums determining the contributions from irreducible interactions in the atom triplets to the second- and third-order elastic moduli of cubic crystals in the case of interactions determined by I9 are presented in the appendix.

Effects of alkyl chain length and anion size on thermal and structural properties for 1-alkyl-3-methylimidazolium hexafluorocomplex salts (CxMImAF6, x = 14, 16 and 18; A = P, As, Sb, Nb and Ta)

A series of 1-alkyl-3-methylimidazolium hexafluorocomplex salts (C(x)MImAF(6), x = 14, 16 and 18, A = P, As, Sb, Nb and Ta) have been characterized by thermal analysis, X-ray diffraction and polarized optical microscopy. A liquid crystalline mesophase is observed for all the C(16)MIm and C(18)MIm salts. The C(14)MIm(+) cation gives a liquid crystalline mesophase only with PF(6)(-). The temperature range of the liquid crystalline mesophase increases with an increase in alkyl chain length or with decrease in anion size. Single-crystal X-ray diffraction revealed that all the C(18)MImAF(6) salts (A = P, As, Sb, Nb and Ta) are isostructural with each other in the crystalline phase and have a layered structure. The interdigitated alkyl chain of the cation has a bent shape like a spoon near the imidazolium ring in the crystalline phase at -100 °C and is tilted with respect to the sheets of the imidazolium headgroups and anions. An increase of temperature increases the ratio of an all-trans conformation to the bent conformation in the crystalline phase. X-ray diffraction and polarized optical microscopy suggested that the liquid crystalline mesophase has a smectic A(2) structure. The interlayer distance increases with a decrease in the anion size since the smaller anion has a stronger coulombic interaction with the imidazolium headgroup, resulting in the decrease of the interdigitated part to give a larger layer spacing.

Structural and magnetic study of mechanically deformed Fe rich FeAlSi ternary alloys

In this work we study systematically the influence of different Al/Si ratios on the magnetic and structural properties of mechanically disordered powder Fe75Al25−xSix, Fe70Al30−xSix and Fe60Al40−xSix alloys by means of Mössbauer spectroscopy, X-ray diffraction and magnetic measurements. In order to obtain different stages of disorder the alloys were deformed by different methods: crushing induction melted alloys and ball milling annealed (ordered) alloys using different number of balls and speed. X-ray and Mössbauer data show that mechanical deformation induces the disordered A2 structure in these alloys. The results indicate that addition of Si to binary Fe–Al alloys makes the disordering more difficult. In addition, X-ray diffraction patterns show that the normalized lattice parameter variation of the disordered alloys of each composition decreases monotonically with Si content, indicating clearly that Si addition opposes the large volume increase found in FeAl alloys with deformation. The study of the hyperfine fields indicates that there is a redistribution of non-ferrous atoms around Fe atoms with the disordering; indeed, there is an inversion of the behavior of the hyperfine field of the Fe atoms. On the other hand, the magnetic measurements indicate that addition of Si to binary Fe75Al25 and Fe70Al30 alloys opposes the magnetic behavior induced by Al in the magnetism of Fe.

Thermal vacancies in Fe 3Al studied by positron annihilation

Vacancies in Fe 3Al intermetallic alloys were investigated by positron annihilation spectroscopy combined with X-ray diffraction. Two complementary techniques of positron annihilation were employed: positron lifetime spectroscopy and coincidence Doppler broadening. The experimental results were combined with ab initio theoretical calculations of positron characteristics. It was found that Fe 3Al quenched from 1000 °C exhibits a mainly disordered A2 structure. Defects in the as-quenched sample were identified as Fe vacancies on the A sub-lattice surrounded by Al nearest neighbors. The concentration of quenched-in vacancies was determined from the positron lifetime results. The samples were subsequently subjected to isochronal annealing which enabled an investigation of the recovery of quenched-in vacancies and the formation of thermal vacancies in B2 phase. It was found that recovery of quenched-in vacancies is accompanied by ordering to the D0 3 structure. The enthalpy and entropy of formation were determined for vacancies in the B2 phase.

Magnetostriction and magnetic properties of Fe-Ga melt-spun ribbons

Fe100-xGax (x = 10–25) melt-spun ribbons, with a width of 8 mm and a thickness of 0.1 mm, were successfully produced regardless of the Ga content of the Fe-Ga alloys. The saturation magnetization of the Fe-Ga melt-spun ribbons decreased and their permeability increased with increasing Ga content. A magnetostriction of 320 ppm was achieved in the Fe87.5Ga12.5 melt-spun ribbon. Annealing of the melt-spun ribbons resulted in further increases in magnetostriction value. A large magnetostriction value of 500 ppm was achieved in the annealed Fe80Ga20 melt-spun ribbon with the A2 (bcc α-Fe) structure.

Purification and biochemical characterization of a secreted group IIA chicken intestinal phospholipase A2

BackgroundSecretory phospholipase A2 group IIA (IIA PLA2) is a protein shown to be highly expressed in the intestine of mammals. However, no study was reported in birds.ResultsChicken intestinal group IIA phospholipase A2 (ChPLA2-IIA) was obtained after an acidic treatment (pH.3.0), precipitation by ammonium sulphate, followed by sequential column chromatographies on Sephadex G-50 and mono-S ion exchanger. The enzyme was found to be a monomeric protein with a molecular mass of around 14 kDa. The purified enzyme showed a substrate preference for phosphatidylethanolamine and phosphatidylglycerol, and didn't hydrolyse phosphatidylcholine. Under optimal assay conditions, in the presence of 10 mM NaTDC and 10 mM CaCl2, a specific activity of 160 U.mg-1 for purified ChPLA2-IIA was measured using egg yolk as substrate. The fifteen NH2-terminal amino acid residues of ChPLA2-IIA were sequenced and showed a close homology with known intestinal secreted phospholipases A2. The gene encoding the mature ChPLA2-IIA was cloned and sequenced. To further investigate structure-activity relationship, a 3D model of ChPLA2-IIA was built using the human intestinal phospholipase A2 structure as template.ConclusionChPLA2-IIA was purified to homogeneity using only two chromatographic colomns. Sequence analysis of the cloned cDNA indicates that the enzyme is highly basic with a pI of 9.0 and has a high degree of homology with mammalian intestinal PLA2-IIA.

First-principles study for electronic structure and physical property of Co-based Heusler alloys

The statistical investigation of the physical property of Co-based Heusler alloys with the atomic composition or configuration dependence are carried out in first-principles approach. In particular, the electronic structure, magnetic moment and electrical resistivity due to disorder alloy effects of Co2MnAl1−zSiz (0.0 < z < 1.0) and Co2Mn1−yFeySi (0.0 < y < 1.0) with the L21, B2 and A2 structure are calculated by using the tight-binding linear muffin-tin orbital method combined with the coherent potential approximation based on the local spin-density functional approximation and by using the Kubo-Greenwood formula, respectively. The obtained results indicate that these properties of the Co-based Heusler alloys significantly depend on the atomic configuration and composition, especially, they are sensitive to the existence of the half-metallic property.