Group Of Periodic Table Research Articles

Tracing mechanism of optically and thermally stimulated luminescence in Lu2O3:Tb,M (M = Hf, Zr, Ti) ceramic storage phosphors

A series of energy storage phosphors, Lu2O3:Tb,M (M = Hf, Zr, Ti), were investigated by means of photo- and thermoluminescence techniques to compare the effect of the co-dopant from the same group of periodic table of elements on charge carriers trapping capability and trap parameters. Most of the investigated processes were tracked individually for the Tb3+ in the two different metal sites offered by the Lu2O3 host – noncentrosymmetric C2 and centrosymmetric C3i. It is proved that both Tb3+ ions participate in hole trapping and electrons are immobilized in traps whose depths are defined by the co-dopant. Deepest traps, ∼1.79 eV, appear upon Ti addition, while Zr and Hf generate traps of very similar, ∼1.40–1.44 eV, depths. The stored energy may be released not only by means of thermal stimulation but also upon the impact of optical photons. Light from the 390–430 nm range of wavelengths was found the most efficient in the latter process. Also deep red radiation of 780 nm releases most of the trapped electrons in Zr/Hf co-doped ceramics but is much less effective in the case of Tb, Ti material. Consistent scheme of electronic levels engaged in charge carriers trapping and subsequent generation of thermo- and optically stimulated luminescence was constructed.

An Overview of Strengths and Directionalities of Noncovalent Interactions: σ-Holes and π-Holes

Quantum mechanics, through the Hellmann–Feynman theorem and the Schrödinger equation, show that noncovalent interactions are classically Coulombic in nature, which includes polarization as well as electrostatics. In the great majority of these interactions, the positive electrostatic potentials result from regions of low electronic density. These regions are of two types, designated as σ-holes and π-holes. They differ in directionality; in general, σ-holes are along the extensions of covalent bonds to atoms (or occasionally between such extensions), while π-holes are perpendicular to planar portions of molecules. The magnitudes and locations of the most positive electrostatic potentials associated with σ-holes and π-holes are often approximate guides to the strengths and directions of interactions with negative sites but should be used cautiously for this purpose since polarization is not being taken into account. Since these maximum positive potentials may not be in the immediate proximities of atoms, interatomic close contacts are not always reliable indicators of noncovalent interactions. This is demonstrated for some heterocyclic rings and cyclic polyketones. We briefly mention some problems associated with using Periodic Table Groups to label interactions resulting from σ-holes and π-holes; for example, the labels do not distinguish between these two possibilities with differing directionalities.

Disentangling Structural Confusion through Machine Learning: Structure Prediction and Polymorphism of Equiatomic Ternary Phases ABC.

A method to predict the crystal structure of equiatomic ternary compositions based only on the constituent elements was developed using cluster resolution feature selection (CR-FS) and support vector machine (SVM) classification. The supervised machine-learning model was first trained with 1037 individual compounds that adopt the most populated ternary 1:1:1 structure types (TiNiSi-, ZrNiAl-, PbFCl-, LiGaGe-, YPtAs-, UGeTe-, and LaPtSi-type) and then validated using an additional 519 compounds. The CR-FS algorithm improves class discrimination and indicates that 113 variables including size, electronegativity, number of valence electrons, and position on the periodic table (group number) influence the structure preference. The final model prediction sensitivity, specificity, and accuracy were 97.3%, 93.9%, and 96.9%, respectively, establishing that this method is capable of reliably predicting the crystal structure given only its composition. The power of CR-FS and SVM classification is further demonstrated by segregating the crystal structure of polymorphs, specifically to examine polymorphism in TiNiSi- and ZrNiAl-type structures. Analyzing 19 compositions that are experimentally reported in both structure types, this machine-learning model correctly identifies, with high confidence (>0.7), the low-temperature polymorph from its high-temperature form. Interestingly, machine learning also reveals that certain compositions cannot be clearly differentiated and lie in a "confused" region (0.3-0.7 confidence), suggesting that both polymorphs may be observed in a single sample at certain experimental conditions. The ensuing synthesis and characterization of TiFeP adopting both TiNiSi- and ZrNiAl-type structures in a single sample, even after long annealing times (3 months), validate the occurrence of the region of structural uncertainty predicted by machine learning.

Detailed first-principles studies on surface energy and work function of hexagonal metals

The surface energies and work functions for ten kinds of Miller-indices surfaces of hexagonal metals, Be, Mg, Tc, Re, Ru, and Os are calculated by means of the density functional theory (DFT) method. The results show that the metals belonging to the same group have a very similar rule in work functions and surface energies. The work functions of (0001), 011-1, and 101-0 surfaces are generally larger than the work functions of 112-1, 112-2, 112-3, and 314-0 surfaces. In contrast to work functions, there is more regularity in the crystallographic orientation dependence of surface energies. However, for the metals belonging to different groups, there are always some differences in the exact order of orientation dependence. It is also shown that the work functions and surface energies of the main group metals decrease as they go from top to the bottom in the same group of periodic table, while for the transition metals, they do not always obey this rule.

Extended Functional Groups (EFG): An Efficient Set for Chemical Characterization and Structure-Activity Relationship Studies of Chemical Compounds.

The article describes a classification system termed “extended functional groups” (EFG), which are an extension of a set previously used by the CheckMol software, that covers in addition heterocyclic compound classes and periodic table groups. The functional groups are defined as SMARTS patterns and are available as part of the ToxAlerts tool (http://ochem.eu/alerts) of the On-line CHEmical database and Modeling (OCHEM) environment platform. The article describes the motivation and the main ideas behind this extension and demonstrates that EFG can be efficiently used to develop and interpret structure-activity relationship models.

A NEW LOOK AT THE PERIODIC TABLE

As science advances, its laws become fewer but of greater scope. In this respect the Periodic Law, which is the basis of the Periodic Table, represents a major step in the progress of chemistry — it affords the natural classification of the elements. The Periodic Table was developed by chemists more than one hundred years ago as a correlation for the properties of the elements. With the discovery of the internal structure of the atom, it became recognized by physicists as a natural law. When the crystalline structure of solids was studied, the nature of the chemical bonds was understood, and the theory of metals was put forward, it became an essential tool not only for chemists and physicists, but for metallurgists as well. Of the 87 naturally occurring elements, 63, i.e., about three fourth are described as metals , 16 as nonmetals , and 9 as metalloids . Chemists should abandon numbering the groups in the Periodic Table and to give descriptive names instead.

Synthesis of metal oxide nanoparticles via a robust "solvent-deficient" method.

We report an efficient, general methodology for producing high-surface area metal oxide nanomaterials for a vast range of metal oxides, including at least one metal oxide nanomaterial from nearly every transition metal and semi-metal group in the periodic table (groups 3-4 and 6-15) as well as several from the lanthanide group (see ). The method requires only 2-3 simple steps; a hydrated metal salt (usually a nitrate or chloride salt) is ground with bicarbonate (usually NH4HCO3) for 10-30 minutes to form a precursor that is then either untreated or rinsed before being calcined at relatively low temperatures (220-550 °C) for 1-3 hours. The method is thus similar to surfactant-free aqueous methods such as co-precipitation but is unique in that no solvents are added. The resulting "solvent-deficient" environment has interesting and unique consequences, including increased crystallinity of the products over other aqueous methods and a mesoporous nature in the inevitable agglomerates. The products are chemically pure and phase pure with crystallites generally 3-30 nm in average size that aggregate into high surface area, mesoporous agglomerates 50-300 nm in size that would be useful for catalyst and gas sensing applications. The versatility of products and efficiency of the method lend its unique potential for improving the industrial viability of a broad family of useful metal oxide nanomaterials. In this paper, we outline the methodology of the solvent-deficient method using our understanding of its mechanism, and we describe the range and quality of nanomaterials it has produced thus far.

Interpretation of Dark Matter and Quark-Gluon Plasma: The Generation of the Periodic Table Elements and Its Phase Diagram: A Novel Millennium Power Plant

This paper presents a novel physical interpretation of the state of matter of the quark-gluon as the most fundamental building blocks in nature. Such a model is derived based on the assumption that dark matter and dark energy behave as a perfect ideal fluid at extremely high temperature. By the virtue of Boltzmann constant of the ideal gas law and NASA’s Cosmic Microwave Background Explorer (CMB) which estimate that the space has an average temperature close to 2.7251 Kelvin, then the equivalent mass-energy of the fundamental particle of the dark matter/dark energy is determined. Moreover, assuming a uniform space dark energy/dark matter density, then the critical temperature at which the dark matter has a unity entity per volume is identified as 64 × 1012 K. The calculated critical temperature of the quark-gluon plasma is found to be proportional to the temperature generated by colliding heavy ions at the Relativistic Heavy Ion Collider (RHIC) and European Organization for Nuclear Research (CERN). Moreover, the individual critical temperatures of the quark-gluon plasma matter at which the elements of the Periodic Table are generated are explicitly determined. The generation temperature trend of the elements of the Periodic Table groups and Periods is then demonstrated. Accordingly, the phase diagram of the quark-gluon state matter is proposed. Finally, a new model of quark-gluon power generation plant is proposed and aims to serve humanity with new energy sources in the new millennium.

Generic trend of work functions in transition-metal carbides and nitrides

Transition-metal carbides and nitrides (TMCs and TMNs) are promising electrode materials for various electronic devices such as metal-oxide-semiconductor field-effect transistors and metal-insulator-metal capacitors. In this paper, the work functions of TMCs and TMNs are discussed systematically. Based upon the origin of the work function, the effect upon transition metal species by different periodic table groups is explained, carbides are compared with nitrides for the same transition metal, and the effect of carbon or nitrogen vacancies is discussed. In addition, a method to estimate the generic trend of the work function is proposed for TMCx, TMNx, TMC1−yNy (transition metal carbonitrides), and TM1−zTM′zC (alloy carbides).

Boron contamination in drinking - irrigation water and boron removal methods

Boron presents in IIIA group of periodic table and has high ionization capacity. Therefore it is classified as a metalloid. Average boron concentration in earth's crust is 10 mg/kg. It presents in the environment as a salts of Ca, Na, and Mg. Boron reserves having high concentration and economical extent are found mostly in Turkey and in arid, volcanic and high hydrothermal activity regions of U.S. as compounds of boron attached to oxygen. Boron is an essential micronutrient for plants, although it may be toxic at higher levels. The range in which it is converted from a nutrient to a contaminant is quite narrow. Boron presents in water environment as a boric acid and rarely borate salts. The main boron sources, whose presence is detected in surface waters, are urban wastes and industrial wastes, which can come from a wide range of different activities as well as several chemical products used in agriculture. In Turkey, the most pollutant toxic element in drinking and irrigation water is boron. Therefore boron removal is very important in terms of human health and agricultural products in high quality. Mainly boron removal methods from drinking water and irrigation water are ion exchange, ultrafiltration, reverse osmosis, and adsorption.

米粒中の元素の偏析と同族置換

米粒中の元素の偏析と同族置換

The secondary ions emission from Si under low‐energy Cs bombardment in a presence of oxygen

Secondary negative ions yields of elements in the IIIrd, IVth, Vth periodic table groups emitted under Cs+ bombardment of Si surface in presence of oxygen are reported. The ion yield variation on oxygen partial pressure in the analytical chamber obtained for different ions allows taking a step forward the development of secondary ion emission model. The ion yield enhancement under particular oxygen surface coverage offers an approach for quantitative analysis of ultra‐shallow semiconductor structures and interfaces. Copyright © 2012 John Wiley & Sons, Ltd.

A comparison of two-component and four-component approaches for calculations of spin-spin coupling constants and NMR shielding constants of transition metal cyanides

Relativistic density functional theory (DFT) calculations of nuclear spin-spin coupling constants and shielding constants have been performed for selected transition metal (11th and 12th group of periodic table) and thallium cyanides. The calculations have been carried out using zeroth-order regular approximation (ZORA) Hamiltonian and four-component Dirac-Kohn-Sham (DKS) theory with different nonrelativistic exchange-correlation functionals. Two recent approaches for representing the magnetic balance (MB) between the large and small components of four-component spinors, namely, mDKS-RMB and sMB, have been employed for shielding tensor calculations and their results have been compared. Relativistic effects have also been analysed in terms of scalar and spin-orbit contributions at the two-component level of theory, including discussion of heavy-atom-on-light-atom effects for (1)J(CN), σ(C), and σ(N). The results for molecules containing metals from 4th row of periodic table show that relativistic effects for them are small (especially for spin-spin coupling constants). The biggest effects are observed for the 6th row where nonrelativistic theory reproduces only about 50%-70% of the two-component ZORA results for (1)J(MeC) and about 75% for heavy metal shielding constants. It is important to employ a full Dirac picture for calculations of heavy metal shielding constants, since ZORA reproduces only 75%-90% of the DKS results. Smaller discrepancies between ZORA-DFT and DKS are observed for nuclear spin-spin coupling constants. No significant differences are observed between the results obtained using mDKS-RMB and sMB approaches for magnetic balance in four-component calculations of the shielding constants.

Aromaticity of pentafulvene’s complexes with alkaline metal atoms

Geometry of pentafulvene’s complexes with the atoms of the first group of Periodic Table (Li, Na, K, Rb, and Cs) are optimized at the B3LYP/6-311 ++G(d, p) level of theory. Two kinds of complexes are considered: (1) those which are in equilibrium geometry, and (2) complexes which are formed by gradual change in the distance between the metal atom and penta-fulvene ring. Aromaticities of the considered complexes in their equilibrium geometries are investigated using different indices included geometry-based (HOMA), magnetism-based (NICS, NICS(1), and NICS(1)zz), π-electron count-based (pEDA), and electronic-based (Shannon Aromaticity; (SA)) indices. All indices are well correlated to each other and to some local (atomic charges) and global (binding-energy) properties, with one exception—HOMA. The same regularity is observed for non-equilibrium complexes.

Bulk Diffusion of Homovalent Non-Magnetic Atomic Probes of Titanium and Zirconium in Tungsten Single Crystals

The bulk diffusion of homovalent non-magnetic atomic probes (APs) from the IVB group of the periodic table of elements (PTE) – Ti and Zr in tungsten single crystals was investigated by sec-tioning, using secondary ion mass spectrometry (SIMS). The Arrhenius dependences had the fol-lowing parameters: DWTi - (D0)WTi = (3.00.4 ) x 10-4 m2s-1, enthalpy QWTi = (576 ± 9) kJ/mole; DWZr - (D0)WZr = (2.3  0.6) x 10-4 m2s-1, QWZr = (561 9) kJ/mole. The measured parameters (D0,Q)WTi,Zr of diffusion of Ti and Zr atomic probes (APs) in W are in accord with the empirical correlation: the diffusion coefficients of the substitutional APs coincide with the self-diffusion coefficients in W at (Tm)W – its melting temperature. Enthalpies QWTi,Zr,Hf of the volume diffusion of homovalent non-magnetic APs of the IVB group of periodic table of elements (PTE) - Ti, Zr and Hf increase with the decrease of relaxation volumes of the complexes «vacancy-IVBAP» in W lattice. The energies (E)WvacIVBAP of elastic relaxation of the complexes «vacancy-IVBAP» in W lattice were estimated. Electron contributions EDN to the energies EWvacIVBAP of interaction of the point defects in complexes «vacancy-IVBAP» increase relative to value EWvacIIIBAP of interac-tion of the point defects in complexes «vacancy-IIIBAP» with the growth of d-electrons number in comparison with the complexes «vacancy-IIIBAP».

Diffuse Phase Transition in Ba(SnxTi1-x) Ceramics and Thin Films

Due to the need to limit the use of Pb in electrical products, dielectric materials based on lead-free perovskite compounds with relaxor behavior are being actively developed. In this study, we carried out an investigation on the perovskite material Ba(SnxTi1-x)O3, whose B-site ions comprise elements from different periodic table groups but have the same valence state of 4+. We fabr icated and evaluated ceramics, single layer solid solution (SS) thin films, and order-controlled superlattice (SL) thin films. The shape of the dielectric anomaly in these materials was demonstrated and the value of parameter γ, calculated from the Curie-Weiss law, was found to be 1.71 for ceramics, 1.86 for SS films and 1.90 for 33% ordered SL films. In addition, the influence of the order-disorder transition on diffuse phase transition (DPT) was clarified.

Spectroscopic Evaluation of the Atomic Size

A new algorithm for evaluating the atomic size is suggested by entailing the atomic spectroscopic data-the wave number. The basic tenet of the present method is (i) to convert a multi-electron atom system to a hydrogenic atom to invoke the Bohr model for the mechanism of electron transition, and (ii) to use the experimental atomic spectroscopic data of multi electron systems to determine the atomic radii. The estimated set of size data appears to satisfy the entire 'sine qua non' of sizes of atoms of the periodic table. Relativistic effect appears to have been significantly included in the suggested algorithm for evaluating the atomic radii. The express periodicity of periods and groups of periodic table exhibited by the computed atomic radii, d and f block contraction and the manifestation of the relativistic effect in the sizes of lanthanoids and actinoids etc speak volume of the efficacy of the present method in computing atomic size. Furthermore, as a validity test, the size data evaluated in the present work have been exploited to calculate some physical descriptors of the real world like equilibrium inter nuclear distances of a good number of hetero nuclear diatomics. We have noted the surprisingly close agreement between the theoretical and the experimental equilibrium inter-nuclear distances.

Wear behavior of adaptive nano-multilayered AlTiN/Me xN PVD coatings during machining of aerospace alloys

Machining of aerospace materials is one of the major challenges of modern manufacturing. Application of nano-multilayered AlTiN/Me x N PVD coatings (where Me x is a transition metal of V–VI groups of periodic table) to cemented carbide tooling results in a significant tool life improvement under conditions of cutting hard to machine alloys such as Ni-based Inconel 718 superalloy and Ti-based TiAl6V4 alloy. Microhardness and coefficient of friction of the coatings were measured during this experiment. Investigations of the coated tool life, wear behavior, chip formation (chip type and undersurface morphology) for cutting tools with nano-multilayered PVD coating were also performed. Morphology of worn tools has been studied using SEM and EDX. This study will show that metallurgical design of the nano-multilayered coating should be tailored to its application. To achieve better tool life when machining Inconel 781, adaptive nano-multilayered AlTiN/MoN coating is recommended, whereas a AlTiN/VN coating is better suited to machining TiAl6V4 alloy. A driving force behind selecting these coatings was a noticeably lower coefficient of friction at elevated temperatures.

Large-magnetostriction ternary alloys obtained from Galfenol through partial substitution of Ga.

In this paper the magnetoelastic characteristics of ternary Fe–Ga–X (X=Ge, Sn) alloys are compared with those of Galfenol (Fe–Ga) within the same range of solute concentration. New magnetostriction and elastic modulus data for Fe–Ga–Ge at six different compositions are presented. The most notable case is that of Fe86.9Ga9.9Ge8.7. Although the tetragonal magnetostriction, λ100, of Fe–Ge is lower overall than that of Fe–Ga, the magnetostriction of the aforementioned ternary alloy equals the value of Galfenol at the same solute concentration, Fe86.9Ga13.1. The theory proposed for explaining the measured λ100 values in the ternary alloys takes into account the total number of electrons each solute contributes to the alloy. The valence of Fe is taken to be “1” from first‐principles calculations. Previously published results on Fe–Ga–Sn [Summers et al., “Magnetostriction of binary and ternary Fe‐Ga alloys,” J. Mater. Sci 42, 9582–9594 (2007)] concur with this theory (Sn and Ge belong to the same periodic table group). The Sn ternary alloys are of economic importance for large‐scale applications given that significant magnetostriction can be achieved while using less expensive solutes. It is also notable that, when compared with Galfenol at a Ga concentration of x=6.2 at. %, the ternary alloy Fe88.1Ga6.2Ge5.7 has a magnetostriction that is larger by a factor of 2.

DFT Study on the Selectivity of Complexation of Metal Cations with a Dioxadithia Crown Ether Ligand

The interactions of a dioxadithia crown ether ligand with Li(+), Na(+), K(+), Mg(2+), Ca(2+), and Zn(2+) cations were investigated using density functional theory (DFT) modeling. The modeling was undertaken to gain insight into the mechanism of the selective complexation of the mono- and dications observed with this ligand experimentally. Two types of conformationally different complexes were located with both mono- and dications. In the first conformer, the cation is bonded to the ether oxygens; in the second conformer, the cation is bonded to the alkoxy and suger oxygens. In general, the complexes formed with dications were found to be more stable than those with monocations, with the stability decreasing with the period number within a given periodic table group of elements. The highest stability was observed for the complexes formed with zinc. The complex formed with lithium was the most stable among those involving monovalent cations. The system interaction energy was decomposed into electrostatic (ES), polarization (P), charge-transfer (CT), exchange (EX), and geometry-deformation (DEF) contributions using the self-consistent charge and configuration method for subsystems (SCCCMS). The stabilizing energy components (ES, P, and CT) exhibit the same trend as the total interaction energy, whereas the destabilizing contributions (EX and DEF) exhibit the opposite trend. It was found that the main contributions responsible for stabilization of the dicationic systems are the P and ES energies; in the monocationic systems, the CT stabilization is equally important. The gas-phase preferences changed when the solvent effect was included. The dioxadithia crown ether ligand preserved its selectivity toward Zn(2+), but the selectivity sequence toward monovalent cations was reversed.