Micromechanism of Cu and Fe alloying process on the martensitic phase transformation of NiTi-based alloys: First-principles calculation

Using first-principles pseudo-potential plane wave method, the formation enthalpy ΔH, binding energy ΔE, elastic constants, and electronic structure were calculated and analyzed carefully for NiTiX (X = Cu, Fe) shape memory alloy. The results show that the Cu or Fe element prefers to occupy the Ni site in the NiTi matrix phase respectively. Compared with the NiTi matrix phase, the ΔH, ΔE, c ₄₄ and c′ of NiTi (Cu) are similar to each other. However, the structural stability of the NiTi phase is improved obviously by the Fe alloying process. Simultaneously, the shear modulus c ₄₄ and c′ of NiTi (Fe) are larger than those of the NiTi matrix phase. Furthermore, Milliken population results indicate that Q _Cu–Ti is smaller than Q _Ni–Ti after the Cu alloying process, but Q _Fe–Ti is larger than Q _Ni–Ti. The electron density difference shows that some covalent bonding exists between Fe and Ti elements. Based on the upward analysis, the difference in the phase stability and elastic constants of NiTiX (X = Cu, Fe) is the substantial mechanism for the different M _s of NiTiX (X = Cu, Fe) although Cu or Fe substitutes for the same atom Ni elements in the NiTi matrix phase.     

First principle study of magnetic and electronic properties of single X (X = Al,Si) atom added to small carbon clusters (C<Subscript> <Emphasis Type="Italic">n</Emphasis> </Subscript>X, <Emphasis Type="Italic">n</Emphasis> = 2–10)

In this paper, the magnetic and electronic properties of single aluminum and silicon atom added to small carbon clusters (C_nX; X = Al, Si; n = 2–10) are studied in the framework of generalized-gradient approximation using density functional theory. The calculations were performed for linear, two dimensional and three dimensional clusters based on full-potential local-orbital (FPLO) method. The total energies, HOMO–LUMO energy gap and total magnetic moments of the most stable structures are presented in this work. The calculations show that C_nSi clusters have more stability compared to C_nAl clusters. In addition, our magnetic calculations were shown that the C_nAl isomers are magnetic objects whereas C_nSi clusters are nonmagnetic objects.     

A Systematic Search for Structures and Stabilities of Asymmetric Clusters (HfInN<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1-6)

In order to find single source precursors (SSP), the structures, relative stabilities, and IR spectra of small asymmetric clusters (HFInN₃) _n (n = 1–6) are systematically investigated by means of the density functional theory at the B3LYP level. The obtained geometries show that the frameworks of clusters (HFInN₃) _n (n = 2–6) prefer to be 2n-membered ring with alternating indium and α-nitrogen atoms. The averaged binding energies reveal that all of asymmetric clusters (HFInN₃) _n (n = 1–6) can continue to gain energy as the cluster size n increasing. The second-order difference of energy (Δ₂E) and the HOMO-LUMO energy gap (E_gap) as a function of the cluster size n both exhibit a pronounced even-odd alternation phenomenon. The influences of cluster size n and temperature T on the thermodynamic properties of clusters are discussed. Judged by enthalpies and Gibbs free energies, the formations of the most stable clusters (HFInN₃) _n (n = 2–6) from the monomer are thermodynamically favorable in the range of 200–800 K.     

Modeling of half-Heusler crystals with the chalcopyrite structure: Li<Subscript>2</Subscript>MgZn<Emphasis Type="Italic">X</Emphasis><Subscript>2</Subscript> (X = N,P, As,Sb)

A model of Li₂MgZnX ₂ half-Heusler compounds with the chalcopyrite structure is considered. The electronic structure is studied from first principles, showing that Li₂MgZnX ₂ are direct-gap crystals, except for pseudo-direct-gap Li₂MgZnP₂, with a band gap of 2.7 eV, 2.2 eV, 3.3 eV, and 2.5 eV for X = N, P, As, and Sb, respectively. The band structure and chemical bonding in the model crystals are found to be similar to those in LiMgX and LiZnX half-Heusler crystals. Total electron density and deformation electron density distributions are obtained. It is found that Mg–X and Zn–X ionic-covalent bonds are stronger than Li–X ionic bonds in Li₂MgZnX ₂ crystals, which allows Li atoms to move in the space between MgX ₄ and ZnX ₄ cation tetrahedra.     

Theoretical study of stepwise chlorinated aluminide clusters Al<Subscript>13</Subscript>Cl<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>−</Superscript></Stack> (<Emphasis Type="Italic">n</Emphasis> = 1–9)

The electronic and geometric structures, energy stabilities, normal mode frequencies, and spin density distributions (in radicals) of different stepwise-chlorinated aluminum clusters Al₁₃Cl _n ^? (n = 1–9) are calculated within the B3LYP approximation of the density functional theory using 6-31G* and 6-311+G* basis sets. The results are compared with analogous computation data on hydrides Al₁₃H _n ^? (n = 1–12) obtained at the same level. The general qualitative pattern for related series of hydrides, chlorides, and iodides (as well as fluorides and bromides) turns out to be similar in many respects. For all Al₁₃X _n ^? clusters with different electronegative substituents X, there is a set of a considerable number of low-lying closely spaced inner isomers (with a centered icosahedral cage), marquee isomers, and outer isomers (capped). The effects found by calculations in centered icosahedral isomers—localization of spin density on the trans-Al* atom in radical anions and its associated trans addition rule for an even substituent and the zigzag (odd-even) dependence of the energies D _n (X) of successive addition of substituents X to the metal cage on n described in the framework of the molecular model of the valence states of the Al ₁₃ ^? superatom—should also be shared by many Al₁₃X _n ^? series with different X’s. The differences between hydrides Al₁₃H _n ^? and chlorides Al₁₃Cl _n ^? of the same type are quantitative. For the hydrides, inner isomers are preferable in the first half of the series (n = 1–6); and in the second half (n = 7–12), outer isomers are more favorable. For the chlorides, icosahedral isomers are preferable only at the very beginning of the series. In the other cases, nonicosahedral structures are most favorable, for which the situation becomes very complicated due to the large number of position isomers and the aforementioned simple rules found for centered icosahedral structures are fulfilled to a considerably less extent or not at all.     

Thermochemistry of the Reaction of Solvated Sodium Ion Clusters with Thymine in the Gas Phase: An Example of the Reaction in Microcosmic Environment

The thermochemistry of the reaction of the microsolvated Na⁺ such as [Na(H₂O) _n ; n?=?1?6]⁺, [Na(NH₃) _n ; n?=?1?6]⁺ and [Na(H₂O) _n (NH₃) _m ; n?+?m?=?2?6]⁺ with thymine (Thy), as an example of a reaction in the microcosmic environment, have been studied in this work, theoretically. It was found that the increase of the number of solvent molecules in the structure of microsolvated Na⁺ is accompanied by the decrease of the standard enthalpy (\(\Delta H_{r}^{^\circ }\)) and Gibbs free (\(\Delta G_{r}^{^\circ }\)) energies of the reaction (Thy?+?[Na(X) _n ]⁺→Thy-Na(X) _n ⁺ ; X?=?solvent molecule). Also, the calculations showed that the electronic intermolecular interaction (?E_int) between the Thy and microslovated Na⁺ decreased with the increase of solvent molecules. For the interaction of the [Na(H₂O) _n ; n?=?4, 5 and 6]⁺ ions with the Thy, there was the probability of forming of the hydrogen bond between water molecules in the structure of solvated Na⁺ and the Thy. The gas phase infrared (IR) spectra of the complexes of the microsolvated Na⁺ with the Thy for different values of n were calculated and compared with each other to follow the change in the frequency of the stretching vibration of the interaction path between the C=O group of the Thy and Na (O…Na) with n. Using the calculated values of \(\Delta G_{r}^{^\circ }\) of the reactions, the mole fractions of the complexes of microsolvated Na⁺ ions with the Thy were calculated at different humidity.     

Paramagnetic centers related to Al,Sc, In,and Nb impurities in KTiOAsO<Subscript>4</Subscript>crystals

Electron paramagnetic resonance (EPR) is applied to study Al-, Sc-, In-, and Nb-doped KTiOAsO₄ (KTA) crystals. Paramagnetic hole centers O^? are observed after ionizing irradiation of KTA crystals. These centers are, as a rule, unstable at room temperature and are slowly annealed for about two weeks. Oxygen ions are bridging two cations in KTA. Near the impurity, two p-orbitals of oxygen atoms participate in covalent bonding with cations, whereas the third p-orbital remains free and under the radiation effect captures the hole thus forming the paramagnetic center of M ⁿ⁺-O^?-M^(n?1)+ (here M ⁿ⁺ is the lattice cation and M^(n?1)+ is the impurity cation of Al, In, Sc, or Nb). In the centers investigated the specific principal direction of the g-factor g ～ 2 is normal to the M ⁿ⁺-O^?-M^(n?1)+ plane, and the main value of g _max falls in this plane. The direction of the O^?-M^(n?1)+ bond is close to the selected direction of the hyperfine interaction with the impurity ion. The models of six hole centers and the found parameters of EPR spectra are discussed.     

Protonation of 3-Arylpropynoic Acid Derivatives in Superacids

According to the ¹H and ¹³C NMR data, 3-arylpropynoic acids and their esters XC₆H _n -C≡C-CO₂R (R = H, Me, Et) having electron-withdrawing substituents in the benzene ring (X = NO₂, CN, COMe, CO₂Me) exist in HSO₃F at ?80 to 0°C as XC₆H _n -C≡C-C⁺(OH)OR ions. Derivatives with other substituents (X = H, F, Me, MeO) in HSO₃F or CF₃SO₃H above ?40°C undergo protonation at the acetylenic carbon atom neighboring to the acid group to give unstable vinyl-type XC₆H _n -C⁺=CH-CO₂R cations which are then transformed into mixtures of stereoisomeric (Z and E) fluorosulfonates or triflluoromethanesulfonates XC₆H _n -CY=CH-CO₂R (Y = OSO₂F, OSO₂CF₃), the E isomer prevailing.     

Radiation-Induced Heterogeneous Processes of Water Decomposition in the Presence of Mixtures of Silica and Zirconia Nanoparticles

The radiation-induced heterogeneous processes of water decomposition on mixtures of silicon dioxide (n-SiO₂) and zirconium dioxide (n-ZrO₂) nanoparticles have been studied. The kinetics of buildup of molecular hydrogen in the radiolytic processes of water decomposition in the test systems has been examined. The reaction rates and the radiation-chemical yield of hydrogen in the radiolysis of water in the presence of n-SiO₂–n-ZrO₂ mixtures with different ratios between the components have been determined. It has been found that the rates and radiation-chemical yields decreased on going from n-ZrO₂ to n-SiO₂. The individual components (n-SiO₂ and n-ZrO₂) and the mixtures of n-SiO₂–n-ZrO₂ and n-SiO₂–n-ZrO₂ + H₂O before and after γ-irradiation have been examined by Fourier-transform IR spectroscopy in order to reveal interactions between the components and to study the mechanism of radiolytic processes. It has been found that the adsorption of water in the test systems occurs via both molecular and dissociative mechanisms. It has been shown that there is no noticeable interaction between the components of the oxide nanoparticles under the conditions of the experiments.     

Solubility of <Emphasis Type="Italic">d</Emphasis>-Element Salts in Organic and Aqueous–Organic Solvents: VI.<Superscript>1</Superscript> Structure and Thermal Stability of Cadmium Iodide and Bromide Solvates with Dimethylacetamide and Dimethylformamide

Five solvates, [CdBr₂(DMF)] _n , [CdBr₂(DMA)] _n , [CdI²(DMF)] ⁿ , [Cd(DMF)₆][Cd₂I₆], and {[Cd(DMA)₆][Cd₅I₁₂] _n } _m , were isolated from the ternary systems CdX₂–L–H₂O (X = Br, I; L = N,N-dimethylacetamide, N,N-dimethylformamide) and characterized by the X-ray single crystal analysis. The structures of the first three solvates is similar to each other in structures and represent a one-dimensional polymer chain, the fourth solvate has the discrete structure containing [Cd(DMF)₆]²⁺ and [Cd₂I₆]^2– ions, and the fifth solvate contains discrete [Cd(DMA)₆]²⁺ cations and the polymer anionic fragment [Cd₅I₁₂] _n ^2n–.     

Crystal structure and triboluminescence of tetraethylammonium tetrakis(thenoyltrifluoroacetonato)europium

An atomic structure of complex Et₄N[Eu(ТТA)₄] (TTA is the thenoyltrifluoroacetonate anion, Et₄N⁺ is the tetraethylammonium cation) possessing strong luminescence and triboluminescence was determined by X-ray crystallography. The crystal system of centrosymmetric crystals is monoclinic: a = 10.2495(1) Å, b = 20.2162(3) Å, c = 23.5788(3) Å, β = 102.551(1)°, space group P2₁/c, Z = 4, d _calc = 1.625 g cm^–3. The crystals of the compound have an isle structure, which comprises individual complex anions [Eu(TTA)₄]^– and tetraethylammonium cations Et₄N⁺. The structural aspects of a possible model for the formation of triboluminescent properties were considered, the role of cleavage planes and disordering was discussed.     

Thermophoto-emf of hot carriers in <Emphasis Type="Italic">γ</Emphasis>-irradiated single crystals of Cadmium Mercury Tellurides

The effect of γ-irradiation on thermophoto-emf of hot carriers in n-Cd_0.94Hg_0.06Тe and р-Cd_0.82Hg_0.18Тe single crystals has been studied. The dependence of the pattern of |U_tp| curves on E in the test Cd_xHg_1—хTe crystals is explained by the change in the degree of spatial heterogeneity of these crystals resulted from the accumulation of point radiation defects at relatively low D_γ and their spatial ordering caused by the introduction of a large number of point radiation defects at higher exposures. The proposed mechanism for the effect of γ-irradiation on the thermophoto-emf of hot carriers explains satisfactorily the dependence of |U_tp| kinetics on radiation dose, sample composition, temperature, and field strength.     

Crystal Structure of <Emphasis Type="Italic">DL</Emphasis>-Valinium Tetrafluoroantimonate(III) Monohydrate

The crystal structure of an antimony(III) fluoride complex of the composition (C₅H₁₂NO₂)SbF₄·H₂O (I) involving a cation of α-amino isovaleric acid (DL-valine, Val) is determined. Crystals are monoclinic: a = 12.2024(2) Å, b = 6.1636(1) Å, c = 15.5167(3) Å, Z = 4, space group P2₁/c. The structure is formed of DL-valinium (C₅H₁₂NO₂)⁺ cations, complex [SbF₄]_n^n? anions having a polymeric chain structure, and crystallization water molecules. The [SbF₄]_n^n? complex anions consist of trigonal SbF4E bipyramids joined together by asymmetric bridging Sb–F(3)···Sb bonds. The structural units are organized into a threedimensional framework via N–H···F, N–H···O, and O–H···F hydrogen bonds.     

Optical Band Gap Energies in Quasi-Metal Carbon Nanotubes

The structure of carbon nanotubes is described by two positive integers (n₁, n₂). The π-electron model of the nanotube band structure predicts that when the difference n₁–n₂ is multiple of three, the energy gap between the valence and conduction bands vanishes so that such tubes should exhibit quasi-metal properties. The band structure of 50 chiral and achiral (n₁, n₂) nanotubes with 4 ≤ n₁ ≤ 18 and n₂ = n₁–3q has been calculated by the linearized augmented cylindrical wave method. Nanotubes have been identified for which the optical band gaps are in the terahertz range (1–40 meV) and which can be used for design of emitters, detectors, multipliers, antennas, transistors, and other nanoelements operating in the high-frequency range.     

Computational Studies on the Mo-Doped Gold Nanoclusters Au<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Mo(<Emphasis Type="Italic">n</Emphasis> = 1–10): Structures,Stabilities and Magnetic Properties

The geometric structures, relative stabilities, magnetic properties of Mo-doped gold clusters Au _n Mo(n = 1–10) have been investigated at the PBE1PBE/def2TZVP level of theory. The results show that molybdenum doping has a significant effect on the geometric structures and electronic properties of Au _n Mo(n = 1–10) clusters. For the lowest energy structures of Au _n Mo(n = 1–10), the two dimensional to three dimensional transition occurs at cluster size n ≥ 8, and their relative stabilities exhibit odd–even oscillation with the change of Au atom number. It is found that charge in corresponding Au _n Mo clusters transfers from Mo atom to Au _n host in the size range n = 1–7, whereas the charge in opposition direction in the size range n = 8–10. In addition, the magnetic properties of Au _n Mo clusters are enhanced after doping single Mo atom into the corresponding gold clusters. Our results are valuable for the design of magnetic material.     

Geometries,stabilities, electronic and magnetic properties of small aluminum cluster anions doped with cobalt: A density functional theory study

The geometrical structures, relative electronic and magnetic properties of small Al_nCo^– (1 ≤ n ≤ 9) clusters are systematically investigated within the framework of density functional theory at the BPW91 level. The single Co doping can dramatically affect the ground state geometries of the 1 Al_n+1^- clusters. At the same time, the resulting geometries show that the lowest energy Al_nCo^– clusters prefer to be three dimensional structures. Here, the relative stabilities are investigated in terms of the calculated average binding energies, fragmentation energies, and second-order energy differences. Moreover, the result of the highest occupiedlowest unoccupied molecular orbital energy gaps indicates that Al₆Co^– clusters have the highest chemical stability for Al_nCo^– (1 ≤ n ≤ 9) clusters. Furthermore, the natural population analysis reveals that the charges in Al_nCo^– clusters transfer from the Al frames to the Co atom. Additionally, the analyses of the local and total magnetic moments of the Al_nCo^– clusters show that the magnetic effect mainly comes from the Co atom.     

Crystal structure of Na<Subscript>4</Subscript>[Na<Subscript>2</Subscript>Cr<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>6</Subscript>] · 10H<Subscript>2</Subscript>O

Single crystals of the Na₄[Na₂Cr₂(C₂O₄)₆] · 10H₂O complex were synthesized for the first time. The structure of the complex was determined by X-ray diffraction analysis. The compound crystallizes in the monoclinic crystal system with the unit cell parameters a = 17.290(4) Å, b = 12.521(3) Å, c = 15.149(3) Å, β = 100.45(3)°, Z = 4, space group Cc. Anionic layers [NaCr(C₂O₄)₃] _2n ^4n? can be distinguished in the crystal structure of the complex. The Na⁺ cations and water molecules, involved in the formation of a hydrogen bond network, are located between the anionic layers.     

An X-ray spectral and theoretical study of the electronic structure and features of interatomic interactions in phenoxysilanes

The electronic structure and features of interatomic interactions providing the Si–O–C₆H₅ bonds in H_4-nSi(OC₆H₅)_n (n = 1–4) were studied by a combined analysis of the X-ray emission and photoelectron spectroscopic data and the results of quantum-chemical calculations. Theoretical calculations were carried out using the density functional theory. The distributions of the density of states were constructed, the correlation energy diagrams were presented, and the main types of interatomic interactions in phenoxysilanes were revealed.     

Synthesis and crystal structure of <Emphasis Type="Italic">N,N</Emphasis>-dimethylbiguanidinium hexafluorosilicate

The complex [(CH₃)₂NC(NH₂)NHC(NH₂)NH₂]SiF₆ (I) was synthesized and its structure was determined by X-ray crystallography. The crystals are monoclinic: a = 7.4346(10) Å, b = 12.7628(10) Å, c = 11.0828(10) Å, β 104.080(10)°, V = 1020.01(18) ų, ρ_calc = 1.780 g/cm³, μ(MoK _α) = 0.302 mm^?1, Z = 4, space group P2₁/c. The crystals of I are composed of SiF ₆ ^2? anions (Si-F, 1.657(2)–1.699(2) Å) and N,N-dimethylbiguanidinium (H₂L²⁺) cations combined in a framework by interionic H-bonds NH···F. In the cations, protonation sites are the terminal imide groups.