The novel material based on strandberg-type hybrid complex (C6H10N2)2[Co(H2O)4P2Mo5O23].6H2O: Experimental and simulations investigation on electronic,optical, and magnetocaloric properties

The hybrid Strandberg complex materials have attracted intensive interest due to their multifunctional properties. In this work, we report the electronic, optical, and magnetocaloric properties of the novel material (C₆H₁₀N₂)₂[Co(H₂O)₄P₂Mo₅O₂₃].6H₂O. First principle calculations based on the density functional theory (DFT) have been performed using full-potential linearized augmented plane waves (FP-LAPW). The crystals of (C₆H₁₀N₂)₂[Co(H₂O)₄P₂Mo₅O₂₃].6H₂O with triclinic structure were characterized by X-ray powder diffraction (XRD). The profiles of the density of states (DOS), the optical spectra including the real and imaginary part of the dielectric function, and the measured magnetocaloric properties were presented and analyzed in detail. The results found are in agreement with experimental measurements. As pertinent results, the compound presents a high absorption coefficient in the visible range. A systematic analysis of the experimental and theoretical results shows a good bandgap, a high optical property, and a low magnetocaloric effect which reveals promising original material in optoelectronic, and photovoltaic applications.     

The effect of B-site substitution on the structural evolution and electrical properties of lead-free (K,Na)NbO3 ceramics

Lead-free (K_0.49Na_0.51)(Nb_1−xSb_x)O₃ piezoelectric ceramics were prepared via the conventional sintering method and the effect of the substitution of Nb with Sb on the phase structure, microstructure and electrical properties of the prepared (K_0.49Na_0.51)(Nb_1−xSb_x)O₃ ceramics was systematically investigated. The prepared ceramics exhibited a single-phase perovskite structure which changed from a standard orthorhombic structure to a pseudocubic structure as x was increased from 0 to 0.1. X-ray diffraction patterns and Raman spectra obtained for the prepared ceramics clearly revealed that the degree of structural symmetry increased with x. Substituting an appropriate amount of Sb⁵⁺ for Nb⁵⁺ was found to improve the microstructure and thereby enhance the piezoelectric/ferroelectric properties. Further increasing the Sb content resulted in a decrease of the average grain size and a deterioration of the performance. The peak values of the piezoelectric constant d₃₃ (182 pC/N) and the electromechanical coupling coefficient k_p (41%) were obtained for the ceramic with x=0.06.     

Molecular orbital calculations on electronic and Li-adsorption properties of sulfur-, phosphorus- and silicon-substituted disordered carbons

To clarify the effect of atom substitution on electronic and lithium (Li) adsorption properties of disordered carbons, we employed circum-coronene (C₅₄H₁₈) as a model cluster for disordered carbons and investigated the stable structures, electronic and Li-adsorption properties of its sulfur-, phosphorus- and silicon-substituted sheets, by using a semiempirical molecular orbital method. Among the three substituted sheets, the silicon-substituted Si₂C₅₂H₁₈ sheet was found to have desirable properties as an anode material of rechargeable Li-ion batteries: planar structure and large amount of Li adsorption. Although the Li-adsorption energy of Si₂C₅₂H₁₈ is smaller than that of B₂C₅₂H₁₈, the dependence of adsorption energy on the number of Li atoms indicates that Si₂C₅₂H₁₈ can adsorb more Li atoms than B₂C₅₂H₁₈. Therefore, silicon- as well as boron-substituted disordered carbons are expected to be promising materials for the anode in Li-ion batteries.     

Density functional theory study on lithium bis[1,2-benzenediolato(2-)-O,O′] borate and its derivatives: electronic structures, energies, and molecular properties

Theoretical studies on electrolyte salts, lithium bis[1,2-benzenediolato(2-)-O,O′] borate (LBBB) and its derivatives, lithium bis[3-fluoro-1,2-benzenediolato(2-)-O,O′]borate (1FLBBB), and lithium bis[tetrafluoro-1,2-benzenediolato(2-)-O,O′] borate(4FLBBB) are carried out using density functional theory (DFT) method and B3LYP theory level for the first time. Bidentate structures involving two oxygen atoms are preferred. The GIAO–DFT results for all molecules suggest that the corresponding RB3LYP/6-31++G(2df,2p) geometries can be deemed reasonably good representations of the geometries of relatively free molecules in solution. Based on these conformations, a linear correlation was observed between the highest occupied molecular orbital (HOMO) energies and the limiting oxidation potentials measured by linear sweep voltammetry, which supports experimental results that inorganic fluorine-containing anions are more resistant against oxidation than their organic counterparts. The correlations were also observed between ionic conductivity and binding energy, solubility and anion polarizability_, thermal stability and the energy difference between E_LUMO and E_HOMO. Wave function analyses have been performed by natural bond orbital (NBO) method to further investigate the cation–anion interactions.     

First principles calculations and synthesis of multi-phase (HfTiWZr)B2 high entropy diboride ceramics: Microstructural,mechanical and thermal characterization

First principles calculations were conducted on (HfTiWZr)B₂ high entropy diboride (HEB) composition, which indicated a low formation energy and promising mechanical properties. The (HfTiWZr)B₂ HEBs were synthesized from the constituent borides and elemental boron powders via high energy ball milling and spark plasma sintering. X-ray diffraction analyses revealed two main phases for the sintered samples: AlB₂ structured HEB phase and W-rich secondary phase. To investigate the performance of multi-phase microstructures containing a significant percentage of the HEB phase was focused in this study. The highest microhardness, nanohardness, and lowest wear volume loss were obtained for the 10 h milled and 2050 °C sintered sample as 24.34 ± 1.99 GPa, 32.8 ± 1.9 GPa and 1.41 ± 0.07 × 10^?4 mm³, respectively. Thermal conductivity measurements revealed that these multi-phase HEBs have low values varied between 15 and 23 W/mK. Thermal gravimetry measurements showed their mass gains below 2% at 1200 °C.     

Systematic study on mechanical and electronic properties of ternary VAlN,TiAlN and WAlN systems by first-principles calculations

Transition-metal aluminium nitrides widely used as protective tool coatings are a class of materials with a combination of high hardness, outstanding wear resistance as well as good chemical stability. In this work, through a well developed structure searching method, the ground-state phase of V_0.5Al_0.5N is verified and systematically studied on its mechanical and electronic properties by comparing with Ti_0.5Al_0.5N and W_0.5Al_0.5N via first-principles calculations. Our results show that the ground-state phase of V_0.5Al_0.5N adopts a hexagonal structure of P6₃/mmc symmetry. Mechanical property studies demonstrate the hexagonal phase has a surprisingly improved hardness of about 38 GPa and enhanced ideal strengths relative to its well-known metastable cubic B1 phase whose hardness is only about 20 GPa. This mechanical enhancement greatly expands the upper limit of the strength and hardness for this type of Al-containing ternary systems. Meanwhile, detailed analysis on strength and elastic anisotropy indicates it also exhibits much better mechanical isotropy. Underlying mechanism of the mechanical enhancement is explored by the electronic analysis in-depth. The position of the E_F is tuned by the introduction of the Al element and this electronic tuning leads to a metallic-to-semiconductor transformation from B1 to the hexagonal phase and the strengthening of the bonds between the metal elements and the N atoms.     

Nucleophilic addition of water to 1-isoquinolinyl phenyl ketone. The synthesis, spectroscopic investigation, crystal and molecular structure and DFT calculations of [ReOBr2(iquinpk-OH)(PPh3)]

The reaction of [ReOBr₃(PPh₃)₂] with 1-isoquinolinyl phenyl ketone in acetone has been examined and the novel complex [ReOBr₂(iquinpk-OH)(PPh₃)] has been obtained. The complex has been characterised by IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structure of [ReOBr₂(iquinpk-OH)(PPh₃)] has been calculated with the density functional theory (DFT) method. The spin-allowed electronic transitions of [ReOBr₂(iquinpk-OH)(PPh₃)] have been calculated with the time-dependent DFT method and the UV–Vis spectrum has been discussed on this basis.     

The energetic and electronic properties of atomic hydrogen on MgO(001) surface: Tight-binding and Ab initio calculations

We report the computational results of hydrogen adsorption atop Mg and O atoms on the MgO(001) surface, followed by its absorption under the target atoms, using two approaches: tight-binding and ab initio methods. We present the energetic and electronic aspects of these interactions and discuss the qualities of the non-self-consistent field tight-binding results compared with the ab initio results. There is the qualitative reproduction of ab initio results in the hydrogen adsorption phase on both types of ions. The tight-binding results are found to be more accurate in the hydrogen absorption phase than in the adsorption phase. In the adsorption calculations the introduction of the surface dipole term in the tight-binding total energy would be required to compensate for the absence of electronic relaxation in the MgO(001) surface.     

Elastic and electronic properties of XB2 (X=V,Nb, Ta,Cr, Mo,and W) with AlB2 structure from first principles calculations

The crystal structure, electronic properties, mechanical properties, and anisotropy of XB₂ (X=V, Nb, Ta, Cr, Mo, and W) were calculated by first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GGA). The results are in good agreement with available theoretical and experimental values. The calculated cohesive energy and formation enthalpy indicate that they are thermodynamically stable structures. The elastic constants satisfy all of the mechanical stability criteria. The mechanical moduli were predicted by the Voigt–Reuss–Hill approximation. The mechanical anisotropy was indicated by the surface constructions of Young's moduli, and the results show that anisotropy of WB₂ is stronger than others. The electronic structure indicates that the bonding behaviors of XB₂ (X=V, Nb, Ta, Cr, Mo, and W) are the combinations of covalent and metallic bonds. The hardness of the borides was also evaluated, and the result reveals that TaB₂ is the hardest compound among them.     

Effect of Mn-doping on optical properties of lead-free (K0.4Na0.6)NbO3 ferroelectric single crystals

Optical properties of <001>-oriented pure (K_0.4Na_0.6)NbO₃ (KNN) and 0.5 wt% Mn-doped KNN (Mn-KNN) single crystals were studied. The refractive indices (n) of both crystals exhibited a normal dispersion behavior in the wavelength range of 300−1100 nm. The modified Sellmeier dispersion equations for n were obtained by least-squares fit. In addition, Sellmeier coefficients were determined by single-oscillator dispersion relation, which related to energy band structures of crystals. Compared with KNN, a decrease about 10 % in transmittance (over 350 nm) was observed in Mn-KNN due to the losses resulting from the increase of domain wall density. Furthermore, a 20 nm blue-shift in the absorption edge was observed for Mn-KNN. Based on Tauc equation, the band gap energies of 3.26 and 3.42 eV were obtained for KNN and Mn-KNN, respectively. The increase of band gap energy in Mn-KNN was attributed to the distortion of BO₆ octahedron building block caused by Mn²⁺ occupying the B-site.     

First-principles study on predicting the crystal structures,mechanical properties and electronic structures of HfCxN1-x

The crystal structures, mechanical properties and electronic structures of HfC_xN_1-x have been predicted by using evolutionary structure search followed by the first-principles calculations in this study. The crystal structures predicted indicate that there are 10 thermodynamic stable phases for HfC_xN_1-x, of which 8 are newly discovered crystal structures and 2 are already known. We investigated the mechanical properties, including the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and Vickers hardness, of all 10 stable phases, and further established the relationship between such properties and the ratio of nitrogen to carbon content. Besides, the Fermi energy level and electronic density of states of these 10 stable phases are calculated as well, and the results reveal the fundamental reason why the mechanical properties change with the ratio of nitrogen to carbon. The predictions of this study agree well with both the experimental data and the previous theoretical evaluations.     

Electrochemical and spectroscopic characterization of poly(1,8-diaminocarbazole): Part I. Electropolymerization and determination of the polymer structure by FTIR studies and DFT calculations

Poly(1,8-diaminocarbazole) (PDACz) films on the Pt electrodes were obtained from acetonitrile (0.1 M LiClO₄) and acidic aqueous solutions (0.1 M HClO₄). The changes in the shape of polymerization curves in the two media are discussed in terms of a limited conductivity window of the fully oxidized PDACz. The polymer structure of the films obtained from acetonitrile and acidic aqueous solution was proposed on the base of FTIR spectra and the results of theoretical calculations. Density functional theory (DFT) was used to calculate a distribution of unpaired-electron spin density for monomer radical cations to predict the coupling positions during polymerization. This method allowed to resolve the problems concerning the monomer linkage, still present after analysis of FTIR spectra of the polymer.     

A first-principles study of the electronic,structural, and optical properties of CrN and Mo:CrN clusters

CrN, one of the most investigated transition metal nitrides, is noted for its wear, corrosion, and oxidation resistance. It also has many other unique chemical and mechanical properties. In the present study, we conducted a density functional theory (DFT) analysis to probe the structural, electronic, and optical properties of pristine and Mo-doped CrN structures in non-crystalline phases using different combinations in which one or two Cr and/or N atoms were substituted by Mo. This study found that the Cr₄Mo₂N₂ structure was chemically and energetically the most stable species among the six considered clusters (Cr₄N₄, Cr₃Mo₂N₃, Cr₄Mo₂N₂, Cr₂Mo₂N₄, Cr₄MoN₃, and Cr₃MoN₄). The DFT-derived electronic structure predicted that the Cr₃Mo₂N₃ and Cr₄MoN₃ clusters possess magnetic susceptibility. Computed infrared (IR), Raman, and ultraviolet–visible (UV–Vis) analyses indicated that the Cr₄N₄ and Cr₄Mo₂N₂ clusters were naturally stable. This should enable these clusters to serve as light-harnessing materials for strategic applications in solar selective surfaces.     

A theoretical investigation on the properties of the new poly(N‐vinylcarbazole)‐3‐methylthiophene (PVK‐3MeT) synthesized graft copolymer

In this article, we present quantum chemical calculations, based on density functional theory (DFT), performed to investigate the geometries and the opto‐electronic properties of a new synthesized graft copolymer based on poly(N‐vinylcarbazole) (PVK) and poly(3‐methylthiophene) (PMeT) named PVK‐3MeT. First, we have theoretically computed and compared the structural, optical, and vibrational parameters of both neutral and doped states. In addition, the excited state was theoretically obtained by the ab initio RCIS/STO‐3G method. To assign the absorption and emission peaks observed experimentally, we computed the energies of the lowest singlet excited state with the time‐dependent density functional theory (TD‐DFT) method. Electronic parameters such as the HOMO‐LUMO band gap, the ionization potential (IP), and electron affinity (EA) are extracted. Calculations show that the PVK‐3MeT copolymer is nonplanar in its ground neutral state. Meanwhile, upon doping or photoexcitation, an enhancement of the planarity is observed, resulting on a decrease of the inter‐ring torsion angle between 3‐methylthiophene units. Such modifications in the geometric parameters induce a dramatic change on the HOMO and LUMO orbitals in the doped or excited states. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

The effect of alkali metal oxide on the properties of borosilicate fireproof glass: Structure,thermal properties,viscosity, chemical stability

The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R₂O–CaO–B₂O₃–SiO₂) systematically. Because the glass would emulsify when Li₂O was added to the glass batch, this article did not discuss Li₂O. The results showed that when the amount of Na₂O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na₂O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased.     

Microstructure and piezoelectric properties of CuO added (K, Na, Li)NbO3 lead-free piezoelectric ceramics

Lead-free Na_0.5K_0.5NbO₃ (NKN) and Na_0.475K_0.475Li_0.05NbO₃ (NKLN) ceramics doped with CuO were prepared by the mixed oxide route. The powders were calcined at 850-930 °C and sintered at 850-1100 °C. Small additions of CuO reduced the sintering temperature and increased the density to 96% theoretical. Cu first appears to enter the A site then the B site. In NKLN the orthorhombic-tetragonal and tetragonal-cubic phase transitions are approximately 150 °C lower and 50 °C higher, respectively than in NKN. With increasing addition of Cu to NKN and NKLN the remanent polarization (P_r) increased and coercive field (E_c) decreased. NKLN prepared with 0.4 wt% CuO exhibited a saturation polarization (P_sat) of 30 μC/cm², remanent polarization (P_r) of 27 μC/cm² and coercive field (E_c) of 1.0 kV/mm. CuO caused the NKLN ceramics to harden considerably; the mechanical quality factor (Q_m) increased from 50 to 260, d₃₃ ∼ 285 and piezoelectric coupling factors were >0.4.     

Long and short range effect of alkali promoters on metal surfaces: K on Rh(111)

Photoemission of physisorbed noble gases has been used to investigate the variation of the surface potential on a potassium-promoted rhodium (111) surface. The results confirm that the predominant effect of potassium is to lower the potential on nearest neighbour sites by 1–1.5 eV, but indicate also that the potential on next nearest neighbour sites is still 0.4–1 eV lower than on unpromoted rhodium, depending on the potassium coverage. Theoretical calculations show that the latter values are in qualitative agreement with the cumulative effect of potassium/rhodium dipoles which form an ordered array on the surface.     

Benzotrifluoromethyl group‐substituted poly(para‐phenylenevinylene): Effect on solubility,optical, and electronic properties

A new organosoluble benzotrifluoromethyl group containing poly(p‐phenylenevinylene) (BTFM‐PPV) has been synthesized via Gilch polymerization. The polymer is soluble in common organic solvents such as tetrahydrofuran, chloroform, dichloromethane, toluene, and xylene. BTFM‐PPV exhibited fluorescence emission peak with a very high blue shift at 474 nm with an excitation wavelength at 420 nm compared with many other PPV derivatives reported earlier. Incorporation of fluorated bezotrifluoromethyl pendent group in the PPV backbone lowers the HOMO and LUMO energy levels of BTFM‐PPV (2.48 eV) which retarded the hole injection and increase the electron injection in the device. The current–voltage (I–V) characteristic of the polymer was measured by fabricating the polymer as ITO/BTFM‐PPV/Al diode. The device performance was markedly improved by incorporation of 4‐fluoro‐3trifluoromethylphenyl units into the polymer main chain. The turn on voltage of the device observed from the I–V measurements was 7 V. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymorph of N,N′-di-n-butylperylene-3,4:9,10-bis(dicarboximide) and their electronic structure

Perylene pigments are known to exhibit a variety of shades in the solid state from vivid red, via maroon to black, although their solution spectra are quite similar. A second phase of the title compound (phase II) has newly been found when the single crystals were grown from the vapor phase. Phase II bears a black color while the previous phase (phase I) exhibits red-maroon. For this reason, the electronic structure of both phases has been investigated on the basis of the crystal structure as well as intermolecular interactions. In both phases, the absorption spectrum is composed of two bands: one is due to individual molecules (i.e. around 450–550 nm) and the second band arises from excitonic interactions between transition dipoles (i.e. around 600 nm in phase I and 625 nm in phase II). The intermolecular interactions along the stacking axis are primarily responsible for the appearance of the second band in both phases. Additionally, the interaction on the molecular plane is found to be slightly hypsochromic in phase I while bathochromic in phase II. This induces a difference in absorption maximum of the second band, leading to two different colors (red-maroon and black) in phases I and II.