Theoretical study on the second hyperpolarizabilities of tetrathiafulvalene (TTF) and tetrathiapentalene (TTP) using highly correlated ab initio MO and the density functional theory methods

We investigate the static second hyperpolarizabilities (γ) of tetrathiafulvalene (TTF) and tetrathiapentalene (TTP) using the ab initio molecular orbital (MO) method. The cationic radical states of these systems (TTF⁺ and TTP⁺) are expected to have large negative γ values, which are rare in organic systems, based on our classification rule of γ. It turns out that at the higher-order electron correlation level TTP⁺ gives a large negative γ value though TTF⁺ gives a positive γ. We also investigate the applicability of the density functional theory (DFT) methods to the calculation of the γ values for these systems. By tuning the mixing parameter of DFT/HF exchange term, a DFT method turns out to semiquantitatively reproduce the γ values of TTP and TTP⁺ at the higher-order electron correlation method, i.e., CCSD(T), while fail in reproducing the γ value of TTF⁺. This suggests the necessity of further improvement in correlation functional for obtaining reliable γ values of charged radical states.     

A high-frequency light-induced electron spin resonance study of conjugated polymer/fullerene composites

Light-induced electron spin resonance (LESR) measurements are reported in composites of MDMO-PPV and PCBM, a soluble derivative of C₆₀. After illumination of the sample, two radicals are formed. One is the remaining positive polaron P⁺ on the polymer backbone and the other the C₆₁⁻ radical anion. Using high-frequency (95 GHz) LESR, it was possible to separate these two contributions to the spectrum on the basis of their g-parameters, and to resolve the g-anisotropy of the radicals. The P⁺-polaron possesses axial symmetry whereas for C₆₁⁻ a lower, rhombic symmetry was observed.     

Crystal structure and magnetic properties of an ionic multi-component complex of fullerene (OMTTF·I3)·C60: Comparison with OMTTF·I3 salts

A new ionic multi-component complex (OMTTF·I₃)·C₆₀ comprising neutral C₆₀ molecules and OMTTF⁺ and I₃⁻ ions has been obtained by the diffusion method. The complex has a layered structure with the alternation of closely packed hexagonal C₆₀ layers and the layers composed of OMTTF⁺ and I₃⁻ ions arranged in a chequer-like manner. The polycrystalline complex shows a strongly asymmetric EPR signal consisting of four components in the 4–293 K range attributable to OMTTF⁺. Temperature dependent magnetic susceptibility indicates an antiferromagnetic interaction of spins localized on OMTTF⁺ with an antiferromagnetic hump near 4.5 K. According to the one-dimensional Heisenberg antiferromagnet model the exchange interaction was estimated to be J/k_B = −3.3 K. Two possible pathways contribute to this interaction: through the diamagnetic I₃⁻ anions and the direct interaction between adjacent OMTTF⁺. The crystal structures of three phases of the OMTTF·I₃ salt are also presented.     

Charge transfer in PDI-derived systems studied with light-induced electron spin resonance

Dissymmetrical perylene-3,4,9,10-tetracarboxydiimide building block (PDI) was used to obtain the dyads with fullerene (PDI-C₆₀) and tetrathiafulvalene (PDI-TTF). Photoinduced electron transfer in these dyads was investigated with light-induced electron spin resonance (LESR) spectroscopy. The LESR signals of the samples in CHCl₃ solutions were recorded in the dark and under light illumination, at room temperature and at about 80 K. It was stated that the LESR signal increases stepwise with the incident light and decreases slowly when the light is switched off. The photogeneration of PDI⁺, TTF⁻ and C₆₀⁻ ion-radicals was observed and analyzed. The principal parameters of the LESR lines of the ion-radicals are determined.     

Effect of hydroxyl radical on the structure of multi-walled carbon nanotubes

In this research, we present the systematic investigation of the effect of hydroxyl radical (HO) on the structure of multi-walled carbon nanotubes (MWNTs) via Fenton oxidation treatment in given conditions: molar ratio of hydrogen peroxide (H₂O₂) and ferrous ion (Fe²⁺) is approximately equal to 10 and pH value is controlled at 3 ± 0.5. Fenton oxidation process was followed and characterized by using Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The experimental results showed that the original graphene structure was disordered/destroyed by the newly generated oxygen-containing functional groups including OH, COOH and quinone groups, which were introduced while MWNTs was treated by Fenton reagents (Fe²⁺–H₂O₂). Moreover, two attackable routes for possible mechanism of interactions between HO and MWNTs were assumed by spectral changes and properties of reactive species, which were described as follows: (l) a preferred attack on defect sites existing in the purified MWNTs sample (2) a synchronous or succedent attack on unsaturated bonds of CC on the sidewalls of MWNTs by electrophilic addition reaction. The possible mechanism indicated that introduction of those functional groups into the structure of MWNTs could be regarded as the results of attacks of HO with double properties of oxidizability and electrophilic addition on defect sites and unsaturated bonds of CC in the MWNTs sample, which were consistent with spectral changes in infrared spectroscopy and Raman spectroscopy.     

In situ UV–vis and Raman spectroscopic studies of the electrochemical behavior of N,N′-diphenyl-1,4-phenylenediamine

The electrochemical behavior of the N,N′-diphenyl-1,4-phenylenediamine (B3) in acid solution has been investigated by in situ UV–vis and Raman spectroscopies. The electrogenerated species semiquinone form (B3⁺) and monoprotonated structure of B3 (B3⁺) have been characterized as the main products of B3 oxidation. The N,N′-diphenyl-1,4-benzoquinonediimine (B2Q1) species has also been characterized in B3 neutral solution and the B3⁺ proton loss was attributed to proton absence in solution. Finally, a mechanism has been proposed concerning the electron and proton transfer that occurs during the oxidation process.     

Infrared and Raman studies of the radical anion of α,ω-diphenyl-1,3,5,7,9-decapentaene as a model compound in polyacetylene

The FT-infrared (IR) and Raman spectra of the radical anion of α,ω-diphenyl-1,3,5,7,9-decapentaene (DP₁₀⁻), a polyene molecule with five conjugated CC bonds, were observed in vacuum condition. The IR absorption spectrum for ionic species of polyene molecule was observed for the first time in the experimental method. The CC stretching band of IR absorption has the weak at 1591–1603 cm⁻¹, while the Raman band has the two intense peaks at 1533 and 1574 cm⁻¹. In IR absorption, the in-plane CH bending has the several strong bands between 1448 and 1551 cm⁻¹, whereas the Raman has a strong band used as a marker of negatively charged polyene at 1272 cm⁻¹. The origin of IR and Raman spectra of DP₁₀⁻ is discussed in terms of a polaron model compound in polyacetylene.     

Effect of boron on the thermodynamic stability of amorphous polymer-derived Si(B)CN ceramics

The reason for the higher thermal persistence of amorphous polymer-derived SiBCN ceramics (T ～ 1700–2000 °C) compared to SiCN ones (T ～ 1500 °C) has been a matter of debate for more than a decade. Despite recent experimental results which indicate a major kinetic effect of boron on the thermal persistence of the ceramics, no experimental investigation of the thermodynamic stability of the materials has been reported. In this work, we present measured energetics of a series of the amorphous ceramics with various boron contents (0–8.3 at.%) using high-temperature oxidative drop-solution calorimetry. Through measurement of the drop-solution enthalpies in molten sodium molybdate at 811 °C, the formation enthalpies of the amorphous ceramics from crystalline components (SiC, BN, Si₃N₄, C) at 25 °C were obtained and found to be between ?1.4 and ?26.6 kJ g-atom^?1. The determined enthalpy data plus the estimated positive entropy of formation values point to the thermodynamic stability of the amorphous ceramics relative to the crystalline phases, but such stabilization diminishes with increasing boron content. In contrast, the higher boron content increases the temperature of Si₃N₄ crystallization despite less favorable energetics for the amorphous phase, implying more favorable energetics for crystallization. Thus the so-called “stability” of SiBCN ceramics in terms of persistence against Si₃N₄ crystallization appears to be controlled by kinetics rather than by thermodynamic stability.     

Design of novel donor-acceptor polymers with low bandgaps

Quantum chemical results on the electronic and geometric structures of some novel donor-acceptor polymers containing alternating electrondonating group X (X = CH₂, SiH₂ or GeH₂) and electron-accepting group Y (Y = C = CH₂, C = O, C = CF₂ or C = C(CN)₂) along the conjugated cis-polyacetylene backbone, obtained on the basis of the one-dimensional tight-binding self-consistent field-crystal orbital (SCFCO) method at the MNDO-AM1 level of approximation, are reported. The optimized geometries of the polymers show a strong dependence on the nature of the electron-donating group X. Polymers derived from X = CH₂ or GeH₂ and Y = C=C (CN)₂ are predicted to have bandgap values of less than 1 eV. An analysis of their π-bond order data and the patterns of their frontier orbitals shows these two polymers to have quinoid-like electronic structures, in contrast to the benzenoid-like electronic structures for the rest of the polymers.     

The annealing and re-oxidation of oxidized CuNi alloys

A study has been made of the effects of an intermediate, isothermal annealing treatment in argon on the oxidation kinetics in dry oxygen of Cu10%Ni and Cu24%Ni at 800°C and Cu80%Ni at 1000°C using a semi-automatic microbalance. Changes in scale morphology and composition have been investigated using various techniques.Oxidation of Cu10%Ni and Cu24%Ni produces external scales consisting of a thick, inner Cu₂O layer and a thin, outer CuO layer, together with nickel-rich internal oxide in the adjacent alloy. Oxidation of Cu80%Ni yields an external scale consisting of a thick, inner NiO layer and a thin, outer CuO layer, together with a few nickel-rich internal oxide particles in the adjacent alloy. During annealing, the outer CuO layers on the three alloys dissociate to give Cu₂O and oxygen. With Cu80%Ni only, further dissociation to give copper metal takes place after long annealing times. In all cases, the annealing treatment leads to a reduction in the cation vacancy gradient across the scale and a reduction in the total vacancy level in the scale due to the reduction in oxygen activity at the oxide-gas interface.In Cu10%Ni and Cu24%Ni, internal oxide formation during annealing stimulates dissociation of the Cu₂O scale near the oxide-alloy interface to give copper metal and oxygen. Similarly, internal oxide formation stimulates dissociation of the NiO layer on Cu-80%Ni, although to a lesser extent than for the copper-rich alloys.During re-oxidation, the kinetics are partly determined by the extent of scale thinning during the prior annealing treatment, giving more rapid weight gains than expected from those recorded during the initial oxidation period. Nevertheless, particularly for Cu-80%Ni, where the scale thinning is relatively small, the reduction in the cation vacancy gradient across the scale and the reduction in the total vacancy level in the scale do result in a reduced oxidation rate compared with the rate recorded during the initial oxidation period.     

Manufacture of a new kind diamond grinding wheel with Al-based bonding agent

A new kind diamond grinding wheel with Al-based bonding agent was prepared in this paper. The influence of sintering temperature to the relative density (R.D.), hardness and service life of diamond grinding wheels with AlSnTi, AlSnTiNiCo, AlSnTiNi and AlSnNiCo bonding agent was studied. The microstructure of different bonding agent sintered at different temperature was observed. The service life of the Al-based grinding wheels was compared with Cu-based or resin-based ones. The results showed that the AlSnTiNiCo is the best composition system in this research. The best sintering temperature is 300 °C. The sample has a high relative density after sintered at 300 °C. The retention of Al-based bonding agent to diamond grit is strong. The service life of this Al-based diamond grinding wheel is about three times as long as that of resin-bonded grinding wheel.     

New 1,3,4-oxadiazole containing materials with the effective leading substituents: The electrochemical properties,optical absorptions,and the electronic structures

The electrochemical and optical absorption properties as well as the thermal stabilities of a series of 1,3,4-oxadiazole dimers 1,3-bis[2-(4-methylphenyl)-1,3,4-oxadiazol-5-yl]benzene (OXD-X) and its derivatives with the different alkoxy substituents on the central benzene ring such as O(CH₂)_n−1CH₃ (OXD-An, n = 3, 7, 10, 16), O(CH₂)_nOC₆H₅CH₃ (OXD-Bn, n = 6), and O(CH₂)_nOC₆H₄NNC₆H₄OCH₃ (OXD-Cn, n = 3, 6, 10) are studied. The DSC measurements exhibit dramatically elevated glass transition temperatures for OXD-X and OXD-An (120–245 °C) in contrast to the well-known PBD (∼60 °C), indicating the better thermal stabilities. From OXD-X to OXD-An, OXD-Bn or OXD-Cn, the cyclic voltammograms and UV–vis absorption spectroscopy display significant variation, in which the later three species show additional lower energy absorptions at λ > 330 nm compared with OXD-X and particularly, both of OXD-Bn and OXD-Cn display an oxidation peak at ∼+1.0 V and two successive redox reactions occur for OXD-Cn. Theoretically, the B3LYP/6-31g calculations explore that these extraordinary properties are due to the influence of the substituents on the benzene ring to the frontier molecular orbital distribution, especially the O(CH₂)_nOC₆H₄NNC₆H₄OCH₃ groups in OXD-Cn deduce the new pictures of the frontier molecular orbitals, causing the electron-transporting behavior originally happening on the molecular skeleton transferred to the side chain.     

Supramolecular associations of poly(ketanil)s with sulfonic acid derivatives of benzenetricarboxamide via Brönsted acid–base interactions: Preparation,spectroscopic morphological and thermal investigations

Supramolecular aggregations have been obtained via ionic self-assembly of conjugated poly(ketanil)s and sulfonic acid derivatives of benzenetricarboxamides. To achieve this goal a new protonating molecule has been synthesized which is a derivative of 1,3,5-benzenetricarboxamide with sulfonic acid group at each of its ends. 1,3,5-benzenetricarboxamides of C₃ symmetry tend to form ordered supramolecular aggregations via π-stacking and this property is retained in their sulfonic acid derivative. Because of their Brönsted acid nature the new molecules can additionally associate conjugated polymers with basic centers such as poly(ketanil)s. Depending on the processing solvent used (MC or DMA) 1,3,5- the sulfonic acid derivative of benzenetricarboxamide and its associations with poly(ketanil)s form aggregations of spherullite-like or feather-like morphologies as evidenced by polarized optical microscopy and atomic force microscopy. The similarity of this supramolecular organization is also corroborated by DSC studies which in both cases show endothermic type transitions of the same origin. The supramolecular acid–base associations are semi-crystalline in nature and exhibit good mechanical properties at room temperature because of a rather low T_g, in the vicinity of 300 K. This unusual lowering of T_g by ca. 90 K as compared to the case of poly(ketanil)s in their basic form is caused by the plasticizing effect of the protonating agent. Finally polyketanil–1,3,5-benzenetricarboxamide sulfonic acid derivatives show tunable photoluminescence which depends on the solvent and SO₃H/CN molar ratio.     

Atom site preference and γ′/γ mismatch strain in NiAlCoTi superalloys

The structure and chemistry of NiCoAlTi quaternary superalloys are investigated at the microstructural and atomic scale. Atom probe tomograghy (APT) is used to quantify phase compositions and elemental partitioning behavior. Using aberration corrected electron microscopy, the site occupancy of the atoms within the A₃ B structure (L1₂–type) γ′ phase is determined via atomic resolution energy dispersive X-ray spectroscopy (EDX). Ni is observed to preferentially occupy the A sub-lattice positions for all alloys, while Al and Ti occupy the B sub-lattice. In contrast, Co's site preference changes from a random distribution to the A sub-lattice as the alloy composition changes, in agreement with theoretical predictions from literature. Finally, the lattice strain across the γ′/γ interfaces is measured as a function of alloy composition.     

Nitridation of Ti6Al4V alloy under ultrasonic impact treatment in liquid nitrogen

X-ray photoelectron spectroscopy and scanning electron microscopy with energy dispersive X-ray microanalysis were employed to study the effect of mechanical treatment on the surface chemical state, composition and morphology of commercial Ti6Al4V alloy. It has been demonstrated that ultrasonic impact treatment of Ti6Al4V in a liquid nitrogen (LN2) environment results in substantial grain refinement and formation of nitrides and oxynitrides of all the alloy components. The mechanochemical synthesis of the nitrides and oxynitrides from LN2 was found to efficiently occur not only within the impacted area but outside it as well. The layer with a high content of incorporated nitrogen and average atomic ratio N/Ti = 0.94 was estimated to be at least ～2 μm thick. As a result of the combined effect of cryogenic deformation, nanoscale grain refinement and nitriding, a 3-fold increase in the microhardness of Ti6Al4V alloy is obtained. The impact treatment in LN2 was observed to be accompanied by material transfer from the hardened steel pin to the alloy followed by incorporation of the pin components into Ti6Al4V and formation of the FeN, FeC and TiC bonds.     

Thermophysical properties of TiB2SiC ceramics from 300 °C to 1700 °C

In the present work, high-frequency induction heating is used to fabricate TiB₂SiC ceramics and the relative density was more than 97%, and then the thermophysical properties of TiB₂SiC ceramics were investigated in detail. The specific heat showed the weak dependence on the test temperature due to the presence of the interface gap because the relative density was not 100%. As the sintering temperature increased, the thermal diffusivity of TiB₂SiC ceramics increased, which was due to the increase of relative density and grain growth. The thermal conductivity of TiB₂SiC ceramics showed a marked increase with increasing grain size and relative density. This could be attributed to a reduction in the number of grain boundaries that interrupt the heat flow path, resulting in an increase in the mean free path of the phonons. Larger grains led to an increase of mean free path of the phonons and thus contributed to a further increase in thermal conductivity.     

Single- and dual-type electrochromic devices based on polycarbazole derivative bearing pendent viologen

In relation to electrochromic (EC) device performance, it is important to avoid unwanted power consumption and to minimize electrochemical degradation by using an EC material, which exhibits the desired EC state under no bias voltage in most of the time. Regarding this point, we prepared single- and dual-type EC devices based on poly(N-methyl-N′-(6-carbazole-1-ylhexyl)-4,4′-bipyridinium dihexafluorophosphate) [P(Cz-V)]. Since polycarbazole is oxidative-coloring and viologen is reductive-coloring, the supplementary EC action provides variety in color, which cannot be achieved by individual EC materials. In the single-type device, the polymer became green P(Cz^α+-V²⁺) at 3 V (versus ITO), bleached P(Cz⁰-V²⁺) at 0 V, and violet P(Cz⁰-V⁺) at −3 V. In the dual-type device, the complementary action of (Cz^α+-V²⁺) and P(Cz⁰-V⁺) upon a bias voltage of 3 V showed higher EC contrast compared to the single-type device.     

Designed fabrication of hard CrCr2O3Cr7C3 nanocomposite coatings for anti-wear application

Nanocrystalline CrCr₂O₃Cr₇C₃ composite coatings were fabricated by electrodeposition followed by thermal treatment. The structures of coatings were investigated using high-resolution transmission electron microscopy and X-ray diffraction analysis. The composition, elemental chemical state, mechanical properties and wear resistance of coatings were determined using energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, nanoindentation and oscillating friction-wear testing, respectively. Wear tracks were observed by scanning electron microscopy. The results show that the as-deposited coating exhibits amorphous structure. The subsequent thermal treatment at 600 °C induces the crystallization and the generation of nanoscale Cr₂O₃ and Cr₇C₃ particles in the Cr-matrix, which results in the hardness of the coating increasing to 21 GPa with slight increase in elastic modulus. Owing to the compromise between high hardness and low elastic modulus, the obtained CrCr₂O₃Cr₇C₃ composite coating exhibits excellent wear resistance.     

Study on the formation of core–rim structure in Ti(CN)-based cermets

Ti(CN)-based cermets were synthesized from Ti(CN)WCMo₂CTaCNiCo composite powders by vacuum-low pressure sintering. The phase evolution and the formation of core–rim structure in Ti(CN)-based cermets were systemically investigated during difference reaction stages at 950–1450 °C. The results show that the secondary carbides such as Mo₂C and TaC are begun to dissolve at 950 °C, finished at 1150 °C, and the solution temperature of WC phase is range from 1150 to 1300 °C, which are result in increase of the cermets lattice constant. At the same time, the inner rim is also formed, and Ti(CN)-based cermets are composed of (Ti, W, Mo, Ta)(CN) and Ni/Co solid solution phase. While at 1350 °C, it was found that the outer rim began to precipitate from the liquid phase with the metal binder. With increase of sintering temperature, mechanical properties of cermets improved obviously were related intimately to the increase of outer rim thickness.     

Oxidation of FeCr alloys in O2/3% H2O

A range of FeCr binary alloys containing 2–100%Cr was exposed in O₂/3%H₂O at 1023–1223K to determine whether the presence of the water had a significant effect on oxidation. Oxidation rates were not significantly different from those in dry oxygen and decreased with increasing time of oxidation. The kinetics of oxidation and the oxide structures both suggested that the early stages of oxidation were controlled by lattice diffusion through layers of FeCr spinel for Fe-2 1/4Cr and Fe-8 1/2Cr, or through (Cr, Fe)₂O₃ scale for alloys containing 16%Cr or more.