The influence of Co doping on the dielectric, ferroelectric and ferromagnetic properties of Ba0.70Sr0.30TiO3 thin films

Ba_0.70Sr_0.30TiO₃ (BST) thin films doped by Co (BSTC) are fabricated by sol-gel method on a Pt/Ti/SiO₂/Si substrate. A strong correlation is observed among the microstructure, dielectric, ferroelectric, ferromagnetic properties and Co concentration. The dielectric constant of BST thin films can be tailored from 343 to 119 by manipulating the Co concentration. The dielectric loss of BSTC thin films are still kept below 0.020 and the tunability is above 30% at a dc-applied electric field of 500 kV/cm. With increasing Co doping up to 10 mol%, the coexistence of ferromagnetism and ferroelectrics is found. Suitable dielectric constant, low-dielectric loss, and high tunability of this kind of thin films can be useful for potential tunable applications.     

Relationship Between Total Surface Tension of Monomer and Its Homopolymer

The surface and interfacial properties of polymers are important for their applications. In one of our previous articles, we discussed the relationship between the dispersive surface tension component and the density and molecular weight of solvents and polymers to seek a simple and easy method to estimate the rationality of surface tension results of polymers. We found that for 30 organic solvents and 12 polymers, there was a good relationship between the dispersive surface tension and the experiential parameter 1/ρ² M ^0.2 _w . In this article, the existence of the squared density term is simply deduced from the general molecular interaction energy equation and is proved with four pairs of polymer/monomer; these are polystyrene/styrene, polyisoprene/isoprene, polymethyl methacrylate/methyl methacrylate, and polyvinyl acetate/vinyl acetate.     

Controllable synthesis and shape-dependent photocatalytic activity of ZnO nanorods with a cone and different aspect ratios and of short-and-fat ZnO microrods by varying the reaction temperature and time

ZnO nanorods with a cone and different aspect ratios and short-and-fat ZnO microrods were synthesized via a hydrothermal reaction of Zn with Zn(CH₃COO)₂ and H₂O. The control over these ZnO nanocrystals with a wurtzite structure and different shapes was achieved by adjusting only the reaction temperature and time. A possible kinetic mechanism was proposed to account for the growth of these ZnO nanocrystals with different shapes. Photocatalytic activities of ZnO nanocrystals with distinctive shapes in the degradation of methyl orange were investigated. The results indicate that the photocatalytic ability of the ZnO nanorods with a cone and different aspect ratios is stronger than that of the short-and-fat microrods.     

Electronic transitions of fluorene, dibenzofuran, carbazole, and dibenzothiophene: From the onset of absorption to the ionization threshold

A comparative study of the electronic transitions of fluorene and its hetero-analogues dibenzofuran, carbazole, and dibenzothiophene was performed in a wide energy range. Gas phase, crystal phase, and linear dichroism electronic transmittance spectra were measured with synchrotron radiation. Electronic transitions to excited singlet states were predicted with time-dependent density functional theory, TD-B3LYP/6-31+G(d,p). Based on the experimental and theoretical results, symmetry assignments of electronic transitions in the vacuum and near-UV region are suggested. The correspondence between excited states in these molecules, similarities, and differences between their electronic spectra are discussed.     

Monte Carlo study of impact ionization in n-type InAs induced by intense ultrashort terahertz pulses

Electron impact ionization induced in n-type InAs by single-cycle pulses of picosecond and subpicosecond duration has been investigated by Monte Carlo method. It is established that the rate of generation of electron–hole pairs decreases with the decrease of the pulse duration. The impact ionization threshold field is found to depend linearly on frequency for the fields oscillating at frequencies much higher than reciprocal momentum relaxation time. Good agreement between calculations and available experimental data has been obtained.     

Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of temperature on the fluorescence emission of carbazole-substituted methylcellulose in dilute aqueous solutions

Fluorescent-labeled polymers, carbazole-substituted methylcelluloses (Cz-MCs) were synthesized through a two-step reaction by firstly introducing epoxy group to carbazole, and then reacting with MC. Structure of Cz-MC was characterized by using FTIR, NMR, elemental analysis and UV–vis spectroscopy. Aggregation behavior of Cz-MCs in dilute aqueous solution was investigated by a thermotropic study performed with dynamic laser light scattering. Cz-MCs displayed concentration self-quenching properties of fluorescence spectra both in H₂O and DMSO. The temperature effect on the fluorescent emission in dilute aqueous solution was explored. The results showed that the degree of substitution of carbazole and thermal aggregation of Cz-MC contributed to the formation of network structure between the molecules, consequently leading to the enhancement or quenching in fluorescence intensity.     

Study on the interaction between urea and cellulose by combining solid-state 13C CP/MAS NMR and extended Hückel charges

In this article, solid-state ¹³C CP/MAS NMR combined with extended Hückel charges was applied to investigate the interaction between urea and cellulose in the NaOH/urea aqueous solvent system. Direct experimental evidence was provided to support the interaction between urea and cellulose. The solid-state ¹³C CP/MAS NMR results revealed that complicated complexes are formed by urea, NaOH and cellulose in the solution. Excess urea exists in a free state, which explains why 7 wt% NaOH/12 wt% urea/81 wt% H₂O is the optimal ratio selection to dissolve cellulose. Based on the correlation in which the computed extended Hückel charge on carbon of urea is approximately inversely proportional to its ¹³C chemical shift, a possible interaction model of cellulose, NaOH and urea was proposed. Interactions exist between any two of urea, NaOH and cellulose, which results in the cellulose chain being surrounded by NaOH and urea molecules. NaOH and urea may be in the same surface layer of cellulose chains.     

Boussinesq方程行波解的存在性

利用平面动力系统方法的分支理论,研究了Boussinesq方程,通过对Boussinesq方程进行行波变换,得到了相应行波系统的首次积分和平衡点,给出了不同参数条件下的相图,证实了Boussinesq方程存在孤立波解和周期波解。