Advanced Materials Research Vols. 335-336

Abstract: Copolymers based on 1, 4-diethoxybenzene (DEB) and 3, 4-ethylenedioxythiophene (EDOT) were electrochemically synthesized and characterized. The structures of the copolymers were established by ¹H NMR and FT-IR spectroscopy. The results indicated the final product was a copolymer instead of a blend or a composite. The physical properties were systematically investigated by cyclic voltammetry, UV-vis absorption and fluorescence. The PL maximum of copolymers presented obviously red-shift to long wavelength as the feed ratio of EDOT in monomer mixture increased.

Abstract: Magneto-rheological fluid (MRF) is non-colloidal suspension. In this paper, it is introduced that MRF will produce magnetic coagulation at an applied magnetic field by analyzing the interact energy between particles in MRF, and the coagulation is chain-like flocculation. The main reason that MRF produced magnetic coagulation is the direction between chain-like structure and magnetic field is the same. According to the studies above, the formula of yield stress for MRF at an applied magnetic field can be deduced. It can be seen from the formula that there is a square relationship between yield stress of MRF and particle magnetization, and the yield stress of MRF is closely related with volume concentration. The conclusions above match the results of existing experiments very well.

Abstract: Arrays of SU-8 photoresist pillars (10 μm ×10 μm × 50 μm) on copper substrates were fabricated by X-ray lithography. The photoresist-coated substrates were irradiated by X-ray from a synchrotron source through patterned silver dots on a graphite mask. After the resist development, the chemically stable and mechanically hardened SU-8 pillars exhibited smooth vertical sidewalls and cross section with up to 10 % dimensional errors from the designated pattern. Cobalt of thickness ranging from 50 to 80 nm was then deposited on these patterned substrates by RF sputtering. These cobalt films on SU-8 pillars showed a lower in-plane magnetization than that of continuous cobalt films because of their smaller grain size. The measurement with out-of-plane magnetic field gave rise to a higher magnetization and this anisotropic behavior was observed only in cobalt-coated pillars.

Abstract: Based on Landau-Devonshire theory, the electrothermal properties of PbTiO₃ bulk and film are computed near the temperatures of their phase transitions. A first-order ferroelectric to paraelectric phase transition is present in PbTiO₃ bulk. The coercive electric field at 700 K is about 25 MV m^-1. High applied electric fields drive the transition to higher temperatures and the P−T curves to be continuous. For PbTiO3 film, the second-order phase transition reduces the excess entropy, and thereby the isothermal entropy change. With increasing electric field, the excess specific heat capacity becomes small, despite higher transition temperatures. The change of in-plane tensile misfit stress lowers the transition temperature. Besides, the adiabatic temperature change and the refrigerant capacity of PbTiO₃ bulk are 4.76 K and 94.1 kJ m^-3, respectively.

Abstract: Hexagonal phase NaYF₄: Eu³⁺ materials were successfully synthesized by a facile EDTA-assisted hydrothermal route. The microstructure, morphology and luminescence property of the as-synthesized samples were characterized by XRD, XPS, SEM, TEM, HRTEM and photoluminescence (PL) spectra. The pristine NaYF₄: Eu³⁺ microprisms have uniform size and morphology with 3-4 micrometers in length and ca. 500 nm in diameter. The annealing treatment afterwards achieved high crystallinity, and moreover, had a remarkable influence on morphologies of the NaYF₄: Eu³⁺ sample. In comparison with the pristine sample, the annealed NaYF₄: Eu³⁺ microcrystals had a markedly enhancement of down-conversion (DC) luminescence properties, which may be due to the high crystallinity and large surface roughness resulted from annealing treatment.

Abstract: The Finite Element Method (FEM) was used for axisymmetric indentation to investigate mechanics properties of piezoelectric solids (PZT-5H). Since piezoelectric materials are usually treated as transversely isotropic elastic materials, a simple linear relationship between indentation load P and indentation displacement h was presented under a cylindrical indenter. Three different cases (uncouple mechanical case, poled substrate-insulating indenter and poled substrate-conducting indenter) were taken into consideration to study indentation responses. The results showed that polarization could more easily damage the poled substrate than the uncoupled case. At the same displacement the highest indentation load existed in the poled/insulating case and the lowest one was in the uncoupled case because of the polarization influence. Electric potential distributions were given to study the direct piezoelectric effects and the electromechanical phenomena. In addition elastic modulus, contact stiffness, and piezoelectric strain constant were calculated directly through the use of the FEM. The determination of the poling direction is another use for the indentation technique, and the discussion of indentation size effect shows that a bigger indenter is followed by a larger indentation load.

Abstract: A copolymer based on 9-(4-pyrrol-1-yl-phenyl)-carbazole(PPC) and 3,4-ethylenedioxythiophene(EDOT) was electrochemically synthesized and characterized. The copolymer film not only presented a stable and well-defined redox process, but also exhibited three different colours(orange, green and greenish blue) under various applied potentials. Maximum optical contrast(△T%) and response time of the film were found to be 31% and 2 s at 1100 nm, respectively.

Abstract: The Tm,Ho:BaY₂F₈ single crystal was successfully grown by the Cz method. The optimal technical parameters obtained are as follows: the pulling rate is 0.5—0.6mm/h; the rotation speed is 5—7rpm; the cooling rate is 10°C/h. The result of XRD curve shows that as-grown Tm,Ho:BaY₂F₈ laser crystal belongs to the monoclynicsystem and space group I41/a, the cell parameters calculated are: a = 0.69829 nm, b = 1.0519 nm, c = 0.42644 nm, β=99.676°, Z=2. Absorption spectra of Tm,Ho:BaY₂F₈ laser crystal at room temperature were measured and analysed, the absorption cross-section at 781nm calculated are 7.66×10^-21cm^-2.

Abstract: In order to elucidate the mechanism of photochromism and spectrum properties observed for spiropyran, the model complexes of spiropyran, in which different substituent and structure are key factors, have been optimized by using ab initio and hybrid DFT programs. The primary relationship between the substituent species and structure and photochromism was given by simulation calculation.

Abstract: A series of the Yb³⁺ -doped phosphate laser glass have been prepared under high temperature and different doping content and the fluorescence and absorption spectrum is observed, respectively. The influences of the Yb³⁺ -doped content on the spectral properties of the glass are analyzed and the optimal mole fraction is 4 %. The emission cross-section and fluorescent lifetime is calculated with McCumber theory. Furthermore, the integrated absorption cross-section, the full width at half maximum of the emission spectra and the laser performance parameters such as least particle count, saturation pump intensity and lowest pump intensity of Yb³⁺ -doped laser glass is calculated.