Advanced Materials Research Vols. 284-286

Abstract: The K₂TiF₆ ,K₂ZrF₆ powder and aluminum were selected as the raw materials to in situ synthesize the particulates reinforced aluminum matrix composites. During the fabrication process the electromagnetic field was imposed. The atomic ratio of Al/Ti/Zr in the particulates is determined as 3/0.4/0.6. The Al₃Ti_0.4Zr_0.6 is a new kind of intermetallic compound, some properties of which fall in between those of Al₃Ti and Al₃Zr. Electromagnetic field plays an important part in fining particles and promoting their uniform distribution. When the electromagnetic induced intensity is 0.05T the particles have 0.5-2μm average size and uniform distribution in matrix. The crystal grains of matrix resemble equiaxed ones. The average size of grains are nearly 100μm, 50μm and 25μm when the electromagnetic induced intensities are 0, 0.025T and 0.05T seperately.

Abstract: A series of new chiral side-chain liquid crystalline polymers with electron donor-acceptor action were prepared containing chiral monomer with donor group and nematic LC monomer with acceptor group. All polymers were synthesized by graft polymerization using polymethylhydro- siloxane as backbone. The mesomorphic properties were investigated by differential scanning calorimetry(DSC), polarizing optical microscopy(POM)，thermogravimetric analyses（TGA） and X-ray diffraction measurements(XRD). The chemical structures of monomers and polymers were confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance spectra(1H NMR and 13CNMR). M1 showed nematic phase and M2 turned out cholesteric phase on heating and cooling cycle. Polymers P3~P8 were cholesteric phase. Experimental results demonstrated that the glass transition temperatures and isotropization temperatures and the ranges of the mesophase temperature increased with increasing the content of chiral agent. All of the obtained polymers showed high thermal stability.

Abstract: A series of rhodium-based complexes were explored theoretically to understand their application in optical materials and potential photocatalytic activity. Better structural description of [RhAu(CNH)₂(PH₂CH₂PH₂)₂]²⁺ (1) were achieved with the ab initio MP2, XαVWN, and SVWN methods. To fine-tune the electronic spectroscopy, two analogues of 1 were taken into account by varying its Au metal center and bridging bidentate ligand. The experimental spectra were well reproduced by our TD-DFT calculations. It was shown that the lowest-energy absorption of homobimetallic Rh-Rh complex occurs in lower-energy region than those of heterobimetallic Rh-Au complexes.

Abstract: In this study, we successfully prepared polymethyl methacrylate (PMMA) /NaYF₄:Yb:Er up-conversion composite luminescence material by solution cast method. PMMA was used for polymer matrix, and NaYF₄:Yb:Er for rare earth up-conversion luminescence component, and this composite material was prepared for holographic display. Fourier transform infrared spectroscopy (FTIR) and luminescent spectroscopy were measured to analyze structure and luminous performance of the composite material respectively.

Abstract: The dielectric characteristics of Barium titanate (BT) based ceramics are evaluated in a broad frequency range at room temperature and at elevated temperature; the measured frequency is 0.1Hz to 1GHz. The results showed that the dielectric constant increases sharply with the decreasing frequency and is higher than 3000 appeared in lower frequency for Mg 1% doped BT bulk ceramics, which may be resulted from space charge polarization becoming more dominant as compared to the dipolar polarization especially when the frequency is lower than 1 kHz. The dielectric relaxation peaks of Mg-doped BT bulk ceramics appeared both at low and radio frequency whereas pure BT ceramics showed relaxation peak only at radio frequency, what's more, the relaxation frequency of Mg-doped sample is rather low than pure barium titanate ceramics. The dielectric relaxation motion approximately obeys Debye relaxation model approved by Cole-Cole diagram. Thermal activation energy is 0.46eV obtained by Volgel-Fulcher law fitting, which demonstrated that dielectric relaxation due to oxygen vacancies in the Mg-doped BT ferroelectric ceramics.

Abstract: In order to obtain materials with more ideal GMI effect, (DZ/Z）max, the substitution effects of R (R = Co, Ni and Cr) for Fe in Fe_63.5R₁₀Cu₁Nb₃Si_13.5B₉ soft magnetic wires have been studied. We found that although the Finemet composition shown excellent GMI effect, the substitution of Co can raise notably the field sensitivity, Q, Ni makes a little improvements of (DZ/Z）max, and Q, and Cr diminishes the undesirable hysteretic effect. In additions, the influence of annealing conditions upon the GMI effect of the best composition Fe_63.5Cr₁₀Cu₁Nb₃Si_13.5B₉ was also investigated. It indicated that the sample obtained by the ways of Joule heating under the application of suitable tensile stress exhibits 200% and 30%¤Oe for (DZ/Z）max and Q, respectively. This sample can serve as a proper choice for magnetic sensors.

Abstract: In the present work, a pulling down method was introduced to prepare the KNbO₃ crystals and the growth results were evaluated. It was found the Pt crucible with 60° cone angle and folds at the seed well was helpful to obtain KNbO₃ crystal with nice integrity. The blue color occurred on the top of KNbO₃ ingot was confirmed to be orthorhombic KNbO₃ by XRD analysis. Some complex domain structures, including 60°, 90° and 180° domains, were happened in the crystal which were attributed to phase transitions when it was cooled down to room temperature.

Abstract: This paper describes the role of the substitution of La³⁺ and Co²⁺ with the formula Sr_1-xLa_xFe_12-yCo_yO₁₉ on the magnetic properties of anisotropic strontium ferrite sintered magnets. The magnets prepared by the ceramic process have been investigated by XRD and B-H hysteresis curve measurements. Our results show that the magnetic induction coercivity (H_cb) and maximum magnetic energy product [(BH)_max] of the substitution magnets [Sr_1-xLa_xFe_12-yCo_yO₁₉ (x > y)] is notably increased without too much decreasing in the intrinsic coercivity (H_cj) and residual flux density (B_r), indicating that the magnetoplumbite crystal structure may be more stable than that of Sr_1-xLa_xFe_12-xCo_xO₁₉ magnets.

Abstract: A reduced-pressure melts growth method was first presented to grow the vacuum ultraviolet double frequency crystal KBe₂BO₃F₂ (KBBF). The bulk KBBF crystal, with a dimension of about 11mm×10mm×5mm, has been grown successfully, and the grown crystal exhibits a high optical homogeneity except for the seed zone. The optical transmittance spectrum of the grown KBBF crystal was measured and it indicated that the high-frequency absorption edge is observed at 160nm, the transmittance is up to about 70% between 250nm and 400nm. The results show that the reduced-pressure melts growth is a promising growth method for bulk KBBF crystal and the grown KBBF crystal is possible for applying as a frequency-doubling device for the vacuum ultraviolet region.

Abstract: A new 2D photonic crystal microcavity is proposed based on the localized modulation and the model match technique. Structure of the new PC cavity is characterized in that several scatters are introduced into the edges of the L3 microcavities. The local field modulation method is applied in the new PC microcavity to optimize the cavity structure, and the quality factor Q and transmission T can be both improved after modulation. During the modulation process, Q and T of the new PC cavity represent an identical variation trend. The Q and T of the optimized PC cavity, with the simulation parameters confined in our work, reach to 240000 and 0.68 respectively.