Xuping Wang

SYNTHESIS OF CaWO4 AND CaWO4:Eu MICROSPHERES BY PRECIPITATION

Nearly monodisperse CaWO4 and CaWO4:Eu3+ microspheres have been synthesized in large scale by a surfactant-assisted solution route, in which cetyltrimethyl ammonium bromide (CTAB) is used. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and photoluminescence (PL) were used to characterize the resulting samples. The results of XRD indicate that the CaWO4 and CaWO4:Eu3+ samples have the scheelite structures. The growth process of these nearly monodisperse spheres with an average diameter around 3.2 μm has been examined. The results of FTIR indicate that CTAB plays an important role in the formation of microspheres. The CaWO4 microspheres exhibit a blue emission band with a maximum at 423 nm. But the CaWO4:Eu3+ microspheres exhibit a red emission band with a maximum at 623 nm.

Electrical and thermoelectric properties of single-wall carbon nanotube doped Bi2Te3

The effects of single-wall carbon nanotube (SWCNT) doping in n-type Bi2Te3 bulk samples on the electrical and thermal transport properties have been studied. Bi2Te3 samples doped with 0–5u2009wt. % SWCNTs were fabricated using solid state reaction and investigated using x-ray diffraction, transmission electron microscopy, and magneto transport measurements. Results show that the 0.5% doping results in the significant enhancement of the Seebeck coefficience to as high as −231.8u2009μV/K, giant magneto resistance of up to 110%, reduction of thermal conductivity, and change of sign of the Seebeck coefficient from n to p type depending on the doping level and temperature. The figure of merit, ZT, of the optimum SWCNT doped Bi2Te3 was increased by 25%–40% over a wide temperature range compared to the undoped sample.

Anomalous laser deflection phenomenon based on the interaction of electro-optic and graded refractivity effects in Cu-doped KTa1−xNbxO3 crystal

An abnormal laser deflection phenomenon in a copper-doped KTa1−xNbxO3 (Cu:KTN) crystal is demonstrated in this Letter. A near-50 mrad beam deflection angle was observed when a voltage of 1.2u2009kV was applied to a Cu:KTN block with size of 2.8u2009mmu2009×u20091.2u2009mmu2009×u20097.5u2009mm at room temperature. The special features of this deflection phenomenon are that the laser beam deflection direction is perpendicular to the electric field direction, and the beam deflection angle remains unchanged when the electric field direction is reversed. The operating principle of the phenomenon is investigated and the origin of the deflection phenomenon is attributed to an interaction between the graded refractivity effect and the quadratic electro-optic effect of the crystal.

CaCu3Ti4O12 ceramics from different methods: microstructure and dielectric

CaCu3Ti4O12 (CCTO) ceramics were synthesized by methods of sol–gel, traditional solid-state reaction, and thermal decomposition of organic solution. The results exhibit that the microstructures and electric characteristics are affected by the methods of synthesis. The X-ray diffraction patterns show that all samples have a perovskite-like CCTO phase. Moreover, CCTO ceramic from traditional solid-state reaction have the phases of TiO2 and CuO. The scanning electron microscopy images show that CCTO ceramics from different methods have different grain sizes, grain boundaries, and densities. Dielectric properties of the CCTO ceramics were characterized in a broad frequency range (10–107xa0Hz) at room temperature. The CCTO ceramics from thermal decomposition of organic solution have the dielectric constant of more than 5xa0×xa0104 at 10xa0Hz. The nonlinear relationship between the current density and the electric field strength can be observed in all the three samples.

Fabrication of SrAl2O4:Eu2+ films on Si substrates via metal–organic solution

SrAl2O4:Eu2+ films were fabricated on the Si substrates by metal–organic solution deposition method and subsequent treatment up to 1100xa0°C. The phase and microstructure of the obtained films were characterized by DTA-TG, XRD, SEM and AFM. The composition of the film was confirmed by XPS. The luminescence properties of the films were measured by spectrophotometer. The effect of annealing temperature on the structure and luminescence was studied. It showed that the films had the pure monoclinic phase and the depth about 2xa0µm. Under the excitation of 254xa0nm, SrAl2O4:Eu2+ films exhibited an intense green emission band peaking at 528xa0nm, which originates from the 4f–5d transition of the Eu2+ ions. The quenching temperature of the emission is about 400xa0K. The results indicated that the SrAl2O4:Eu2+ films have good potential for use as a green phosphor for displays and/or white light emitting diodes.

Synthesis and Characteristics of Hierarchical Co3O4 Powders

Co3O4 samples with hierarchical structure were synthesized successfully by the morphology-conserved transformation method. The XRD and XPS results show that the obtained samples have the typical spinel Co3O4 phase. The FT-IR spectrum shows that the precursors consist of Co–EG coordination polymer. The SEM images show that the obtained samples have the morphology of flower-like microspheres. The authors found that the key step of the obtaining of hierarchical Co3O4 flower-like microspheres by the morphology-conserved transformation method is to construct flower-like microstructures of the cobalt-containing precursors via manipulating the synthetic parameters in a facile ethylene glycol–mediated solvothermal reaction.

Thermal and spectroscopic characteristics of disordered melilite Nd:BaLaGa3O7 crystal

A disordered Nd:BaLaGa3O7 laser crystal was successfully grown by the Czochralski method. The effective segregation coefficient of Nd3+ in BaLaGa3O7 crystals was measured to be 1.12. A series of thermal properties, including specific heat, average linear thermal expansion coefficient, thermal diffusivity and thermal conductivity, were systematically determined as a function of temperature. The thermal conductivity increased with increasing temperature. The polarized absorption and emission spectra were measured at room temperature. Nd:BaLaGa3O7 possessed a large absorption bandwidth of 18 nm at 808 nm and an emission bandwidth of 32 nm at 1060 nm. According to the Judd–Ofelt theory, the spontaneous transition probabilities, the fluorescence branching ratios, and the radiation lifetime were calculated. The stimulated emission cross section for the4F3/2 → 4I11/2 transition was calculated to be 4.24 × 10−20 cm2. Thermal and optical properties have shown that Nd:BaLaGa3O7 crystals are potential alternative gain media for ultrafast lasers.

Optical, dielectric and ferroelectric properties of KTa0.63Nb0.37O3 and Cu doped KTa0.63Nb0.37O3 single crystals

KTa0.63Nb0.37O3 and Cu doped KTa0.63Nb0.37O3 single crystals were grown by the Czochralski method. The phase, optical and electric properties were characterized. The differences of XRD and color for KTa0.63Nb0.37O3 and Cu doped KTa0.63Nb0.37O3 single crystals are observed. Emission bands corresponding to Cu0 and Cu+ except of emission bands originating from KTa0.6Nb0.4O3 host were observed in the emission spectra of the KTa0.63Nb0.37O3:Cu single crystals. On the basis of these differences, we speculate the dominating existence of Cu0 and residual existence of Cu+ in KTa0.63Nb0.37O3 single crystal. The existence of Cu0 in KTa0.63Nb0.37O3 single crystal influences the optical and dielectric properties of crystal. The higher dielectric constant of Cu doped KTa0.63Nb0.37O3 single crystal than that of pure KTa0.63Nb0.37O3 single crystal is induced by the decrease of the resistance of the grain.

Low-temperature synthesis of KTa0.55Nb0.45O3 powders and thin films via metal-organic solution

Potassium tantalite niobate powders and thin films were synthesized via metal-organic solution. The synthesized powders and thin films have a tetragonal phase with the perovskite structure. The powders show a cubic shape with sizes in the range of 120–230xa0nm. The emission spectrum of powders shows emissions peaked at 413, 451 and 468xa0nm, related to the electron-hole recombination of localized exciton Ta4+–O1− and Nb4+–O1− in a regular octahedron (TaO6 and NbO6). The polarization-electric field hysteresis loop of thin films is rectangular. The current–voltage characteristic of thin films shows a feature of linear to nonlinear transition, which is related to the space-charge-controlled mode of electrical conduction in solids.

Synthesis and characteristics of KTa0.5Nb0.5O3 thin films

KTa0.5Nb0.5O3 thin films were synthesized via a metal-organic solution. Characteristics were measured, such as X-ray diffraction pattern, surface morphology and roughness, and electric properties. The synthesized films have a (100) preferential growth orientation on Si (100) substrate. The homogeneous microstructure and smooth surface benefit to the good electric properties of the thin films. The current density-voltage characteristic shows an unexpected feature of the transition from linear to nonlinear, which can be explained by the space-charge-limited mode. Dielectric constant and loss of the thin films decrease with the increase of frequency. The decrease of dielectric loss is related to the decrease of net polarization in material. The decrease of dielectric constant can be explained by Debye formula. The phase transition temperature Tc is about 102xa0°C for KTa0.5Nb0.5O3 materials.