Advanced Materials Research Vols. 105-106

Abstract: The new type PbTiO3 based ceramic conductive powders were prepared with a special technology, gaseous penetration, which is making rare earth La penetrate into PbTiO3 powders in the gaseous state at high temperature. Through XRD analysis, it is found that there are some new compounds such as LaTiO3 and LaTi3O49 formed after penetration of La, which indicates that the gaseous penetration made La element enter PbTiO3 powders and the complex reactions took place during the penetration process. Through SEM, it can be deduced that the rare earth elements occupied the atom vacancies, formed the new phases and made the grains of La-penetrated PbTiO3 based powders become smaller and finer with less pores and appeared as dispersing structure. All these led to a significant change in electric conductivity, and when the La3+ content in the solvent was 0.02, the penetration temperature was 950°C and the penetration time was 4h, the resistivity at room temperature was the smallest, which decreased from 8.3×108Ω.m to 8.2×10-4Ω•m.

Abstract: BaTiO3 powders modified with Sm, La, Cu, Al, Zn were prepared by solid doping and gaseous penetration method and their components, structure, superficies and electric properties were characterized. The results show that the resistivity of the modified powders is decreased after both solid doping and gaseous penetration, and it is more obviously after gaseous penetration. Among all the metals being discussed, Sm has the most significant influence on decreasing the resistivity of modified powders. The room temperature resistivity of Sm-penetrated BaTiO3 powders is the lowest, which decreases from 8.3×1010Ω•m (pure BaTiO3 powders) to 1.65×105Ω•m. SEM investigation illustrates that the powders are in uniform grain size. No apparent pores and small grains are found. XRD analysis indicates that the doping process only leads to the changes of the peak width and intensity without new phases appearing, but characteristic peaks of Sm2TiO5, SmTiO3, and Ba10.37Sm17.08Ti36O108 can be detected after gaseous penetrated, which leads to the decrease of the resistivity of modified BaTiO3 powders.

Abstract: Sm2O3 optical thin film is a new photovoltaic material and has potential applications in optical switches, date recording device and magnetic device. Using samarium dichloride as raw material, Sm2O3 optical thin films were prepared by sol-gel and hydrothermal process on glass and Si (100) substrates. The phase compositions, morphologies and optical properties of the as-prepared thin films were analyzed by X-ray diffraction (XRD), atomic force microscope (AFM) and UV-vis spectrophotometer (UV-vis). Results show that the Sm2O3 thin films prepared by sol-gel method exhibit an obvious (110) orientation growth on glass substrates, while the Sm2O3 thin films prepared with hydrothermal method have no obvious orientation. The as-prepared films have excellent absorbency of UV light and are transparent to visible light. The band gap of the Sm2O3 films prepared by hydrothermal method is narrower than that of those obtained by sol-gel method. The absorbency of UV light and transparence to visible of the Sm2O3 films prepared by sol-gel method are obviously improved in comparison with those deposited by hydrothermal process.

Abstract: Zinc sulphide (ZnS) thin films were deposited on the indium tin oxide (ITO) substrates by a novel, simple cathodic electrodeposition method under atmospheric pressure. These thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence spectrum (PL) at room temperature. The effects of deposition voltage on the phase composition, morphology and photoluminescence behavior of the thin films were investigated. XRD analysis shows that the deposited thin films is highly preferential growth along (200) orientation. Both AFM and XRD analyses indicate that the surface of the ZnS thin films is composed of uniform grains of around 50 nm in diameter. With the increase in the deposition voltages, the crystallization of the obtained thin films improves and the grain size of the ZnS thin films increases. Photoluminescence emission peaks are observed at at 475~490 nm and 500 ~530 nm at room temperature for an excitation of 210 nm.

Abstract: Self-propagating high-temperature synthesis with reduction process was used to fabricate LaB6 ceramic powder from La2O3-B2O3-Mg system. The combustion reaction carried out in inert atmosphere (Ar) and the combustion temperature was about 1600°C. The products were washed with dilute hydrochloric acid and distilled water, respectively, to remove LaBO3, Mg3B2O6, MgO and other impurities. The influence of compact pressure and addition of SHS diluent on the grain size was studied. The result indicates that as the compact pressure increased, the mean size of powder decreased gradually. The addition of diluents reduced the synthesis temperature, and as the amount of diluent increased, the grain size of LaB6 powder was found to reduce continuously. Microstructure analyses show that the mean grain size of LaB6 powder prepared by SHS with reduction process is less than 500 nm, which is finer compared with the grain size prepared by traditional process.

Abstract: To prevent the potential cracking of gel fibers, La modified lead zirconate titanate (PLZT) ceramic fibers with diameter within 50µm were achieved by embedding into PLZT powders during the heat treatment. Then the 1-3 PLZT fiber/interpenetrating polymer network (IPN) piezoelectric composites were prepared by casting the IPN precursors onto the well aligned ceramic fibers. The influences of the heating temperatures and La amounts on the dielectric constant, dielectric loss with frequencies and piezoelectric constant of PLZT were investigated in detail. The morphologies of fibers and composites were observed by biological microscope. And also, the dielectric constant of PLZT fibers and PLZT fiber/IPN piezoelectric composites were detected.

Abstract: Green phosphor of La(BO3, PO4): Ce, Tb was synthesized by means of sol-gel method and conventional solid state method. The thermal formation process was characterized by thermogravimetric analysis (TG) and (DTA). The effects of synthesis method and conditions on the crystal and morphological structure were investigated by (XRD) and (SEM). The results revealed that La (BO3, PO4): Ce, Tb phosphors with monocline structure and high purity were successfully prepared by sol-gel method. Compared with solid state method, the products synthesized by sol-gel method presented well developed crystal structure, small particle size, narrow size distribution and high luminescent performances. The product synthesized at 1050°C for 2h had better emission intensity.

Abstract: Titania nanotube arrays were fabricated by anodic oxidation of a pure titanium foil. The morphology, structure and optical properties of the nanotube arrays were characterized by SEM, XRD and UV-Vis spectrum. The effect of anodic oxidation parameters on the morphology was investigated. The growth mechanism of the titania nanotube arrays was discussed. The results show that the vertical oriented TiO2 nanotube arrays can be obtained at 20V for 60min in 0.5wt%HF+1mol/L H3PO4 solution. The aperture size of nanotube is 60nm~80nm and the thickness of tube wall is about 10nm. The spectral absorptivity of TiO2 nanotube arrays membrane calcined at 600°C towards ultravlolet light 349.7nm and visible light 443.9nm was relatively higher. It is also found that the crystal structure is greatly affected by calcining temperature.

Abstract: In this study, SnO2-based ceramics, with CuO as sintering aid and Sb2O3 as activator of the electrical conductivity, was obtained by pressure-less sintering at 1100°C ~ 1470°C. Addition of antimony leads to a higher densification temperature. Densification behavior and microstructure development are strongly dependant on CuO and Sb2O3. CuO gives rise to a liquid phase; Sb2O3 retards the formation of liquid phase and hinders the growth of grain. The electrical resistivities of SnO2-based ceramics vary in a wide range from 10-2 to 107 Ω•cm, depending on starting compositions and processing conditions. The electrical resistivities of samples with different amounts of CuO and Sb2O3 show different trends with the increasing of sintering temperature. The addition of antimony rapidly promotes electrical conductivity of SnO2-based ceramics containing CuO as the solid solution reaction of Sb2O3-SnO2. As the additions of CuO and Sb2O3 are the same, the electrical resistivity arrives the minimal value of 4.72×10-2 Ω•cm for 99%SnO2+0.5%CuO +0.5%Sb2O3 at 1470°C. More content of Sb2O3 than CuO causes the degression of density and the rising of electrical resistivity of ceramics.

Abstract: Effect of NaAc on the anodic growth of TiO2 nanotube arrays is described. NaAc-added approach yields longer nanotubes relative to samples grown from NaAc-free electrolyte. And the growth rate of TiO2 nanotubes has pH independency in NaAc-added electrolytes. The key to achieve a high aspect ratio TiO2 nanotube arrays is to decrease the chemical dissolution rate at the mouth of the tube by adding NaAc as protective coating. Adsorption of Ac- species on the TiO2 surface is shown to markedly decrease the chemical dissolution rate of the tube mouth, resulting in longer nanotube length.