Search

Abstract The 0D-1D Lithium titanate (Li4Ti5O12) heterogeneous nanostructures were synthesized through the solvothermal reaction using lithium hydroxide monohydrate (Li(OH)·H2O) and protonated trititanate (H2Ti3O7) nanowires as the templates in an ethanol/water mixed solvent with subsequent heat treatment. A scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM) were used to reveal that the Li4Ti5O12 powders had 0D-1D heterogeneous nanostructures with nanoparticles (0D) on the surface of wires (1D). The composition of the mixed solvents and the volume ratio of ethanol modulated the primary particle size of the Li4Ti5O12 nanoparticles. The Li4Ti5O12 heterogeneous nanostructures exhibited good capacity retention of 125 mAh/g after 500 cycles at 1C and a superior high-rate performance of 114 mAh/g at 20C.

Pyrochlore Bi2(Zn1/3Ta2/3)2O7 (BZT) films were prepared by pulsed laser deposition on Pt/TiO2/SiO2/Si substrates. In contrast to bulk monoclinic BZT ceramics, the BZT films have a cubic structure mediated by an interfacial layer. The dielectric properties of the cubic BZT films [[variant_greek_epsilon]∼177, temperature coefficient of capacitance (TCC) ∼-170 ppm/°C] are much different from those of monoclinic BZT ceramics ([variant_greek_epsilon]∼61, TCC ∼+60 ppm/°C). Increasing the thickness of the BZT films returns the crystal structure to the monoclinic phase, which allows the dielectric properties of the BZT films to be tuned without changing their chemical composition. [ABSTRACT FROM AUTHOR]

Aluminum-doped ZnO (AZO) films were epitaxially grown on sapphire (0001) substrates using pulsed laser deposition. As-deposited AZO films had a low resistivity of 8.01×10-4 Ω cm. However, after annealing at 450 °C in air, the electrical resistivity of the AZO films increased to 1.97×10-1 Ω cm because of a decrease in the carrier concentration. Subsequent annealing of the air-annealed AZO films in H2 recovered the electrical conductivity of the AZO films. In addition, the conductivity change was reversible upon repeated air and H2 annealing. A photoluminescence study showed that oxygen interstitial (Oi′) is a critical material parameter allowing for the reversible control of the electrical conducting properties of AZO films. [ABSTRACT FROM AUTHOR]

Abstract: Tunable Ba6Ti2(Nb1−x Ta x )8O30 (BTN-xTa; x =0, 0.25, 0.4) thin films with a tetragonal tungsten bronze structure (TTB) were deposited on platinized Si substrates using the pulsed laser deposition (PLD) technique and their properties were investigated from the viewpoint of orientation and ferroelectric phase transition. Crystal structures and dielectric properties were characterized using an X-ray diffractometer and an impedance analyzer. Pure BTN (BTN-0Ta) thin films showed tunability as high as 60% and the tunability decreased as the amounts of Ta-substitution increased at 150kV/cm and at 1MHz. The dielectric constants also decreased from 436 to 88 at 1MHz through the Ta-substitution. The low tunability and dielectric constants of Ta-substituted thin films were mainly ascribed to the lowered ferroelectric transition temperature (T c). Ferroelectric BTN (BTN-0Ta) thin films may have been changed into a paraelectric state through the Ta-substitution since the T c of BTN thin films were shifted to temperatures far below room temperatures (approximately −60°C). [Copyright &y& Elsevier]

BiFeO3 (BFO) nanopowders were synthesized at low temperatures via a hydrothermal process with the aid of triethanolamine (TEA) and their structural, optical, and photocatalytic properties were investigated. As a result of a strong reaction between TEA and Fe ions, pure BFO nanopowders without any secondary phases could be synthesized at temperatures as low as 130°C. BFO nanopowders exhibited a strong absorption in the visible-light regime, which resulted in the efficient photocatalytic activity for decomposition of organic compounds. [ABSTRACT FROM AUTHOR]

Abstract: Eu2+-doped BaAl2O4 green phosphors were prepared by a conventional solid-state reaction and the effects of Dy3+ co-doping on the photoluminescence property were investigated. The phosphors were characterized by X-ray powder diffraction (XRD), fluorescence spectroscopy, field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD showed that all prepared samples exhibited a hexagonal BaAl2O4 phase. Fluorescence spectroscopy showed that the photoluminescence efficiency increased with increasing Eu2+ concentration until 3mol% then decreased at higher concentrations due to concentration quenching effect. Moreover, Dy3+ co-doping increased the photoluminescence efficiency of the Eu2+-doped BaAl2O4 phosphor. [Copyright &y& Elsevier]

We demonstrated the formation of monodispersed spherical aluminum hydrous oxide precursors with tunable sizes by controlling the variables of a forced hydrolysis method. The particle sizes of aluminum hydrous oxide precursors were strongly dependent on the molar ratio of the Al(3+) reactants (sulfates and nitrates). In addition, the systematic phase and morphological evolutions from aluminum hydrous oxide to γ-alumina (Al(2)O(3)) and finally to α-Al(2)O(3) through thermal dehydrogenation were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). After annealing the amorphous aluminum hydrous oxide in air at 900 °C and 1100 °C for 1 h, we observed complete conversion to phase-pure γ- and α-Al(2)O(3), respectively, while maintaining monodispersity (125 nm, 195 nm, 320 nm, and 430 nm diameters were observed). Furthermore, both γ- and α-Al(2)O(3) were found to be mesoporous in structure, providing enhanced specific surface areas of 102 and 76 m(2) g(-1), respectively, based on the Brunauer-Emmett-Teller (BET) measurement., (This journal is © The Royal Society of Chemistry 2011)

Epitaxial anatase thin films were grown on single-crystal LaAlO3 substrates by a sol-gel process. The epitaxial relationship between TiO2 and LaAlO3 was found to be [100]TiO2||[100]LaAlO3 and (001)TiO2||(001)LaAlO3 based on X-ray diffraction and a high-resolution transmission electron microscopy. The epitaxial anatase films show significantly improved photocatalytic properties, compared with polycrystalline anatase film on fused silica substrate. The increase in the photocatalytic activity of epitaxial anatase films is explained by enhanced charge carrier mobility, which is traced to the decreased grain boundary density in the epitaxial anatase film.