Hydrothermal routes to various controllable morphologies of nanostructural lithium aluminate

The α-LiAlO₂ powders have been successfully prepared by a hydrothermal route based on using the surfactant of heax-adecyltrimethyl ammonium bromide (CTAB) as the template. One-dimensional (1D) nanorods with higher and lower aspect ratio, 2D mesoporous microsheets were respectively observed with different concentration of the surfactants. A high specific surface area up to 151 m²/g was obtained by this method. The formation mechanism of the nanostructural lithium aluminate was proposed.     

Formation and control of mechanism for the preparation of ultra-fine barium strontium titanate powders by the citrate precursor method

A modified citrate precursor method, combining the advantages of the nitrate autocombustion method by introducing the nitric acid, was successfully used to synthesize ultrafine Ba_0.70Sr_0.30TiO₃ powders. Slight agglomerated and homogenized BST powders, with an average particle size of 20 nm, were obtained at 800 °C. Combining the results of TG/DTA and XRD, it can be concluded that the formation of BST powders takes place via two reaction mechanisms: decomposition of an intermediate oxycarbonate mechanism (DIOm) at low temperature, and solid-state reaction mechanism (SSRm) between nanocrystalline carbonates and amorphous TiO₂ at high temperature. TEM shows higher amount of CA led to BST powders of better quality in morphology. Based on results of chemical analysis, it is suggested that higher amount of CA drives the mechanism to tend to DIOm. By simply adjusting the ratio of reagents, the reaction mechanism can be dominated and we can greatly control the final morphology of the powders.     

Solvothermal Synthesis, Structure and Optical Property of Nanosized CoSb(3) Skutterudite

Binary skutterudite CoSb₃ nanoparticles were synthesized by solvothermal method. The nanostructuring of CoSb₃ material was achieved by the inclusion of various kinds of additives. X-ray diffraction examination indicated the formation of the cubic phase of CoSb₃. Structural analysis by transmission electron microscopy analysis further confirmed the formation of crystalline CoSb₃ nanoparticles with high purity. With the assistance of additives, CoSb₃ nanoparticles with size as small as 10 nm were obtained. The effect of the nanostructure of CoSb₃ on the UV–visible absorption and luminescence was studied. The nanosized CoSb₃ skutterudite may find application in developing thermoelectric devices with better efficiency.     

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO2 nanopowders

Mesoporous anatase TiO₂ nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3-4 nm. The specific BET surface area of the as-synthesized sample was about 193 m²/g. Mesoporous anatase TiO₂ nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO₂, nanofibers TiO₂ mesoporous TiO₂, and commercial TiO₂ nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using the mesoporous anatase TiO₂ was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm², the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm², Voc of 0.704 V and ff of 0.649.     

OPAA template-directed synthesis and optical properties of metal nanocrystals

Ag and Cu nanocrystals (NCs) were assembled into ordered porous anodic alumina (OPAA) by a single-potential-step chronoamperometry technique. The composition, morphology, microstructure, and optical property were analyzed by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and optical absorption spectroscopy. The results indicate that metallic NCs/OPAA composite possesses a significant surface plasmon resonance absorption. For continuous electrodeposition, metallic nanowires are smooth and uniform with face-centered cubic (fcc) single-crystalline structure; however, for interval electrodeposition, the nanowires are bamboo-like or pearl-chain-like with fcc polycrystalline structure. The length of the nanoparticle nanowires or the single-crystalline nanowires can be controlled well by adjusting the experimental cycle times or the continuous depositing time. The transverse dipole resonance of metallic NCs enhances and displays a blue shift with increasing electrodeposition time or experimental cycle times, which is consistent with Zong''s results but contradictory to Duan''s results. The formation mechanisms of the nanoparticle nanowires and the single-crystalline nanowires were discussed in detail.     

Synthesis of nanocrystalline magnesium titanate by an auto-igniting combustion technique and its structural, spectroscopic and dielectric properties

Nanocrystalline magnesium titanate was synthesized through an auto-ignited combustion method. The phase purity of the powder was examined using X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and Raman spectroscopy. The transmission electron microscopy study showed that the particle size of the as-prepared powder was in between 20 and 40 nm. The nanopowder could be sintered to 98% of the theoretical density at 1200 °C for 3 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant (?_r) of 16.7 and loss factor (tan δ) of the order of 10⁻⁴ were obtained at 5 MHz when measured using LCR meter. The quality factor (Q_u × f) 73,700 and temperature coefficient of resonant frequency (τ_f) −44.3 ppm/°C, at 6.5 GHz are the best reported values for sintered pellets obtained from phase pure nanocrystalline MgTiO₃ powder.