Jikang Jian

Structure and phase transition of BiFeO3 particles prepared by hydrothermal method and the verification of crystallization–dissolution–crystallization mechanism

The optimal synthesis temperature of BiFeO3 is found. The cube BiFeO3 powders have a hexagonal perovskite structure with a space group R3c, while the sphere-like BiFeO3 powders have a rhombohedral structure with a space group R3m. The growth mechanism of crystallization–dissolution–crystallization has been summarized and verified. The effect of the reaction time on the particle size in hydrothermal synthetic experiment is studied. The magnetic properties of samples prepared under different alkali concentration have been measured by vibrating sample magnetometer. It is indicated that the samples with different morphologies exhibit different magnetic properties. A reasonable explanation for this phenomenon has been given in this paper.

Preparation of CdTe nanostructures with different crystal structures and morphologies

CdTe nanorods and various branched nanostructures with different crystal structures were have successfully prepared via the catalyst-assisted vacuum thermal evaporation (CVTE) technique using various experimental parameters. SEM and XRD studies were carried out on the as-prepared CdTe nanostructures. The results show that the morphologies and crystal structures of the products were strongly influenced by the growth conditions and the mole ratios of Bi and CdTe. In the high mole ratio (0.08:1) of Bi and CdTe, CdTe branched nanostructures of CdTe were obtained, while nanorods of CdTe were formed at a lower mole ratio of 0.05:1. The crystal structure of products is either Zinc blende or a two-phase mixture of zinc blende and wurtzite. The content of the wurtzite phase were found to increase with increasing growth temperature. Our results also reveal that high growth temperature tends to form the wurtzite phase, and stacking faults may exist in materials grown in higher temperatures. These nanostructures grow following the vapor–liquid–solid (VLS) mechanism.

Synthesis and characterization of micron-size pyrite crystals

Mixed solvent of ethanol and water using FeSO 4 ⋅7H 2 O and (NH 2 ) 2 CS as precursors with polyvinylpyrrolidone as surfactant was used to synthesize cubic FeS 2 (pyrite) crystals. Crystalline phase and surface morphologies of the crystals were characterized by X-ray diffraction and scanning electron microscopy, respectively. Volume ratio of solvent, reaction temperature, reaction time, and sulfur source were found to be the key parameters for the formation of pure pyrite crystals. Optimal micron-size pyrite crystals were successfully grown from a mixed solvent of ethanol and water with a volume ratio of 3:2, heated to a reaction temperature of 180 °C, and maintained for 36 h with thiourea as the sulfur source.

Synthesis of Ultra-long TiO2 Microrods via Molten Salt Method

A facile strategy has been developed based on a molten salt method to prepare the ultra-long TiO2 microrods. The materials are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) and UV-visible spectroscopy (UV-vis). The SEM studies show microrods composed of ultra-long TiO2 microrods length up to 200–500 μm, with uniform dispersal and chemically homogeneous, high-purity feature. The PL spectra exhibits three distinct features originated from direct transition from the conduction band to the valence band and oxygen vacancies. The bandgap is deduced to be 3.08eV from absorbance spectra.