Changku Sun

Structure study of single crystal BaTiO3 nanotube arrays produced by the hydrothermal method

High aspect ratio BaTiO(3) nanotube arrays with single crystal structure were fabricated by the hydrothermal method at low temperature (150 degrees C). Numerous structure study methods, including x-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS), were used to investigate the structure of single crystal BaTiO(3) nanotube arrays. TEM observation shows that BaTiO(3) nanotubes have identical crystallographic orientation through their growth directions. EPR and XPS studies show that the obtained BaTiO(3) nanotubes contain perceptible oxygen vacancies. Those oxygen vacancies are responsible for the observed green emission band at 545 nm (2.27 eV) detected by photoluminescence study.

Ferroelectric PbTiO3 nanotube arrays synthesized by hydrothermal method

Lead titanate nanotube arrays with perfect nanotubular structure and excellent piezoelectric property were formed by hydrothermal method. The nanotubular structure proved to have strong influences on both Curie temperature and piezoelectric properties of PbTiO3 nanotube arrays. The Curie temperature of PbTiO3 nanotube arrays was detected to be 620°C. Perfect piezoelectric properties with a maximum displacement of 0.88nm and d33* of 120pmV−1 were observed in PbTiO3 nanotube arrays.

Photoluminescence of ZnO nanorod-TiO2 nanotube hybrid arrays produced by electrodeposition

The fabrication and structure characterization of ZnO nanorod-TiO2 nanotube hybrid arrays are reported. ZnO nanorods were electrodeposited onto the TiO2 nanotubes to form nanorod-nanotube hybrid arrays. Scanning electron microscopy showed that the ZnO nanorods were tightly grown together with TiO2 nanotubes. And the as-prepared ZnO nanorods have single crystal structures, which were grown along the [0001] direction. Both photoluminescence (PL) signals of ZnO nanorods and TiO2 nanotubes were observed in the PL spectrum of hybrid arrays. The observed PL signals of ZnO nanorods with visible broadband emission were induced by structure-dependent defects in ZnO nanorods.

Phase transition in BaTiO3 nanotube arrays

Temperature dependence of phase composition and phase transition in the BaTiO3 nanotube arrays were examined by x-ray diffraction and Raman analyses. The BaTiO3 nanotube arrays exhibited a distinct phase transition behavior from −190 to 300 °C. Tetragonal phase was found to coexist with cubic phase in the BaTiO3 nanotube arrays above Curie temperature. The inner stress as well as size effect in the BaTiO3 nanotube arrays is responsible for the diffuse ferroelectric phase transition and the formation of multiphases coexistence at high temperature.

Stress induced Curie temperature shift in high-aspect ratio PbTiO3 nanotube arrays

High-aspect ratio PbTiO3 nanotube arrays with a length of 20 μm were synthesized by hydrothermal method. Curie temperature of the specimen (at about 620 °C) was found to be dispersive and much higher than PbTiO3 bulks. Ferroelectric to paraelectric phase transition in the high-aspect ratio PbTiO3 nanotube arrays was studied by Raman scattering and XRD. The nanotubular structure plays an important role in optimizing the stress distribution in the nanotube arrays. It was found that optimized two-dimensional compressive stress was responsible for the shift of Curie temperature in PbTiO3 nanotube arrays.

Low-Temperature Sintering of Negative?Positive-Zero-Type Temperature-Stable Ceramics with ZnO?B2O3 Flux and SrCO3 Additive

To demonstrate that tungsten–bronze-based NP0 (negative–positive zero, also called C0G) specification ceramics can be sintered at a low temperature to reduce the cost of capacitor production, systematic investigation has been performed on the structure and dielectric properties of such ceramics doped with SrCO3 in various amounts and ZnO–B2O3 powders of different compositions as sintering aids. A novel dielectric ceramic material with good permittivity, low dielectric loss, and a near-zero temperature coefficient was obtained at a sintering temperature of 900 °C, meeting NP0 specifications. The analysis reveals the pyrochlore phase formation of the low-temperature-fired ceramics with no SrCO3 addition, which verifies the beneficial role of Sr in facilitating the production of pure phases. The results also suggest that the ceramics serve as a promising candidate for fabricating inexpensive multilayer capacitors with pure Ag as the inner electrode.