Yunxiang Hu

Optical characteristics of GaAs nanowire solar cells

The reflectance, transmittance, and absorptance of GaAs nanowire (NW) arrays are calculated by solving Maxwells equations using the finite element method. The model is compared with measurement results from well-ordered periodic GaAs NW arrays fabricated by dry etching. The model results are also compared with the reflectance measured from NWs grown by the Au-assisted vapor-liquid-solid method. The optimum NW diameter, periodicity (spacing between NWs), and length are determined to maximize absorptance of the AM1.5G solar spectrum and short circuit current density in a NW array solar cell. The optimum NW diameter, period, and length were 180 nm, 350 nm, and 5 μm, respectively, giving a photocurrent density from the NW of 27.3 mA/cm2 and corresponding to 91.3% absorption of the AM1.5 G solar spectrum. The photocurrent density saturated for NW lengths greater than 5 μm. A gold nanoparticle at the top of the NWs (used in the vapor-liquid-solid NW growth process) substantially reduced the optimum photocurren...

Influence of TiO2/Sb2O3 ratio on ZnO varistor ceramics

Abstract The influence of TiO2/Sb2O3 (Ti/Sb) ratio on the microstructure development and electrical properties of varistor ceramics in ZnO–(Bi2O3–TiO2–Sb2O3)–CoO–MnO2 system was investigated. Characterization of varistors was performed by XRD, SEM, d.c. degradation behavior, and electrical measurements. It is found that the Ti/Sb ratio greatly influences the microstructure and electrical properties of the ZnO varistor. The specimen with Ti/Sb ratio of 5 has the lowest breakdown field (20V/mm) and improved d.c. degradation behavior.

Synthesis and characterization of NiP-TiO2 ultrafine composite particles

Ultrafine particles TiO2-NiP were successfully synthesized by an electroless plating technique. TEM and XRD were used to characterize the particles’ morphology and composition.

Grain-oriented sodium bismuth titanate-based lead-free piezoelectric ceramics prepared using the pulsed strong magnetic field and template grain growth

In this paper, 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNBT6) lead-free piezoelectric ceramics have been prepared using the gelcasting technology. The dielectric and piezoelectric properties of these ceramics have been investigated. The specimens were sintered at 1100–1200 °C after grain-oriented under the pulsed strong magnetic field during the solidification of the green bodies. Compared with the BNBT6 samples without applying magnetic field, the ceramics textured by applying 5 T pulsed magnetic field has a coercive field with reduction of 400 V/mm, which makes the polarization process easier. Meanwhile, it is noted that the orientation degree increases with increasing sintering temperature, whereas the piezoelectric constant and electromechanical coupling coefficients are improved. If SrTiO3 seed grain is introduced, the orientation degree can reach 0.70 and the relative density of the sintered ceramics is up to 96%. The dielectric properties are anisotropic in directions vertical and parallel to the applied ma...

Microstructure and properties of low-voltage ZnO varistor ceramics

The influences of pre-firing process and sintering temperature on the microstructure and electrical properties of ZnO-Bi2O3-TiO2-Sb2O3-MnO2-CoO low-voltage varistor ceramics were studied. Especially, twin boundaries and exaggerated grain growth (EGG) were observed here, and the mechanism of EGG was discussed. It seems that the formation of twin boundaries has a correlation with Sb2O3 content and sintering temperature, and that twin boundaries have a great influence in grain growth of ZnO.

The properties of RE-TM magneto-optical films

Abstract In this paper, the magnetic, magneto-optical and galvonomagnetic properties, and their temperature dependence for LRE-TM SmCo, SmCoDy and HRE-TM TbFeCo magneto-optical films as high density recording media prepared by rf magnetron sputtering or evaporation are reported. By adding Dy to SmCo thin film, the SmCoDy thin film is more suitable for magneto-optical recording, its domain size being below 0.63 μm. The Kerr enhancement and corrosion protective effects of AIN and AlSiN for optimum design of the multi-layer structure of magneto-optical disk are described. The instruments of measuring the magneto-optical Kerr effect and magneto-optical recording domain characteristics of thin films are reviewed.

Stability of BaTiO3 aqueous suspensions with PVA-b-COOH

The present paper studied the stability and rheological behavior of BaTiO3 aqueous suspensions with block copolymers of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PVA-b-COOH) as dispersants. The effects of polymerization degree of PVA group, content of acid group, and the dispersant concentration on the stability were investigated by means of sedimentary and rheological experiments. The stabilization mechanisms were discussed.

Kerr effect enhancement and corrosion resistance improvement by AlN and AlSiN films (abstract)

RE‐TM amorphous thin films with perpendicular magnetic anisotropy are promising for use in erasable optical recording media. In order to improve the drawback of easy oxidation and lower C/N of RE‐TM films, some protective layers such as SiO, SiO2, ZnS, AlN, and Si3N4 films were studied.1,2 We have studied the Kerr effect enhancement and corrosion resistance improvement by AlN and AlSiN films. AlN and AlSiN films were prepared on glass, PC, and PMMA substrates by a rf magnetron sputtering system with three targets using low sputtering power. The films have a high refractive index (2–2.15), high optical transparency (over 90%), and high stability. The relation between optical properties and rf reactive sputtering conditions (Ar: N2 ratio, total pressure, sputtering power, sputtering time), composition, spectral transmittance, and uniformity of sputtering AlN and AlSiN films were studied. The Kerr rotation angle was up to 1.5° in AlN/TbFeCo/glass and AlSiN/TbFeCo/glass multilayer structures (laser is inciden...

Growth and characterization of all-inorganic lead halide perovskite semiconductor CsPbBr3 single crystals

As a typical representative of all-inorganic lead halide perovskites, cesium lead bromide (CsPbBr3) has attracted significant attention in the context of photovoltaics and other optoelectronic applications in recent years. In this paper, CsPbBr3 single crystal growth was conducted by a creative electronic dynamic gradient (EDG) method. The crystal structure was systematically investigated using scientific instruments and equipment. X-ray diffraction techniques, including X-ray diffraction (XRD), temperature-dependent X-ray powder diffraction and the X-ray rocking curve, were used to identify the phase and to investigate phase transition rules. Electron diffraction techniques, including high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and electron backscatter diffraction (EBSD), were used to investigate the crystal micro-structure. The final results indicated that the grown CsPbBr3 crystal was a perfect single crystal preferentially orienting in the (110) direction and met the basic demand of its applications.

Influences of the electroless nickel electrode on the electrical characteristics of BaTiO3-based PTCR ceramics

Abstract This paper investigated the influences of the microstructure of electroless nickel electrode on the a.c. shock characteristics of BaTiO3-based PTCR ceramics and the degradation and failure of PTC thermistors with electroless nickel electrode. In the experiments, we coated metal nickel electrode on the surface of PTCR ceramics samples by employing the different electroless plating baths and analyzed the microstructure of electroless nickel electrodes by SEM. The experimental results indicated that the various baths made the microstructure of nickel electrodes different. The nickel electrodes from acid bath possessed the densified stacked structure, which resulted in being cracked when being shocked by 220 V, 3 A a.c. power; owing to having sparse branch-and-tendril structure, those from alkaline bath had no effects on the ceramics samples being shocked. The work came to the conclusion that the microstructure of electroless nickel electrodes varied the thermal stress in the body of PTCR ceramics. In addition, the a.c. shock characteristics of BaTiO3-based PTCR ceramics were related to the content of phosphorus in the electroless nickel-phosphorus alloy and thickness of the nickel electrodes. According to the experiments, the thickness of the electroless nickel alloy should be less than 1 μm and the phosphorus content, 4 wt.% in the alloy.