Key Engineering Materials Vols. 602-603

Abstract: Polycrystalline Ti-Co co-substituted M-type ferrites Ba (TiCo)_xFe_12-2xO₁₉ (x=0.25,0.5, 0.75, 1.0 ) samples were prepared by the citrate precursor method. The particle structure and morphology of the products were characterized by X-ray powder diffraction (XRD) and Field Emission Scanning Electron Microscope (FE-SEM). The effects of the substitution rate on the magnetic properties of samples were analysed by magnetic measurement with the Vibrating Sample Magnetometer (VSM) of Physical Properties Measurement System (PPMS). The XRD patterns show that only one type of crystalline phase can be detected and the substitution did not change the crystal structure. The SEM micrographs of Ba (TiCo)_xFe_12-2xO₁₉ calcined at 450 °C for 5h, and then 950°C for 5h show that the M-type ferrite particles were homogeneously shaped and the grain sizes had no obvious differences when the substitution rate changed. The magnetic hysteresis loops illustrate that the coercivity (Hc) decreased rapidly with the increasing of Ti-Co substitution, while the saturation magnetization (Ms) changed slowly.

Abstract: Transition metal (TM) doped NiO is a promising candidate of p-type oxide diluted magnetic semiconductors (DMSs), which shows obvious room-temperature ferromagnetism. When researching the magnetic properties of DMSs, it is very important to get rid of ferromagnetic impurity phases by optimizing the preparation process. For this purpose, pure NiO thin films have been deposited by a pulsed laser deposition method and annealed by different annealing process. As-deposited or low-temperature annealed films show room-temperature ferromagnetism and high-temperature annealed films are not ferromagnetic. Nickel metal should be the origin of ferromagnetism in these thin films. On the other hand, high annealing temperature influences the microstructure of the film surface a lot. These results show a useful method to eliminate ferromagnetic impurity in NiO thin films and to optimize the preparation parameters of TM doped NiO thin films.

Abstract: In the present paper, the sintering behavior and the THz absorption properties of B₂O₃ doped Ca [(Li_1/3Nb_2/3)_0.95Zr_0.15]O₃ (CLNZ) ceramics are investigated. The results indicate that the sintering temperature of CLNZ ceramic can be significantly lowered by the doping of B₂O₃. The crystal structure evolution, phase assemblage as well as the microstructure properties are investigated by XRD and SEM respectively. The sintering mechanism is investigated based on microstructure analysis, where the liquid phase sintering is proposed to control the whole sintering process. The relative density of the B₂O₃ doped CLNZ ceramics possess the optimum value when the B₂O₃ doping content x is 1.5wt%. The THz absorption properties of B₂O₃ doped CLNZ ceramics sintered at 1020°C are investigated and are related to the microstructure, phase assemblage and crystal structure factors.

Abstract: In this work, zinc sulfide (ZnS) thin films were prepared by radio frequency (RF) magnetron sputtering on glass substrates. The effects of sputtering power, working pressure, substrate temperature and annealing treatment on the structural and optical properties of ZnS films were studied using X-ray diffraction and UV-visible spectrometer in detailed.

Abstract: The hybridization of graphene with oriented ZnWO₄ photocatalysts effectively enhanced the photocatalytic activity. The enhancement in photocatalytic performance was relied on the amount of graphene and the optimal hybridized amount of graphene was about 2 wt%. The photocatalytic activity was increased by about 3 times after ZnWO₄ was hybridized with graphene under UV irradiation. The enhancement mechanism of the photocatalytic activity is attributed to the higher separation efficiency and the inhibition of recombination of photoinduced electron-hole pairs.

Abstract: Spectral selectivity absorber is a key component in the solar collectors, which absorbs solar energy and converts it to thermal energy by heating liquid water. Metal nanowire arrays (NWAs) have potential to be used as solar collector because of good optical absorption in the visible region. In the paper, we use finite-difference time-domain (FDTD) solutions to calculate the optical absorption and spectral selectivity of nickel (Ni) NWA/AAO composites. By changing the length (L), fill-factor (FF), and surface roughness, we simulate the optical absorption and the spectral selectivity in terms of structural parameters of Ni NWA/AAO composites. Results demonstrate that Ni NWA/AAO composites with the length of 2 μm and the fill-factor of 0.13 (the diameter is 0.04 μm) have good optical absorption and spectral selectivity,and rough surfaces is better for higher conversion efficiency of Ni NWA/AAO composites.

Abstract: This work presents a novel approach for preparing Cu-loaded TiO₂ nanotube arrays through alternating current electrodeposition. The Cu content loaded on the arrays was controlled by changing the concentration of Cu (NO₃)₂ solution, deposition voltage and time. The surface morphology and crystal structure of Cu-loaded TiO₂ nanotube arrays were characterized by scanning electron microscopy (SEM) and the X-ray diffraction (XRD). The effects of Cu content on the photoelectrochemical property were studied in detail. Results show that Cu-loaded TiO₂ nanotube arrays have evidently enhanced photoelectrochemical activity. The photocurrent of Cu-loaded TiO₂ nanotube arrays prepared in 0.00625 mol/L Cu (NO₃)₂ solution at 12 V for 20 seconds was 5.7 and 2.3 times as that of unloaded TiO₂ nanotube arrays under visible and UV radiation, respectively.

Abstract: In this work, sodium tantalate (NaTaO₃) microrods were successfully prepared by anodic oxidation of tantalum in 30% NaOH electrolyte. The morphology and structure of microrods were characterized by scanning electronic microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. SEM analysis shows the formation of microrods with an average length of 12.8 μm and a diameter of 2.3 μm. XRD analysis reveals that the as-prepared microrods are amorphous. After annealing in nitrogen at 800 °C, the amorphous NaTaO₃ microrods transform into orthorhombic structure. Experimental results indicate that the microrods have a high photoelectrochemical property. The possible formation mechanism of NaTaO₃ microrods has also been discussed.

Abstract: In the present work, the light-emitting property of silicon coating was explored and the related morphologies and chemical structure of silicon coating were characterized. Silicon coating was prepared by vacuum plasma spray technique and chemically treated by HNO₃/HF vapor. The coatings before and after the vapor etching were characterized by field emission scanning electron microscopy and micro-raman spectroscopy. The photoluminescence spectra of the silicon coatings treated with different time were examined. It is found that pores of micrometer and microcracks formed on the surface of silicon coatings after the treatment. The treated silicon coatings exhibited room temperature visible photoluminescence with emission wavelength around 650 nm after excitation. The results of micro-raman measurement proved that there were polysilane and oxygen related functional groups appeared on the coating surface after the vapor treatment, which was supposed to be responsible for the photoluminescent phenomena.

Abstract: Gold nanorods with different aspect ratios, exhibiting localized surface plasmon resonance in a tuned longitudinal mode, were prepared by employing a seed mediated growth approach. Their third-order nonlinear optical properties were investigated by using femtosecond Z-scan technique at 800 nm. All the prepared gold nanorods with different aspect ratios exhibited a reverse saturation absorbance behavior, and the value of effective nonlinear absorption coefficient reaches its maximum when the longitudinal surface plasmon resonance peak of the gold nanorods located near the excitation wavelength.