Zhiyuan Ling

A simple method for fabrication of highly ordered porous α-alumina ceramic membranes

By taking anodic aluminum oxide membranes as the starting materials and selectively removing the outer layers from the unit cells of anodic aluminum oxide membranes after a proper hydrothermal treatment, highly ordered porous α-alumina ceramic membranes are fabricated successfully. This fabrication method might be a new approach for the preparation of α-alumina ceramic membranes with nanochannel-array architecture not only at the submicron scale but also at the nanometer scale. The obtained membranes are anticipated to become a new generation of filters and supports for catalysts or absorbents, and have wide applications in the fields of nanomaterial synthesis, biology and electronic devices.

Controlling Transmission Spectra of Photonic Crystals under Electrochemical Oxidization of Aluminum

The transmission spectra for photonic crystal in anodic alumina have been investigated with the periodic anodization voltage function, including the time, periodicities, and voltage. The shift of the transmission dips can be related to the current density-time curve. The intensity of the diffraction light in anodized alumina is determined by the branched channel, including the length and the pore diameter, and the periodicities. The width of the transmission dip is affected by the distribution of the distance between the two branched channels and the variety of the pore diameter from the initial to the bottom of the film. Photonic crystal of anodized alumina for the optimized function of voltage is obtained with the 4.7% transmission intensity at 735 nm of the transmission dip and 89.3% transmission intensity at 900 nm.

Tuning Optical Properties of Photonic Crystal of Anodic Alumina and the Influence of Electrodeposition

In this paper, the tuning optical properties in a photonic crystal of an anodic alumina were investigated together with the influence of the metal electrodeposition on the photonic crystal with an Al substrate. The transmission spectra of the photonic crystal show the redshift of the transmission dip with increasing anodic voltage and the blueshift of the color with observable angles obeying the Bragg law. The electrodeposited metal layer strongly absorbs the reflecting light from the Al substrate, and it makes the photonic crystals with an Al substrate show vivid colors.

Electrical conduction of intrinsic grain and grain boundary in Mn-Co-Ni-O thin film thermistors: Grain size influence

Mn1.85Co0.3Ni0.85O4 (MCN) thin films with pure spinel phase and different grain size were prepared on Al2O3 substrates by chemical deposition method. Temperature dependent ac impedance spectroscopy was employed to analyze the grain size influence on the electrical conduction of intrinsic grain and grain boundary (GB) in MCN thin films. The conduction mechanisms of grain and GB both followed the small-polaron hopping model. It was found that the hopping types of GB (nearest-neighbor-hopping (NNH)) and grain (a transition from variable-range-hopping (VRH) to NNH) were not affected by the grain size, while the resistance, characteristic temperature, and activation energy of grain and GB were affected by the grain size in varying degrees. Additionally, the mechanisms concerning the dependence of electrical conduction of grain and GB on the grain size of MCN thin films were discussed in detail. These studies will also provide a comprehensive understanding of the conduction behaviors of a system with mixed NNH ...

Unique AAO films with adjustable hierarchical microstructures

Anodic aluminium oxides (AAO) films with adjustable hierarchical microstructures were synthesized via a simple unsteady state anodization process. Moreover, novel nano-/submicron-/micron-porous AAO films can be obtained by further film removal and low voltage anodization processes.

The Role of Stress in the Self-Organized Growth of Porous Anodic Alumina.

Ridges and depressions were formed on the barrier layer during chemical and physical etching of porous anodic alumina (PAA) from the bottom side, indicating nonuniform etching rate around each cell. These behaviors cannot be explained solely by the well-known composition variation, but were in line with the hexagonal distribution of stress within the barrier layer of each cell. Such stress variation should be attributed to the interactions of neighboring cells undergoing volume expansion. These interactions could account for the self-organization of PAA.

Microstructure evolution and electrical property improvement of Mn-based thin film thermistors with the sandwich structure

Mn1.85Co0.3Cu0.3Ni0.55O4 (MCCN), Mn1.85Co0.3Ni0.85O4 (MCN) thin film and MCN–MCCN–MCN sandwich structural thermistors were prepared on Pt/TiO2/Ti/SiO2/Si substrates by sol–gel technique. The crystalline structure, surface and cross-sectional morphologies of the prepared thermistors were analyzed by XRD and FESEM, respectively. The electric properties, such as the resistivity-temperature behaviors, sensitivity, stability, and dielectric constant, were investigated in detail. Compared with the MCCN and MCN thin film thermistors, the MCN–MCCN–MCN sandwich structural thermistor showed good microstructure, low resistivity, high sensitivity, small aging coefficient and moderate dielectric constant. The results showed that the multi-layer structure was an effective way to improve and adjust the properties of NTC thin film thermistors.

Evolution of depolarization temperature of PLZT from normal to relaxor ferroelectrics

Lead lanthanum zirconate titanate (PLZT x/59/41) ceramics with x from 0 to 6.5 mol. % are synthesized by the traditional solid-state reaction method. The temperature dependences of dielectric and resonant responses are used to characterize the depolarization processes of poled samples. It is found that the temperature of anti-resonance frequency minima (Tmin-a) accords completely with dielectric loss peak temperature (Tloss). The Tloss instead of anomalous dielectric peak temperature (Td*) can be regarded as depolarization temperature (Td). The Td* deviated from the Tloss suggests that the depolarization process in all the samples includes two stages: domain decoupling and polarization disorientation. With La content increasing, the Tloss decreases and the temperature difference ΔT between Tloss and dielectric peak temperature (Tm) increases nearly linearly. Since all studied samples have similar depolarization and freezing processes and the 0 mol. % La sample behaves like a normal ferroelectric, here we suggest that there may be no essential difference in depolarization process between relaxor and normal ferroelectrics.Lead lanthanum zirconate titanate (PLZT x/59/41) ceramics with x from 0 to 6.5 mol. % are synthesized by the traditional solid-state reaction method. The temperature dependences of dielectric and resonant responses are used to characterize the depolarization processes of poled samples. It is found that the temperature of anti-resonance frequency minima (Tmin-a) accords completely with dielectric loss peak temperature (Tloss). The Tloss instead of anomalous dielectric peak temperature (Td*) can be regarded as depolarization temperature (Td). The Td* deviated from the Tloss suggests that the depolarization process in all the samples includes two stages: domain decoupling and polarization disorientation. With La content increasing, the Tloss decreases and the temperature difference ΔT between Tloss and dielectric peak temperature (Tm) increases nearly linearly. Since all studied samples have similar depolarization and freezing processes and the 0 mol. % La sample behaves like a normal ferroelectric, here we ...

Effective Sintering Aids of Boric Frit and Lithium Salts for Low-Temperature Sintering of Dielectric Ceramics

The sintering temperature of the dielectric ceramics had been lowered more than 300°C with 1.5 ∼ 6wt% combination additives of boric frit and lithium salts in present work. The combined effect of the additives of boric frit and lithium salts could be applied on different structures, such as a perovskite structure (SrTiO 3 ,CaZrO 3 ), a new tungsten bronze-type structure (Ba 4.5 Nd 9 Ti 18 O 54 ) and other structures (Ba 2 Ti 3 Nb 4 O 18 , Ba 3 Ti 4 Nb 4 O 21 ). Low loss (tanδ ∼10−4) dielectrics with a variety of dielectric constant (30∼300) were obtained in the systems of Ba-Ti-Nb-O, Sr-Ti-O, Ca-Zr-O and Ba-Nd-Ti-O with the boric frit and lithium salts sintered at 900∼1000°C.