Zhang Jia-Liang

First Principles Study on Electronic Structure of PbFe0.5Nb0.5O3

The full potential linearized augmented plane wave (FLAPW) method is used to study the crystal structure and electronic structure properties of PbFe0.5Nb0.5O3 (PFN). The optimized crystal structure, density of states, band structure and electron density distribution have been obtained to understand the ferroelectric behaviour of PFN. The analysis result of the density of states shows there is an obvious change of Nb d states in the paraelectric-to-ferroelectric phase transition. The polarization result shows that the contribution to ferroelectricity of Nb atoms is larger than that of Fe atoms. In ferroelectric phase there is a hybridization of Fe d–O p and Nb d–O p in ferroelectric PFN. This is consistent with the result of the electronic band structure. This hybridization is responsible for the tendency to its ferroelectricity.The full potential linearized augmented plane wave (FLAPW) method was used to study the crystal structure and electronic structure properties of PbFe0.5Nb0.5O3 (PFN). The optimized crystal structure, density of states, band structure and electron density distribution have been obtained to understand the ferroelectric behavior of PFN. From the density of states analysis, it is shown that there is a hybridization of Fe d - O p and Nb d - O p in ferroelectric PFN. This is consistent with the calculation of electronic band structure. This hybridization is responsible for the tendency to its ferroelectricity.

Atmospheric Pressure Cold Argon/Oxygen Plasma Jet Assisted by Preionization of Syringe Needle Electrode

An atmospheric pressure nonequilibrium argon/oxygen plasma jet assisted by the preionization of syringe needle electrode discharge is reported. With the syringe needle plasma as its pre-ionization source, the hybrid barrier-jet was shown to generate uniform discharge with a lower breakdown voltage and a relatively low gas temperature varying from 390 K to 440 K, even when the vol.% oxygen in argon was up to 6%. Utilizing the actinometry method, the concentration of atomic oxygen was estimated to be about in an orders of magnitude of 1017 cm−3. The argon/oxygen plasma jet was then employed to clean out heat transfer oil, with a maximum cleaning rate of 0.1 mm/s achieved.

Atmospheric Pressure Plasma Jet in Ar and O2/Ar Mixtures: Properties and High Performance for Surface Cleaning

An atmospheric pressure plasma jet generated in Ar and O2/Ar mixtures has been investigated by specially designed equipment with double power electrodes at 20~32 kHz, and their effects on the cleaning of surfaces have been studied. Properties of the jet discharge are studied by electrical diagnostics, including the waveform of discharge voltage, discharge current and the Q-V Lissajous figures. The optical emission spectroscopy is used to measure the plasma parameters, such as the excitation temperature and the gas temperature. It is found that the consumed power and the excitation temperature increase with increase of the discharge frequency. On the other hand, at the same discharge frequency, these parameters in O2/Ar mixture plasma are found to be much larger. The effect on surface cleaning is studied from the changes in the contact angle. For Ar plasma jet, the contact angle decreases with increase of the discharge frequency. For O2/Ar mixture plasma jet, the contact angle decreases with increase of discharge frequency up to 26 kHz, however, further increase of discharge frequency does not show further decrease in the contact angle. At the same discharge frequency, the contact angle after O2/Ar mixture plasma cleaning is found to be much lower compared to the case of pure Ar. From the results of quadrupole mass-spectrum analysis, we can identify more fragment molecules of CO and H2O in the emitted gases after O2/Ar plasma jet treatment compared with Ar plasma jet treatment, which are produced by the decomposition of surface organic contaminants during the cleaning process.

An Indirect Method for Measuring Electron Density of Atmospheric Pressure Plasma Jets

An indirect method for measuring the electron density of radio frequency atmospheric pressure plasma jets (RF-APPJ) based on the discharge voltage and current waveforms is presented. An equivalent circuit of the plasma discharge is assumed by taking into account the electrode capacitance, serial resistance and inductance of the bulk plasma, as well as the sheath impedance. Based on the circuit model, the electron density can be obtained according to Ohms law. By using this method, the effects of the electrode shape and discharge gap on the electron density are discussed.

Diagnosis of Electron, Vibrational and Rotational Temperatures in an Ar/N2 Shock Plasma Jet Produced by a Low Pressure DC Cascade Arc Discharge

In this paper, a low pressure Ar/N2 shock plasma jet with clearly multicycle alternating zones produced by a DC cascade arc discharge has been investigated by an emission spectral method combined with Abel inversion analysis. Plasma emission intensity, electron, vibrational and rotational temperatures of the shock plasma have been measured in the expansion and compression zones. The results indicate that the ranges of the measured electron temperature, vibrational temperature and rotational temperature are 1.1 eV to 1.6 eV, 0.2 eV to 0.7 eV and 0.19 eV to 0.22 eV, respectively, and it is found for the first time that the vibrational and rotational temperatures increase while the electron temperature decreases in the compression zones. The electron temperature departs from the vibrational and the rotational temperatures due to non-equilibrium plasma effects. Electrons and heavy particles could not completely exchange energy via collisions in the shock plasma jet under the low pressure of 620 Pa or so.

The Effect of High-Pressure Arc Discharge Plasma on the Degradation of Chlorpyrifos

A study is conducted to determine the effect of a kind of high-pressure arc discharge plasma on the degradation rate and kinetic equations of chlorpyrifos in different solvents with the treated times and concentrations as variables. The degradation rate was sorted in different solvents as water, methanol, acetone and then acetoacetate. The tendencies of the degradation rates with treated time in water and methanol were optimally fitted with first-order kinetics equations while those in acetone and acetoacetate were fitted with zeroth-order kinetics equations. The difference was attributed to the stronger polarity of water and methanol. The weak correlation of the degradation rates with time was mainly because the high-temperature of the arc discharge tube and the chemically-active species generated by the discharge. The degradation half-life was extended with increase of chlorpyrifos concentration. A degradation half-life less than 3 min was achieved for chlorpyrifos in water and methanol when the initial concentration was less than 300 μg/ml.

Discharge Modes Suggested by Emission Spectra of Nitrogen Dielectric Barrier Discharge with Wire-Cylinder Electrodes

In this paper, nitrogen dielectric barrier discharge (DBD) plasma was generated in a quartz tube with coaxial wire-cylinder electrodes at atmospheric pressure. By varying the nitrogen gas flow (FN) in the range of 0-1 m3/h, the plasma optical emission spectra (OES) were measured and studied. The vibration (Tvib) and rotation temperature (Trot) of nitrogen were obtained, by fitting the rovibronic bands of N2(C3Πu – B3Πg, 0-1), and by the Boltzmann plot method for purposes of comparison. Tvib increased up to 2481 K with increasing nitrogen flow till 0.2 m3/h, and then decreased with further increasing FN, while Trot decreased monotonously and approached to ~350 K for FN ≥ 0.6 m3/h. The intensity of N2(C3Πu – B3Πg, 0-0, 1-0, 0-3) and N2+ (B2Σu+ – X2 Σ+g, 0-0) exhibited similar evolution with increasing FN to those of the Tvib and Trot, respectively. The discharge photos revealed that the discharge filaments gradually decreased with increasing FN, and eventually disappeared, which implied that a discharge mode transition emerged with increasing FN. The possible mechanism for the discharge mode transition is studied in detail according to the vibration (Tvib) and rotation temperature (Trot) of nitrogen.

Structure evolution of positive column striations in DC glow discharge

DC glow discharges were achieved in nitrogen, argon and helium with a specially structured quartz tube fitted by two planar electrodes, to study the formation and evolution of positive column striations. By changing the discharge conditions such as discharge current and gas pressure, the striation spatial structure varied obviously and evolved gradually. In the paper, the gas pressure, gas flow velocity and discharge current were altered deliberately to study evolution of the striations. The luminance photos of striations were recorded by a scientific camera and then the luminance intensity distribution of striations was figured out by using self-developed image processing scheme to show the striation structure. The resulted striation structure shows perfect spatial periodicity. The striation wavelength is constant with constant discharge, although the luminance peaks of striations attenuate from cathode to anode. In view of discharge in nitrogen, the structure characteristics of striations (striation wavelength and attenuation coefficient) were investigated quantitatively by scanning discharge current, pressure and gas flow velocity. The results told us that striation wavelength risen linearly with the logarithm of the discharge current while it varied slightly with pressure and was hardly related with gas flow velocity.

Feasibility of Trace Alcohol Congener Detection and Identification Using Laser-Induced Breakdown Spectroscopy

In this paper, a feasible scheme is reported for the detection and identification of trace alcohol congeners that have identical elemental composition using laser-induced breakdown spectroscopy (LIBS). In the scheme, an intensive pulsed laser is used to break down trace alcohol samples and the optical emission spectra of the induced plasma are collected for the detection and identification of alcohol molecules. In order to prepare trace alcohol samples, pure ethanol or methanol is bubbled by argon carrier gas and then mixed into matrix gases. The key issue for the scheme is to constitute indices from the LIBS data of the alcohol samples. Two indices are found to be suitable for alcohol detection and identification. One is the emission intensity ratio (denoted as H/C) of the hydrogen line (653.3 nm) to the carbon line (247.9 nm) for identification and the other is the ratio of the carbon line (as C/Ar) or the hydrogen line (as H/Ar) to the argon lines (866.7 nm) for quantitative detection. The calibration experiment result shows that the index H/C is specific for alcohol congeners while almost being independent of alcohol concentration. In detail, the H/C keeps a specific constant of 34 and 23 respectively for ethanol and methanol. In the meanwhile, the C/Ar and H/Ar indices respond almost linearly to the alcohol concentration below 1300 ppm, and are therefore competent for concentration measurement. With the indices, trace alcohol concentration measurement achieves a limit of 140 ppm using a laser pulse energy of 300 mJ.

高密度CaCu 3 Ti 4 O 12 陶瓷的介电性质

利用热压方法制备了高密度的CaCu 3 Ti 4 O 12 陶瓷, 研究了其微观结构、晶格结构和介电性质。实验发现, 短时间热压方法制备的陶瓷的相对密度就能达到98.3%, 并且微观结构呈现晶粒尺寸双峰分布的特点。XRD显示热压方法制备的陶瓷中含有少量的Cu 2 O第二相, 而经过退火处理的热压陶瓷则只含有CuO第二相。热压方法制备的陶瓷和经过退火处理的热压陶瓷的室温介电频谱上有两个介电弛豫, 而常规方法制备的陶瓷只有一个。并且热压方法制备的陶瓷的低频介电常数高达2×10 5 , 经过退火处理的热压陶瓷的低频介电常数更是达到1×10 6 。本研究进一步讨论了其微观结构和介电性质之间的关系。利用热压方法制备了高密度的CaCu 3 Ti 4 O 12 陶瓷, 研究了其微观结构、晶格结构和介电性质。实验发现, 短时间热压方法制备的陶瓷的相对密度就能达到98.3%, 并且微观结构呈现晶粒尺寸双峰分布的特点。XRD显示热压方法制备的陶瓷中含有少量的Cu 2 O第二相, 而经过退火处理的热压陶瓷则只含有CuO第二相。热压方法制备的陶瓷和经过退火处理的热压陶瓷的室温介电频谱上有两个介电弛豫, 而常规方法制备的陶瓷只有一个。并且热压方法制备的陶瓷的低频介电常数高达2×10 5 , 经过退火处理的热压陶瓷的低频介电常数更是达到1×10 6 。本研究进一步讨论了其微观结构和介电性质之间的关系。