Shao Hua Luo

The Role of Niobium in (Ca, Si, Ce, Nb)-Doped TiO2 Varistors

The present work attempted to investigate the effect of Nb addition on the electrical properties of the (Ca,Si,Ce,Nb)-doped TiO2 ceramics. The content of added niobium is in the range 0.1-1.0mol %, while that of the other additives keeps constant. The results showed that an optimal composition doped with 0.8mol% Nb2O5, followed by sintering at 1350°C, was obtained with low V1 mA of 7.22V, high nonlinear coefficient of 5.76, ultrahigh dielectric constant (er = 86000) as well as relatively low loss (tgd = 0.52) in room temperature at 1 kHz. SEM studies show that change of niobium had significant influence on grain growth and micro structural characteristics of the sintered samples.

Effects of Glass Frits on the Properties of Luminescent Ceramics

Sr4Al14O25: Eu2+, Dy3+ luminescent ceramics with high brightness and long afterglow were prepared using glass frits as binders by sintering at lower temperature and air atmosphere. The effects of glass frits on the properties of luminescent ceramics were discussed. The analytical results indicate that the surface structure and adhesion with phosphor are influenced by glass frits and sintering temperature. When sintered at 850°C, the samples with frit1 or frit2 obtained good surface morphology and good adhesion. The sample with frit2 sintered at 850°C yielded the better surface morphology and good adhesion. The sample with frit1 sintering at 850°C possessed the better luminescent properties.

Spinel Li4Ti5O12/C Composites as Potential Anode Materials of Lithium Batteries

Here the spinel Li4Ti5O12/C composites were prepared by a modified high temperature solid-state reaction. The as prepared Li4Ti5O12/C composites showed enhanced electrochemical lithium insertion performance in reversible capacity and rate capabilities. The improved electrochemical properties are attributed to the reduced grain size and the improved electronic conductivity caused by the pyrolytic carbon incorporated into the spinel Li4Ti5O12 particle. The spinel Li4Ti5O12/C composites with improved electrochemical properties may find versatile applications in various energy storage devices.

Surface Modification of Long Afterglow Sr4Al14O25: Dy,Eu Phosphor by Silica Coating

In order to improve water resistance of phosphors and the stability of particles in aqueous suspensions, the phosphor particles were coated with varying amounts of silica via the hydrolysis of tetraethyl orthosilicate. The composite particles were characterized by transmission electron spectroscopy, BET N2 gas adsorption, sedimentation time studies and fluorescent spectrometer. The specific surface area of the silica-coated phosphor particles showed a non-systematic increase. In comparison to the uncoated phosphor (3.65m2/g), silica coatings of 13, 25, 50, 75wt% yielded specific surface areas of 15.19, 14.29, 37.90 and 226.12 m2/g respectively. This behavior can be explained based on a heterocoagulation coating mechanism in which silica clusters adsorb onto the phosphor particles surface. The sedimentation data display the stability of the coated particles improved as the silica content increased. The excitation and emission spectra show that the luminescent properties of the phosphors are unimpaired or even better. The optimum luminescent properties obtained when coating 50wt% silica after calcining at 400oC.

Improvement of Electrochemical Properties of LiFePO4/Carbon Composite Doped by Al3+ Ions

LiFePO4/Carbon composite doped by Al 3+ ions was prepared by solid-state reaction process, and the structure and electrochemical properties of the resultant products were investigated. Olivine structure of the composites at different dopant content was discovered by XRD patterns. No oxidation and reduction of iron element on the surface of powder were confirmed by XPS spectrum. Raman spectra and cyclic voltammetry curves indicate that Al ions have entered LiFePO4 lattice and resulted in crystalline defects of lithium vacancy (V′Li). Owing to the presence of V′Li, lithium ion diffusion speed was enhanced significantly. By utilization of lithium vacancy and carbon coating, superior electrochemical properties of composite at room temperature was achieved.

Improvement of the Electrochemical Performance of LiFePO4 Cathode Composite Material Using a In Situ Pyrolysis Carbon Synthesis Procedure

LiFePO4/Carbon composite cathode material was prepared by pelleting and subsequent pyrolytic cracking process in N2 atmosphere with carbon source of polyvinyl alcohol (PVA). XRD crystal analysis indicates that single LiFePO4 phase and amorphous carbon can be found in the products. SEM observation shows a special micro-morphology of sample, which is favorable for enhancement of electrochemical properties. The discharge capacity of the LiFePO4/C composite was 135 mAh/g, close to the charge capacity of 153 mAh/g at low rate of 0.1C. At 0.2C, the specific capacity was about 117.4 mAh/g, which is satisfied for power source of Electric Vehicle for its flat discharge platform.

Effect of La2O3 and CeO2 on Nb2O5 Doped TiO2 Ceramic Varistors

The influence of La2O3 and CeO2 on a new class of polystalline ceramics with electrical properties based on TiO2 was investigated. The content of added La and Ce is in 1 at%, while that of the other addition is always maintained at a constant value. The disks were sintered at 13800C for 4 hours. La2O3 was found to precipitate at the grain boundaries, probably inducing electronic interface states that can trap charges at the TiO2-TiO2 interface and lead to significantly increase the nonlinear behavior. The values for α (» 4.2) and V1mA(» 26 V) support that finding. It was found CeO2 that as a dopant did not strongly influence the nonlinear values of the systems as did La2O3, indicating that it could have formed a solid-state solution with TiO2 in the grains, but did not segregate sufficiently at the grain boundaries. In present work, impedance analyzer, X-ray spectrometer, and scanning electron microscope (SEM) were used.

Effect of Li+ and Mn2+ Doping on the Electrical Properties of SrTiO3-Based Varistor Ceramics

Effect of Li+ and Mn2+ doping on the electrical properties of SrTiO3-based varistor ceramics was investigated. The results showed that the varistor ceramics cannot possess ideal electrical properties when only Li+ or Mn2+ was doped. However, when Li+ and Mn2+ were properly doped together, the samples acquired excellent electrical properties: V1mA = (5.7 ~ 11.7)V/mm; α = 6.8 ~ 11.0; er = (2.4 ~ 4.4) × 105; tan d = (7.1 ~ 10.4)%. When the contents of Li2CO3 and MnCO3 were 1.00 mol% and 0.05 mol% respectively, the nonlinear coefficient α reached the largest value of 11.0. Compared with only Mn2+ doping, the addition of Li+ increases the α value significantly.