Papers by Author: Xiao Lin Liu

Abstract: Bismuth ferrite (BFO), one of very few multiferroics with simultaneous coexistence of ferroelectric and magnetic ordering, has attracted much attention due to its potential applications for new memory devices. In this work, 30~90 nm BFO powders with single rhombohedral phase were prepared by chemical coprecipitation method and after calcining of 500oC. Photocatalytic properties of the powders and dielectric properties of BFO ceramic were characterized, respectively. Cut-off wavelength of the powders at 590 nm exhibited efficient ultraviolet photocatalytic activity, which has been demonstrated by a photocatalytic result. 0.3g BFO powders can make 10 ppm RhB aqueous solution (100 ml) to decolorize and RhB decomposition rate reached to 95% during 3 hr UV irradiation. BFO ceramic can be obtained by sintering the green disc compacted with BFO powders at 800oC for 1h. Its dielectric constant is t about 250, and its dielectric loss is 0.03 at below 100 oC in the frequency range of 102 ~ 104 Hz and up to 1200 at 200 oC under 1 kHz, respectively. Reduced polarization is found due to higher loss and lower dielectric constant of the ceramic when the measuing frequency is more than 104 Hz. Magnetic hysteresis loop of BFO ceramic also shows weaker magnetic property, which may be attributed to size confinement effect of the nanostructures.

Abstract: Sintering behavior of pure and Nb-doped barium titanate powders prepared by high-gravity reactive precipitation (HGRP) process was investigated. A thermal dilatometer was employed to monitor the sintering shrinkage continuously during sintering. TEM and SEM were used to characterize the microstructures of the samples. The experimental results confirmed that Nb-doped BaTiO3 ceramics sintered at 1220°C for 2 h reached a larger densification of 97.0% relative density compared with 94.6% of pure BaTiO3 ceramics sintered at 1265°C for 2 h, and Nb-doped BaTiO3 ceramics had a smaller grain size (1.2μm) than that of pure BaTiO3 ceramics (2μm).

Abstract: In this work, a sub-micron grained sized (<500nm) ceramic (> 92% of theoretical) has been obtained using nano-sized BaTiO3 powders synthesized through a high-gravity reactive precipitation (HGRP) process. Permittivity of the prepared ceramic is greater than 2500. Also, low change ratio of temperature in the range of −55°C~ 125°C
i.e.< ±15% renders the ceramic to meet the EIA X7R characteristics. In the ceramic compositions, Dy2O3, BaCO3, CaCO3, MnCO3 and MgO were used as dopants. After being mixed and dry-pressed, the above mentioned compositions in reducing atmosphere (N2 and 5% H2) were sintered at 1210°C−1290°C for 2h, respectively. Experimental results show that HGRP BaTiO3 powders have good dielectric properties. The dielectric properties as well as the microstructure of the ceramic are both sensitive to the change of sintering temperature.

Abstract: Precursors of calcium strontium zirconate (Ca0.8Sr0.2ZrO3) were synthesized by oxalate coprecipitation method. TG-DTA was used to characterize the thermal decomposition behaviors of the precursors. The XRD results revealed that the powders crystallized as cubic Ca0.8Sr0.2ZrO3 with increasing heating temperature up to 1000°C. Calcium strontium zirconate ceramics were obtained under conventional sintering conditions by using the as-prepared Ca0.8Sr0.2ZrO3 powders. The SEM micrographs of the ceramics sintered at 1450oC exhibited narrow grain-size distribution with the average grain size around 0.7 4m. The dielectric properties showed that, dielectric constant of the Ca0.8Sr0.2ZrO3 was about 24.0 and dielectric loss was 0.002 at the frequency of 1GHz and the room temperature.

Abstract: The sensitivity of CuO dispersed on fluorite-type oxide, namely CeO2 was studied in this work. Mixed oxide sample of nanostructured CuxCe1-xO2-y of various composition were generated by step chemical precipitation method. Distinct copper species were identified as a function of copper content by X-ray photoelectron spectroscopy, X-ray powder diffraction, the special surface areas, transmission electron microscopy, scanning electron microscopy analysis, and sensing properties to CO. It was found that only small amounts of copper are sufficient to promote the sensitivity of CeO2 by several orders of magnitude, which excessive amounts of copper (Cu/(Cu+Ce)>0.12) are detrimental to the sensing properties of nanocompositions. The possible causes for this behavior are also discussed.

Abstract: The dielectric properties and sintering activity of nano-BaTiO3 powders synthesized by HGRP method were investigated. The starting BaTiO3 powders were calcined at different temperatures from 700 to 900°C to improve their crystallinity and the mean particle size of BaTiO3 powders obtained increased from 40nm to 80nm. After being formed by conventional dry pressing the green bodies were sintered at 1100°C and 1200°C for 2hr in air. The effects of both calcinating and sintering temperatures on the sinterability, dielectric property and microstructure of BaTiO3 ceramics were discussed. The experimental results showed that the BaTiO3 powders have high sintering activity and the highest dielectric constant of this material at room temperature may reach 2880.

Abstract: Sintering behavior and mechanism of barium titanate powders prepared by high-gravity reactive precipitation (HGRP) process has been investigated by a dilatometer. The mean particle size of barium titanate powders prepared by HGRP was about 80 nm. Pure BaTiO3 pellets were sintered at a constant heating rate of 2.0 K/min and the temperature of shrinkage-onset for pellet was 1060°C. The maximal shrinkage was 165um and the maximum of shrinkage rate was 8.0 x 10-3 / min at 1170°C. The sintering mechanism for the initial stages of sintering was determined by isothermal dilatometric measurements and was found to be viscous flow.

Abstract: Nano-sized barium titanate powders were prepared by the high-gravity reactive precipitation (HGRP)-hydrothermal method. The properties and defects of hydrothermal barium titanate crystallites were investigated by TEM, XRD and FTIR. The mean particle size of the hydrothermal barium titanate was about 70 nm with narrow particle size distribution. The crystallite phases and OH defects were focused. The results show that the powders without heat treatment were crystallized as cubic-BaTiO3 and the absence of tetragonal with increasing calcined temperature to 1100°C. The IR results exhibited the OH defect content in the crystallites was to increase the heat treatment temperature and reduced the probability of forming barium vacancies.