Papers by Author: Bo Ping Zhang

Abstract: High density BaTiO₃ ceramics have been prepared by the addition of CuO-Bi₂O₃-B₂O₃ mixed oxide. The results indicate that the sintering temperature of BaTiO₃ bulk can be decreased by about 300°C and high dielectric behavior can be remained. The CuO-Bi₂O₃-B₂O₃ additives can increase the breakdown strength, and leads to an obvious enhancement of the energy density, which is nearly 2 times of pure BaTiO₃.

Abstract: Li-doped (Na, K)NbO₃ lead-free piezoelectric ceramics with nominal composition of [Li_0.065(Na_0.535K_0.48)_0.95]NbO₃ were prepared by normal sintering method, and its phase structure, microstructure and electric properties were studied with a special emphasis on the influence of sintering temperature in the range of 950-1020 oC. The result of XRD analysis indicates that a polymorphic phase transition (PPT) separating orthorhombic and tetragonal phases was found at the temperature of 950 oC, whereby enhanced piezoelectric properties of d₃₃=255 pC/N and k_p= 44.5% were obtained although the density was low. Our study indicates that the importance of PPT for enhancing electric properties in niobate-based ceramics at low temperature.

Abstract: LixTixNi1-2xO (x =0, 10 and 20 at. %) thin films with 200 nm in thickness were deposited on Pt/Ti/SiO2/Si (100) by a sol-gel spin-coating method. All samples have a uniform microstructure. The grain sizes grew from 100 nm to 300 nm by co-doping Li and Ti. The LiTiNiO thin films consist of NiO, NiTiO3 and Li2NiO2, while the Li-free thin films consist of NiO, NiTiO3 and NiTi0.99O3. The dielectric properties of the LiTiNiO thin films improved obviously by co-doping Li and Ti, but excess Li increases the amount of Li2NiO2 phase and decreases the dielectric properties. The dielectric constants at 100 Hz for the Li0.1Ti0.1Ni0.8O and Li0.2Ti0.2Ni0.6O thin films are 506 and 388 respectively. Appropriate co-doping contents of Li and Ti are important to obtain a high dielectric property.

Abstract: Nanometer La2CuO4 particles have been prepared using chemical precipitation method. The reaction mechanism, microstructure and phase composition of the samples were investigated by TG-DTA, XRD, SEM. The XRD results showed that pure La2CuO4 phase can be obtained by calcining the La-Cu-O-H precursor powders at 900 oC for 2 h, and the impurity phase will appear in the La2CuO4 ceramic as increasing the sintering temperature over 1200 oC. La2CuO4 ceramic samples sintered at 950 oC for 6 h exhibit good thermoelectric properties. Seebeck coefficient can reach 714 μV/K, and power factor is about 2.33×10-5 W/mK2.

Abstract: Li and Ti co-doped NiO thin films with 200 nm in thickness were deposited onto Pt/Ti/SiO2/ Si(100) substrates using a sol-gel spin-coating method. The effect of Ti doping content on microstructure and dielectric properties of Li0.10TixNi0.90-xO (x=5-20mol%) thin films was investigated. XRD results showed that all the Li0.10TixNi0.90-xO thin films consisted of a mixture of NiO, Li2NiO2 and NiTiO3 oxides. The intensities of the diffraction peaks for the NiTiO3 phase increased and those for NiO decreased with increasing Ti content, suggesting that a part of NiO phase combined with Ti to form NiTiO3 phase. The dielectric constants of all the Li0.10TixNi0.90-xO thin films at 102 Hz at room temperature ranged from 200 to 400 and increased with increasing Ti content. The frequency stability of the dielectric constant for the Li0.10TixNi0.90-xO thin films was also improved greatly with increasing Ti content.

Abstract: LiTiNiO thin films were deposited on Pt/Ti/SiO2/Si(100) substrates using a sol-gel spin-coat method. The effects of annealing temperature and annealing time on microstructures and dielectric properties of the thin films were investigated. SEM images showed the thin films had uniform and dense microstructure and the grain size increased with increasing temperature and time. The LiTiNiO thin films consisted of complex oxides which proportions were mainly dependent on the annealing condition. The LiTiNiO thin film annealed at 600°C for 1h showed the highest dielectric constant and frequency stability, while prolonging annealing time even at 600°C resulted in the decrease in the frequency stability of the dielectric constants.

Abstract: Au/SiO2 nano-composite multilayer thin films with different thickness were prepared on a quartz substrate by magnetron plasma sputtering. The microstructure, morphology and optical properties of the films were investigated by using TEM and optical absorption spectra. [Au/SiO2]×5 and [Au/SiO2] × 11 multilayer thin films have well-defined interface. The thickness of the multilayer was 60nm and 130 nm for the thin films with 5 and 11 layers, respectively. The optical absorption peaks due to the surface plasma resonance appeared at a wavelength of 560 nm for the both [Au/SiO2]×5 and [Au/SiO2]×11 thin films. The intensity of the absorption peak increased with increasing numbers of deposition layers. The optical absorption spectra of Au/SiO2 multilayer thin films are well agreement with the theoretical optical absorption spectra calculated from rewritten Maxwell–Garnett effective medium theory.

Abstract: Single-phase polycrystalline CoSb3 skutterudite was prepared through a new combination of mechanical alloying (MA) and spark plasma sintering (SPS). In order to investigate the influence of MA conditions on the microstructure and thermoelectric properties, MA synthesis were carried out under various conditions with different milling times. The powder sample MAed for 6h still consisted of metal Sb, and then transformed to CoSb3 with a little amount of metal Sb and CoSb2 phases after MA for 15h. Further prolonging the MA time resulted in the decomposition of CoSb3 to CoSb2 phase. The average grain size of the SPSed samples decreased from 650nm to 250nm as MA-time was prolonged from 6 to 24h. Lattice parameters estimated form XRD patterns increase with the increasing MA time. All samples SPSed at 600°C for holding 5 min show an n-type conduction. The electrical resistivity was 1030, 895, 410, 260 μm for the samples from the MA-derived powders with MA-time of 6, 15, 24 and 33h at room temperature, respectively, then reduced to 60 μm at 400°C for all samples. An optimum MA time is 24 h in which the sample shows the highest power factor 612μW/m*K2 at 150°C.

Abstract: Highly dense Na1-xKxNbO3 (x=0.2~0.8) ceramics were successfully prepared using spark plasma sintering (SPS) at temperature as low as 920°C. Solid solutions were formed during the composition range investigated. The piezoelectric constant and planar mode electromechanical coupling coefficient are significantly dependent on the Na/K ratio, with the maximum value of 148 pC/N and 38.9% at the composition Na0.5K0.5NbO3.

Abstract: AZ31B Magnesium alloy sheets with about 1 mm in thickness were rolled by one pass and several passes from the extruded ingots with different thickness. The effects of processing variables on microstructure and mechanical properties of AZ31B Mg alloy sheets were investigated. XRD indicated that AZ31B magnesium alloy sheets have a dominant texture with (000l) orientated plane. The large deformation results in the formation of fine and homogeneous microstructure due to the recrystallization during extruding and hot-rolling. The thinnest sheet rolled by several passes showed equiaxed grains with 5-10μm in diameter. The fine grains result in the increase in the strength and the ductility. The tensile strength of the sheet rolled by several passes reached 292 MPa and the elongation was twice as larger as that rolled by one pass.