Papers by Author: Pi Yi Du

Abstract: The preparation and characterization of silver powders with spheric shape and different sizes by chemical reduction of silver ions in the presence of ethanol amine using hydrochinone (C6H6O2) as the reducing agent are described. The size distribution, microstructure, and the phase composition of the obtained Ag Powders were characterized by the Laser Particle Size Analyzer, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and the X-ray diffraction (XRD). The Ag powder was in face-centered cubic crystal structure with spheric morphology. The average tap density of silver powders is up to 4.0g/cm3. It was also found that the size of the Ag particles can be adjusted conveniently to a certain degree by varying the silver ions content, the addition amount of dispersing agent, the aging time, the temperature of the reaction, and the concentration ratio of hydrochinone to Ag+.

Abstract: Ni0.5Zn0.5Fe2O4-BaTiO3 composites were prepared by calcining Ni0.5Zn0.5Fe2O4 with BaTiO3 at 1220°C for 3 h. Both μ′ and μ″ of the composites decrease rapidly, but the cut-off frequency shifts to higher level with increasing BaTiO3 content. The dielectric constant of the composites increases quickly with increasing BaTiO3 content below 50% and keeps a high and nearly unchangeable value with increasing BaTiO3 above 50%. The composites with BaTiO3 content between 20% and 40% are suitable to use for the magneto-electric devices under high applied frequency due to its high permeability and low dielectric loss.

Abstract: Ferroelectric/ferromagnetic multiphase powdered composites, consisting of PbTiO3 as ferroelectric phase and NiFe2O4 (PbFe12O19) as ferromagnetic phase, were successfully prepared in situ by sol-gel process. The phase structure, morphology and magnetism properties were observed. Biphase powdered ME composite consisting of PbTiO3 and NiFe2O4 is obtained at 700oC. Triphase composite consisting of PbTiO3, NiFe2O4 and PbFe12O19 is obtained above 750oC. With increasing heat-treatment temperature, the particles combine more tightly and the particle size decreases. The saturation magnetization (σs) and the initial permeability (μi) increase with the increase of NiFe2O4 content. The coercive force (Hc) increases with the increase of PbFe12O19 content.

Abstract: PST/Bi2Ti2O7 composite thin films were prepared by sol-gel method through heavily doping Bi3+ into lead strontium titanate (PST). The film with mono pyrochlore phase of Bi2Ti2O7 was also fabricated by controlling the Ti content in precursors. XRD, SEM and impedance analyzer measured the phase status, morphology and dielectric properties of the thin films, respectively. As a result, in the composite thin films, there was some Pb and Sr dissolved in Bi2Ti2O7, and the amount of dissolving ions decreased with the reduction of their composition in precursors. Bi4Ti3O12 impurity in crystalline Bi2Ti2O7 was due to the instability of Bi, and excess Ti in stoichiometry could make the film maintain to be mono pyrochlore phase. PST/Bi2Ti2O7 composite thin films had lower permittivity and lower dielectric loss than mono PST thin films.

Abstract: (PbySr1-y)ZnxTi1-xO3-x thin films were prepared on ITO/glass substrate by sol–gel process using dip-coating method. The phase structure, morphology, and dielectric properties of thin films were investigated by XRD, SEM and impedance analyzer, respectively. The perovskite phase structure was exhibited in the Zn-doped PST thin films. The formation ability of the thin films of the perovskite phase and its grain size decreased with the increase in doping Zn. The dielectric constant of the thin film was influenced by oxygen vacancies which could be controlled by Zn doping.

Abstract: The synthesis of aluminum titanate solid solution (Al2(1-x)MgxTi1+xO5, x=0, 0.1, 0.2) powders was realized by solid state reaction method using fine commercial α-Al2O3, TiO2 and MgO powders as raw materials. The effect of the introduced amount of MgO on the phase formation of aluminum titanate solid solution was investigated by XRD following the phase evolution. It was revealed that the introduction of MgO strongly affects the formation of Al2(1-x)MgxTi(1+x)O5 solid solution. The easily formed MgTi2O5 acts as the nucleus prompting the formation and lowering the synthesis temperature. The microstructure and properties of the solid solution ceramics were also studied by SEM and measuring the fracture strength and the thermal expansion coefficient.

Abstract: Aluminum phosphate is one of the best inorganic binders, and the addition of chromium oxide can improve the properties of the binder. In this work, the phase evolutions in chromium phosphate system and aluminum-chromium-phosphate system during heat-treatment were investigated. The initial binder solutions were prepared by dissolving Al(OH)3 and Cr2O3 in aqueous H3PO4 solution. The binder solutions consolidated at 100°C. The as-consolidated products were heated at different temperature. The experimental results showed the phase evolution of the consolidated products as: amorphous phase in 300~800°C, Cr(PO3)3 and Cr4(P2O7)3 in 900~1200°C for chromium phosphate system binder; amorphous phase in 300~1000°C, Cr(PO3)3 and AlPO4 in 1100°C, Cr4(P2O7)3 and AlPO4 in 1200°C for aluminumchromium- phosphate system binder. The addition of chromium oxide demonstrates to strengthen amorphous network, which further improves the thermal stability.

Abstract: Srm-3Bi4TimO3m+3 (m =3, 4, 5, and 6) bulk ceramics were prepared by conventional solid-state reaction process. Their phase structures and morphologies were observed by XRD and SEM respectively. The dielectric properties and hysteresis loops of the ceramics were measured by impedance analyzer and hysteresis meter respectively. Results showed that the lattice parameters along the c axis are 32.79, 41.11, 48.83, and 58.17Ǻ for m=3, 4, 5, and 6 respectively. The microstructures of plate-like crystalline phases are shown in all the ceramics with different m. Curie temperature of Srm-3Bi4TimO3m+3 decreases from 668°C to 295°C with increasing m from 3 to 6. The remnant polarizations Pr are 32.46 and 19.44 μC/cm2 for odd m of 3 and 5, and 11.84 and 10.58 μC/cm2 for even m of 4 and 6 respectively.

Abstract: The phase composition of (1-x)BaO·xSrO·0.7TiO2·0.3Nb2O5 (BSTN) composite ceramics was analyzed by XRD, and the effect of Sr/Ba ratio on the dielectric properties of BSTN was investigated by impedance analyzer. The results showed that any sample with different x value contained two phases-the perovskite phase and the tungsten bronze phase. The dielectric constants of BSTN basically decreased while the tanδ increased with the increase in x value. Both dielectric constant and tanδ decreased with the applied frequency increased for the same x value. There were two Curie points for BSTN composite ceramics. The first one belonging to the perovskite phase decreased with the increase in x value, but the second one belonging to the tungsten bronze phase kept almost constant at about 300°C.

Abstract: Lead zirconate titanate (PZT) ceramics are of great technological interest due to their excellent piezoelectric and ferroelectric properties. In the present work, a modified coprecipitation method for PZT phase preparation was proposed by combining the advantages of partial oxalate method and coprecipitation method. Firstly, the zirconium and titanium hydroxides were coprecipitated to form the precipitate of (Zr,Ti)O(OH)2. Then, the lead hydroxide was precipitated into a ammonia solution in which the precipitate of (Zr,Ti)O(OH)2 obtained above was well dispersed. The single perovskite PZT phase was directly synthesized without any intermediate phase appearing by calcinations the precursor at 500oC-800oC. The method proposed in the paper is an effective route for the synthesis of PZT powders.