Papers by Author: Qing Xu

Abstract: Bi2V0.9Co0.1O5.5-δ with a pure Aurivillius phase was synthesized by a sol-gel method using EDTA and citric as mixed complexing agents. It was found that homogeneous and fine powder (100-200 nm) with a pure Aurivillius phase can be produced by calcining the complex precursor at 450 °C for 1h in air. The sintering properties of Bi2V0.9Co0.1O5.5-δ were investigated in the range of 560-680 °C with respect to relativity density. Sintering at 640 °C was ascertained to be preferred for Bi2V0.9Co0.1O5.5-δ, producing a dense microstructure with uniform grains around 3-5 μm. The Bi2V0.9Co0.1O5.5-δ ceramic exhibits an oxygen ionic conductivity of 1.0×10-1 S·cm-1 at 600 °C. The difference between the activation energies for the ionic conducting in low and high temperature regions is qualitatively interpreted in terms of an order-disorder phase transition. This research demonstrates the advantage of the EDTA-citrate method in preparing Bi2V0.9Co0.1O5.5-δ with respect to the simplicity of synthesis process, desired morphology of synthesized powder, low sintering temperature and superior ionic conducting properties of ceramic specimen.

Abstract: Vanadium pentoxide xerogel films intercalated by poly (ethylene oxide), PEO, were prepared using direct intercalation method via a sol-gel route. The electrical and electrochromic characterization of the films were conducted. The electrical properties along and across V-O layers have been evaluated. The results indicate that the proper amount of PEO can increase the electrical conductivity and charge density of the films. The electrochromism of the films upon lithium intercalation was investigated by ex-situ transmittance measurement. The films display a reversible multichromism (orange
green
blue) upon Li+ ion insertion/extraction.

Abstract: Using Zr(NO3)4.5H2O as Zr source, PZT powder with a single-phase perovskite structure was synthesized by a sol-autocombustion method at a calcining temperature of 700°C. Compared with a solid-state reaction method, the calcining temperature of PZT can be lowered by 200°C when using the sol-autocombustion method. PMZN ceramic was prepared at a sintering temperature of 1050°C with the resulting PZT powder as a base, which can lower the sintering temperature by 150°C. The microstructure of the PMZN ceramic was investigated by XRD and SEM, and the dielectric and piezoelectric properties were measured. The results showed that the PMZN piezoelectric ceramic has a tetragonal perovskite structure, showing the main electrical properties as follows: Kp = 0.54, Qm = 1073, tgd £ 0.001, e33 T/ e0 = 1236, d33 = 454pC/N, and fs =136.1KHz.

Abstract: The electron structure of Pb(Zr1/2Ti1/2)O3(PZT), Pb(Zn1/3Nb2/3)O3(PZN) and Pb(Mn1/3Sb2/3)O3 (PMS) systems was calculated by the SCF-DV-Xα calculation method. The effects of ABO3-type perovskite and pyrochlore ceramic electron structure on their piezoelectricity were also studied. The results showed that the ferroelectric phase is more stable than paraelectric phase and the necessary condition of stable existing ferroelectric is the mixed orbit of O2p orbit and the out layer d orbit of B-site atom. The stability of ferroelectricity can be indicated by the strength of mixed orbit. When (Zr, Ti) was substituted by Mn1/3Sb2/3, Zn1/3Nb2/3, if it could form tetragonal perovskite structure, the total system energy would reduce and the mixed orbit will enhance, which improves the ferroelectricity of PZT system. However, if it forms a cubic pyrochlore structure, the ferroelectricity would lose because the covalent bond strength of B-O (axial direction) and B-O (vertical axial direction) is different obviously, which lead to the system structure become unstable.

Abstract: The sintering and electronic conducting properties of La0.8Ca0.2CrO3 synthesized by a glycine-nitrate process (GNP) were investigated in comparison with that synthesized by the conventional solid state reaction (SSR) method. The results demonstrate the advantage of the GNP method in producing La0.8Ca0.2CrO3 ceramic. Compared with the powder synthesized by the SSR method, that synthesized by the GNP method shows a higher sinterability due to its fine morphology. The relative densities of the ceramics made by the GNP and SSR methods attain 96.5 % and 96.0 % when sintering at 1450°C and 1550°C, respectively. In the case of similar relative densities, the ceramic made by the GNP method (sintered at 1450°C) exhibits superior electronic conducting properties to that made by the SSR method (sintered at 1550°C). This is attributed to a desired microstructure of the ceramic made by the GNP method.

Abstract: Structures, ferroelectric and piezoelectric properties of (Na0.5Bi0.5)0.90Ba0.10TiO3 ceramic sintered at different temperatures were investigated. The results confirm an important role of sintering temperature on the structure and electrical properties of the ceramic. It was found that the increase of sintering temperature in the range of 1110-1160
promoted the development of crystal structure and microstructural densification, leading to an improvement in ferroelectric properties, poling process and piezoelectric properties. Further increase of the sintering temperature above 1160
resulted in a slight deformation of ceramic specimens. With respect to sintering behavior and piezoelectric properties, a relatively narrow sintering temperature range near 1150
was ascertained to be preferred for the ceramic.

Abstract: xPb(Ni1/3Nb2/3)O3-yPb(Mn1/3Nb1/3Sb1/3)O3-(1-x-y)Pb(Zr0.48Ti0.52)O3 ceramics have been prepared by a columbite two-step method. NiNb2O6, MnNb2O6 and MnSb2O6 were used as precursors to produce the pseudoquintnary system ceramics. X-ray diffraction (XRD) results indicate that the pseudoquintnary system ceramics have a single-phase perovskite structure. The piezoelectric and dielectric properties of the ceramics were investigated as functions of x or y. The addition of Pb(Ni1/3Nb2/3)O3 makes the piezoelectric properties
to become ‘soft’, while the addition of Pb(Mn1/3Nb1/3Sb1/3)O3 makes the piezoelectric properties to be ‘hard’. The Curie temperature (Tc) of the pseudoquintnary system decreases with the increase of Pb(Ni1/3Nb2/3)O3 or Pb(Mn1/3Nb1/3Sb1/3)O3 contents. The preferred piezoelectric properties were obtained in the composition with x=0.06 and y=0.06.