Papers by Author: Ying Song

Abstract: A series of (Ca0.9Gd0.1)3Co4O9/xAg(x=0, 0.1, 0.15, 0.2) ceramics were prepared by a polyacrylamide gel method and Spark Plasma Sintering. Scanning electron microscopy (SEM) revealed that small size Ag particles were dispersed into the (Ca0.9Gd0.1)3Co4O9(CGCO) matrix. The electrical conductivity of the composites was obviously higher than that of (Ca0.9Gd0.1)3Co4O9, and increased with increase of Ag content. However, the addition of Ag seemed to have a negative impact on the Seebeck coefficient (S) of the composites samples due to its poor S. Since the increase of electrical conductivity (σ) is more significant than the degradation of S, the power factor (P=σS2) was found to be improved by the addition of Ag. At 973 K, the P value of the sample with x =0.2 reached 3.17×10-4 W•m-1•K-2, which was 12.5% higher than that of Ca3Co4O9(CCO) bulk material.

Abstract: A series of polycrystalline (Ca1-xBix)3Co4O9 ( x = 0.0 ~ 0.075 ) powders were synthesized rapidly by a polyacrylamide gel method. The dense ceramics were fabricated using the spark plasma sintering ( SPS ) technique. Effects of Bi substitution on high temperature thermoelectric properties of Ca3Co4O9 were evaluated. Both the electrical conductivity and Seebeck coefficient increased with increasing Bi content up to x = 0.05, thus leading to an enhanced thermoelectric power factor. The Bi substituted sample with x = 0.05 obtained in this study has the highest thermoelectric power factor in the measured temperature range. It reaches 4.810-4 Wm-1K-2 at 700 °C, which is 26 % higher than that of Ca3Co4O9 without Bi substitution, and is by up to 15 % larger as compared to the Bi substituted sample synthesized by the solid state reaction method and the SPS technique due to the high chemical homogeneous powder prepared by the polyacrylamide gel method.

Abstract: The layered cobalt oxides as thermoelectric (TE) materials are introduced in detail on their developments, representative systems, some theories, unsolved problems and approaches for improving performances. TE performances of the layered cobalt oxides are discussed from structures, doped situations, processes and the dimensionless figure of merit. In contrast with other TE materials, the layered cobalt oxides show many promising applications. The theory of Seebeck coefficient and hopping conduction mechanism in the layered cobalt oxides are discussed. Heike formula explains that Seebeck coefficient origins from electronic spin states and proportions of different value states of Co ion. An unbalance of the spin and orbital degrees of freedom between Co3+ and Co4+ sites results in the large Seebeck coefficient. On the basis of the Boltzmann transport equation, Seebeck coefficient is decided by energy band structures. High state density near Fermi Energy band is responsible for the coexistence of large Seebeck coefficient and high electrical conductivity. Hopping conduction mechanism found in experiments is a main transport way of charge carriers at high temperature for the layered cobalt oxides. Through different materials systems and theories analysis, unsolved problems and new approaches for improving TE performances are put forward.

Abstract: Hydroxyapatite (HA) coatings were deposited on titanium substrate by means of pulsed laser deposition (PLD) with Nd:YAG laser. Deposition was carried out at 20 Pa of water vapor atmosphere and at room temperature. An Nd:YAG laser operating at a repetition rate of 10 HZ was used for deposition. In above deposition condition, the HA coatings deposited by PLD at room temperature are amorphous phase, and Ca/P ratio in HA coatings decreases with increasing water vapor pressure. The amorphous HA coatings were recrystallized after hydrothermal treatment at 190°C for 10 h. The bonding strength of the HA coating to the Ti substrate is up to 19.6 MPa. The structure and morphology of samples were characterized by X-ray diffraction, Fourier transform infrared reflection specterophotometry, scanning electron microcopy. The atomic ration of Ca and P was semiquantitatively determined by electron probe micro analyzer.

Abstract: Ca3(PO4)2/ZrO2 dental composite ceramics using for CAD/CAM system were prepared and the effects of weak phases on microstructures and mechanical properties were studied. The results showed that intergranular spreads happened with the increasing Ca3(PO4)2 contents due to the discontinuity of weak interfaces between Zirconia and Calcium phosphate in matrix. So the flexural strength and hardness of the Ca3(PO4)2/ZrO2 composite ceramics were decreased effectively, which improved the machinability of the composites. On the other hand, strong interfaces between Zirconias increased the integrality of the ceramic structures. ZrO2 composite Ceramics with 15% Ca3(PO4)2 were sintered at 1350°C. The flexural strength is 300.44MPa, fracture toughness is 4.36 MPam1/2, and hardness is 6.69 GPa. The cutting exponent of the Ca3(PO4)2/ZrO2 composite ceramics is obviously lower than that of the common commercial Vita Mark II and Dicor MGC ceramics, which shows good mechanical properties and machinability.

Abstract: A modified polyacrylamide precursor method is presented to synthesize BaSm2Ti4O12 microwave dielectric ceramics. Under an alkaline circumstance, all the cations together with the monomer and bridging agent were dispersed into a hydrous solution with the aid of chelating agent EDTA. This mixture was initiated at about 90°C, dried, calcined at 1000°C for 2hs and finally turned into well-crystallized and single-phased BaSm2Ti4O12 ceramic powder, which was modeled and sintered at 1250°C for 2hours into well-sintered ceramics. Differential thermal analysis, thermogravimetric analysis, X-ray powder diffraction and transmission electron microscope were used to characterize the process. Microwave dielectric properties measured by a resonating cavity method contain a dielectric constant (εr) about 77.0 and quality factor (Q×f) lager than 11000.

Abstract: BaTi4O9 - BaPr2Ti4O12 microwave dielectric ceramic composite powders were prepared by a polyacrylamide gel route using ethylenediaminetetraacetic acids (EDTA) as a chelating agent. This method provides a fast, cheap, reproducible and easy to scale-up way to prepare homogeneous mixed phases compounds. A light green, molecular-level, homogeneously mixed gel was prepared by the gelification of acrylamide. The precursors and derived oxide powders were characterized by thermal analysis (TG-DSC) and X-ray powder diffraction (XRD). Two phases and well-crystallized BaTi4O9 - BaPr2Ti4O12 composite powders were obtained at 1200 °C for 4 h.

Abstract: The Pb(Zr0.52Ti0.48)O3 thin films with 0-2at.%Gd dopants (denoted as PGZT) were prepared on Pt/Ti/SiO2/Si substrates by a sol-gel technique and a rapid thermal annealing process. The structures of PGZT films were characterized and the ferroelectric properties such as P–V loop, C–V and I–V characteristics were investigated. Improved polarization (2Pr = 46.373 μC/cm2) and the low leakage current (J = 1.5×10-9 A/cm2 at the electric field of 400 kV/cm) were obtained in the PZT thin film with 1at.% Gd dopant, which was better than that of the pure PZT thin film (2Pr = 39.099 μC/cm2, J = 4.3×10-8A/cm2). With the Gd contents up to 2at.%, a decreased remanent polarization was found.