Su Wen-Bin

Nonlinear Electrical Behaviour of Composite SnO2–Zn2SnO4 System

We have found a new composite SnO2?Zn2SnO4 varistor material and the effect of different content ratios of SnO2 to Zn2SnO4 on this system is investigated. The lowest breakdown voltage (EB = 6.4?V/mm) and the highest relative dielectric constant (?r = 1.54?104) with higher nonlinear coefficient (? = 4.5) is obtained when the ratio of SnO2 to ZnO equals 100/35. The disappear of the Zn2SnO4 peak in x-ray diffraction (XRD) spectra of the SnO2+2.5?mol%ZnO sample and the electric insulation behaviour of the samples with 2.5?mol% ZnO and 200?mol% ZnO indicate that 2.5?mol% ZnO can be dissolved into SnO2 lattices and some reaction contributing to nonlinear electrical behaviour should occur between SnO2 and Zn2SnO4. The role of oxygen on the grain boundary is confirmed by the degradation of nonlinear electrical properties and the increase of relative dielectric constant of the samples annealed in nitrogen-rich atmosphere.

Thermoelectric properties of Sr0.61Ba0.39Nb2O6−δ ceramics in different oxygen-reduction conditions*

The thermoelectric properties of Sr0.61Ba0.39Nb2O6−δ ceramics, reduced in different conditions, are investigated in the temperature range from 323 K to 1073 K. The electrical transport behaviors of the samples are dominated by the thermal-activated polaron hopping in the low temperature range, the Fermi glass behavior in the middle temperature range, and the Anderson localized behavior in the high temperature range. The thermal conductivity presents a plateau at high-temperatures, indicating a glass-like thermal conduction behavior. Both the thermoelectric power factor and the thermal conductivity increase with the increase of the degree of oxygen-reduction. Taking these two factors into account, the oxygen-reduction can still contribute to promoting the thermoelectric figure of merit. The highest ZT value is obtained to be ~0.19 at 1073 K in the heaviest oxygen reduced sample.The thermoelectric properties of Sr0.61Ba0.39Nb2O6−δ ceramics, reduced in different conditions, are investigated in the temperature range from 323 K to 1073 K. The electrical transport behaviors of the samples are dominated by the thermal-activated polaron hopping in the low temperature range, the Fermi glass behavior in the middle temperature range, and the Anderson localized behavior in the high temperature range. The thermal conductivity presents a plateau at high-temperatures, indicating a glass-like thermal conduction behavior. Both the thermoelectric power factor and the thermal conductivity increase with the increase of the degree of oxygen-reduction. Taking these two factors into account, the oxygen-reduction can still contribute to promoting the thermoelectric figure of merit. The highest ZT value is obtained to be ~0.19 at 1073 K in the heaviest oxygen reduced sample.

Cu Doping Effect on Electrical Resistivity and Seebeck Coefficient of Perovskite-Type LaFeO3 Ceramics

Perovskite-type LaFe1?xCuxO3 (x = 0.10, 0.14, 0.18) solid solution is prepared with the conventional solid-state reaction technique. The electrical resistivity and the Seebeck coefficient are measured in the temperature range 473?1073K to elucidate the Cu doping effect on the thermoelectric properties of the LaFeO3. The electrical resisitivity of LaFe1?x Cux O3 shows semiconducting behavior. The temperature dependence of the electrical resistivity indicates that the adiabatic small-polaron hopping mechanism is dominant for their electric transportations. The activation energy decreases with the increasing Cu content as well as the increasing temperature. The Seebeck coefficient changes from a negative value to a positive value around 510 K, and increases with rising temperature up to 710K, then becomes saturated around 200?V/K. The Seebeck coefficient decreases with the substitution of Cu atoms in the temperature range of 573?1073 K, while the electrical resistivity decreases with the substitution of Cu atoms in the whole measured temperature. Overall the power factor increases with rising temperature, and the highest value of power factor is 54 ?W/K2 m for x = 0.10 of Cu doping.

Nonlinear Electrical Behaviour of the TiO2?Y2O3?Nb2O5 System

The nonlinear and dielectric properties of a new TiO2-based varistor system, TiO2Y2O3Nb2O5, have been investigated. The (Nb, Y)-doped TiO2 ceramics have nonlinear coefficients of α = 5-8 and a lower breakdown electrical field of 6-12 Vmm-1, in which the varistor of (99.3 mol%)TiO2(0.6 mol%)Y2O3(0.1 mol%)Nb2O5 composite sintered at 1400°C has a nonlinear coefficient of α = 7.8 and a maximum breakdown electrical field of 12 Vmm-1 at 1 mAcm-2. Also, the relative dielectric constants of the composite reach more than 85 000, which is almost unchanged within the temperature range from -20 to 280°C and the frequency range of 0.5 K-2 MHz. Due to these properties the (Nb, Y)-doped TiO2 varistor has varistor-capacitance bifunctional components, which are quite useful in the situation that the voltage protection and high-frequency noise absorption are meanwhile required.

Nonlinear Electrical Characteristics of Antimony and Copper Doped Tin Oxide Based Varistor Ceramics

The novel CuO-doped dense tin oxide varistor ceramics are investigated. The densification of tin oxide varistor ceramics could be greatly improved by doping copper oxide additives. The introduction of antimony additives into a SnO2.CuO ceramic system would make it possess excellent nonlinearity. The sample doped with 0.05 mol% Sb2O3 possesses the highest nonlinearity coefficient (α = 17.9) and the lowest leakage current density (JL = 52 μA cm−2) among all the samples. A modified defect barrier model is introduced to explain the formation of the grain-boundary barrier. The nonlinear behaviour of (Cu, Sb)-doped SnO2 varistor system could be explained by the barrier model.

Enhancement of Thermoelectric Performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 Ceramics by A-Site Cation Nonstoichiometry*

Sr0.9Ba0.1-x Ti0.8Nb0.2 O3 ceramics (x=0, 0.01, 0.02 and 0.05) are prepared by solid state reaction, whose thermoelectric properties are investigated from 323 K to 1073 K. By introducing A-site nonstoichiometry, the absolute See-beck coefficient is enhanced, while the electrical resistivity is surprisingly reduced due to the significantly enhanced carrier mobility. These results are dramatic in thermoelectric materials, effectively enhancing the power factor. Moreover, the thermal conductivity is reduced, thus the thermoelectric performance of Sr0.9Ba0.1 Ti0.8Nb0.2O3 ceramic is significantly enhanced by A-site nonstoichiometry.