TiO2和MgO掺杂的ZnO导电陶瓷材料

以ZnO为基添加Al2O3、TiO2和MgO制备了导电陶瓷;研究了TiO2、MgO掺杂含量对ZnO陶瓷相对密度、电阻率和电阻温度系数的影响;测试分析了ZnO导电陶瓷在小电流和脉冲大电流下的伏安特性.结果表明,掺Ti有利于致密烧结,TiO2含量为0.6%(质量分数)时,样品相对密度为96%,室温小电流下测试其电阻率为8.14Ω·cm;添加适量MgO能降低电阻率且可改善电阻温度系数,MgO含量为0.4%(质量分数)时,小电流电阻率为5.67Ω·cm;室温小电流下样品伏安特性接近线性,在脉冲大电流下呈现一定非线性特性.     

Crystallization and microstructural behaviour of strontium titanate borosilicate glass ceramics with Bi2O3 addition

Glasses in the system (65 −x) [SrO·TiO₂] − (35) [2SiO₂·B₂O₃] − (x) [Bi₂O₃] wherex = 1, 5, 10 (wt%) prepared by melting in alumina crucible (1375–1575 K), were subjected to different heat treatment schedules followed by DTA studies. Crystallization study showed the formation of Sr₂B₂O₅ as major phase at low temperature (≈950°C) heat treatment. At high temperatures, TiO₂ and SrTiO₃ with or without Sr₂B₂O₅ crystallize out depending on heat treatment. In this paper, the influence of variation in composition, thermal treatment on the nature of crystallizing phases as well as on the resulting microstructures are investigated through XRD, IR and SEM. Uniform crystallization was achieved by suitable addition of Bi₂O₃ and proper heat treatment.     

Degradation of 4-chlorophenol in TiO2, WO3, SnO2, TiO2/WO3 and TiO2/SnO2 systems

The present study was undertaken to evaluate the degradation performance of 4-chlorophenol (4-CP) using TiO2/WO3 and TiO2/SnO2 systems. A BET surface area analyzer, UV-vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA) were employed to characterize the photocatalyst. The band edge wavelength increased to 475 nm and gap energy decreased to 2.61 eV in the TiO2/WO3 system as compare to the single TiO2. Although the specific surfaces area of TiO2/WO3 decreases due to its larger size as compared to either TiO2 or WO3, the 4-CP degradation efficiency significantly increased as compared to single TiO2 or WO3 system at 435 nm wavelength. The TiO2/WO3 degradation of 4-CP at 369 nm was in fact inhibited. For TiO2/SnO2, the degradation efficiency also suffered at 369 nm, and only slightly increased compared to otherwise hardly 4-CP degraded in single TiO2 or SnO2 system. Since there is a significant accumulation of byproducts, the buildup of these intermediates on the catalyst surface may be responsible for their poor performance.     

Enhanced thermoelectric properties of WO3 by adding SnO2

Tungsten trioxide (WO₃) doped with stannic oxide (SnO₂) was prepared by a conventional mixed oxide processing route. The microstructure of the SnO₂-added WO₃ ceramics samples were investigated by X-ray diffraction and scanning electron microscopy. The grain size and porosity decreased with the increasing SnO₂ content. The sign of the Seebeck coefficient for all samples was negative over the entire temperature range, i.e., n-type conduction. The addition of SnO₂ to WO₃ led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient. This indicates that the power factor was significantly enhanced by adding SnO₂ to WO₃. The thermoelectric power factor was maximized to 7.77 μW m^?1 K^?2 at 1,023 K for the 10.0 mol% sample.     

Influence of the additives and processing conditions on the characteristics of dense SnO2-based ceramics

Three different SnO₂-based powder mixtures, containing 2 wt% CuO as sintering aid and Sb₂O₃ in amounts from 0 to 4 wt% as activator of the electrical conductivity, were sintered to high density at temperatures in the range 1000–1400°C and soaking times from 1 to 6 h. Densification behaviour and microstructure development are strongly dependent on the presence of CuO, that gives rise to a liquid phase, and on Sb₂O₃ that retards the liquid phase formation and hinders grain growth. Cu and Sb cations can enter s.s. in the SnO₂ network with different oxidation states and in different positions, depending on the sintering conditions. The characteristics of the grain boundary phase, of the SnO₂ solid solutions and their modification depending on thermal treatments were analyzed. The electrical resistivity values varied in a wide range from 10^–1 to 10⁴ cm, depending on starting composition and processing conditions: in terms of the final density and of the electrical conductivity, the optimal sintering conditions were found to be 1200°C, for 1–3 h. The electrical resistivity was related to the microstructural features, particularly to the characteristics of the resulting SnO₂-based solid solutions.     

SnO2-Zn2SnO4复合陶瓷的介电性质研究

通过传统陶瓷制备工艺制备了致密的SnO2-Zn2SnO4复合陶瓷,研究了不同SnO2、Zn2SnO4复合比例对陶瓷介电性质的影响及其高介电性质产生的机理。研究发现,40Hz时,该复合陶瓷的相对介电常数高达104,远高于SnO2、Zn2SnO4陶瓷,且样品的相对介电常数、导纳随组分的变化规律一致。进一步研究发现,样品的电容随着施加偏压的变化满足肖特基势垒电容公式,这表明,SnO2-Zn2SnO4复合陶瓷的高介电行为起源于晶界处的双肖特基势垒。     

Structural properties of fluorozirconate-based glass ceramics doped with multivalent europium

The structure/property relationships of fluorochlorozirconate glass ceramics as a function of divalent and trivalent europium (Eu) co-doping and thermal processing have been investigated; the influence of doping ratio on the formation of barium chloride (BaCl(2)) nanocrystals therein was elucidated. X-ray absorption near-edge structure spectroscopy shows that the post-thermal annealing changes the Eu valence of the as-poured glass slightly, but during the melting process Eu(3+) is more strongly reduced to Eu(2+), in particular, when doped as a chloride instead of fluoride compound. The Eu(2+)-to-Eu(3+) doping ratio also plays a significant role in chemical equilibrium in the melt. X-ray diffraction measurements indicate that a higher Eu(2+) fraction leads to a BaCl(2) phase transition from hexagonal to orthorhombic structure at a lower temperature.     

Properties of SnO2-based ceramics

Some SnO₂-based ceramics of the ternary and binary systems SnO₂-Sb₂O₃-CuO have been prepared and some of their properties have been measured. It was observed that most of their properties, which include density, porosity, d.c. electrical conductivity, as well as the crystal occurrence, were dependent on the presence of CuO. Crystal phase occurrence was investigated using the X-ray diffraction technique and it was found that the phases were predominantly SnO₂ and Sb₂O₄ crystals. The d.c. conductivity at different sintering temperatures was found to be enhanced by the simultaneous presence of Sb₂O₃ and CuO.     

Dielectric properties and microstructural behaviour of B-site calcium-doped barium titanate ceramics

Dielectric properties and microstructural behaviour of Ba_1–x Sr _x Ti_1–y Ca _y O_3–y ceramics, where strontium and calcium were doped on the barium and titanium sites, respectively, within the range 0x0.24 and 0y0.05, were investigated. Calcium addition decreased the tetragonality,c/a, increased the unit cell volume, and lowered the Curie temperature, which were all attributed to the occupancy of Ca²⁺ ions on titanium sites. When sintered at a low oxygen partial pressure of 10^–9 MPa, a resistivity higher than 10¹¹ cm was maintained for the formulations containing B-site calcium substitution more than 0.5 mol %. With increasing the amount of calcium addition, the Curie peak was depressed and completely broadened for the compositions with calcium addition more than 3 mol %, where the average grain size was smaller than 1 m. Co-firing with nickel electrodes in a reducing atmosphere also depressed the Curie peak and inhibited the grain growth due to the diffusion of nickel into the dielectrics.     

纳米SnO2、ZnO及ZnO／SnO2复合材料的气敏性能研究

以ZnO、S如纳米颗粒及ZnO／SnO2复合纳米材料分别作为气敏基料制成旁热式气敏元件,运用扫描电镜观察产物的形貌,用静态配气法对浓度为100ppm的甲烷气体进行气敏性能的测试。结果表明,这几类元件的最佳工作温度及灵敏度差异较大,当工作温度为350℃时SnO2纳米颗粒的气敏性能最佳。此温度下,SnO2响应时间和恢复时间也比纯ZnO纳米颗粒分别缩短了2S和3S。     

掺杂Fe2O3的牙科用氧化锆陶瓷着色研究

采用粉体掺杂方法在3Y-TZP陶瓷中添加不同质量分数的Fe2O3，研究Fe2O3对材料的着色效果及力学性能的影响。结果表明，掺杂Fe2O3着色后的3Y-TZP陶瓷三点弯曲强度略有下降，但不同掺杂量的测试结果均在1000MPa以上。肉眼观察，掺杂Fe2O3的氧化锆陶瓷呈黄色，颜色均匀，透光性良好，正反面色差小；色度值测试结果显示，随Fe2O3含量的增加陶瓷呈颜色由浅到深、亮度逐渐降低的梯度变化，且L^＊值和b^＊值均在中国人牙相应色度值范围内。Fe2O3着色3Y-TZP陶瓷接近自然牙色，且着色后材料的强度仍能满足牙科修复材料的要求。     

Structural and optical properties of nitrogen doped ZnO films

Zinc oxide is getting an enormous attention due to its potential applications in a variety of fields such as optoelectronics, spintronics and sensors. The renewed interest in this wide band gap oxide semiconductor relies on its direct high energy gap (E_g ∼ 3.437 eV at low temperatures) and large exciton binding energy. However to reach the stage of device production the difficulty to produce in a reproducible way p-type doping must be overcome.In this study we discuss the structural and optical properties of ZnO films doped with nitrogen, a potential p-type dopant. The films were deposited by magnetron sputtering using different conditions and substrates. The composition and structural properties of the films were studied combining X-ray diffraction (XRD), Rutherford backscattering (RBS), and heavy ion elastic recoil detection analysis (HI-ERDA). The results show an improvement of the quality of the films deposited on sapphire with increasing radio-frequency (RF) power with a preferentially growth along the c-axis. The ERDA analysis reveals the presence of H in the films and a homogeneous composition over the entire thickness. The photoluminescence of annealed samples evidences an improvement on the optical quality as identified by the well structured near band edge recombination.     

Structural and spectroscopic characterization of Yb doped Lu2O3 transparent ceramics

Yb³⁺ doped Lu₂O₃ transparent ceramics were fabricated by the solid-state reaction method and sintered in H₂ atmosphere. Structural and spectroscopic properties of Yb:Lu₂O₃ ceramics were studied. The Yb:Lu₂O₃ ceramic structure, and the lattice parameter are refined with the Rietveld method. Yb:Lu₂O₃ has broad absorption and emission bands with a long fluorescence lifetime (1.31 ms). The energy level diagram is calculated based on the absorption and emission spectra, Yb³⁺ in Lu₂O₃ ceramics exhibits a big splitting energy of the ²F_7/2 ground state (1023 cm⁻¹). Furthermore, the gain cross-section (σ_g) is estimated with different β values.     

Preparation and characterization of doped WO3 photocatalyst powders

WO₃ semiconductor particles, useful in solar energy conversion processes, were doped with transition metal ions, Ti(III), V(IV), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Ru(III) by a high-temperature sintering technique. The method of preparation of these photocatalysts is described in detail. The structural changes effected during sintering were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis indicated that the monoclinic crystal structure of WO₃ was not altered during sintering. SEM studies showed that the sizes of the particles ranged from 1 to 10 μm and the crystallinity was increased due to doping. The dopants were found to be mostly distributed on the surface of WO₃ particles.     

Low-fired microwave dielectrics in ZnO-TiO2 ceramics doped with CuO and B2O3

The microwave dielectric properties and the microstructure of low-firing zinc titanate ceramics have been investigated. The microstructure of these ceramics have been studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and it was found that CuO addition has the important effect of stabilizing the Zn₂TiO₄ phase. When the sintering temperatures are in the range of 870–950 °C, dielectric constant values ( _r ) saturate at 21–25, the Q×f value is 20 000 GHz (at 10 GHz). The temperature coefficient of resonant frequency ( _f ) was 10 ppm °C^–1. Therefore, the 0.5 wt %-CuO and 1.0 wt %-B₂O₃ doped ZnO-TiO₂ ceramics can be used in multi-layer microwave devices requiring low sintering temperature.