氧化钇稳定二氧化锆(YSZ)微波烧结陶瓷的复阻抗谱分析

研究了8mol%Y2O3掺杂ZrO2(8YSZ)材料微波烧结陶瓷在300～850℃温度范围内的交流复阻抗谱,获得了该材料的温度-离子电导率曲线,并与常规烧结的陶瓷体进行了比较.结果发现8YSZ的微波烧结陶瓷的晶界势垒在550℃被击穿,常规烧结陶瓷的晶界势垒在500℃被击穿.击穿后晶界电阻消失,离子电导率的变化主要由晶粒电导率的变化决定.在击穿温度点以下,陶瓷体的离子电导率随温度的升高呈波浪式上升,即曲线呈上升～下降～上升趋势.     

烧结工艺对PMN—PT陶瓷介电,压电性能的影响

采用熔盐法得到了ＰＭＮ－ＰＴ陶瓷,研究了在不同烧结温度下ＰＭＮ－ＰＴ陶瓷的介电、压电性能,分析讨论了烧结温度、烧成密度、晶粒大涉以及晶界玻璃相与介电、压电性能的关系。结果表明,适当的晶粒大小以及采用不同烧结温度和退火工艺消除晶界玻璃相有利于压电、介电性能的提高,并对可能的机理进行了分析。     

烧结助剂对Nd∶YAG透明陶瓷微观结构和激光性能的影响

通过烧结Y_2O_3,Al_2O_3和Nd_2O_3粉体注浆的陶瓷胚体制备了Nd∶Y_3Al_5O_(12)(Nd∶YAG)透明陶瓷,研究了MgO和TEOS烧结助剂对陶瓷微观结构的影响和助烧结机理,分析了微观结构对陶瓷激光性能的影响。研究结果表明不加入烧结助剂,烧结后的样品晶界处存在大量的气孔,加入0.1%的MgO后,气孔数量减少,晶粒粒径变小,能够抑制晶界出现杂相,TEOS在陶瓷烧结过程形成的液相有助于气孔的排除。通过调节烧结助剂和烧结时间,制备出透光性达到83.1%的Nd∶YAG透明陶瓷,实现了1.4 W的激光输出。     

基于Monte Carlo方法对陶瓷微观结构演化的模拟

从晶粒生长概率、晶粒取向数的选择方法、晶粒和气孔的生长速度控制等方面改进了Monte Cario方法.根据晶粒生长机理模拟了在不同烧结温度、烧结时间条件下陶瓷微观结构的演化过程,并通对纳米Al2O3陶瓷在不同温度、不同时间条件下的烧结试验研究证明了模拟结果与试验结果相吻合.采用的Monte Carlo方法可以准确、快速地预测陶瓷烧结时微观结构的演化.     

Ba1-xLaxTiO3陶瓷的晶界再氧化机理研究

不同La施主掺杂浓度的BaTiO3陶瓷在H2／Ar的还原气氛下烧结后，再在氧分压PO2=260Pa的气氛（Ar和O2的混合气体）下进行氧化，通过氧流量计检测还原样品在再氧化过程的吸氧行为；用TEM分析样品氧化后显微结构的变化，测定了在不同最高氧化温度下氧化样品的PTCR效应以及复阻抗图谱．结果表明；氧流量计在升温阶段检测到三个不同行为的吸氧峰，峰Ⅰ（起始温度-250℃）为氧空位的填充过程；峰Ⅱ（起始温度-800℃）和峰Ⅲ（起始温度-1250℃）为还原相的氧化过程，具体来说，峰Ⅱ是通过晶界扩散提供氧使靠近晶界附近的区域被氧化；而峰Ⅲ是由晶格扩散过程控制，氧化过程从晶界逐渐向晶粒内部区域扩展，并伴随着富Ti的Ba6Ti17O40相的沉淀．在还原相向氧化相的转变过程中，于晶界处形成了两个具有晶界势牟的电结构单元而使陶瓷旱现强PTCR效应．     

碳化硼固相烧结微观结构演化的同步辐射CT观测

利用同步辐射CT (SR-CT) 技术,在碳化硼陶瓷样品烧结过程中对其进行实时投影成像,并应用滤波反投影算法和数字图像处理技术,得到了样品在整个烧结过程中内部微结构演化的二维和三维重建图像,实现了对陶瓷固相烧结过程实时、无损的观测.通过重建图像清晰观测到了陶瓷样品在烧结三个阶段中颗粒接触、烧结颈形成、晶粒和气孔长大、气孔球化并收缩等烧结现象;统计了样品在不同烧结时刻的孔隙率,得到了孔隙率随烧结时间和烧结时间对数的变化曲线,并根据曲线分析了样品在不同烧结时刻致密化速率的变化,得到了烧结中期孔隙率和时间对数的线性关系.实验结果和现有烧结理论相吻合,并为进一步完善烧结理论以及建立扩散和本构模型提供了有效的实验数据.     

Al2O3透明陶瓷显微结构的研究

采用高纯Al2O3(＞99.9%)粉末为原料,用无压烧结工艺制备Al2O3透明陶瓷.研究了添加剂Y2O3、烧结温度、保温时间等对Al2O3透明陶瓷显微结构和光学性能的影响.实验结果表明,适量的Y2O3能够抑制Al2O3晶粒的生长,改善烧结性能,但添加量过多会使Al2O3陶瓷气孔略有增加.在1800℃烧结的样品密度接近理论密度,具有较好的光学性能.延长保温时间能够使晶粒长大的同时有效排除晶界处少量气孔.     

晶界相和晶界对AlN陶瓷热导率的影响

本文研究了掺杂CaO-Y2O3热压烧结和常压烧结AlN陶瓷的晶界相及其产生过程和除氧机制；分析了峡谷种烧结工艺烧制的AlN陶瓷的晶界成份测定不同晶界相含量和晶界成份对应的AlN陶瓷的热导率。     

不同烧结工艺Ba1-xSrxTiO3陶瓷结构与电学性能研究

通过传统固相法制备了不同锶含量的钛酸锶钡陶瓷,研究不同烧结温度和保温时间条件下钛酸锶钡陶瓷的物相、微观形貌、介电和铁电特性。结果表明,随烧结温度的升高和保温时间的延长,陶瓷的结晶度先增加后减少,其中1280℃烧结4h的陶瓷结晶度最好,而且随着Sr含量的增加其晶粒粒度减小,Pr下降,P-E回线变窄且倾斜,同时介电常数下降,且表现出一定的频率、温度弥散特征。     

晶界相和晶界对AlN陶瓷热导率的影响

本文研究了掺杂CaO Y2 O3热压烧结和常压烧结AlN陶瓷的晶界相及其产生过程和除氧机制 ;分析了两种烧结工艺烧制的AlN陶瓷的晶界成份 ;测定了不同晶界相含量和晶界成份对应的AlN陶瓷的热导率     

Statistics on the AC ageing characteristics of single grain boundaries of ZnO varistor

The statistical AC ageing characteristics of single grain boundaries of ZnO varistor were investigated in this paper using the microcontact measurement method. ZnO varistor sample deposited with micro-electrodes was degraded under the ageing stress of 0.85 V_1mA at 135 °C. The electrical properties of 100 grain boundaries were measured after ageing with different time. The results indicate that the distribution of nonlinear coefficients concentrates to the lower region and the leakage current gradually increases in the ageing process. Meanwhile, more grain boundaries with lower breakdown voltage emerge as the ageing time increases, which means that the nonlinearities of these grain boundaries become weak.     

Pore deformation and grain boundary migration during sintering in porous materials: a phase-field approach

Grain growth in porous ceramics is a complex process due to the variety of interactions between pores and grains. In this study, the pore deformation and grain boundary migration during porous ceramic sintering are simulated by the phase-field method, and the variety of diffusions during sintering is considered. Pores of different shapes and sizes are induced into the simulations to investigate the grain boundary migration and pore deformations during grain growth. Simulation results indicate that the porous microstructure is determined by the contacting mode between pore surface and grain boundaries, which is in good agreement with experimental observations. The efficiency of the grain boundary migration is analyzed via calculating the forces applied on the interfaces between grains and pores, and the mechanism of the pore deformation during grain boundary migration is discussed. Therefore, controlling the grain–pore microstructure by adjusting the synthesis process is essential to reach the desired mechanical and physical properties of sintered materials.     

Mass transport via grain boundary in Pr-based ZnO varistors and related electrical effects

Mass transport and the grain boundary formation behaviors in Pr, Co-doped ZnO ceramics are strongly affected by firing atmosphere and temperature. Drastic change of grain boundary morphology and mass transport behavior were observed in the specimens sintered between 1350 and 1500°C which is ascribed to the increase of the vaporization contents of zinc oxide and praseodymium oxide with the formation of liquid phase. The penetration of liquid (ZnO–PrO_x) into the grain boundaries of sintered, Co-doped ZnO pellets resulted in varistors with breakdown voltages per grain boundary in the 1–3 V range and nonlinearity coefficients of 15–58.     

Microstructure and electrical properties of Pr<Subscript>6</Subscript>O<Subscript>11</Subscript> doped ZnO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-based varistors

The microstructure and electrical properties of ZnO-Bi₂O₃-based varistor ceramics doped by Pr₆O₁₁ in the content range of 0–5.49 wt% were investigated at different sintering temperatures (1,100, 1,150, 1,175, 1,200 °C). The increase of sintering temperature leads to more dense ceramics, which increases the nonlinear property, whereas it decreases the voltage-gradient and leakage current. With increasing Pr₆O₁₁ content, the breakdown voltage increases because of the decreases of ZnO grain size. The improvement of non linear coefficient together with the decrease of leakage current are related to the uniformly distribution of secondary phases along the grain boundaries of the ZnO. The varistors sintered at 1,175 °C with the 3.37 wt% Pr₆O₁₁ doping possess the best electrical properties: the varistor voltage, nonlinear coefficient, and leakage current are 340 V/mm, 46 and 0.63 μA, respectively.     

合成工艺对ZnVSb基压敏陶瓷性能的影响

研究了三种合成工艺对ZnVSb系压敏电阻烧结、显微结构和性能的影响。通过对陶瓷密度、显微结构及电学特性的检测、分析发现：化学计量比相同情况下，与V2O5＋Sb2O3预热处理工艺相比，以SbVO4取代Sb2O3合成工艺及传统氧化物合成工艺逐步加剧了尖晶石相在材料中的形成和掺杂元素在晶界的偏聚；导致材料内部晶界势垒逐渐升高，材料的非线性系数及压敏电压逐渐上升。研究结果为ZVSb系压敏电阻材料的设计、制备提供了新的思路。     

Microstructure and properties of low-voltage ZnO varistor ceramics

The influences of pre-firing process and sintering temperature on the microstructure and electrical properties of ZnO-Bi₂O₃-TiO₂-Sb₂O₃-MnO₂-CoO low-voltage varistor ceramics were studied. Especially, twin boundaries and exaggerated grain growth (EGG) were observed here, and the mechanism of EGG was discussed. It seems that the formation of twin boundaries has a correlation with Sb₂O₃ content and sintering temperature, and that twin boundaries have a great influence in grain growth of ZnO.     

粉料埋烧的TiO2瓷半导化和电学非线性研究

基于一次烧结工艺，采用埋烧和裸烧两种方法制备组分相同(Sr，Bi，Si，Ta)掺杂的TiO2陶瓷。通过复阻抗特性、晶粒电阻、晶界电阻、压敏电压、非线性系数及势垒高度的测定，研究埋烧与裸烧工艺对TiO2陶瓷的半导化以及电学非线性特性的影响。结果表明，采取粉料埋烧有利于晶粒半导化，降低压敏电压。     

Effect of grain size and Cu-rich phase on the electric properties of CaCu3Ti4O12 ceramics

The CaCu₃Ti₄O₁₂ ceramics were prepared by the traditional solid-state reaction method under different sintering conditions. The XRD patterns show that crystal structures of the samples are basically single-phase pseudo-cubic, except little second phases of CuO and Cu₂O in the samples sintered in air at 1050 and 1100 °C, respectively, for 12 h. The SEM results indicate that the pellet sintered at 1100 °C for 12 h possess larger grain size and more Cu-rich phases at the grain boundaries than the pellet sintered at 1050 °C for 12 h. It is interesting that the pellet sintered at 1050 °C under the pressure of 5 Gpa for 3 h shows smaller grain size (~1 μm) and no Cu-rich phases due to the higher pressure during the sintering process. The results show that the grain size has a reverse effect on the values of the permittivity and the values of breakdown electric field (E _b) and nonlinear coefficient. The pellet sintered at 1100 °C for 12 h exhibits a higher permittivity, but with a lower breakdown electric field (E _b) and a lower nonlinear coefficient due to larger grain size. The pellet sintered at 1050 °C under the pressure of 5 Gpa for 3 h exhibits a lower permittivity, but with a higher breakdown electric field (E _b) and a higher nonlinear coefficient due to smaller grain size. The Cu-rich phases at grain boundaries can raise the resistance of the grain boundary leading to the lower dielectric loss tangent, which has been supported by the results of impedance spectroscopy analysis.     

Effect of spark plasma sintering on microstructure and electrical properties of ZnO-based varistors

Conditions for the elaboration of varistors by spark plasma sintering (SPS) are investigated, using 70 nm zinc oxide nano-particles. For this purpose, the system constituted of zinc oxide, bismuth oxide and other metal oxide is used. Material sintering has been performed by SPS at various temperatures and dwell times. Determination of the microstructure and chemical composition of the as-prepared ceramics are characterized by scanning electron microscopy and X-ray diffraction analysis. Micro-structural analysis revealed the presence of ZnO, spinel and bismuth rich phases. ZnO based Varistor samples sintered within climb speeds 100 and 400 °C/min are compared. The nonlinear electrical characteristics, current–voltage, are measured. The breakdown voltage of the varistors strongly depends on grain sizes. The results show that the best varistors are obtained by SPS at sintering temperatures ranging from 900 to 1200 °C.     

Effects of annealing on the grain boundary potential barrier of ZnO varistor

Effects of post heat treatment on the potential barrier at the grain boundaries of ZnO varistors will be discussed from the viewpoints of the surface state density and the donor concentration. Leakage current of varistors at a low electric field increases by annealing at 750° C in air or nitrogen due to the lowered barrier height corresponding to the decrease of surface state density, which may be explained with the phase transformation of the bismuth-rich intergranular layer. It is also observed that theV-I non-linearity of the annealed ceramics is generally recovered as the annealing (in air) time is extended. This can be explained by the heightened barrier potential attributed to the decrease of donor concentration in ZnO grains, which was confirmed by aid ofC-V measurements. The decrease of donor concentration by the annealing in air can be considered to be responsible for the thermal oxidation of interstitial zinc ions or oxygen vacancies.