Abnormal high dielectric constant in SmFeO3 semiconductor ceramics

The dielectric properties and impedance spectroscopy (IS) of perovskite SmFeO₃ ceramics were studied in the frequency range of 100 Hz-1 MHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant of ∼10⁴ at room temperature. The response is similar to that observed for relaxor-ferroelectrics. IS data analysis indicates the ceramic to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 20 and more resistive grain boundaries. We conclude, therefore that grain boundary effect is the primary source for the high effective dielectric constant in SmFeO₃ ceramics.     

Impedance analysis of MnCoCuO NTC ceramic

Impedance spectroscopy is often used to analyse the electrical properties of ceramic materials having high-resistive grain boundaries, such as ZnO and SrTiO₃. Fewer attempts have been made at using this technique for the analysis of inhomogeneous electronic ceramics consisting of grains with differing composition, such as those occurring in negative temperature coefficient (NTC) thermistors. In this study, we have attempted to adopt ac impedance spectroscopy together with other techniques to analyse an NTC thermistor ceramic material.An Mn, Co and Cu multielements transition metal oxide (MnCoCuO) ceramic was prepared by using homogeneous precipitation employing oxalic acid. This material displayed a typical NTC effect, showing an electrical resistance decrease with temperature when dc electrical measurement was performed. The ac impedance spectroscopy analysis showed that there were two peaks in impedance and conductance versus frequency plot. By using an alternative representation of impedance spectra Z″/f versus Z′, three distinct relaxation frequency ranges were identified. They are believed to originate, respectively, from the electrode, phase 1 (rich-Cu phase) and phase 2 (poor-Cu phase) grains existing in this ceramic. SEM observation and EDX analysis clearly showed existence of two distinct phase grains. The resistance values were derived from phases 1 and 2 grains based on ac impedance data. The sum of the resistance values was in good agreement with that from dc measurement in the temperature range of 30-95 °C. The material constant, B, for the two phases was also calculated, giving 3100 and 3600 K for phases 1 and 2, respectively.     

Microstructural,dielectric, impedance and electric modulus studies on vanadium—doped and pure strontium bismuth niobate (SrBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>) ceramics

SrBi₂Nb₂O₉ (SBN) and SrBi₂(Nb_0.9V_0.1)₂O₉ (SBVN) ceramics were fabricated from the powders consisting of μm sized grains, obtained via the solid state reaction route. V₂O₅ was found to be an effective microstructure modifier and grain growth truncator for SBN ceramics. X-ray structural studies carried out on SBVN ceramics confirmed the existence of preferential orientation (c-planes) of the grains. V₂O₅ addition has substantially improved the sinterability of SBN and enabled to achieve high density (95%) which was otherwise difficult in the case of pure SBN. The dielectric properties of SBN ceramics were significantly enhanced by the partial replacement of Nb ions by pentavalent vanadium ions. The complex impedance diagrams of dense SBVN ceramics exhibited only one semicircle indicating a significant contribution from the grains. In contrast, the impedance plots for the porous (density 88%) SBN ceramics show an additional low-frequency semicircle which was attributed to the blocker (pore) size effects. The dielectric behavior of SBN and SBVN ceramics was rationalized using the impedance and modulus data.     

Preparation,characterization, electrical properties and giant dielectric response in (In + Nb) co-doped TiO<Subscript>2</Subscript> ceramics synthesized by a urea chemical-combustion method

Pure rutile phase of nanocrystalline (In?+?Nb) co-doped TiO₂ (INTO) ceramics were prepared by a chemical combustion method using urea as fuel. Dense ceramic microstructure can be obtained by sintering INTO nanocrystalline powders. Good dispersion of In³⁺ and Nb⁵⁺ co-doping ions in the microstructure is observed. Notably, high dielectric permittivity (≈20,674) and low loss tangent (≈0.054) at a low frequency and 30?°C are achieved in the (In_1/2Nb_1/2)_0.015Ti_0.985O₂ ceramic. Using an impedance spectroscopy, the INTO ceramics are confirmed to be electrically heterogeneous, consisting of semiconducting and insulating phases. The giant dielectric response in INTO ceramics can suitably be explained by the interfacial polarization. The low value of the loss tangent of INTO ceramics is attributed to a large value of resistivity of insulating phase.     

Electrical hetero-structure of Nd0.1Sr0.9TiO3 ceramic for energy storage applications

Both high dielectric constant and high bulk resistance was required to meet high energy storage density in high-voltage ceramic capacitors. In this paper, Nd_0.1Sr_0.9TiO₃ (NSTO) ceramic with pure tetragonal perovskite structure was prepared by solid state reaction route. Dielectric response of NSTO ceramic was investigated in the temperature range of ?60 to 550 °C over the frequency 20 Hz–1 MHz. Complex impedance spectroscopy (IS) analysis was employed to study the electrical conductive behavior of NSTO ceramic. IS results revealed that the NSTO ceramic showing electrical hetero-structure, which includes semiconducting grains, inter-grains and insulating grain boundaries. The space charge polarization at heterointerfaces by conductive charge carries was contributed to high dielectric constant, while insulating grain boundaries to high bulk resistance for NSTO ceramic. The mechanism of such electrical hetero-structure formation associated with charge compensation induced by trivalent Nd ions substitution for divalent Sr, as well as the first and second ionization of oxygen vacancies was discussed tentatively.     

快离子陶瓷晶界阻抗的分布模型

以电导率分布模型为基础的模拟计算可以解释快离子陶瓷晶界部分的非理想阻抗谱。讨论了几率函数的分布参数对阻抗图形的影响。对 Nasicon 陶瓷晶界阻抗谱进行了拟合计算和确定出电阻分布性质。     

超重力下燃烧合成大体积凝固态Al2O3/ZrO2（4Y）研究

通过在铝热剂中引入ZrO2(4Y)混合粉末,以超重力下燃烧合成方式,制备出Al2O3/ZrO2(4Y)自生复合陶瓷板材,并研究了复合陶瓷微观结构、生长机理与力学性能.XRD、SEM与EDS结果显示,Al2O3/32%ZrO2(4Y)复合陶瓷基体为亚微米t-ZrO2纤维成三角对称分布其上、取向各异的棒状共晶团,而Al2O3/37%ZrO2(4Y)复合陶瓷则以分布均匀的微米级t-ZrO2球晶为基体.Al2O3/32%ZrO2(4Y)复合陶瓷的强化归因于小尺寸共晶团边界及残余压应力增韧、相变增韧机制引发的高断裂韧性所致;同时,细小t-ZrO2球晶所具有的小尺寸缺陷及相变增韧与微裂纹增韧机制所引发的高断裂韧性也使Al2O3/37%ZrO2(4Y)复合陶瓷得以强化.     

A novel method to regulate the density of BaTiO3 ceramics for positive temperature coefficient resistance via tape casting

BaTiO₃ ceramics for positive temperature coefficient resistance (PTCR) were fabricated via tape casting technique and reduction/reoxidation process. A novel method was used to regulate the density of the ceramics via changing binder amount in tape casting green bodies. The influences of different amounts of the binder on density, electrical properties, and microstructure of ceramics were investigated. The BaTiO₃ ceramic monolith without internal electrodes with an addition of binder of 0.84 wt% was sintered in reducing atmosphere at 1150 °C and reoxidized at 800 °C for 1 h showed a resistivity of 56 Ω·cm and a PTCR jump about 3.2 orders of magnitude. The green and sintered density of the samples decreased with the increasing binder amount. The room temperature resistivity increased monotonically with the binder amount. However, the correlation of the PTCR jump with binder amount showed a contrary tendency. These electrical properties can be explained by the Jonker model. The influences of sintering temperature on the density of BaTiO₃ ceramics with different binder amount were also discussed. In addition to the ceramic monoliths without internal electrodes, multilayer elements with internal electrodes were also prepared.     

Influence of the sintering process on the PTCR effect of chip-type Ba1.022–x Sm x TiO3 ceramics prepared by the reduction sintering-reoxidation method

We investigated the effects of sintering temperature and reoxidation annealing on the positive temperature coefficient of resistance (PTCR) effect of Ba_1.022–x Sm _x TiO₃ ceramics that were sintered at 1,180–1,260 °C for 30 min in a reducing atmosphere and reoxidized at 800 °C for 1 h. Results indicated that the room-temperature (RT) resistivity and resistance jump of the ceramics decreased with increasing sintering temperature; moreover, the samples exhibited a remarkable PTCR effect with a resistance jump of 3.3 orders of magnitude and achieved a low RT resistivity of 374.4 Ω cm at a lower sintering temperature. Furthermore, the higher grain-boundary resistivity of the ceramics obtained at a high reoxidation temperature after sintering at low temperature was estimated using an impedance analyzer. In addition, the voltage versus current behavior was investigated in present study.     

Cr_2O_3对氧化钙陶瓷烧结过程的影响

研究Cr2O3添加剂对氧化钙陶瓷烧结性能的影响。结果表明:Cr2O3能促进氧化钙陶瓷烧结密度和抗水化性能的提高,并且随着添加剂含量的增加,陶瓷抗水化性能不断提高;提高烧结温度,能提高陶瓷密度和抗水化性能;在烧结过程中,生成的CaCr2O4为液相,连结CaO晶粒,促进陶瓷烧结,增大了陶瓷的烧结密度,CaCr2O4包裹在CaO晶粒表面,能大幅度提高陶瓷抗水化性能。     

Nanocrystalline PbIn<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> ceramics and its properties

A ferroelectric relaxor PbIn_0.5Nb_0.5O₃ (PIN) ceramics has been obtained using a modified ceramic technology, with the sintering stage preceded by compression and shear straining of the synthesized charge in Bridgman anvils. The dimensions of ceramic grains after this pretreatment are spread over a range from 100 to 1250 nm. A comparative investigation of the properties of PIN ceramics obtained using the standard and modified technology showed that the proposed mechanical action at the charge preparation stage can be used for controlled modification of the properties of ferroelectric ceramics.     

Effect of sintering atmosphere on the microstructure and dielectric properties of barium strontium titanate glass–ceramics

The sintering of barium strontium titanate glass–ceramics in nitrogen modified their dielectric properties significantly compared to the sintering in air. The experimental results demonstrate that the glass–ceramics sintered at low temperatures contain a major phase Ba₂TiSi₂O₈ (BTS), known as fresnoite. The fresnoite phase disappeared and the barium strontium titanate perovskite phase became the major phase when the sintering temperature was increased. In addition, the microstructure observation showed that both the proportion of crystal phase and the crystal size increase obviously with the increase of sintering temperature. Most importantly, impedance spectroscopy has been employed to study the electrical responses arising from the glass and the crystal phases in the glass–ceramics sintered at low temperatures and high temperatures. The magnitudes of impedance and modulus changed significantly for the glass–ceramics sintered at the two temperature ranges. The activation energy calculated from the complex impedance, complex modulus and dc conductivity suggests that the dielectric relaxation for the glass phase and the glass–crystal interface may be attributed to the motion of the dipole associated with oxygen vacancy. And for the barium strontium titanate perovskite glass–ceramics, the motion of the electrons from the second ionization of oxygen vacancies leads to dc electrical conduction. The mechanism for the giant dielectric properties of the glass–ceramics sintered at high temperatures in nitrogen is discussed.     

Study of the humidity effect in the electrical response of the KSbMoO6 ionic conductive ceramic at low temperature

The effect of sorbed water vapor on the electrical response of a ceramic, metallic complex oxide (KSbMoO₆) with characteristics of ionic conductor has been studied by means of several experimental techniques aiming to explore its application as a humidity sensor. Electrical behavior was studied employing impedance spectroscopy, thermoelectric analysis and charging current analysis, showing that the incorporation of water actually determines the main electrical features of the system. It has been observed that water is present in the system in two basic forms: loosely associated on the sample surface and tightly bound inside the ceramics. Impedance measurements performed under atmospheres of different relative humidity allow to differentiate between such kinds of sorbed water. We propose that the dissociation of water molecules generates mobile protons responsible of the observed impedance patterns. In addition, we conclude that the design of humidity sensors based on materials of ceramic structure should count on a proper understanding of the underlying ionic transport mechanisms.     

Fabrication of high Tc lead free (1???x)BaTiO3�CxBi0.5K0.5TiO3 positive temperature coefficient of resistivity ceramics using reoxidation method

(1 ?C x)BaTiO₃?xBi_0.5K_0.5TiO₃ (abbreviated as BT?CBKT, where x = 0, 0.1 and 0.2) ceramics were prepared by solid state reaction method. All ceramic samples were sintered in a pure N₂ flow atmosphere, subsequently reoxidized at a temperature range of 800?C1,100 °C in air for several hours. The influences of BKT content and reoxidation on the positive temperature coefficient of resistivity (PTCR) behavior of ceramic samples were investigated. BT?CBKT ceramic samples sintered in N₂ possessed relatively low room temperature resistivity (??_RT) and showed weak PTC effect. Through an appropriate reoxidation, the ceramic samples re-obtained PTC effect of almost three orders of magnitude. With the addition of BKT, the Curie temperature (Tc) was enhanced by ~50 °C than the pure BT ceramics.     

Effect of Abrasion on the Crystal Structure of ZnS and ZnSe Ceramics

Zinc sulfide and zinc selenide ceramic samples prepared by hot pressing (HP) and chemical vapor deposition (CVD) have been subjected to dry grinding simulating dust erosion of these materials under real service conditions. It has been demonstrated that photoluminescence measurements allow one to follow the degradation of the crystal structure of ceramic grains by monitoring the intensity of structure-sensitive emission bands. The crystal structure of ZnS, a harder material, has been shown to be less sensitive to abrasion. Moreover, the abrasion resistance of the ceramics produced by CVD exceeds that of the HP ceramics of the same composition.     

Effects of Li and Fe doping on dielectric relaxation behavior in (Li,Fe)-doped NiO ceramics

High permittivity (Li, Fe)-doped NiO (LFNO) ceramics are prepared by a simple PVA sol–gel route and their dielectric properties are investigated as functions of temperature and frequency. It is found that the concentrations of Li and Fe have strong influences on the microstructure and dielectric properties of the LFNO ceramics. Two thermally activated dielectric relaxations are observed in the Li_0.05Fe_0.10Ni_0.85O ceramic sample with the activation energies of 0.448 and 0.574 eV for the high- and low-frequency relaxations, respectively. By using a complex impedance analysis, it is believed that the high-frequency relaxation is closely related to the transport properties inside the grains, and the low-frequency relaxation might be ascribed to the interfacial polarization at the interface layers of grain boundaries and/or NiFe₂O₄ secondary phase layers.     

B2O3对BaO-Sm2O3-TiO2微波介质陶瓷性能的影响

为了满足微波器件小型化的需要,开发高介电常数的低温烧结微波介质材料成为一种趋势.采用复合掺杂低熔点氧化物来降低BaO-Sm2O3-TiO2系(BST)微波介质陶瓷的烧结温度,通过X射线衍射和扫描电子显微镜分析其物相组成和显微结构,用阻抗分析仪测量了陶瓷材料的介电性能.结果表明:在Ba4(Sm1-0.15Bi0.15)28/3Ti18O54的基质陶瓷材料中,复合掺杂3%的ZnO和2%的B2O3时,其烧结温度为1060℃,得到的BST微波介质陶瓷的介电性能为:εr≈64,tanδ≈1.2×10-3,τf=-8.3×10-5/℃.     

Transmutation isotope diffusion in YBaCuO ceramics

The diffusion of a transmutation isotope generated in YBaCuO ceramics irradiated by high-energy charged particles is mathematically analyzed. The model is based on the assumption that copper isotope atoms created in subsurface layers of ceramic grains segregate at the grain boundaries in the course of subsequent annealing and then rapidly diffuse via intergranular regions in depth of the material and penetrate into the bulk of grains.     

Nb掺杂TiO2压敏陶瓷的施主掺杂固溶度

研究了不同烧结温度TiO2压敏陶瓷的显微结构、施主掺杂固溶度和电学性能。采用SEM和EDS测试了其显微结构和晶粒化学组成。随烧结温度增加,TiO2晶粒迅速长大,显微结构均匀致密,但过高的烧结温度将导致较多气孔。1350℃为比较合适的烧结温度,其晶粒大小为15μm左右。在施主掺杂浓度一定的条件下,施主掺杂离子Nb5+在TiO2晶粒中的固溶度、晶粒电子浓度和电导率随烧结温度上升而增加,晶粒电阻率随烧结温度上升而下降。以能谱中O为参考确定TiO2晶格数量计算得到的固溶度及其电学性能更符合实验测试结果。