Nb掺杂对（Sr,Pb）TiO3基陶瓷半导体晶粒及晶界导电特性的影响

研究了施主掺杂的（Ｓｒ，Ｐｂ）ＳｉＯ３陶瓷，探讨不同的施主Ｎｂ掺杂浓度对材料电阻率和显微结构的影响，通过复阻抗解析，分别得到施主浓度的变化对材料晶粒和晶界电阻率的影响规律。结果表明随施主浓度的增加，晶粒和晶界电阻率变化呈现相似的Ｕ型曲线，但晶界的电阻率值及变化幅度远大于晶粒，证明了晶界对材料的电阻特性起主导作用。     

CuO掺杂对WO_3压敏电阻微结构和电学性能的影响

研究了CuO掺杂对WO_3压敏电阻微结构和电学行为的影响,样品采用传统的陶瓷工艺制备.微结构通过扫描电子显微镜(SEM)观察,相结构和成分借助于X射线衍射(XRD)和能谱(EDS)进行分析.结果表明,微量的CuO掺杂能够促进WO_3陶瓷的致密化和晶粒生长.根据I-V特性测量结果,0.2%(摩尔分数)CuO掺杂的WO_3陶瓷具有线性伏安特性和极小的电阻率.CuO含量的继续增加使样品的非线性电学行为和电阻率又获得恢复,这是因为偏析于晶界处的CuO与两侧的晶粒形成了n-p-n型的双肖特基势垒.     

掺杂对Y—TZP陶瓷结构和电性能的影响

本文研究了掺杂对钇稳定四方ZrO_2(YTZP)陶瓷材料结构和电性能的影响。通过密度测定,SEM和电性能测量分析可知:掺杂的Y-TZP材料晶粒呈不规则多边形且分布均匀,晶粒平均尺寸在0.4μm左右。掺杂材料的电导激活能均小于未掺杂YTZP材料的电导激活能;材料的晶粒电阻率随掺杂种类和浓度的变化不大,而掺杂Fe_2O_3和SiO_2的Y-TZP陶瓷材料则呈现较小的晶界电阻率.     

Effect of heat treatment on precipitation behaviour and high temperature strength in a wrought Co-base superalloy

The effects of solution and ageing temperatures on the grain boundary reaction as well as on matrix precipitation in the interior of the grains were investigated using wrought Co-base superalloy HS-21. The grain boundary reaction occurred during furnace-cooling after solution-heating. The phase that precipitated in the grain boundary reactions nodule was M₂₃C₆ carbide. It also occurred during ageing after solution treatment, but the extent of it was considerably influenced by cooling procedure after solution heating. The activation energy of the grain boundary reaction was 244 kJ mol^–1 for the early stage of the grain boundary reaction in HS-21 alloy, and was considered to be the activation energy of grain boundary diffusion of chromium. The extent of the matrix precipitation that occurred during ageing was also influenced by the cooling procedure. Creep rupture tests were carried out at 1088 K in air. An excellent combination of long rupture life and large ductility was attained on a specimen, which involved both the grain boundary reaction nodules (about 7% in area fraction) and the matrix precipitates. The improvement of creep rupture properties results from the retardation of brittle intergranular fracture, which is achieved by grain boundary serration owing to the grain boundary reaction and by the increase of strength in the interior of grain due to the matrix precipitation.     

Structural and electrical conductivity studies on undoped and copper-doped nanocrystalline zinc sulphide

Zinc sulphide (ZnS) and copper-doped zinc sulphide nanocrystallites (ZnS:Cu) of average size 4 and 3 nm, respectively, have been synthesized by chemical precipitation method. Structural and morphological studies using X-ray and high resolution transmission electron microscopy (HRTEM) measurements have confirmed hexagonal structure for the samples. Using impedance spectroscopy, the effect of grain interior and grain boundary regions on the electrical conductivity have been studied at various temperatures. In the high temperature region, the grain boundary contribution to conduction is found to be larger than that of the grain interior region. Further, the activation energies of charge carriers in both the grain interior and grain boundary regions have been determined. The conduction mechanism of copper-doped zinc sulphide nanocrystallites have been studied at various temperatures and the results are reported.     

Effects of pre-ageing and cold working on grain-interior and grain-boundary reactions of Ag-Pd-Cu alloys

The effects of pre-ageing and cold working on grain-interior and grain-boundary reactions of Ag-Pd-Cu alloys were investigated by electrical resistivity measurements, hardness tests, and optical microscopic observations. Hardness values of the grain interior after the final thermomechanical treatment increased 20%–30% above the values after conventional ageing. The hardness values of alloys preaged at 400°C for 1 min and then cold worked at 30% are the highest (H_v=320).     

Microstructures and electrical properties of copper oxide doped terbium oxide ceramics

The effects of copper oxide (CuO) on the microstructure and electric properties of nonstoichiometric compound terbium dioxide (Tb₄O₇) ceramics were investigated. Results included a reduction in the sintering temperature to 1,100 °C, a grain size of 4.2 μm, and a density of 96.2 %, which are larger than the values in previous investigation for Tb₄O₇ ceramics (grain sizes between 0.4 and 1.0 µm). Among the sintered ceramics, the sample doped with 10.0 wt% CuO showed the maximum nonlinear coefficient α = 43.5, which is obviously greater than α = 3.03 of the pure sample. Doping with 10.0 wt% CuO also exhibited nonlinearity α = 2.14 even at 1,123 K. In addition, the impedance spectra of the sample doped with 5.0 mol% CuO showed the largest grain boundary semicircle; 0 and 20 % samples showed both inductive and capacitive reactance.     

细晶粒BaTiO3陶瓷电阻率的尺寸效应

在不同的测试电压条件下,对不同晶粒尺寸的BaTiO3陶瓷室温下的电阻率进行了测量;结合室温下的复阻抗谱,采用简化的等效电路模型和净极化电流的理论,分析了高、低频率下晶粒和晶界对瓷体电阻的影响.     

Studies on semiconductive (Ba0.8Sr0.2) (Ti0.9Zr0.1)O3 ceramics

In order to produce semiconductive (Ba_0.8Sr_0.2) (Ti_0.9Zr0.1)O₃ ceramics (BSZT), providing low resistivity for boundary-layer capacitor applications, a controlled valency method and a controlled-atmosphere method were applied and studied. In the controlled-valency method, trivalent ions (La³⁺ Sb³⁺) and pentavalent ions (Nb⁵⁺, Sb⁵⁺, Ta⁵⁺) were doped into BSZT ceramics, while in the controlled-atmosphere method, samples were sintered in air and a reducing atmosphere. The doped BSZT ceramics sintered in the reducing atmosphere showed much lower resistivities and smaller temperature coefficient of resistivity (TCR) than those sintered in air, indicating that low partial pressure of oxygen will increase the solubility of the donor dopant and enhance the grain growth. In addition, a small negative TCR at low temperature, as well as a small positive TCR at higher temperature, are also observed for specimens fired in a reducing atmosphere. The former is attributed to the semiconductive grain and the latter to the small barrier layer formed at the grain boundary.     

Sm2O3掺杂BaTiO3陶瓷的结构与电性能研究

采用溶胶-凝胶法制备了掺杂不同浓度Sm₂O₃(分别为0.001,0.002,0.003,0.005,0.007mol)的BaTiO₃陶瓷,并对其结构与电性能进行了研究.结果表明:Sm₂O₃掺杂BaTiO₃陶瓷的晶型在室温下为四方相,而且随着Sm₂O₃掺杂浓度的增加,BaTiO₃陶瓷的晶粒尺寸变小,说明Sm₂O₃掺杂对BaTiO₃陶瓷晶粒的生长有一定的抑制作用;Sm₂O₃掺杂BaTiO₃陶瓷的电阻率比纯BaTiO₃陶瓷明显下降,当添加量为0.001mol时,电阻率最小,.从4.3×109Ω·m下降为6.536×103Ω·m;Sm₂O₃掺杂BaTiO₃陶瓷的晶粒电阻随着温度的变化,呈现NTC效应,而晶界电阻随着温度的变化,呈现PTC效应,且晶界电阻远远大于晶粒电阻,说明该材料的PTC效应是由晶界效应引起的.     

Enhancement of the Grain Boundary Conductivity in Ceramic Li0.34La0.55TiO3 Electrolytes in a Moisture‐Free Processing Environment

The grain boundary resistivity problem of highly conductive bulk Li_0.34La_0.55TiO₃ perovskite has been investigated by means of impedance spectroscopy and solid‐state NMR of samples processed in controlled atmospheres. The samples were sintered in air, synthetic air, and oxygen, in which the level of moisture varied. A dry atmosphere is critical to obtain dense ceramics with a low grain boundary resistivity. The grain boundary conductivity is five times higher for samples sintered in oxygen atmosphere due to the suppression of Li₂CO₃ secondary phase formation, which is responsible for low lithium ion diffusion at the grain boundary.     

The microstructure and microwave dielectric properties of zirconium titanate ceramics in the solid solution system ZrTiO4–Zr5Ti7O24

Zirconium titanate (ZT) ceramics having compositions in the range of ZrTiO4-Zr5Ti7O24 were prepared via the mixed oxide route, using ZnO and CuO as sintering aids and Y2O3 as stabilizer. Specimens were sintered at 1450°C for 4 h and then cooled at 6°C h-1, 120°C h-1 or air-quenched. All products exhibited densities exceeding 95% of the theoretical values. The amount of ZnO and CuO in the products decreased as the cooling rate decreased and as the content of TiO2 increased. Energy dispersive analytical spectroscopy studies suggested that a grain boundary phase, rich in ZnO and CuO, existed as a continuous layer. Both composition and cooling rate were found to have significant effects on the microstructure of the zirconium titanate ceramics. Transmission electron microscopy showed that as the TiO2 content increased, a superstructure with a tripled a-axis developed, but there was no obvious change in the lattice parameters. As the cooling rate decreased, extra peaks were observed in X-ray spectra and the lattice parameter in the b direction shortened dramatically; both are associated with cation ordering. A short-range commensurate superstructure with a ZTTZZTTZTTZZTT (or ZTTZZTTZTTZZTT) stacking sequence was observed in the ordered ZrTiO4 specimens. All the samples showed poor dielectric properties at microwave frequency (4 GHz). The low dielectric Q values (400–1000) were due to the presence of the structural stabilizer, Y2O3, within the grains. The Q value increased slightly with increasing TiO2 content. The air-quenched samples had the highest Q values (850–1000); slower cooling led to the formation of microcracks within the samples and the reduction of Q values. The relative permittivity was controlled by bulk composition, the presence of a grain boundary phase, microcracks, oxygen vacancies and cation ordering. The ordering of cations and the presence of microcracks reduced the relative permittivity; rapidly cooled samples with higher TiO2 content had higher relative permittivities (with a maximum of 44.3 for air-quenched Zr5Ti7O24). This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect on the grain interior and grain boundary reactions by Cr addition to low gold content alloys

The effect on grain interior and grain boundary reactions by Cr addition to low gold content alloys were investigated by electric resistivity measurements, hardness tests, optical microscopic observations, and TEM observations. The grain interior reactions were accelerated by the chromium addition while grain boundary reactions were retarded. The formation of AuCu l type ordered phase in the grain interior was accelerated, and the T-T-T curve of AuCu l type ordered phase shifted to higher temperatures and shorter times with increasing chromium content.     

Nd扩渗PbTiO_3陶瓷的制备及其电性能研究

采用气相法对PbTiO3陶瓷扩渗Nd元素 ,经Nd扩渗 ,PbTiO3陶瓷的电性能发生了十分显著的变化。通过正交实验 ,确定了最佳扩渗条件 ,当Nd的浓度为 1.5 % (w) ,扩渗时间为 4h ,扩渗温度为 86 0℃时 ,PbTiO3陶瓷的导电性最好 ,其室温电阻率从 2 .0× 10 1 0 Ω·m下降为 10 .5Ω·m。经Nd扩渗的PbTiO3陶瓷的晶粒电阻随着温度的变化 ,呈现PTC效应 ,而晶界电阻随着温度的升高 ,呈急剧连续降低状态 ,总电阻的变化规律与晶界电阻的变化相一致 ,但PTC效应已不存在 ,有向导电体过渡的趋势。     

Effect of segregative additives on the positive temperature coefficient in resistance characteristics of n-BaTiO3 ceramics

The influence of B₂O₃, and Al₂O₃ as segregative additives in modifying the ρ–T characteristics has been studied in BaTiO₃ ceramics with positive temperature coefficient of resistance (PTCR). Reaction of Al₂O₃ at the grain boundary regions of BaTiO₃ ceramics leads to the segregation of the secondary phase, BaAl₆TiO₁₂ resulting in broad PTCR jump, whereas B₂O₃ addition gives rise to steeper resistivity jump. Microstructure studies by SEM reveal the formation of coherent second phase layer of barium aluminotitanate surrounding the BaTiO₃ grains. The EDX results shows varying Al to Ti ratio in the early stage of phase formation in BaAl₆TiO₁₂ resulting in electrically active layer around the BaTiO₃ grains. The TiO₂-excess melt formation results in lower resistivity for 2–4% Al₂O₃ containing n-BaTiO₃ ceramics whereas at higher alumina contents, BaAl₆TiO₁₂ phase becomes dominant leading to higher resistivity in the sample. Complex impedance analyses support the three-layer regions, corresponding to the contributions from grain interior resistance (R _g), grain boundary resistance (R _gb), and that from secondary phase (R _sec). Electron paramagnetic resonance spectroscopy (EPR) indicated barium vacancies, V _Ba ^/ as the major electron trap centers which are activated across the tetragonal-to-cubic phase transition. A charge trapping mechanism is proposed wherein the segregation of secondary phases bring carrier redistribution among the various acceptor states thereby affecting the electrical conductivity of n-BaTiO₃ ceramics. The presence of Al³⁺–O⁻–Al³⁺ or Ti⁴⁺–O⁻–Al³⁺ type hole centers at the grain boundary layer (GBL) regions results in charge redistribution across the modified phase transition temperature due to symmetry-related vibronic interactions resulting in broad PTCR characteristics extending to higher temperatures.     

Effects of CuO、MoO3 and WO3 dopping on magnetic properties of NiZn ferrites

研究了CuO、MoO3和WO3掺杂对NiZn铁氧体电磁性能的影响.研究表明,适量的CuO掺杂能提高材料烧结密度并降低磁晶各向异性常数,从而提高材料的起始磁导率,但居里温度也有一定程度的下降.当主配方中CuO含量(摩尔分数)为4%时能最好的兼顾材料高磁导率和高居里温度的要求.而MoO3和WO3掺杂则均能引起晶界附近阳离子空位增多,从而加速晶界移动,促进晶粒尺寸增大,进而提高材料的起始磁导率.同时,由于W离子具有较强的占据铁氧体A位替代Fe3 的趋势,需要更大的掺杂量才能达到磁导率的峰值,其居里温度和饱和磁感应强度也低于相应MoO3掺杂的材料.     

Influence of sintering and annealing temperature on grain boundary barrier layer capacitors in a modified reduction-reoxidation method

To produce grain boundary barrier layer capacitors with a simpler fabrication process and more-stable dielectric characteristics, a modified reduction-reoxidation method was developed. Nb₂O₅-doped (Ba_0.8 Sr_0.2)(Ti_0.9 Zr_0.1)O₃ (BSTZ) was calcined at 1170 °C for complete formation of ABO₃ phases. After calcination CuO was added to BSTZ as a liquid-phase promoter and insulating boundary layer material. The ceramics were sintered in a reducing atmosphere, and then the fired samples were annealed in air to reoxidize the reduced CuO to form insulating layers. The dielectric constant of the fabricated capacitors was decreased for higher annealing temperature, longer annealing time and smaller grain size. The loss tangent of the fabricated capacitors was increased for BSTZ with more CuO added, and was almost unchanged with annealing temperature, annealing time and grain size because of the existence of an insulating boundary layer material (CuO).     

Optimized sintering properties and temperature stability of MgZrTa<Subscript>2</Subscript>O<Subscript>8</Subscript> ceramics with CuO addition for microwave application

Microwave dielectric ceramics CuO–modified MgZrTa₂O₈ were synthesized by the conventional solid-state reaction method. The effects of CuO additives on the sintering characteristics and microwave dielectric properties have been investigated. With CuO addition, the sintering temperature of MgZrTa₂O₈ ceramics can be effectively lowered from 1475 to 1375 °C without decreasing its dielectric properties obviously and the temperature coefficient of the resonant frequency of MgZrTa₂O₈ ceramics have been optimized to near-zero. The crystalline phase exhibited a wolframite crystal structure and no second phase was detected at low addition levels. The grain growth of CuO–modified MgZrTa₂O₈ ceramics was accelerated due to liquid phase effect. The relative dielectric constants (ε_r) were correlated with apparent density and were not significantly different for all levels of CuO concentration. The quality factors (Q?×??) and temperature coefficient of resonant frequency (τ_?), which were strongly dependent on the CuO concentration, were analyzed by the grain size and the dielectric constant respectively. A best Q?×?? value of 116400 GHz and τ_? value of ?6.19 ppm/℃ were obtained for specimen with 0.05 wt% CuO addition at 1375 °C.     

The structure and semiconducting properties of cadmium selenide films

CdSe films about 1 μm thick were vacuum deposited on unheated glass substrates. Reflection electron diffraction studies showed the growth of a one-dimensional {00.1} texture orientation of the hexagonal phase. Films of lower resistivity were characterized by a larger grain size and better ordering, whilst films of higher resistivity contained amorphous regions and were less ordered. A study of the carrier type, the concentration, the Hall mobility and the variation in the bond length u along the hexagonal c axis of “as-deposited” and heat-treated films showed that the lower resistivity films incorporated a small cadmium excess, which increased with heat treatment, resulting in higher carrier concentrations and a further lowering of the resistivity. Large increases in the resistivities of films deposited at high rates were attributed to the depletion of the small individual grains.     

Structural and high temperature conduction studies of (Na<Subscript>0.46</Subscript>Bi<Subscript>0.46</Subscript>Ba<Subscript>0.08</Subscript>) (Mn<Subscript>x</Subscript>Ti<Subscript>1−x</Subscript>O<Subscript>3</Subscript>)–CuO lead-free piezoelectric ceramics

Polycrystalline lead-free (Na_0.46Bi_0.46Ba_0.08)(Mn_xTi_1?xO₃)?+?0.2CuO ceramics (x?=?0.0, 0.5, 2.0, 3.0 wt%) were prepared via solid-state reaction method. X-ray diffraction (XRD) analysis confirmed the formation of single-phase perovskite structure and indicated the presence of morphotropic phase boundary, where the tetragonal and rhombohedral phases co-existed for all the synthesized compositions. Scanning electron microscopy (SEM) analysis revealed that the average grain size decreased with the increase in Mn content. Impedance spectroscopy (IS) indicated that Mn doping was found to decrease the grain boundary resistance. Two semi-circles were observed for higher Mn content which indicates the contribution of both bulk grains and grain boundaries. Non-Debye type and temperature dependent relaxation phenomenon was also revealed by IS studies. The activation energies at different frequencies were found to be 0.05–0.9 eV, indicating hopping charge conduction mechanism. These results have comprehensive implications for the expanded use of BNT based lead free piezoelectric ceramics for practical applications.