Synthesis and Microwave Dielectric Properties of Cu‐Doped ZnAl2O4

Spinel materials of composition Zn_1?xCu_xAl₂O₄ (ZCA, x = 0–0.015) were prepared via the conventional solid‐state route. The lattice structure, microstructure, and microwave dielectric properties were investigated as a function of Cu content. Cu doping was found to improve the sinterability and, meanwhile, significantly increase the quality factor (Q × f₀), which is due to the Cu‐O bond is stronger than Zn‐O bond, and inhibit the oxygen vacancy considered to be responsible for the enhanced Q × f₀ value of ZCA materials. The best microwave dielectric properties were obtained in Zn_0.99Cu_0.01Al₂O₄ with ε_r = 8.69, Q × f₀ = 69,300 GHz and τ_f = ?58.3 ppm/°C, which was sintered at 1520°C for 3 h in air.     

添加Li_2O的CaO-B_2O_3-SiO_2系微晶玻璃的性能研究

以Li_2O为烧结助剂,采用DTA、XRD、SEM等分析手段研究了添加1.0～2.5 wt%Li_2O对CaO-B_2O_3-SiO_2(CBS)系微晶玻璃性能的影响.结果表明:Li_2O降低了CBS系微晶玻璃的玻璃转变温度和析晶温度.未添加Li_2O的试样在930 ℃烧结,而添加Li_2O的试样可以在820 ℃以下烧结,Li_2O显著降低了试样的烧结温度.当Li_2O添加量为1.0wt%时,试样可以在760～820 ℃范围内烧结,800 ℃烧结试样介电常数为5.71,介电损耗为0.0024(测试频率为10 MHz).     

Synthesis,Microstructure, and Microwave Dielectric Properties of Spinel ZnGa2O4 Ceramics

Spinel ZnGa₂O₄ ceramics were synthesized by conventional solid‐state method and their microwave dielectric properties were investigated. The phase evolution and microstructures of specimens were studied by XRD and SEM. The textured surface microstructures of ZnGa₂O₄ ceramics formed at high sintering temperatures. The spinel‐structured ZnGa₂O₄ ceramics sintered at 1385°C exhibited excellent microwave dielectric properties: a dielectric constant (ε_r) of 10.4, a quality factor (Q × f) of 94.600 GHz, and a temperature coefficient of resonant frequency (τ_f) of ?27 ppm/°C. ZnGa₂O₄ ceramics have a low sintering temperature, a wide temperature region, and a small negative τ_f value. They are promising candidate materials for millimeter‐wave devices.     

NaxCo2O4热电材料Co位掺杂的研究进展

介绍了NaxCo2O4氧化物热电材料的基本结构和热电性能;重点讨论了NaxCo2O4热电材料的研究进展;对NaxCo2O4材料的掺杂(掺入Ni,Cu,Mn,Ru)研究和NaxCo2O4材料研究中存在的问题进行了评述。     

Ta_2O_5掺杂Bi_2O_3–ZnO–Nb_2O_5陶瓷的晶体结构、结晶化学及介电性能

采用固相反应法制备Bi1.5ZnNb1.5–xTaxO7陶瓷,研究了不同掺杂量Ta2O5对Bi2O3–ZnO–Nb2O5陶瓷相结构、晶体化学特性和介电性能的影响。结果表明:当x≤0.1时,样品均保持单一的立方焦绿石结构(α–BZN)。通过对样品结晶化学计算发现,随着Ta2O5掺杂量的增加,晶格常数a逐渐减小,结晶化学参数键价和AV(O')[A4]增大,AV(O)[A2B2]减小,48f(O)坐标ξ增加。在组成样品晶体结构的多面体中,由6个48f(O)组成的八面体结构(BO6)逐渐变得扭曲,而6个48f(O)和2个8b(O')组成的六面体结构逐渐变得规则,向正立方体结构变化。室温下样品的介电常数和损耗随Ta2O5掺杂量的增加而减小,弛豫度逐渐减小。     

CuO和B2O3复合掺杂对BaTi2O5陶瓷的降温烧结与电性能研究

采用非均相共沉淀法制备Ba Ti2O5粉体,以固相烧结法制备了Cu O和B2O3复合掺杂的Ba Ti2O5陶瓷,并对样品进行了XRD、SEM表征和电性能测试。结果表明:掺杂后制得的Ba Ti2O5陶瓷在1100℃烧结2 h的致密度达到96.71%,晶粒发育较完整,在室温下具有良好的铁电滞后特征,在测试频率1 KHz时,Ba Ti2O5陶瓷的介电常数为εr=71.96,说明在烧结过程中加入复合烧结助剂Cu O和B2O3可以促进液相形成并减少了气孔率,从而提高了陶瓷的致密度和介电性能。     

La2Mo2O9掺杂钛酸铋钠铁电陶瓷的微观结构与光电性能

铁电陶瓷的极化内建电场可分离光生载流子并有效降低载流子间的复合率,但是其高带隙限制了对光的吸收.本文以具有良好铁电性能的Bi0.5 Na0.5 TiO3(BNT)陶瓷为基体,通过掺杂La2 Mo2 O9降低光学带隙,提高光电流密度.样品使用传统固相法制备,随后分析了此陶瓷的XRD、拉曼、光吸收、光电流、铁电和介电性质....     

Optical and Microwave Dielectric Properties of Zn‐Doped MgAl2O4 Transparent Ceramics Fabricated by Spark Plasma Sintering

(Mg_1?xZn_x)Al₂O₄ transparent ceramics were fabricated by spark plasma sintering technique at 1325°C for 10 min. A small mount of Zn²⁺ addition to MgAl₂O₄ ceramics was very effective to the performance improvement, while further increase in Zn‐doped content would give rise to the optical transmittance deterioration. The optical and microwave dielectric properties of MgAl₂O₄ transparent ceramics were improved by Zn substitution for Mg. The in‐line transmittance of the (Mg_1?xZn_x)Al₂O₄ (x = 0.02) ceramics can be as high as 70% at λ = 550 nm and 86.5% at λ = 2000 nm, respectively. The dielectric constant ε_r of (Mg_1?xZn_x)Al₂O₄ just varied from 8.32 to 8.54, however, the Q × f value increased significantly up to a maximal value of 66,000 GHz at x = 0.02. Moreover, the τ_f of (Mg_1?xZn_x)Al₂O₄ transparent ceramics changed from ?74 to ?65.5 ppm/°C. With the increasing of Zn‐doped content, the average grain size and the porosity increased, which was the primary reason for the change in optical and microwave dielectric properties.     

改进的共沉淀法制备铝酸锌超微颗粒

以改进的共沉淀法合成铝酸锌超微晶体。得到的白色ZnAl2O4前躯体用热重-差热分析仪(TG-DTA)进行表征,白色的ZnAl2O4粉末用X射线衍射(XRD)、扫描电子显微镜(SEM)进行表征。结果表明,在表面活性剂辅助下,共沉淀法得到了具有尖晶石结构的铝酸锌超微颗粒,而且颗粒粒径小、粒度均匀、分散性好;粉体的结晶质量和粒径随煅烧温度变化而变化。得到的ZnAl2O4:Eu3+的发光性能用荧光光谱仪进行表征,结果表明,十六烷基三甲基溴化铵对样品的发光性能有显著的影响。     

Mechanical and Optical Properties of ZrO2 Doped Silicate Glass Ceramics

Silicon - In the present study, we report the physical and optical properties of low-cost glass (soda-lime silicate glass) fabricated from local minerals, obtained from Hazara division Khyber...     

Mn掺杂ZnCo2O4纳米片阵列的制备及电化学性能研究

通过水热合成再煅烧的方法在泡沫镍表面生长出了Mn掺杂的ZnCo2O4纳米片阵列。利用XRD、SEM、EDS-面扫描、XPS对样品的结构/形貌和掺入的Mn元素的分布情况进行了表征。然后,再进一步对样品进行了循环伏安曲线、恒电流充放电和循环稳定性的测试。结果表明,样品在电流密度为3 mA/cm2时,比电容达到了2 134.1 F/g;在电流密度为10 mA/cm2时,循环1 000圈,电容保持率为98.59%。因此,合成的样品比电容较高且循环稳定,是一种较为理想的超级电容器的电极材料。     

Thermal Properties of Hf‐Doped ZrB2 Ceramics

The effect of Hf additions on the thermal properties of ZrB₂ ceramics was studied. Reactive hot pressing of ZrH₂, B, and HfB₂ powders was used to synthesize (Zr_1?x,Hf_x)B₂ ceramics with Hf contents ranging from x = 0.0001 (0.01 at.%) to 0.0033 (0.33 at.%). Room‐temperature heat capacity values decreased from 495 J·(kg·K)^?1 for a Hf content of 0.01 at.% to 423 J·(kg·K)^?1 for a Hf content of 0.28 at.%. Thermal conductivity values decreased from 141 to 100 W·(m·K)^?1 as Hf content increased from 0.01 to 0.33 at.%. This study revealed, for the first time, that small Hf contents decreased the thermal conductivity of ZrB₂ ceramics. Furthermore, the results indicated that reported thermal properties of ZrB₂ ceramics are affected by the presence of impurities and do not represent intrinsic behavior.     

自燃法合成NaxCo2O4粉末及其热电性能

用自燃法结合粉末冶金工艺制备了具有高度定向结晶的NaxCo2O4热电陶瓷材料.对制得的样品进行了X射线衍射和扫描电镜分析,并进行了热电性能测试.结果表明:所获得的粉末是具备层状晶体结构的γ-NaxCo2O4.由于NaxCo2O4陶瓷材料具有气孔而降低了材料的电导率.增大材料中的Na含量可提高材料的功率因数和Seebeck系数,但降低了材料的电导率.     

掺杂玻璃助剂的Ba5Nb4O15陶瓷烧结特性及介电性能

引入玻璃烧结助剂,采用液相烧结手段制备了低温烧结Ba5Nb4O15微波介质陶瓷.采用X射线衍射和扫描电子显微技术分析了陶瓷的物相组成和微观形貌.研究表明:陶瓷主晶相为Ba5Nb4O15,铋硅酸盐玻璃在陶瓷中以液相形式存在,促使陶瓷烧结温度从1300℃降至1100℃.添加4wt.％铋硅酸盐玻璃的Ba5Nb4O15陶瓷在1100℃烧结,具有良好的微波性能:相对介电常数εr=39.01,品质因子Q × f=12214GHz.     

Dielectric Properties of Pure and Gd‐Doped HfO2 Ceramics

The pure, 2 at.%, and 20 at.% Gd‐doped HfO₂ ceramics were prepared by the standard solid‐state reaction technique. Dielectric properties of these ceramics were investigated in the temperature range 300–1050 K and frequency range 20–5 × 10⁶ Hz. Our results revealed an intrinsic dielectric constant around 20 in the temperature below 450 K for all tested ceramics. Two oxygen‐vacancy‐related relaxations R1 and R2 were observed at temperatures higher than 450 K, which were identified to be a dipolar relaxation due to grain response and a Maxwell–Wagner relaxation due to grain‐boundary response, respectively. The dielectric properties of the pure and slightly doped (2 at.%,) samples are dominated by the grain‐boundary response, which results in a colossal dielectric behavior similar to that found in CaCu₃Ti₄O₁₂. The doping level of 20 at.% leads to the structural transformation from monoclinic phase to cubic phase. The dielectric properties of the heavily doped HfO₂ are dominated by the grain response without any colossal dielectric behavior.     

掺杂ZnO-B2O3低温烧结BiNbO4介质陶瓷的研究

研究了烧结助剂ZnO-B2O3对BiNbO4陶瓷烧结特性及介电性能的影响.结果表明ZnO-B2O3形成晶界玻璃相存在于晶粒之间,促进烧结,大幅度降低BiNbO4陶瓷的烧结温度,促使瓷体晶粒尺寸均匀和致密;但ZB的质量分数大于3%,阻碍晶粒长大,破坏晶体结构和排列,导致材料的缺陷和本征损耗增加,从而降低材料的介电性能.ZnO-B2O3的掺杂量以1%为最佳,在880℃保温4h,可达到97%理论密度,在100MHz测试频率下,εr=42,tanδ＜1.5×10-3.     

Er2O3掺入对氧化铝复合陶瓷的耐磨性和微观结构影响

以工业Al2 O3为主要原料,CaO-MgO-SiO2作为烧结助剂的体系中,研究了Er2 O3的添加对高铝瓷的耐磨性的影响.结果表明:过量添加Er2 O3明显提高了陶瓷样品的烧结温度,陶瓷的耐磨性能也被恶化.而微量添加Er2O3对陶瓷的烧结温度影响不大,且耐磨性能提高了约22％.     

Preparation and Electric Properties of Dense Nanocrystalline Zinc Oxide Ceramics

This communication reports on the preparation and electric properties of dense nanocrystalline ZnO ceramics. By spark plasma sintering, nanocrystalline (∼100 nm) ZnO ceramics with a high density of 98.5% were obtained at a very low temperature of 550°C. Electric property measurement revealed a novel conduction nonlinearity in the sample sintered at 500°C. This phenomenon is due to the nanometerization of ZnO crystal and the grain boundary layer with an amorphous interfacial layer.     

铁酸钴纳米晶体的制备及机理

以ＦｅＳＯ４·７Ｈ２Ｏ和ＣＯＳＯ４·７Ｈ２Ｏ为原料,首先制备出晶粒细小的盐渍化碱式碳酸盐前驱体．在５００℃焙烧１ｈ后,制备出ＣｏＦｅ２Ｏ４纳米晶体材料,经ＸＲＤ和ＴＥＭ检测,粒径为４０ｎｍ,粒度均匀．     

Extremely Enhanced Nonlinear Current–Voltage Properties of Tb‐Doped CaCu3Ti4O12 Ceramics

Nonlinear current–voltage properties of CaCu₃Ti₄O₁₂ ceramics were extremely enhanced by doping with Tb. Substitution of Tb to CaCu₃Ti₄O₁₂ resulted in a decrease in grain size due to the ability of Tb ions to inhibit grain boundary mobility. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were degraded after doping with Tb. Surprisingly, the nonlinear electrical properties were strongly enhanced. The best properties with a nonlinear coefficient of ~29.67 and breakdown electric field strength of ~1.52 × 10⁴ V/cm were obtained in the Ca_0.775Tb_0.15Cu₃Ti₄O₁₂ ceramic. These extremely enhanced properties were attributed to modification of grain boundary electrical response due to the effect Tb substitution.