溶胶-凝胶法制备的LiLaxFe5-xO8纳米晶材料的微波吸收特性

采用溶胶-凝胶法制备了掺稀土元素镧的锂铁氧体纳米晶粉末，就镧元素的含量对锂铁氧体吸波性能的影响进行了对比研究。实验表明，用聚乙二醇凝胶法制备的LiLaxFe5-xdO8纳米晶粉末，当x=0.03时，对微波吸收效果最佳，在涂层厚度1.2mm，测试频段为7.5～11.9GHz内,35dB带宽为2.5GHz，在10.6GHz处，吸收峰值达45dB。     

W型六角铁氧体的制备及吸波性能

首先用柠檬酸溶胶-凝胶(sol-gel)法制备了BaCo2Fe16O27型六角铁氧体,经不同温度焙烧后,分析产物的结构和形貌,确定出较优的焙烧温度,然后以此工艺制备W型Ba(Zn1-x Cox)2Fe16O27(x＝0,0.2,0.6,0.8,1.0)六角铁氧体,分析其吸波性能.研究表明,x＝0.8时,样品的有效吸波带宽可拓宽到12～18 GHz整个波段,吸收峰值可提高到-20dB.     

纳米钴、镍铁氧体的制备与吸波性能

采用柠檬酸盐溶胶-凝胶法制备纳米钴、镍铁氧体.采用X射线衍射(XRD)、原子力显微镜(AFM)分析了铁氧体物相组成及微观形貌;用振动样品磁强计测定产物磁滞回线.以苯丙乳液为基相制备铁氧体涂层,用网络分析仪测试了涂层的吸波性能.结果表明,凝胶缓慢升温至850℃处理,得到结晶度良好的尖晶石型纳米钴、镍铁氧体,钴铁氧体平均粒径为36nm,镍铁氧体平均粒径为56nm.在5GHz～12GHz频段内,涂层的微波反射损耗大部分在10dB以上,具有良好的吸波性能.     

W型铁氧体BaCoZnFe_(16)O_(27)的制备及吸波性能

以金属硝酸盐为原料,采用溶胶-凝胶法制备了W型BaCoZnFe16O27铁氧体。利用XRD,SEM和矢量网络分析仪对样品的结构、形貌和吸波性能进行了分析与测试。并考察了焙烧温度、焙烧时间对W型铁氧体的形成及吸波性能的影响。结果表明,当焙烧温度为1200℃、焙烧时间为2h,前驱体可全部转化为单一晶相的W型铁氧体。钴锌共掺杂致使W型BaCoZnFe16O27的磁晶各向异性场和自然共振频率发生改变,进而改善了样品在低频波段的吸波性能。单一晶相的BaCoZnFe16O27铁氧体在5.5GHz处对电磁波具有良好的吸收,最大吸收强度达-18dB,吸收大于5dB的频带带宽为1GHz。     

漂珠/钡铁氧体复合材料的制备及性能

采用溶胶-凝胶自蔓延燃烧法在漂珠表面包覆钡铁氧体颗粒涂层,制备了漂珠/钡铁氧体复合材料。利用扫描电镜(SEM)、X射线衍射仪(XRD)、振动样品磁强计(VSM)及矢量网络分析仪等表征手段,研究了样品的显微形貌、结构、磁性能及吸波性能。结果表明,包覆后漂珠表面形成了均匀致密的钡铁氧体涂层,经850℃高温热处理2h后产生了钡铁氧体的晶相物质。制备的复合材料在2～18 GHz范围内具有较好的介电损耗和磁损耗性能,当吸波材料厚度为3.0 mm时,在8.4 GHz的反射损耗峰值为–15.44 dB,反射损耗小于–12 dB的带宽为4.2 GHz。     

PANI/SrFe12O19复合材料的结构和吸波性能

采用氧化物法制备了导电聚苯胺(PANI)铁氧体磁性复合颗粒.利用透射电子显微镜(TEM)、X射线衍射仪(XRD)和傅里叶红外光谱仪(FT-IR)等分析手段观测了复合粒子的形貌、结构和性能,采用矢量网络分析仪在0.5～20GHz频段内测试了材料的吸波性能.实验结果表明,具有核/壳结构的导电聚苯胺复合材料具有较好的吸波性能.当SrFe12O19和Li0.45Zn0.1Fe2.45O4掺入量分别为15wt%和5wt%时,最大衰减为24.7dB,-8dB带宽达4.4GHz.因此通过调整复合体中铁氧体的含量和种类,可以调整其特性以满足不同需求.     

磁织构化处理对NiZn铁氧体基复合电波吸收材料吸波特性的影响

以NiZn铁氧体为主吸收剂,添加其他介质制成复合电波吸收材料,经垂直和平行磁场磁织构化处理后,在7.5~12GHz波段测试其吸波性能,发现样品的最大反射衰减量由原来的30.5dB分别增高到36.0dB和31.7dB,匹配厚度略增,面密度略降,吸收峰移向低频,10dB带宽略增.垂直和平行磁场织构化的双层结构,其吸波性能与单层相比有所改变.     

导电聚苯胺/γ-Fe2O3纳米复合物的红外与微波吸收性能

用溶胶-凝胶法制备了γ-Fe2O3纳米粉料,然后通过原位聚合方法制备了质子酸掺杂的聚苯胺(PANI)/γ-Fe2O3纳米复合材料.对其形貌、微结构以及电导率分别用X射线衍射仪(XRD)、透射电镜(TEM)和四探针法进行了表征,用矢量网络分析仪和傅立叶红外谱仪(FTIR)测试分析了样品的微波、红外吸收特性.发现PANI/ 5 wt% γ-Fe2O3复合材料在7～18GHz频率范围内最大反射式吸波衰减为-25dB, 吸波衰减小于-8dB的有效带宽为4.6GHz,比未复合的导电聚苯胺和纳米γ-Fe2O3材料具有更优越的微波吸收性能,但随着γ-Fe2O3的含量分别增加到10%和20% 时,复合物的带宽变窄,微波吸收性能下降;另外,PANI/ 5wt% γ-Fe2O3复合物与纳米γ-Fe2O3材料以及导电聚苯胺相比,红外吸收特性得到了显著增强,在3276cm-1波数附近的透过率仅为17%、1700cm-1 ～1100cm-1范围内透过率均小于40%.同时对PANI/γ-Fe2O3纳米复合材料的微波和红外吸收机理进行了初步探讨.     

ZnO-羰基铁复合纳米粒子的吸波特性

采用高能球磨法制备了氧化锌-羰基铁复合体吸波剂,研究了材料在0~20GHz频率下的吸波特性。实验表明,随着球磨时间的延长,吸波剂颗粒尺寸减小,吸收峰强度增高。通过对比不同样品的吸波特性发现,氧化锌作为介电材料包覆在羰基铁颗粒上,使得吸收谱向低频方向扩展,吸波效果明显增强。所制备的球磨30h的氧化锌-羰基铁3mm厚样品的-5dB带宽达到10.8GHz,-8dB带宽达到5.1GHz,最大吸收峰为-30dB。     

(La0.5Na0.5)xBa1-xFe12O19纳米铁氧体粉末的微波吸收特性

利用柠檬酸溶胶-凝胶自蔓延燃烧法合成掺杂稀土元素镧的M型六角铁氧体(La0.5Na0.5)xBa1-xFe12O19 (x=0.0,0.1,0.3,0.5)纳米粉末,铁氧体的晶型通过X射线衍射得到证实,研究了镧含量对铁氧体的复介电常数、复磁导率的影响.实验结果表明,添加适量的稀土镧能显著地改善铁氧体的吸波性能,掺杂量为x=0.3的样品微波性能最佳.     

Phase Formation,Dielectric, Ferroelectric and Magnetic Properties of Cr2O3 Doped (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

Abstract

In this paper, we studied the effect of Cr₂O₃ doping (0–0.8?wt%) on the phase formation, dielectric, ferroelectric and magnetic properties of (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ (BCTZ) ceramics prepared by the solid state combustion method. All samples were prepared with a calcined and sintered temperature of 1050?°C and 1450?°C, respectively, for 2?h. The results of the XRD patterns showed the coexistence between the tetragonal (T) and orthorhombic (O) phases for all samples, and the tetragonal phase increased with increasing amounts of Cr₂O₃. The dielectric constant decreased when Cr₂O₃ increased. The P-E hysteresis loops of the BCTZ ceramics doped with Cr₂O₃ between 0 and 0.2?wt% showed slim and saturated loops. By increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, the P-E loops were unsaturated and a leakage current was produced. The undoped BCTZ ceramics exhibited diamagnetic behavior. The sample with 0.2?wt% Cr₂O₃ showed ferromagnetic behavior. Increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, caused the ceramics to exhibit paramagnetic behavior. Doping with Cr₂O₃ led to improper ratios between the tetragonal and orthorhombic phases, decreased density and increased porosity which caused a decrease in the electric properties.     

Effect of Rare Earth Europium Substitution on the Microstructure,Dielectric, Ferroelectric and Pyroelectric Properties of PZT Ceramics

Polycrystalline samples of Europium modified lead Zirconate titanate (Pb_{1 – x} Eu_x)(Zr_0.55Ti_0.45)_{(1 – x/4)}O₃ with x = 0.00, 0.02, 0.04, 0.06 has been prepared by mixed oxide (MO) method at sintering temperature of 1250C. The structural characterization of the samples investigated by X-ray diffraction technique exhibit tetragonal structure. PEZT (2/55/45) ceramics show single perovskite phase. Scanning electron micrographs depict uniform, densely packed structure. Dielectric, Pyroelectric and Ferroelectric studies have been performed and are reported and discussed in this paper. PEZT (2/55/45) show good current responsivity (F_i), voltage responsivity (F_v) and detectivity (F_d), in comparison to other compositions under study. Moreover its ferroelectric properties (high remanent polarization with low coercive field) make it suitable material for nonvolatile memory applications.     

SYNTHESIS AND CHARACTERIZATION OF NICKEL FERRITE-BARIUM TITANATE CERAMIC COMPOSITES

ABSTRACT

Magnetoelectric composites were synthesized from piezoelectric BaTiO₃ and ferrimagnetic NiFe₂O₄. These two phases are mixed, mechanically milled and heat treated. A characterization is made by means of electronic microscopy and x-ray diffraction. The results of the magnetic, electric, ferroelectric and piezoelectrical response of two different compositions are obtained. The composites are superparamagnetic in all the measured temperature range. It was observe a magnetic change induced by a structural transition of the ferroelectric phase. The composites behaves as an acceptable mechanical resonator when the content of the ferroelectric phase is equal or greater than 60 wt.%.     

Fabrication and electrical properties of PC-PNZT-PVDF-GO composites

The objectives of this research are to fabricate and investigate new smart composites for the sensing and actuation applications in civil engineering. The fabrication and properties of cement-based piezoelectric ceramic composites are emphasized. However, cement-based piezoelectric composites are still difficult to obtain great electrical properties due to the evidence of some pores in the composites. Therefore, a novel approach to effectively improve their polarization of piezoelectric ceramic is to add a semiconductor (graphene oxide) and an insulator (polyvinylidene fluoride) phases between piezoelectric particles by the introduction of a small volume fraction of a third phase. Microstructure of the new composites was investigated using Scanning electron microscope (SEM). Dielectric permittivity and ferroelectric properties were then investigated.     

SYNTHESIS AND CHARACTERIZATION OF SB-SUBSTITUTED (K0.5Na0.5)NbO3 PIEZOELECTRIC CERAMICS

ABSTRACT

Lead-free piezoelectric ceramics (K_0.5Na_0.5)(Nb_1-xSb_x)O₃+0.5 mol.%MnO₂, where x = 0 ÷ 0.10, with single phase structure and rhombohedral symmetry at room temperature were prepared by conventional ceramic technology. The optimal sintering temperatures of compositions were within 1100°–1140°C. MnO₂ functions as a sintering aid and effectively improves the densification. The samples reached density from 4.26 g/cm³ for undoped (K_0.5Na_0.5)NbO₃ to 4.40 g/cm³ for Mn/Sb⁵⁺ co-doped ceramics. The co-effects of MnO₂ doping and Sb⁵⁺ substitution lead to significant improvement in dielectric and piezoelectric properties: ε at the T_c increased from 6000 (KNN) to 12400 (x = 0.04), d₃₃ = 92 ÷ 192 pC/N, k_p = 0.32 ÷ 0.46, k_t = 0.34 ÷ 0.48.     

Pb(Mg1/3Nb2/3)0.97Ti0.03O3 Ferroelectric Thin Films, Deposited by Laser Ablation on TiN Bottom Electrodes

Pb(Mg_1/3Nb_2/3)_0.97Ti_0.03O₃ (PMNT) polycrystalline thin films were deposited on Titanium Nitride electrode at different temperatures by laser ablation, using a wavelength of 248 nm. The morphology of the films was analyzed by scanning electron microscopy (SEM). The nature of the ferroelectric layer-electrode interface is studied by transmission electron microscopy (TEM) as well as the effect of its characteristics in the performance of the multilayer system. The influence of the annealing temperature on the dielectric properties was studied by hysteresis and fatigue measurements.     

平衡态与非平衡态等离子体物性参数计算模型研究

等离子体的宏观特性和内部微观过程紧密联系在一起。研究等离子体粒子组分构成以及对组分有强烈依赖关系的热力学参数、输运参数等物性参数,将为深入了解等离子体的形成机理奠定微观理论基础。笔者从元素化学计量守恒、道尔顿分压定律、质量作用定律、等离子体电荷准中性条件出发,总结了计算平衡态和非平衡态等离子体化学组分的基本方法。在此基础上,介绍了等离子体热力学参数(质量密度、焓值、熵值与比热)和输运参数的计算方法,并阐述了目前等离子体物性参数计算研究中存在的主要问题。     

Study of the structure and electrical properties of PMN-PNN-PT ceramics near the morphotropic phase boundary

A series of Pb(Mg_1/3Nb_2/3)O₃-Pb(Ni_1/3Nb_2/3)-O₃-PbTiO₃ (PMN-PNN-PT) ceramics with compositions of (1–x)(0.67PMN-0.33PT)-x(0.64PNN-0.36PT) (x = 0.1–0.9) were synthesized using the columbite precursor method. The phase structures, as well as the dielectric and piezoelectric properties of the ceramics were investigated in detail. X-ray diffraction results demonstrate that all the samples possess a pure perovskite structure. It is found that the morphotropic phase boundary (MPB) region of the PMN-PNN-PT ternary system is located near the line connecting the MPBs of the PMN-PT and PNN-PT binary systems. A high value of the maximum dielectric constant (ɛ_m = 45540, at 1 kHz), together with a high value of the piezoelectric coefficient (d₃₃ = 780 pC/N), were obtained for the composition x = 0.2. The results show that a partial substitution of PNN-PT for PMN-PT can lead to improved electrical properties in this ternary system.     

Effect of Gd doping on crystalline orientation,structural and electric properties of PZT thin films prepared by Sol-Gel methods

Gadolinium (Gd)-doped lead zirconium titanate (PGZT) thin films have been prepared by Sol-Gel methods to investigate the effects of Gd doping on crystalline orientation, structural and electric properties of lead zirconium titanate (PZT) films according to doping concentration from 0% to 5%. Conventional heat process and appropriate doping concentration, without introducing a single crystal seed layer, were used for obtaining (100)-oriented PGZT thin films with dense columnar structures. The maximum dielectric constant (1310.35 at 100 Hz) and the optimum ferroelectric properties were obtained for 2% Gd-doped film. 1% Gd-doped PZT film exhibited excellent piezoelectric properties.     

国产耐热导线的机电性能研究

耐热铝合金导线是一种能够大幅度提高载流量的新型导线.在输电线路上推广应用普通耐热铝合金导线,具有显著的经济效益和社会效益。近年来国产普通耐热铝合金导线的大量试验数据表明,国内部分厂家生产的普通耐热铝合金导线的主要机械和电气性能,已达到或超过进口产品的水平,为我国电网大规模地采用国产耐热导线奠定了基础。