氟化钙掺杂对钛酸锶钡陶瓷结构和介电性能的影响

研究了Ca F2掺杂对钛酸锶钡(Ba0.6Sr0.4Ti O3,BSTO)陶瓷的结构和介电性能的影响。采用传统烧结工艺制备了Ca F2掺杂的BSTO陶瓷,对其晶体结构、微观形貌和介电性能进行了研究。XRD结果显示,Ca F2掺杂BSTO陶瓷为钙钛矿结构,当掺杂量≥3%(质量分数)时,基体中出现第二相Ba Ca Ti O4。添加少量Ca F2(0.5%)可明显减小晶粒尺寸,随掺杂量继续增加,晶粒尺寸变化不明显。Ca F2掺杂降低了BSTO陶瓷的介电常数和介电可调性,减小了其介电损耗,提高了材料的综合使用性能。     

低锐度F—P干涉具调谐TEA CO2激光器理论分析

从理论上计算了低锐度F-P干涉具有直接输出耦合调谐TEA CO2激光器的输出特性，结果表明：通过改变干涉具的间距，激光器的输出波长可在9μm带和10μm带之间切换；而且，输出一般为多波长，每个波长包含精细纵模结构，纵模的数目和谱线展宽有关，理论计算还给出了输出脉冲波形和脉冲能量随波长的分布。     

氧化铝掺杂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3陶瓷介电性能的影响

Zr4+取代Ti4+的Ba0.6Sr0.4(Zr0.2Ti0.8)O3固溶体在降低介电常数的同时,保持了BST固溶体优异的可调性。为降低BST材料的介电损耗和介电常数,以氧化铝为改性剂对Ba0.6Sr0.4(Zr0.2Ti0.8)O3材料(BSZT材料)进行了掺杂。随着氧化铝掺杂质量分数从1%到10%增加,BSZT材料的介电常数从5000降低到了1550(100kHz),介电损耗降低到0.001(100kHz)以下,而材料的介电可调性保持在35%左右(1.5kV/mm)。X射线衍射图谱表明,烧结后得到的BSZT材料具有典型的钙钛矿结构。扫描电子显微镜观察表明,氧化铝的掺杂使得陶瓷致密度较高,晶粒均匀。     

BSTO/MgO复相铁电陶瓷的调谐性分析

基于目前的实验数据,构建了复合材料模型解释Ba0.55Sr0.45TiO3/MgO复相铁电陶瓷的调谐性。结果表明,所分析的三种模型中,球状填充模型能较好的解释Ba0.55Sr0.45TiO3/MgO体系中介电常数的调谐性与偏压电场的关系,特别当Ba0.55Sr0.45TiO3的质量分数小于50%时,模型分析结果与实验数据吻合较好。     

Conservation of Permittivity and Tunability of Ferroelectrics Over Temperature

The existence of an intersection point of electric field strength dependencies of permittivity of ferroelectrics at different temperatures is theoretically described by Ginzburg-Devonshire (GD) theory and experimentally confirmed by studying (Ba_0.3Sr_0.7)TiO₃ (BSTO) and SrTiO₃ (STO) thin film varactors. GD analysis enables one to propose a way to improve the thermal stability of ferroelectric microwave devices. In particular, parameters of a L-band digital (0°/180°) phase-shifter fabricated from thick BSTO film varactors were stabilized in the temperature range T = (210–310) K by application of variable to DC control voltages.     

Growth and Dielectric Properties of Ferroelectric BaTiO3 Thin Films for Cantilever-Type Microsensors

ABSTRACT

Ferroelectric BaTiO₃ (BTO) thin films were deposited on Si, silicon-on-insulator (SOI) and MgO substrates by pulsed laser deposition. The orientations of the films, polycrystalline and epitaxial phase, were controlled by the lattice mismatch between the BTO film and substrates. The structural properties and surface morphologies were examined using X-ray diffractometer and atomic force microscope. The dielectric properties of BTO films were investigated using metal-ferroelectric-metal (MFM) and interdigital co-planar capacitors. Conductive oxide layers, SrRuO₃(SRO) and La_0.5Sr_0.5CoO₃ (LSCO), were grown on Si and SOI substrates as bottom electrodes. For MFM capacitors based on Au/BTO/SRO/Si and Au/BTO/LSCO/SOI layer structures, a little asymmetric capacitance-voltage curves were obtained with about 36% capacitance tunability. The remanent polarizations were about 21 μC/cm² and the coercive fields were about 71 kV/cm. For an interdigital capacitor based on Au/BTO/MgO layer structure, a little lossy capacitance-voltage curve was obtained with about 64% capacitance tunability.     

0.15CoAl0.2Fe1.8O4-0.75BaTiO3纳米磁电复合材料的电场诱导介电特性研究

采用溶胶-凝胶法制备了0.15CoAl0.2Fe1.8O4-0.75BaTiO3纳米磁电复合材料。XRD分析表明,制备的样品中包含钙钛矿(BaTiO3相)和尖晶石结构(CoAl0.2Fe1.8O4相),没有其它明显杂相生成。扫描电镜表明,颗粒平均粒径约为45nm,且压磁相均匀分布于压电相中。研究了该纳米磁电复合材料在外加偏置静电场诱导下的介电常数随频率的变化,分析了直流偏置电场诱导下的相对介电常数变化值Δεr和调谐率K。随着偏置电场的增大,Δεr和K都变大;随着频率的增加,Δεr和K都减小。并且,在外加偏置电压为3kV/cm时可以获得相对较大的调谐率(4.05%)。     

Dielectric and Ferroelectric Properties of Ba(Zr0.35Ti0.65)O3 Thin Films Grown by a Sol-Gel Process

The Ba(Zr_0.35Ti_0.65)O₃ (BZT) thin films were deposited via sol-gel process on LaNiO₃-coated silicon substrates. XRD showed that the crystallinity of BZT film grown on LaNiO₃ coated silicon substrates is better than that of BZT film grown on Pt. Both films showed perovskite phase and polycrystalline structure. The temperature dependent dielectric measurements revealed that the thin films had the relaxor behavior and diffuse phase transition characteristics. The capacitor tuning was about 44% for each BZT film grown on LaNiO₃/Pt and Pt electrodes at 1 MHz. Especially, the values of dielectric loss at 1 MHz ranged from 0.02 to 0.009 in the bias range of 0 to 514 kV/cm, respectively. The leakage currents density of thin films grown on LaNiO₃/Pt and Pt electrodes at 300 kV/cm was about 8.5 × 10^–7 and 1.1 × 10^–5 A/cm², respectively. This work demonstrates a potential use of BZT films for application in tunable microwave devices.     

Dielectric Characteristics and Tunability of Barium Stannate Titanate Ceramics

Ba(Ti_{1 –x} Sn _x )O₃ solid solutions were prepared by a solid state reaction method, and their dielectric and tunable characteristics were investigated together with the microstructures and diffused phase transition behaviors. The dielectric relaxation behaviors were observed and became stronger with increasing x.The obvious field dependence of the present system was observed with high dielectric constant and low loss at relatively lower DC electric field. The excellent tunable dielectric characteristics were achieved for x= 0.15 at room temperature: tunability 56%, tan 0.003 at 10 kHz under 7.6 kV/cm, indicating that it is a promising candidate for electric-field tunable dielectrics working at room temperature.