Bi基焦绿石结构陶瓷的介电频率特性

在低频、射频和微波波段频率下,借助HP4192A阻抗分析仪和HP8720ET/ES网络分析仪,对3种Bi基焦绿石结构介电陶瓷材料BZN[(Bi1.5Zn0.5)(Zn05Nb1.5)O7]、BZS[(Bi1.5Zn05)(Zn0.5Sb1.5)O7]和BCZN[(Bi1.5Ca0.5)(Zn0.5Nb1.5)O7]的介电频率特性进行了分析研究.结果发现:介电常数随着Bi基焦绿石结构中氧八面体间隙增大而增大;从低频到射频,BZN(ε≈160)、BZS(ε≈42)和BCZN(ε≈81)三体系介电常数都较高且很稳定,其介质损耗都很低(Tanδ≈10-4);在微波频段(4GHz)下,介电常数分别约为98.596、30.573和56.451.     

钛酸锶的宽频带介电谱

利用计算机自动控制的超低频介电谱测量装置和HP4192A阻抗分析仪，在10^-4Hz～10^5Hz宽这九个数量级的范围内测量了钛酸锶陶瓷的频域介电谱。其频域复介电常数可很好地拟合为两项之和。其中超低频项来自于晶界间空间电荷运动的贡献，高频项来自于晶粒内部空间电荷运动的贡献。高频项复介电常数的实部在频率增大时变为负值，这说明介电谱用频域方法来描述是有缺陷的，其测量结果无法用传统的介电极化加以解释。     

(Mg0.95Ca0.05)TiO3晶体的激光加热基座法生长及其性质测定

采用激光加热基座法(LHPG)生长出了共晶系(Mg0.95Ca0.05)TiO3。晶体。通过粉末X射线衍射分析了所生长晶体的晶相，采用扫描电镜和显微拉曼光谱技术研究了所生长晶体的微观结构。(Mg0.95Ca0.05)TiO3晶体由CaTiO2和Mg-TiO2两种晶体复合而成。介电测量结果表明：(Mg0.95Ca0.05)TiO3晶体沿生长方向具有较大的介电常数和较小的共振频率温度系数。     

高密度CaCu_3Ti_4O_(12)陶瓷的介电性质

利用热压方法制备了高密度的CaCu3Ti4O12陶瓷,研究了其微观结构、晶格结构和介电性质。实验发现,短时间热压方法制备的陶瓷的相对密度就能达到98.3%,并且微观结构呈现晶粒尺寸双峰分布的特点。XRD显示热压方法制备的陶瓷中含有少量的Cu2O第二相,而经过退火处理的热压陶瓷则只含有CuO第二相。热压方法制备的陶瓷和经过退火处理的热压陶瓷的室温介电频谱上有两个介电弛豫,而常规方法制备的陶瓷只有一个。并且热压方法制备的陶瓷的低频介电常数高达2×105,经过退火处理的热压陶瓷的低频介电常数更是达到1×106。本研究进一步讨论了其微观结构和介电性质之间的关系。     

Pb掺杂BaO-Nd_2O_3-TiO_2系微波介质陶瓷及其低频测量方法的研究

初步研究了微波介质陶瓷 Ba3.75Nd9.5Ti18O54在 Pb掺杂后的显微组织及晶体结构的变化 ,并验证了用低频介电测量数据估算微波介质陶瓷材料介电性质的可行性。研究结果表明 ,掺入少量 Pb以后 ,Ba3.75Nd9.5Ti18O54 介电陶瓷的微观结构有显著变化 ,介电性能 ,尤其是相对介电常数εr有明显的提高。     

氟化非晶碳薄膜的低频介电性质分析

研究了电子回旋共振等离子体技术沉积的氟化非晶碳(α-C：F)薄膜的低频(10^2～10^6Hz)介电性质。发现α-C：F薄膜的低频介电色散随源气体CHF3／C6H6的比例、微波入射功率而改变。结合薄膜键结构的红外分析,发现薄膜中C=C相对含量的增大是导致低频介电色散增强的原因,而C—F相对含量的增大则使低频介电色散减弱。     

Pb掺杂BaO—Nd2O3—TiO2系微波介质陶瓷及其低频量方法的研究

初步研究了微波介质陶 Ｂａ３．７５Ｎｄ９．６Ｔｉ１８Ｏ５４在Ｐｂ掺杂后的显微组织与及晶体结构的变化，并验证了用低频介电测量数据估算微波介质陶瓷材料介电性质的可行性。研究结果表明，掺入少量Ｐｂ以后，Ｂａ３．７５Ｎｄ９．５Ｔｉ１８Ｏ５４介电陶瓷的微观结构有显著变化，介电性能，尤其是相对介电常数εｒ有明显提高。     

铁电陶瓷/铁氧体叠层共烧体的介电特性

采用电介质物理学等效电路分析方法研究了Pb(Ni1/3Nb2/3)O3基铁电陶瓷与NiZnCu铁氧体叠层共烧体的介电频率响应,探讨了共烧体界面对介电性能的影响.结果表明,叠层共烧体的介电常数随频率的增加而减小,介电损耗随着频率的增加先增大后减小,有明显的损耗峰出现;界面扩散层对叠层共烧体电学响应有影响,叠层共烧体等效电路可视为介电材料层、铁氧体材料层和界面扩散层C re-R re等效电路的串联,并且界面扩散层会对叠层共烧体低频部分的介电响应起作用.     

等静压力诱导的PMN-PT单晶介电弛豫特性研究

研究了不同等静压力下的PMN-PT单晶的介电常数(εr)与温度(T)的关系,以及常温下介电常数(εr)及损耗(tanδ)与压力(p)之间的关系.发现了PMN-PT单晶在压力作用下出现明显的介电频率弥散现象.当等静压力增大到一定压力时,PMN-PT单晶的介电常数值迅速降低,介电频率弥散更加显著,且出现弛豫特性,介电损耗的弛豫特征更加明显.随着频率的增加,介电损耗峰对应的峰值压力向高压方向移动.其根本原因是压力诱导的介电-压力弛豫特性导致的.     

NaCu_3Ti_3NbO_(12)和NaCu_3Ti_3SbO_(12)陶瓷的巨介电性质及NaCu_3Ti_3SbO_(12)陶瓷的低介电损耗特性

利用传统的固相反应工艺制备了NaCu3Ti3NbO12和NaCu3Ti3SbO12陶瓷,对它们的介电性质和晶格结构进行了研究。结果显示,两种陶瓷都存在低频介电常数高于7×103的巨介电行为;在室温或者更低温度下,两种陶瓷的介电频谱(40 Hz~110 MHz)的实部只出现一个介电弛豫,而更高温度下的介电频谱的实部则会有两个介电弛豫;XRD结果显示两种陶瓷中都含有少量的CuO第二相。这些实验结果能用CCTO陶瓷中的内阻挡层电容效应解释。NaCu3Ti3SbO12陶瓷的室温介电损耗在40 Hz到7 kHz的宽频率范围内低于0.05,并且其1 kHz的介电损耗在-50~80℃的宽温度范围内低于0.05,这对于实际应用有重要意义。     

Dielectric response ofp-terphenyl

Dielectric properties ofp-terphenyl crystals (large- and small-grained polycrystalline layers and compressed pellets) have been measured. An anisotropy of the dielectric properties of the crystals has been found. The dielectric losses in disorderedp-terphenyl structures proved to be of injected carrier origin: a discontinuous change of dielectric losses in the disordered structures being found near 285 K.     

Effect of cobalt (Co<Superscript>2+</Superscript>) concentration on structural,optical, thermal and mechanical properties of potassium acid phthalate (KAP) crystals

Single crystals of pure and Co²⁺ (0.2, 0.4 and 0.6 mol%) doped KAP crystals were grown by low temperature slow evaporation method. The grown crystals were subjected to various characterization techniques such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV–visible spectroscopy and Second Harmonic Generation studies. The XRD profile confirms that Co²⁺ ions incorporated into the KAP crystal lattice. The existence of functional groups in the grown crystals have been studied by FTIR analysis. Optical transmission is decreased when doping Co²⁺ concentration increase. After melting point, no decomposition is found in the pure crystal. Vickers micro hardness studies revealed that the doped crystals possess very high hardness values. The dielectric constant, dielectric loss and thermal stability values have been measured as a function of frequency and temperature respectively for the doped crystals.     

Irradiation effect on the electrical properties of corundum and quartz single crystals

The radiation effects in corundum and quartz crystals have been assessed at temperatures from 25 to 450°C and gamma doses from 10⁴ to 10⁹ rad. The radiation effects on the conductivity and dielectric losses of the crystals have been shown to be nonlinear, with extrema and inflections. The conductivity of corundum is characterized by three-step kinetics, with pronounced carrier generation in the range 100–200°C and restoration of parameters at 400°C in crystals irradiated to high doses. Both corundum and quartz crystals have extrema tanδ(t) in at different gamma doses. The peaks (200–250 and 50–150°C) grow with increasing frequency, without shifting to higher temperatures. The peaks seem to be due to different mechanisms of dielectric losses. The dose dependences of tanδ and σ have been compared up to 5 × 10⁹ rad and have been shown to correlate with one another. The extrema have been interpreted in terms of the Vul model. We have analyzed the possible origins of the loss maxima and have evaluated the activation energies for ionic polarization and conduction in the materials studied. We assume that the dielectric losses in the irradiated crystals are determined by conduction and polarization.     

Dielectric behaviour of strontium tartrate single crystals

Strontium tartrate trihydrate (STT) crystals have been grown in silica hydrogel. Various polarization mechanisms such as atomic polarization of lattice, orientational polarization of dipoles and space charge polarization in the grown crystals have been understood using results of the measurements of dielectric constant (έ′) and dielectric loss (tan δ) as functions of frequency and temperature. Ion core type polarization is seen in the temperature range 75–180°C, and above 180°C, there is interfacial polarization for relatively lower frequency range. One observes dielectric dispersion at lower frequency presumably due to domain wall relaxation.     

Thermal,FT-IR and dielectric studies of gel grown sodium oxalate single crystals

Oxalic acid metabolism is important in humans, animals and plants. The effect of oxalic acid sodium salt is widely studied in living body. The growth of sodium oxalate single crystals by gel growth is reported, which can be used to mimic the growth of crystals in vivo. The grown single crystals are colourless, transparent and prismatic. The crystals have been characterized by thermogravimetric analysis, FT-IR spectroscopy and dielectric response at various frequencies of applied field. The crystals become anhydrous at 129·3°C. Coats and Redfern relation is applied to evaluate the kinetic and thermodynamic parameters of dehydration. The dielectric study suggests very less variation of dielectric constant with frequency of applied field in the range of 1 kHz-1 MHz. The nature of variation of imaginary part of complex permittivity, dielectric loss and a.c. resistivity with applied frequency has been reported.     

Effect of Background Fe Impurities on the IR Absorption and Dielectric Response of High-Resistivity ZnSe Single Crystals

High-resistivity zinc selenide crystals containing background impurities have been studied by IR spectroscopy and dielectric spectroscopy. Their IR absorption spectra contain a band attributable to the presence of background Fe impurities in the material. The dielectric characteristics of the ZnSe crystals lead us to conclude that, because of a nonuniform distribution of background impurities, they have the form of matrices containing inclusions.     

Dielectric anisotropy and electrical properties of the copper phthalocyanine (CuPc): 4–4′-n-Heptylcyanobiphenyl (7CB) composite liquid crystals

Dielectric anisotropy and electrical properties of the copper phthalocyanine (CuPc): 4–4′-n-heptylcyanobiphenyl (7CB) composite liquid crystals have been investigated. Liquid crystals exhibit dielectrically-controlled positive dielectric anisotropy (p-type Δɛ) and the dielectric anisotropy changes from positive to negative dielectric anisotropy (n-type Δɛ) behavior with frequency of applied electrical field. The critical frequency f_c values for the 7CB and CuPc doped 7CB liquid crystals were found to be 602 kHz and 518 kHz, respectively. This indicates that CuPc doping causes a decrease in the critical frequency. The splay elastic coefficients of the 7CB and CuPc doped 7CB liquid crystals were determined and CuPc doping increases the splay elastic coefficient of 7CB liquid crystal. The 7CB liquid crystal exhibits a voltage-controlled differential negative resistance (VCNR) behavior and CuPc doping affects significantly VCNR behavior of 7CB.     

Growth and properties of benzil doped benzimidazole (BMZ) single crystals

In the present work, we have made an attempt to study the effect of benzil doping on the properties of benzimidazole single crystals. For this purpose we have grown pure and benzil doped benzimidazole single crystals by vertical Bridgman technique. The grown crystals were characterized by various characterization techniques. The presence of dopants confirmed by powder X-ray diffraction (XRD). Crystalline perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD). The transmittance, electrical property and mechanical strength have been analysed using UV-vis-NIR spectroscopic, dielectric and Vicker's hardness studies. The relative second harmonic generation efficiency of pure and doped benzimidazole crystals measured using Kurtz powder test.     

Enhancement of Omnidirectional Photonic Bandgaps in One-Dimensional Superconductor–Dielectric Photonic Crystals with a Staggered Structure

In this paper, the properties of the omnidirectional photonic bandgap (OBG) realized by one-dimensional (1D) photonic crystals with a staggered structure which is composed of superconductor and isotropic dielectric have been theoretically investigated by the transfer matrix method (TMM). From the numerical results, it has been shown that such OBG is insensitive to the incident angle and the polarization of electromagnetic wave (EM wave), and the frequency range and central frequency of OBG can be tuned by the ambient temperature of system, the average thickness of superconductor layer, the average thickness of dielectric layer, and staggered parameters, respectively. The bandwidth of OBG can be notably enlarged with increasing average thickness and staggered parameter of superconductor layer. Moreover, the frequency range of OBG can be narrowed with increasing the average thickness, staggered parameter of dielectric layer, and ambient temperature, respectively. The damping coefficient of superconductor layer has no effect on the bandwidth of OBG under low-temperature conditions. It is shown that 1D superconductor–dielectric photonic crystals (SDPCs) have a superior feature in the enhancement of frequency range of OBG. This kind of OBG has potential applications in filters, microcavities, and fibers, etc.