Synthesis and microstructural TEM investigation of CaCu3Ru4O12 ceramic and thin film

CaCu₃Ru₄O₁₂ (CCRO) is a conductive oxide having the same structure as CaCu₃Ti₄O₁₂ (CCTO) and close lattice parameters. The later compound is strongly considered for high density parallel plates capacitors application due to its so-called colossal dielectric constant. The need for an electrode inducing CCTO epitaxial growth with a clean and sharp interface is therefore necessary, and CCRO is a good potential candidate. In this paper, the synthesis of monophasic CCRO ceramic is reported, as well as pulsed laser deposition of CCRO thin film onto (001) NdCaAlO₄ substrate. Structural and physical properties of bulk CCRO were studied by transmission electron microscopy and electron spin resonance. CCRO films and ceramic exhibited a metallic behavior down to low temperature. CCRO films were (001) oriented and promoted a CCTO film growth with the same orientation.     

Influences of Sr2+ Doping on Microstructure,Giant Dielectric Behavior,and Non-Ohmic Properties of CaCu3Ti4O12/CaTiO3 Ceramic Composites

The microstructure, dielectric response, and nonlinear current-voltage properties of Sr²⁺-doped CaCu₃Ti₄O₁₂/CaTiO₃ (CCTO/CTO) ceramic composites, which were prepared by a solid-state reaction method using a single step from the starting nominal composition of CCTO/CTO/xSrO, were investigated. The CCTO and CTO phases were detected in the X-ray diffraction patterns. The lattice parameter increased with increasing Sr²⁺ doping concentration. The phase compositions of CCTO and CTO were confirmed by energy-dispersive X-ray spectroscopy with elemental mapping in the sintered ceramics. It can be confirmed that most of the Sr²⁺ ions substituted into the CTO phase, while some minor portion substituted into the CCTO phase. Furthermore, small segregation of Cu-rich was observed along the grain boundaries. The dielectric permittivity of the CCTO/CTO composite slightly decreased by doping with Sr²⁺, while the loss tangent was greatly reduced. Furthermore, the dielectric properties in a high-temperature range of the Sr²⁺-doped CCTO/CTO ceramic composites can be improved. Interestingly, the nonlinear electrical properties of the Sr²⁺-doped CCTO/CTO ceramic composites were significantly enhanced. The improved dielectric and nonlinear electrical properties of the Sr²⁺-doped CCTO/CTO ceramic composites were explained by the enhancement of the electrical properties of the internal interfaces.     

Structural,thermal and electrical properties of poly(methyl methacrylate)/CaCu3Ti4O12 composite sheets fabricated via melt mixing

Poly(methyl methacrylate) (PMMA) and CaCu₃Ti₄O₁₂ (CCTO) composites were fabricated via melt mixing followed by hot pressing technique. These were characterized using X-ray diffraction, thermo gravimetric, thermo mechanical, differential scanning calorimetry, fourier transform infrared (FTIR) and Impedance analyser for their structural, thermal and dielectric properties. Composites were found to have better thermal stability than that of pure PMMA. However, there was no significant difference in the glass transition (T _g ) temperature between the polymer and the composite. The appearance of additional vibrational frequencies in the range 400–600 cm^?1 in FTIR spectra indicated a possible interaction between PMMA and CCTO. The composite, with 38 vol% of CCTO (in PMMA), exhibited remarkably low dielectric loss at high frequencies and the low-frequency relaxation is attributed to the interfacial polarization/MWS effect. The origin of AC conductivity particularly in the high-frequency region was attributed to the electronic polarization.     

Effect of the addition of B2O3 and BaO-B2O3-SiO2 glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu3Ti4O12

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics was investigated. Both single-component (B₂O₃) and multi-component (30 wt% BaO-60 wt% B₂O₃-10 wt% SiO₂ (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B₂O₃ glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B₂O₃ content resulted in its segregation at the grain boundaries associated with a reduction in the grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples.     

Thermal analysis of phase transitions in perovskite electroceramics

Perovskite oxide ceramics have found wide applications in energy storage capacitors, electromechanical transducers, and infrared imaging devices due to their unique dielectric, piezoelectric, pyroelectric, and ferroelectric properties. These functional properties are intimately related to the complex displacive phase transitions that readily occur. In this study, these solid–solid phase transitions are characterized with dielectric measurements, dynamic mechanical analysis, thermomechanical analysis, and differential scanning calorimetry in an antiferroelectric lead-containing composition, Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_0.92Ti_0.08]_0.98O₃, and in a relaxor ferrielectric lead-free composition, (Bi_1/2Na_1/2)_0.93Ba_0.07TiO₃. The (Bi_1/2Na_1/2)_0.93Ba_0.07TiO₃ ceramic develops strong piezoelectricity through electric field-induced phase transitions during the poling process. The combined thermal analysis techniques clearly reveal the differences in unpoled and poled ceramics.     

Core–Shell Structured Polystyrene/BaTiO3 Hybrid Nanodielectrics Prepared by In Situ RAFT Polymerization: A Route to High Dielectric Constant and Low Loss Materials with Weak Frequency Dependence

A novel route to prepare core–shell structured nanocomposites with excellent dielectric performance is reported. This approach involves the grafting of polystyrene (PS) from the surface of BaTiO₃ by an in situ RAFT polymerization. The core–shell structured PS/BaTiO₃ nanocomposites not only show significantly increased dielectric constant and very low dielectric loss, but also have a weak frequency dependence of dielectric properties over a wide range of frequencies. In addition, the dielectric constant of the nanocomposites can also be easily tuned by varying the thickness of the PS shell. Our method is very promising for preparing high‐performance nanocomposites used in energy‐storage devices.     

The effect of crosslinking on thermal and mechanical properties of perfluorocyclobutane aromatic ether polymers

As the minimum features in semiconductor devices decrease, it is a new trend to incorporate copper and polymers with dielectric constant less than 3.0 to enhance the performance of the devices. Two fluorinated polymers, poly(biphenyl perfluorocyclobutyl ether) (BPFCB) and poly(1,1,1-triphenyl ethane perfluorocyclobutyl ether) (PFCB), are newly developed polymers with dielectric constants below 3.0. These two polymers have a similar backbone structure, but PFCB has the capability of crosslinking. To know the implications of these two polymers in the semiconductor industry, properties that are important for the integral reliability of Integral Circuits (IC), such as thermal and mechanical properties, should be understood. This comparative study shows that the crosslinking in perfluorocyclobutane aromatic ether polymer can reduce vertical thermal expansion and increase glass transition temperature (T_g) while water absorption, crystalline-like phase, and dielectric constant are slightly increased. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1383–1392, 1998     

Fabrication of thermoplastic polyurethane composites with a high dielectric constant and thermal conductivity using a hybrid filler of CNT@BaTiO3

Thermoplastic polyurethane composites with an excellent dielectric constant and high thermal conductivity were obtained using CNT@BaTiO₃ as a filler through a low-speed melt extrusion method. Before preparing the hybrid filler for the composite, the filler particles were surface modified to ensure that the outer surfaces could facilitate the reaction among particles to form the hybrid and ensure complete dispersion in the thermoplastic polyurethane matrix. After confirming the proper surface treatment of the filler particles using infrared spectroscopy, thermal degradation analysis and field emission scanning electron microscopy, they were used to prepare the composite materials at a processing temperature of 200 °C. The thermal stability, thermomechanical properties, mechanical properties, thermal conductivity, and dielectric properties of the composites were investigated. Compared to the neat thermoplastic polyurethane matrix, the prepared composite exhibited a higher thermal stability, approximately 300% higher storage modulus, higher tensile strength and elongation at break values, approximately three times higher thermal conductivity (improved from 0.19 W/(m.K) to 0.38 W/(m.K), and approximately five times larger dielectric constant at high frequencies (at 1 MHz a dielectric constant of 19.2 was obtained).     

Functional nanocomposites for energy storage: chemistry and new horizons

Energy storage devices are one of the hot spots in recent years due to the environmental problems caused by the large consumption of unsustainable energy such as petroleum or coal. Capacitors are a common device for energy storage, especially electrical energy. A variety of types including electrolytic capacitors, mica capacitors, paper capacitors, ceramic capacitors, film capacitors, and non-polarized capacitors have been proposed. Their specific applications depend on their intrinsic properties. Dielectric capacitors have reasonable energy storage density, with current research focusing on the enhancement of energy density and making the materials more flexible as well as lightweight. Improvement strategies are based on the premise that use of two or more different materials (e.g. polymers and ceramics/metals) at an optimal formulation can result in properties that combine the advantages of the precursor materials. Different polymers especially fluoropolymers (e.g. PVDF and PVDF based co-polymer) are the main components in dielectric nanocomposites for capacitors with high energy storage performance. In this article, we have briefly summarized the recent advances in functional polymers nanocomposites for energy storage applications with a primary focus on polymers, surface engineering, functional groups and novel synthesis/manufacturing concepts applied to new materials. The article presents a unique integrated structure and approaches providing key knowledge for the design and development of novel, low-cost, multifunctional next-generation energy storage materials with improved efficiency.     

Microstructure and dielectrical responses of pure and cobalt-doped CaCu3Ti4O12 ceramics by sol鈥揼el synthesis route

Cobalt-doped CCTO (CaCu₃Ti₄O₁₂) ceramics were prepared by a conventional sol–gel synthesis method and the effects of Cobalt doping on the microstructures and dielectrical properties were investigated. The phase composition and microstructure were studied by means of X-ray diffraction (XRD) and high resolution scanning electron microscopy (HRSEM). Efficient crystalline phase formation accompanied by Cobalt induced lattice constant expansion was confirmed through XRD studies. HRSEM results show that doping effectively enhanced grain growth or densification. A compositional study reveals the variation of Cobalt diffusion in CCTO structure by the reduction of Ti presence according to the doping ratio. The dielectric constant reached a value as high as (ε_r?=?25,400 at 1,000 and ε_r?=?111,000 at 1,050?°C) at a cobalt-doping concentration of x?=?0.2 at low frequency (50?Hz). The dielectrical constant and dielectric loss of the pure and cobalt-doped CCTO ceramics was measured for different concentrations and discussed in detail.     

The synthesis and properties of CaCu3Ti4O12 thin films

The CaCu₃Ti₄O₁₂ (CCTO) thin films were synthesized via a metal‐organic solution containing stoichiometric amounts of the metal cations at 700 °C for 1 h. The stable metal‐organic solution was prepared by dissolving calcium nitrate, copper nitrate, and tetrabuty titanate in grain alcohol. The phases, microstructures, and electric properties of CCTO thin films were characterized by X‐ray diffraction, scanning electron microscopy, atomic force microscope, and electric measurements. The results show that the CCTO thin films have homogeneous microstructure, smooth surface, low leakage current, and high values of dielectric constant. The low leakage current can be attributed to the small surface roughness. The high value of dielectric constant can be attributed to the internal barrier layer capacitor mechanism and metal‐insulator‐semiconductor junction of CCTO thin films. Copyright © 2013 John Wiley & Sons, Ltd.     

Ab-initio study of electronic,optical, thermal,and transport properties of Cr4AlB6

Theoretical investigation of different physical parameters of Cr₄AlB₆ have been done within the framework of density functional theory. Cr₄AlB₆ is a no band gap material. Its Cr-3d states contributes the most at the Fermi level. Thermal properties are investigated using quasi-harmonic Debye model as implemented in Gibbs code for different values of pressure and temperature. Study of transport property suggests that its electrical conductivity increases nonlinearly with increase in temperature but the relative change in its value is very low whereas its thermal conductivity increases linearly with the increase in temperature and relative increase in thermal conductivity is very high. The behavior of Cr₄AlB₆ is anisotropic and property is ceramic. It has potential applications in making ceramic capacitors. Its reflectivity is high in low energy region. It suggests that material can be used as coating material for far-infrared radiation. Study of the transport property suggests that because of very high value of thermal conductivity, it can be used for heat sink applications.     

Investigation on the growth of CaCu3Ti4O12 thin film and the origins of its dielectric relaxations

Using the radio frequency magnetron sputtering, CaCu₃Ti₄O₁₂ (CCTO) thin films were deposited on platinized silicon substrates. The influence of annealing temperature on structures and morphologies of the thin films was investigated. The high annealing temperature increased the crystallinity of the films. Temperature dependence of the dielectric constant revealed an amazing different characteristic of the dielectric relaxation at ∼10 MHz, whose characteristic frequency abnormally increased with the decrease of the measuring temperature unlike the relaxations due to extrinsic origins. Meanwhile, the dielectric constant at high frequencies was close to the value derived from the first principle calculation. All these gave the evidences to ascribe this relaxation to the intrinsic mechanism.     

All-organic polymer blend dielectrics of poly (arylene ether urea) and polyimide: Toward high energy density and high temperature applications

The development of high-performance dielectric films with high energy density and temperature stability is extremely desired for modern electronics and power systems. Herein, a simple and low-cost approach is proposed to fabricate all-organic blend films prepared from poly (arylene ether urea) (PEEU) and polyimide (PI) via solution casting and thermal imidization process. The incorporation of PEEU in PI matrix significantly improved dielectric breakdown strength and dielectric constant of PI. More precisely, blend film with 15 wt% PEEU exhibited highest energy density 5.14 J/cm³ at 495.65 MV/m, with enhanced dielectric constant of 4.73 and very low dissipation factor of 0.299%. Furthermore, the dielectric properties of the PEEU/PI blend displayed wonderful temperature stability in the range of − 50–+ 250°C, and great frequency stability between 10 and 10⁶ Hz. The blend film also exhibited excellent heat resistance and presented valuable potential in thin film capacitors for high voltage direct current system.     

Enhancement of thermal conductivity and tensile strength of liquid silicone rubber by three-dimensional alumina network

ABSTRACT

Rapidly increasing demands for higher integration density and stability of electronic devices embrace higher requirements for thermally conductive silicone rubber, which is promisingly used in ultra-thin components. In this work, alumina whiskers (AWs) and alumina flakes (AFs) are used to modify liquid silicone rubber (LSR) by fabricating binary (AFs/LSR) or ternary (AWs/AFs/LSR) composites. The thermal conductivity and mechanical strength of the binary and ternary composites were investigated. Thermal conductivity of the binary AFs/LSR composite (25AFs/LSR) was 0.1990 W m^?1 K^?1, while the thermal conductivity of the ternary AFs/AWs/LSR composite (20AFs/5AWs/LSR) was 0.2655 W m^?1 K^?1. Furthermore, the tensile strength of the ternary AWs/AFs/LSR composites increased by 180.9% as compared with the binary system, increased to 7.81 MPa from 2.78 MPa due to the introduction of 1 wt% AWs. As a reason, a significant synergistic effect of AWs and AFs in the enhancement of both thermal and mechanical properties of the LSR was proved. Furthermore, the dielectric property measurements demonstrated that the ternary composites exhibited a lower dielectric constant and dielectric loss, indicating that the AWs/AFs/LSR composites were qualified to be applied in the field of electronic devices.     

Highly Flexible Dielectric Films from Solution Processable Covalent Organic Frameworks**

Covalent organic frameworks (COFs) are known to be a promising class of materials for a wide range of applications, yet their poor solution processability limits their utility in many areas. Here we report a pore engineering method using hydrophilic side chains to improve the processability of hydrazone and β-ketoenamine-linked COFs and the production of flexible, crystalline films. Mechanical measurements of the free-standing COF films of COF-PEO-3 (hydrazone-linked) and TFP-PEO-3 (β-ketoenamine-linked), revealed a Young's modulus of 391.7 MPa and 1034.7 MPa, respectively. The solubility and excellent mechanical properties enabled the use of these COFs in dielectric devices. Specifically, the TFP-PEO-3 film-based dielectric capacitors display simultaneously high dielectric constant and breakdown strength, resulting in a discharged energy density of 11.22 J cm⁻³. This work offers a general approach for producing solution processable COFs and mechanically flexible COF-based films, which hold great potential for use in energy storage and flexible electronics applications.     

Optical and electrical properties of copper alumina nanoparticles reinforced chlorinated polyethylene composites for optoelectronic devices

The incorporation of transition metal oxide fillers into the polymer matrix through solution mixing polymerization imparts enhanced electrical and thermal properties. The present work focused on the optical properties, crystallinity, thermal stability, temperature-dependent conductivity, dielectric constant and modulus of chlorinated polyethylene/copper alumina (CPE/Cu–Al₂O₃) nanocomposites. Optical absorption measured using an ultraviolet–visible (UV–visible) spectrometer shows enhanced intensity and a blue shift for CPE/Cu–Al₂O₃ nanocomposites. The bandgap energy of CPE/Cu–Al₂O₃ nanocomposites was lower than pure CPE and minimum bandgap energy was recorded for a 7 wt% composites. The X-ray diffraction demonstrates that Cu–Al₂O₃ nanoparticles were uniformly introduced into the CPE matrix. Thermogravimetric analysis (TGA) manifests improved thermal stability of nanocomposites. Dielectric properties decrease with frequency, whereas AC conductivity increases with frequency, and both AC conductivity and dielectric properties increase with temperature. The maximum AC conductivity and dielectric constant were obtained for 7 wt % nanofiller loaded sample. For all systems, the activation energy for electrical conductivity decreases with rising temperatures. The experimental dielectric constant values of CPE nanocomposites were correlated with different theoretical models. The Bruggeman model was in good agreement with the experimental permittivity. The impedance experiments showed a decreasing trend with temperature, indicating the semiconducting nature of prepared nanocomposites.     

An anion substitution route to low loss colossal dielectric CaCu3Ti4O12

An anion substitution route was utilized for lowering the dielectric loss in CaCu₃Ti₄O₁₂ (CCTO) by partial replacement of oxygen by fluorine. This substitution reduced the dielectric loss, and retained a high dielectric constant that was essentially temperature independent from 25 to 200 °C. In particular, CaCu₃Ti₄O_11.7F_0.3 exhibited a giant dielectric constant over 6000 and low dielectric loss below 0.075 at 100 kHz within a temperature range of 25-200 °C. Fluorine analysis confirmed the presence of fluorine in all samples measured.     

Dielectric,thermal, and mechanical properties of CeO2‐filled HDPE composites for microwave substrate applications

Cerium oxide‐filled high density polyethylene (HDPE) composites for microwave substrate applications were prepared by sigma‐blend technique. The HDPE was used as the matrix and the dispersion of CeO₂ in the composite was varied up to 0.5 by volume fraction, and the dielectric properties were studied at 1 MHz and microwave frequencies. The variations of thermal conductivity (k_eff), coefficient of thermal expansion (α_c) and Vicker's microhardness with the volume fraction of the filler were also measured. The relative permittivity (ε_eff) and dielectric loss (tan δ) were found to increase with increase in CeO₂ content. For 0.4 volume fraction loading of the ceramic, the composite had ε_eff = 5.7, tan δ = 0.0068 (at 7 GHz), k_eff = 2.6 W/m °C, α_c = 98.5 ppm/°C, Vicker's microhardness of 18 kg/mm² and tensile strength of 14.6 MPa. Different theoretical approaches have been used to predict the effective permittivity, thermal conductivity, and coefficient of thermal expansion of composite systems and the results were compared with the experimental data. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 998–1008, 2010     

Thermal behavior of BST//PVDF ceramic–polymer composites

In this paper, we report the results of a study of microstructure and thermal behavior of ceramic–polymer composites composed of barium strontium titanate Ba_0.6Sr_0.4TiO₃ (BST60/40) and polyvinylidene fluoride (PVDF). The Ba_0.6Sr_0.4TiO₃ ceramic powder was prepared by the sol–gel method. Thermal evolution of the dried gel as well as ceramic powder was studied by simultaneous thermal analysis. The composite BST60/40//PVDF was obtained by hot pressing method for volume fraction of BST60/40 ceramic powder c _v = 50 %. The morphology of BST60/40//PVDF composite powder was observed by transmission electron microscopy and the morphology of BST60/40//PVDF composite sample was observed by scanning electron microscopy. Temperature dependence of dielectric constant and dielectric loss factor of BST60/40//PVDF composites was measured in the frequency range of f = (10 × 10³–1 × 10⁶) Hz. Dynamic mechanical properties of BST60/40//PVDF composites were measured by dynamic mechanical thermal analysis DMTA.