Ba0.5 Sr0.5 TiO3/PMMA复合材料介电性能研究

采用溶胶凝胶法（sol-gel）制备了Ba0．5Sr0．5TiO3／PMMA复合材料粉体。应用红外光谱（IR）、偏光显微镜（PLM）、扫描电镜（SEM）等分析手段，对样品进行了表征与分析，研究了乙烯基三乙氧基硅烷偶联剂在BST55／PMMA复合材料制备过程中起的桥联作用，并讨论了MMA和BST55物质的量比与其介电性能的关系。结果表明，在凝胶化过程中，适量的偶联剂不仅起着交联剂的作用，而且能改善复合材料的粒子聚集态；而复合材料的介电常数远远低于BST55陶瓷，且随着PMMA含量的增加而有所降低。     

Developing the dielectric mechanisms of polyetherimide/multiwalled carbon nanotube/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites

ABSTRACT: Various amounts of multiwalled carbon nanotubes [MWNTs] were embedded into polyetherimide [PEI] to form PEI/MWNT composites, and their dielectric properties were measured at 1 MHz. The Lichtenecker mixing rule was used to find a reasonable dielectric constant for the MWNTs used in this study. The dielectric constants of the developed composites were significantly increased, and the loss tangents were significantly decreased as 2.0 wt.% (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 ceramic powder [BSTZ] was added to the PEI/MWNTs to form PEI/MWNT/BSTZ composites. The Lichtenecker and Yamada mixing rules were used to predict the dielectric constants of the PEI/MWNT and PEI/MWNT/BSTZ composites. Equivalent electrical conduction models of both composites were established using the two mixing rules. In addition, the theoretical bases of the two mixing rules were used to explain the measured results for the PEI/MWNT and PEI/BSTZ/MWNT composites.     

High-temperature dielectric and energy storage properties of Bi0.5Na0.5TiO3-based ceramics modified by Sr0.8Na0.4Nb2O6

Sr_0.8Na_0.4Nb₂O₆ with a tungsten bronze structure is introduced into perovskite-structured 0.94(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃ composition (abbreviated as BNT-BT-xSNN, x = 0-0.04). The temperature stability of dielectric properties and energy storage performance is found to be effectively enhanced by Sr_0.8Na_0.4Nb₂O₆ dopant. When x is 0.03, the temperature ranges covering |ε'-ε'_150°C|/ε'_150°C ≤15% and tanδ ≤ 0.02 are 43°C-404°C and 90°C-422°C, respectively. More importantly, ε′ can be retained as high as 3304 at 150°C. Besides, the variances of energy storage density and its efficiency are 6.4% and 5.3%, respectively, in the temperature range from room temperature (RT) to 180°C. Therefore, this work provides a new method of compositional modification in BNT-based materials to improve their temperature stability of dielectric and energy storage properties.     

Effects of adding B2O3 on microwave dielectric properties of 0.9625MgTiO3-0.0375(Ca0.5Sr0.5)TiO3 composite ceramics

A series of 0.9625MgTiO₃-0.0375(Ca_0.5Sr_0.5)TiO₃ composite ceramics added with different amounts of B₂O₃ (1-5 wt%) were prepared via the solid state sintering method using the pre-synthesized raw MgTiO₃ and (Ca_0.5Sr_0.5)TiO₃ powders by molten-salt reaction. The sintering temperature of 0.9625MgTiO₃-0.0375(Ca_0.5Sr_0.5)TiO₃ composite ceramics can be reduced from 1275°C to 1175°C due to the liquid phase sintering effect of B₂O₃. When the adding amount of B₂O₃ was more than 2 wt%, a new phase MgTi₂O₅ could be detected by X-ray diffraction, which would substantially degrade the dielectric properties of the obtained ceramics. Resultantly, the quality factor (Q·f) and dielectric constant (ε_r) of the samples increase first and decrease later with increasing addition amount of B₂O₃. In addition, the temperature coefficient of resonant frequency (τ_f) progressively increases with increasing content of B₂O₃. By sintering at 1175°C for 4 hours, the obtained 0.9625MgTiO₃-0.0375Ca_0.5Sr_0.5TiO₃ composite ceramics with 2 wt% B₂O₃ possess the optimal microwave dielectric properties of ε_r = 18.9, Q·f = 57 000 GHz and τ_f = −1.2 ppm/°C.     

Morphology and properties of polystyrene/agave fiber composites and foams

In this work, agave fibers were blended with polystyrene to produce foamed and unfoamed composites. The effect of fiber size and density reduction on the morphological, thermal, mechanical, and rheological properties, as well as crystallinity and water absorption kinetics of the composites was assessed. The results show that Young's modulus and tensile strength increased with increasing fiber content, but decreased with density reduction. Increasing fiber content and decreasing the size of the fibers both increased crystallinity of the composites. Finally, water uptake and diffusion coefficient were found to increase with increasing fiber content for all sizes. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Core-shell structure strategy and oxygen vacancy engineering of 0.1LaMnO3@0.9(Ba0.5Sr0.5)TiO3 ceramics towards tuning electrical properties

In recent years, core-shell structures have attracted much attention for their potential in tuning the functional properties of materials and have become an effective method for preparing high-performance materials. In this work, core-shell structured 0.1LaMnO₃@0.9(Ba_0.5Sr_0.5)TiO₃ nanoparticles were fabricated by sol-gel method and dense ceramics were prepared at different sintering temperatures. The phase composition, morphology, chemical state and electrical properties were systematically investigated. Structural analysis confirmed the formation of 0.1LaMnO₃@0.9(Ba_0.5Sr_0.5)TiO₃ core-shell nanostructures. The results show that the prepared samples exhibit typical negative temperature coefficient characteristics in the range of 50–1000 °C, which is derived from the effect of carrier pairs and oxygen vacancies on the electrical properties. This study provides new insights from structure to material into guiding the development and design of advanced thermistor materials for temperature sensing applications.     

Colossal dielectric permittivity in (Al+Nb) co-doped Ba0.4Sr0.6TiO3 ceramics

Stimulated by the outstanding colossal permittivity behavior achieved in trivalent and pentavalent cations co-doped rutile TiO₂ ceramics, the co-doping effects on the dielectric behavior of Ba_0.4Sr_0.6TiO₃ ceramics were further explored. In this work, (Al + Nb) co-doped Ba_0.4Sr_0.6TiO₃ ceramics were synthesized via a standard solid state ceramic route. The structural evolution was analyzed using X-ray diffraction patterns and Raman spectra. Dense microstructures with no apparent change of grain morphology were observed from the scanning electron microscopy. A huge enhancement of dielectric permittivity was obtained with 1 mol% (Al + Nb) doping and excellent dielectric performances (ε_r ∼ 20,000, tanδ ∼ 0.06 at 1 kHz) were achieved after further heat treatment. The formation of electron pinned defect dipoles localized in grains may account for the optimization of dielectric behaviors and the corresponding chemical valence states were confirmed from the XPS results.     

Preparation and dielectric properties of sulfonated poly(aryl ether ketone)/acidified graphite nanosheet composites

Percolative dielectric composites of sulfonated poly(aryl ether ketone) (SPAEK) and acidified graphite nanosheets (AGSs) were fabricated by a solution method. The dielectric constant of the as‐prepared composite with 4.01 vol % AGSs was found to be 330 at 1000 Hz; this was a significant increase compared to that of pure SPAEK. Through the calculation, a low percolation threshold of the AGS/SPAEK composite was confirmed at 3.18 vol % (0.0318 volume fraction) AGSs; this was attributed to the large surface area and high conductivity of the AGSs. Additionally, our percolative dielectric composites also exhibited good mechanical performances and good thermostability, with a tensile strength of 71.7 MPa, a tensile modulus of 1.91 GPa, a breaking elongation of 16.4%, and a mass loss temperature at 5% of 336°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40028.     

Effect of MgO/La2O3 additives on sintering behavior and microwave dielectric properties of (Sr,Ca)TiO3-(Sm,Nd)AlO3 ceramics

The effect of MgO/La₂O₃ additives on phase composition, microstructures, sintering behavior, and microwave dielectric properties of 0.7(Sr_0.01Ca_0.99)TiO₃−0.3(Sm_0.75Nd_0.25)AlO₃ (7SCT-3SNA) ceramics prepared via conventional solid-state route were systematically investigated. MgO/La₂O₃ as additives showed no obvious influence on the phase composition of the 7SCT-3SNA ceramics and all the samples exhibited pure perovskite structures. The presence of MgO/La₂O₃ additives effectively reduced the sintering temperature of 7SCT-3SNA ceramics due to the formation of a liquid phase at a relatively low temperature during sintering progress. The 0.5 wt% MgO doped 7SCT-3SNA sample with 0.5 wt% of La₂O₃, sintered at 1320 °C for 4 h, was measured to show superior microwave dielectric properties, with an ε_r of 45.57, a Q×f value of 46205 GHz (at 5.5 GHz), and τ_f value of −0.32 ppm/°C, which showed dense and uniform microstructure as well as well-developed grain growth.     

Preparation and properties of polystyrene/SiCw/SiCp thermal conductivity composites

The silicon carbide whisker (SiCw) and silicon carbide particle (SiCp) were employed to prepare polystyrene/silicon carbide whisker/silicon carbide particle (PS/SiCw/SiCp) thermal conductivity composites, and the titanate coupling reagent of NDZ‐105 was introduced to functionalize the surface of fillers. The thermal conductive coefficient λ improved from 0.18 W/mK for native PS to 1.29 W/mK for the composites with 40% volume fraction of SiCw/SiCp (volume fraction, 3 : 1) hybrid fillers. Both the thermal decomposition temperature and dielectric constant of the composites increased with the addition of SiCw/SiCp hybrid fillers. At the same addition of SiCw/SiCp hybrid fillers, the surface modification of hybrid fillers by NDZ‐105 could improve the thermal conductivity and the mechanical properties of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of surface modified silicon carbide/polystyrene nanocomposites

A simple method is reported to coat silicon carbide (SiC) nanoparticles with polystyrene (PS) to improve the interfacial adhesion between polymer matrix and SiC nanoparticles. The morphology of untreated SiC nanoparticles, PS coated SiC (p‐SiC) nanoparticles, SiC/PS nanocomposites, and p‐SiC/PS nanocomposites are observed. The HRTEM image of p‐SiC shows that the thickness of PS on the surface of SiC is about 1.5–2.0 nm, which is consistent with the TGA results. With 24.7 vol % untreated SiC nanoparticles dispersed into PS matrix, the thermal conductivity (λ) of the SiC/PS composites increases by about 192%. However, when the same volume fraction of p‐SiC nanoparticles is used, the increase is about 353%. This big difference could be attributed to the promoted dispersion of the p‐SiC in the PS matrix. The measurements of glass transition (T_g), dielectric constant (ε), and tensile strength at break (σ_b) also support this explanation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Rheological,mechanical, and electrical properties of Sr0.7Bi0.2TiO3 modified BaTiO3 ceramic and its composites

Porous BaTiO₃-based relaxor ferroelectric ceramics with lamellar structure were achieved by ice templating method, and the rheological properties of ceramic slurry for freeze casting were deeply studied. Epoxy resin was then backfilled to generate ceramic–epoxy resin composites. Ceramic–epoxy composites with a lamellar structure were obtained when using a slurry with a ceramic content of 45 wt.%. The nanoindentation results showed that the introduction of ceramic materials into the epoxy resin can significantly improve the penetration resistance and hardness of the material. The dielectric and ferroelectric properties of the composites were also characterized. The interaction between the highly coupled dipoles in the polymers results in a decrease in the breakdown field strength of the composite. The dielectric constant reached up to ∼800. At 220 kV/cm, W_rec = 0.62 J/cm³, and η was ∼80%. At low frequencies, W_rec was ∼0.16 J/cm³, which indicated good stability.     

Bi掺杂(Ba,Sr,Ca)TiO3陶瓷的结构及介电和铁电性能

采用固相反应技术制备了铋掺杂(Ba1-xCax)0.925Bi0.05TiO3(x=0.10,Bi-BCT)和(Ba1-xSrx/2Cax/2)0.925Bi0.05TiO3(Bi-BCST)(x=0.10,Bi-BSCT)铁电陶瓷,研究了样品的结构、介电和铁电性能。结果表明:在Bi-BCT陶瓷中存在一种弥散的老化效应,点缺陷引起的可逆畴翻转机制能够合理地解释Bi-BCT陶瓷中异常的双电滞回线,这种机制有望进一步解释Bi-BSCT陶瓷中异常的介电行为。     

Thermal and dielectric properties of the aluminum particle/epoxy resin composites

Microsized aluminum/epoxy resin composites were prepared, and the thermal and dielectric properties of the composites were investigated in terms of composition, aluminum particle sizes, frequency, and temperature. The results showed that the introduction of aluminum particles to the composites hardly influenced the thermal stability behavior, and decreased T_g of the epoxy resin; moreover, the size, concentration, and surface modification of aluminum particles had an effect on their thermal conductivity and dielectric properties. The dielectric permittivity increased smoothly with a rise of aluminum particle content, as well as with a decrease in frequency at high loading with aluminum particles. While the dissipation factor value increased slightly with an increase in frequency, it still remained at a low level. The dielectric permittivity and loss increased with temperature, owing to the segmental mobility of the polymer molecules. We found that the aluminum/epoxy composite containing 48 vol % aluminum‐particle content possessed a high thermal conductivity and a high dielectric permittivity, but a low loss factor, a low electric conductivity, and a higher breakdown voltage. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High permittivity and low dielectric loss of the (Ca0.9Sr0.1)1-xLa2x/3Cu3Ti4O12 ceramics

In this work, we have systematically studied the effects of La³⁺/Sr²⁺ dopants on the crystal structure, microstructure, dielectric response and electrical properties of (Ca_0.9Sr_0.1)_1-xLa_2x/3Cu₃Ti₄O₁₂ (x = 0, 0.025, 0.05 and 0.075) ceramics. XRD results show that the lattice parameter increases with the increase in the La³⁺ content. SEM micrographs illustrate that a small amount added of La³⁺ can reduce the grain size of CCTO during sintering. With increasing La³⁺ content, the grains grow larger. Dielectric measurements indicated that all doped samples synthesized by the solid-state reaction exhibit giant dielectric constants ε'>10⁴ over a large frequency range (10 Hz to 1 MHz) and at any temperature below 600 K. In particular, the ceramic with x = 0.05 exhibits a colossal dielectric permittivity ～5.49 × 10⁴; which increases by about 50% compared to that of the undoped ceramic. In addition, the doped ceramic also presents a low dielectric loss ～ 0.08 at 20 °C and 0.6 kHz. The giant dielectric properties of these samples can be explained by the (IBLC) model.     

Energy storage properties and transparency in (Ba0.6Sr0.4)1-1.5xBixTi1-x(Mg1/3Nb2/3)xO3 ceramics

Fully densified (transparent) ceramic with small grain size is highly desired to improve the field breakdown strength (BDS) and its scattering. Sintering behavior, microstructural evolution, electric, dielectric, and energy storage properties of (Ba_0.6Sr_0.4)_1-1.5xBi_xTi_1-x(Mg_1/3Nb_2/3)_xO₃ (x = .04–.10) ceramics have been studied in this paper. Phase pure cubic perovskite is observed for the x = .04 composition. Nb-rich tungsten bronze type and Ti-rich barium titanate secondary phases are present in the x > .05 compositions. A multiphasic transparent ferroelectric ceramic with ∼74.2% (780 nm) transmittance and a high refractive index of ∼2.3 within the visible region could be successfully obtained for the x = .10 composition by traditional ceramic process. The x = .09 composition demonstrates good energy storage performance (recoverable energy density W_rec = 3.74J/cm³, efficiency η = 77% and BDS = 390kV/cm) with extremely low scattering in BDS, suggesting potential application in large sized energy storage capacitor.     

Dielectric properties of Sr0.5Ca0.5TiO3: x Pr3+ ceramics

The frequency dependent dielectric and AC conductivity properties of different concentrations of Pr³⁺ doped Sr_0.5Ca_0.5TiO₃ ceramics were investigated for the frequency range 100 Hz to 2 MHz at different temperatures. The morphology of the prepared samples was analyzed by using Field-Emission Scanning Electron Microscope images. The value of dielectric constant and dielectric loss decreases with increase in the frequency of the applied signal in all the samples. Also, the value of dielectric constant and dielectric loss decreased with doping of different concentrations of Pr³⁺ ions. The conductivity of the samples obeys Jonscher's power-law and shows a decrease with increasing doping concentration of Pr³⁺ ions. The higher value of real and imaginary part of impedance at lower frequency indicates the space charge polarization of the material and its absence at higher frequencies was confirmed from the low value of impedance at higher frequency region. The Cole- Cole parameters of the samples were calculated and the semi-circle observed indicates a single relaxation process and can be modeled by an equivalent parallel RC circuit. At lower frequency region, the value of dielectric constant and dissipation factor increases with increase in the temperature. Also the value of conductivity increases with temperature at high frequency region, due to the enhanced mobility of charge carriers.     

Enhanced structural,dielectric, ferroelectric,and piezoelectric properties of (1−x)Ba0.9Sr0.1TiO3–(x)Ba0.7Ca0.3TiO3 ceramics derived using mechano‐chemical activation technique

The effect of Ba_0.7Ca_0.3TiO₃ (BCT) substitution on the structural, dielectric, ferroelectric, and piezoelectric properties of mechano‐chemically synthesized lead‐free (1?x)Ba_0.9Sr_0.1TiO₃‐(x)Ba_0.7Ca_0.3TiO₃ (x=0.0, 0.10, 0.20, 0.35, and 0.50) ceramics have been investigated. XRD patterns confirms the formation of tetragonal phase with P4mm space group. The results indicate a strong influence of BCT substitution on the structural and electrical properties of Ba_0.9Sr_0.1TiO₃ (BST) ceramic. BST–BCT ceramic for x=0.35 have shown high dielectric constant ε_m~21 800, high remnant polarization P_r~10.16 μC/cm², large piezoelectric charge constant D₃₃~293 pC/N, large piezoelectric voltage constant g₃₃~5.80 mV·m/N, and highest dielectric breakdown strength E_bd~224 kV/cm among the five synthesized samples. The correlation between structural, dielectric, ferroelectric, and piezoelectric properties of the BST ceramic with increasing BCT content have been systematically described on the basis of domain wall motion and grain size effect.     

Effect of ZnO doping on the microstructure and microwave dielectric properties of 0.2CaTiO3-0.8(Li0.5Sm0.5)TiO3 ceramics

0.2CaTiO₃-0.8(Li_0.5Sm_0.5)TiO₃-xZnO(x = 0, 0.3, 0.6, 0.9, 1.2 wt%, 0.2CT-0.8LST-xZnO) with orthogonal perovskite structure were fabricated by the solid state method. The effects of ZnO additives on the microwave dielectric properties of 0.2CT-0.8LST ceramics were systematically investigated. With increasing the dopant (x) concentration, the dielectric constant (ε_r) and the temperature co-efficient of resonance frequency (τ_f) decreased, however, the Q × f values increased. The relationship between vibration mode and microwave dielectric properties was studied using Raman spectroscopy. The Q × f value of ceramics was related to the half-height width of Raman scattering. Narrower Raman scattering peaks corresponded to longer microwave energy propagation decay times and higher Q × f value. Based on X-ray photoelectron spectroscopy (XPS), the addition of Zn²⁺ ions limited the reduction of Ti⁴⁺ cations. The excellent dielectric properties were obtained when x = 1.2 wt% with ε_r = 100.25, Q × f = 6525 GHz, and τ_f = ?12.12 ppm/°C.     

Microstructure and dielectric response of (Ba,Sr)TiO3 filler-dispersed resin composites

Resin-matrix composites dispersing low-loss dielectric ceramic filler have received a considerable interest for high-frequency application, because of their good shape flexibility and controllable dielectric properties. In this study, (Ba,Sr)TiO₃-type ceramic particles have been synthesized by KCl molten salt method to serve as filler particle for resin-matrix dielectric composite. Dielectric measurement confirmed that the composite fabricated by tape-casting demonstrated two times higher dielectric constant of 50.4 than the other composites fabricated by direct-casting using a metal mold. Pore-size distribution as well as ceramic filler content was strongly correlated with the formation of electrical flux in the composites to enhance dielectric constant.