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1.
Two series of polyaniline–TiO2 nanocomposite materials were prepared in base form by in situ polymerization of aniline with inorganic fillers using TiO2 nanoparticles (P25) and TiO2 colloids (Hombikat), respectively. The effect of particle sizes and contents of TiO2 materials on their dielectric properties was evaluated. The as-synthesized polyaniline–TiO2 nanocomposite materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermal analysis (DTA/TGA), and X-ray diffraction (XRD). Dielectric properties of polyaniline–TiO2 nanocomposites in the form of films were measured at 1 KHz–1 MHz and a temperature range of 35–150 °C. Higher dielectric constants and dielectric losses of polyaniline–TiO2 nanocomposites than those of neat PANI were found. PANI–TiO2 nanocomposites derived from P25 exhibited higher dielectric constants and losses than those from Hombikat TiO2 colloids. Electrical conductivity measurements indicate that the conductivity of nanocomposites is increased with TiO2 content. The dielectric properties and conductivities are considered to be enhanced due to the addition of TiO2, which might induce the formation of a more efficient network for charge transport in the base polyaniline matrix.  相似文献   

2.
Poly(vinylidene fluoride)/lead zirconate titanate nanocomposite thin films (PVDF/PZT-NPs) were successfully prepared by mixing fine Pb(Zr0.52,Ti0.48)O3 nanoparticles (PZT-NPs) into a PVDF solution under ultrasonication. The mixture was spin coated onto glass substrate and then cured at 110 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize the structure and properties of the obtained thin-film nanocomposites. The dielectric properties of the PVDF/PZT-NPs were analyzed in detail with respect to frequency. In comparison with pure poly (vinylidene fluoride), the dielectric constant of the nanocomposite (15 vol.% PZT-NPs) was significantly increased, whereas the loss tangent was unchanged in the frequency range of 100 Hz to 30 MHz. The nanocomposites exhibited good dielectric stability over a wide frequency range. Different theoretical approaches were employed to predict the effective dielectric constants of the thin film nanocomposite systems, and the estimated results were compared with the experimental data.  相似文献   

3.
Structural, optical and dielectric properties of Ni doped ZnO samples prepared by the solid state route are presented. X-ray diffraction confirmed the substitution of Ni on Zn sites without changing the hexagonal structure of ZnO. NiO phase appeared for 6% Ni doping. Fourier transform infrared measurements were carried out to study phonon modes in Ni doped ZnO. Significant blueshift with Ni doping was observed in UV–visible studies, strongly supported by photoluminescence spectra that show a high intensity UV emission peak followed by the low intensity green emission band corresponding to oxygen vacancies and defects. The photoluminescence analysis suggest that doping of Ni can affect defects and oxygen vacancies in ZnO and give the possibility of band gap tuning for applications in optoelectronic devices. High values of dielectric constant at low frequency and a strong dielectric anomaly around 320 °C were observed.  相似文献   

4.
A study was conducted of the effects of sintering temperature and CaF2 additives on densification, microstructure, dielectric property and thermal conductivity of AlN–BN composites. Increasing sintering temperature and CaF2 contents help to improve the densification, thermal conductivity, and purification of the grain boundaries. Thermal conductivity value reached 110 W m−1 K−1 for AlN–BN composites with 3 wt.% CaF2 and sintered at 1850 °C. Increasing sintering temperature decreases relative dielectric constant and tan δ. The increase in CaF2 content increases relative dielectric constant and decreases tan δ. Relative dielectric constants values were between 7.29 and 7.64 and dielectric loss tangent values ranged from 6.36 to 7.83 × 10−4 at 1 MHz.  相似文献   

5.
Lead indium niobate, Pb(In1/2Nb1/2)O3 (PIN), is an interesting ferroelectric due to a transition from a disordered to an ordered state by long-time thermal annealing. However, the temperature related to the maximum dielectric constant (Tmax) of PIN in relaxor phase is low (at 1 kHz, Tmax = 66 °C). In this study, lead titanate PbTiO3 (PT) was added to PIN with compositions (1 − x)PIN–xPT (for x = 0.1–0.5) to increase their Tmax. The influence of stress on dielectric properties of (1 − x)PIN–PT ceramics was then investigated. The dielectric properties were measured under various uniaxial compressive stresses up to 400 MPa. The results showed the reduction of dielectric constant in 0.9PIN–0.1PT with superimposed compression load. For other compositions, dielectric constants first increased with compressive stress, then decreased when the stress was further increased up to 400 MPa. The loss tangent of all composition was found to decrease with increasing compressive stress.  相似文献   

6.
Undoped and nickel (Ni)-doped ZnO thin films were spray deposited on glass substrates at 523 K using 0.1 M of zinc acetate dihydrate and 0.002–0.01 M of nickel acetate tetrahydrate precursor solutions and subsequently annealed at 723 K. The effect of Ni doping in the structural, morphological, optical and electrical properties of nanostructured ZnO thin film was investigated using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV–vis Spectrophotometer and an Electrometer respectively. XRD patterns confirmed the polycrystalline nature of ZnO thin film with hexagonal wurtzite crystal structure and highly oriented along (002) plane. The crystallite size was found to be increased in the range of 15–31 nm as dopant concentration increased. The SEM image revealed the uniformly distributed compact spherical grains and denser in the case of doped ZnO thin films. All the films were highly transparent with average transmittance of 76%. The measured optical band gap was found to be varied from 3.21 to 3.09 eV. The influence of Ni doping in the room temperature ethanol sensing characteristics has also been reported.  相似文献   

7.
Structural and optical properties of Al doped ZnO nanoparticles prepared by the thermal decomposition method are presented. X-ray diffraction studies confirmed the substitution of Al on Zn sites without changing the hexagonal structure of ZnO. Also, lattice parameters, the crystallite size and other physical parameters such as strain, stress and energy density were calculated from various modified forms of W–H equation and their variation with the doping of Al is discussed. A blue shift in the energy band gap attributed to increase in carrier concentration (Burstein Moss Effect) is observed by absorption spectra. Photoluminescence studies show a strong and dominant peak corresponding to the near band edge emission in ultraviolet range and a broad band in the range 420–520 nm corresponding to defects and oxygen vacancies. Phonon modes were studied by FTIR measurements. The tunability of the band gap of ZnO nanoparticles could eventually be useful for potential optoelectronic applications.  相似文献   

8.
The effect of WO3 addition on the phase formation, the microstructures and the microwave dielectric properties of 1 wt% ZnO doped 0.95MgTiO3–0.05CaTiO3 ceramics system were investigated. Formation of second phase MgTi2O5 could be effectively restrained through the addition of WO3, but should be in right amount. WO3 as additives could not only effectively lower the sintering temperature of the ceramics to 1310 °C, but also promote the densification. A dielectric constant εr of 20.02, a Q×f value of 62,000 (at 7 GHz), and a τf value of −5.1 ppm/°C were obtained for 1 wt% ZnO doped 0.95MgTiO3–0.05CaTiO3 ceramics with 0.5 wt% WO3 addition sintered at 1310 °C.  相似文献   

9.
A series of poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE))/barium strontium titanate (BST) nanocomposites were fabricated by solution casting method. The addition of BST nanoparticles could enhance both the dielectric constant and the displacement of the resultant composite significantly. The surface activation of BST nonaparticles with KH550 was confirmed as an effective way to improve the breakdown strength of the composite. The high electric displacement (D > 15 μC/cm2), breakdown field (>200 MV/m) and low dielectric loss in P(VDF-CTFE)/BST nanocomposites suggest that the high electrical energy density may be desirable. That indicates the potential application of this class of copolymer/ceramics nanocomposites for high energy storage components.  相似文献   

10.
Non-stoichiometric pyrochlore ceramics with formula Bi1.5+xZnNb1.5O7+1.5x were systematically investigated. Crystal structures of the compounds were studied by X-ray diffraction (XRD) technique. The structures were identified as pure cubic pyrochlores when |x| < 0.1. Dielectric and optical properties of the compositions when x = −0.1, 0 and 0.1 were studied. All samples have high resistivities and low dielectric loss. With increasing x in Bi1.5+xZnNb1.5O7+1.5x, the lattice constant, permittivity, temperature coefficient of permittivity and thermal expansion coefficient increased, while dielectric loss decreased. Raman spectra indicated that the intensity of Bi–O stretching become stronger with increasing x. A vibration mode emerging at 861 cm−1 when x = −0.1 means that the B–O coordination environment is significantly more disordered. Absorption spectra suggested that the bandgap energy become lower from 2.86 to 2.70 eV as lattice constants increased. Strong absorption occurs at wavelengths from 433 to 459 nm, shows that samples have the ability to respond to wavelengths in the visible light region.  相似文献   

11.
A new pulse technique for grain resistivity measurement in varistor ceramics is suggested. Such technique allows obtaining more precise value of the grain resistivity due to the use of the concept of differential electrical resistance. This technique can be used in the current density range where the overheating of varistor sample is insignificant. The technique was verified using commercial ZnO varistors. Grain resistivities of 0.60±0.02 Ω cm at 293 K and of 3.40±0.13 Ω cm at 77 K were obtained. This result indicates the negative temperature coefficient of grain resistance in ZnO varistor in the range (77–293) K. The contribution of the grain boundaries to the current–voltage characteristic of ZnO varistor is estimated on the basis of the measured grain resistivity and the current–voltage data. It is shown that the electrical conduction in ZnO varistor is controlled by grains if the current density exceeds approximately 1000 А сm−2.  相似文献   

12.
Ca–Ni co-substituted samples of nanocrystalline spinel ferrites with chemical formula Mg1−xCaxNiyFe2−y O4 (x=0.0–0.6, y=0.0–1.2) were synthesized by the micro-emulsion method and were annealed at 700 °C for 7 h. The synthesized samples were characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM) and dielectric measurements. The XRD and FTIR analysis reveals that single phase samples can be achieved by substituting Ca and Ni ions at Mg and Fe sites respectively in cubic spinel nano-ferrites. The crystallite size of the synthesized samples was found in the range 29–45 nm. The saturation magnetization (Ms) increases from 9.84 to 24.99 emu/g up to x=0.2, y=0.4 and then decreases, while the coercivity (Hc) increases continuously from 94 to 153 Oe with the increase in dopants concentration. The dielectric properties of these nano materials were also studied at room temperature in the frequency range 100 MHz to 3 GHz. The dielectric parameters were found to decrease with the increased Ca–Ni concentration. Further the peaking behavior was observed beyond 1.5 GHz. The frequency dependent dielectric properties of all the samples have been explained qualitatively on the basis of the Maxwell–Wagner two-layer model according to Koop's phenomenological theory. The enhanced magnetic parameters and reduced dielectric properties make the synthesized materials suitable for switching and high frequency applications, respectively.  相似文献   

13.
Lead free 0.94(K0.5Na0.5NbO3)–0.06(LiNbO3) (KNN–LN) system was synthesized by conventional solid state reaction route (CSSRR). The KNN–LN system was calcined at 850 °C for 6 h for the formation of single perovskite phase whereas the sintering was done at 1050 °C, 1080 °C and 1100 °C for 4 h, respectively. The KNN–LN samples sintered at 1080 °C show better properties: room temperature (RT) dielectric constant (?r) ∼936, dielectric loss (tan δ) ∼0.016 at 1 MHz, a relatively high bulk density (ρ) ∼4.385 g/cm3, which is 97.5% of the theoretical density (TD ∼ 4.51), remnant polarization (Pr) ∼6.4 μC/cm2 and coercive field (Ec) ∼9.6 kV/cm have been observed.  相似文献   

14.
Nd2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 (abbreviated to BNKT) binary lead-free piezoelectric ceramics were synthesized by the conventional mixed-oxide method. The results show that the BNKT ceramics with 0–0.15 wt.% Nd2O3 doping possesses a single perovskite phase with rhombohedral structure. The grain size of BNKT decreased with the addition of Nd2O3 dopant. The temperature dependence of the dielectric constant ?r revealed that there were two-phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. A diffuse character was proved by linear fitting of the modified Curie–Weiss law. At room temperature, the specimens containing 0.0125 wt.% Nd2O3 with homogeneous microstructure presented excellent electrical properties: the piezoelectric constant d33 = 134 pC/N, the electromechanical coupling factor Kp = 0.27, and the dielectric constant ?r = 925 (1 kHz).  相似文献   

15.
PbO–SrO–Na2O–Nb2O5–SiO2 glass–ceramics were prepared via roll-quenching followed by controlled crystallization from 700 °C to 900 °C. The effects of PbO and SrO contents on crystallization and dielectric properties were investigated. The results show that Pb2Nb2O7, Sr2Nb2O7 and their solid solutions crystallize at 700 °C, NaNbO3 is the primary phase at 800 °C, Pb2Nb2O7 disappears and PbNb2O6 forms at 900 °C. The dielectric properties of the glass–ceramics formed through controlled crystallization has a strong dependence on the phase compositions that were developed during heat treatment. The highest dielectric constants (∼600) are found in samples with 6.0 mol% SrO annealed at 900 °C for 3 h. The dielectric–temperature characteristics of the samples show stability over the range from −60 °C to 180 °C, except the sample without SrO heated at 900 °C.  相似文献   

16.
Nanoscaled tungsten oxide (WO3) particles coated on ZnO nanorods (ZNRs) were newly synthesized by combining a hydrothermal technique with a chemical solution process. The structure, morphologies and compositions of the as-prepared WO3–ZNR nanocomposites were characterized through XRD, FESEM, TEM and Raman measurements. The results revealed that pure monoclinic WO3 nanoparticles with an average size range of 18–26 nm were distributed on the surfaces of ZNRs and attached strongly. Particularly, the optical properties as well as photocatalytic characteristics of pure ZNRs and WO3–ZNR nanocomposites with different loadings of WO3 were also examined. The absorption of WO3–ZNR nanocomposites was redshifted due to effective immobilization of WO3 on ZNRs. Under irradiation of a 55 W compact fluorescence lamp, the photocatalytic activities of the WO3–ZNR nanocomposites were superior to those of pure ZNRs and P25 in the degradation of resorcinol (ReOH). Furthermore, WO3–ZNR nanocomposites showed very favorable recycle use potential and high sedimentation rate. Other endocrine disrupting chemicals (EDCs) such as phenol, bisphenol A (BPA) and methylparaben were also successfully photodegraded under identical conditions. These characteristics showed the practical applications of the WO3–ZNR nanocomposites in indoor environmental remediation.  相似文献   

17.
Bi1−xBaxFeO3 (x=0.05, 0.10 and 0.15) nanoparticles were synthesized by the sol–gel method. X-ray diffraction and Raman spectroscopy results showed the presence of distorted rhombohedral structure of Bi1−xBaxFeO3 nanoparticles. Rietveld refinement and Williamson–Hall plot of the x-ray diffraction patterns showed the increase in lattice parameters, unit cell volume and the particle size. Infrared spectroscopy and Raman analysis revealed the shifting of phonon modes towards the higher wavenumber side with increasing Ba concentration. These samples exhibited the optical band gap in the visible region (2.47–2.02 eV) indicating their ability to absorb visible light. Magnetic measurement showed room temperature ferromagnetic behavior, which may be attributed to the antiferromagnetic core and the ferromagnetic surface of the nanoparticles, together with the structural distortion caused by Ba substitution. The magnetoelectric coupling was evidenced by the observation of the dielectric anomaly in the dielectric constant and the dielectric loss near antiferromagnetic Neel temperature in all the samples.  相似文献   

18.
CaCu3Ti4O12 has a giant dielectric constant of up to 104 at room temperature and has great potential for various technological applications. In this work, CaCu3Ti4O12 ceramic powder was synthesized by heating a stoichiometric amount of CaCO3, CuO and TiO2 in molten NaCl–KCl and Na2SO4–K2SO4, respectively. The synthesis temperature was decreased from 1000 °C (required by conventional solid-state reactions) to 750 °C for NaCl–KCl or to 850 °C for Na2SO4–K2SO4. The flux type has a larger influence on the phase compositions and morphology of the resultant powders than the synthesis temperature does. The dielectric constant of the resulting ceramics is more than 104 over the wide frequency range from 100 Hz to 100 kHz. The dielectric loss tangent of the resulting ceramics is lower than 0.2 in the frequency range from 100 Hz to 100 kHz. The dielectric behavior of both samples is similar to the results obtained for CaCu3Ti4O12 ceramics that were synthesized by the sol–gel method.  相似文献   

19.
Structural and electrical properties of sintered zinc-titanate ceramics   总被引:1,自引:0,他引:1  
The aim of this work was an investigation of structural and electrical properties of sintered zinc-titanate ceramics obtained by mechanical activation. Mixtures of ZnO and TiO2 were mechanically activated in a planetary ball mill up to 90 min and sintered isothermally in air for 120 min at 1100 °C. The phase composition in the ZnO–TiO2 system after milling and sintering was analyzed using the XRD method. Microstructure analyses were performed using SEM. The results of electric resistivity, capacitance and loss tangent of the sintered samples were obtained. The existence of zinc-titanate as a dielectric was proved (?r = 12.5, Q = 386.1, tgδ = 0.0026, ρ = 1.02 Ωm).  相似文献   

20.
Lead free piezoelectric Bi0.5(Na0.5K0.5)0.5TiO3 (pure and 1 wt.%, 2 wt.%, 4 wt.% Sb-doped) ceramics were synthesized away from its MPB. The crystalline nature of the BNKT ceramic was studied by XRD and SEM. Depolarization temperature (Td) and transition temperature (Tc) were observed through phase transitions in dielectric studies which were found to increase after Sb-doping, thus increasing its usable temperature range. In the study of relaxation behavior, the activation energy for relaxation was found to be 0.33, 0.43, 0.57 and 0.56 eV for pure and Sb-doped samples, respectively. All samples were found to exhibit normal Curie-Weiss law above their Tc. Doping of Sb was found to restrain the diffused character of the pure sample. In P-E loop, Sb-doping was found to increase the ferroelectric properties.Pure and Sb-doped BNKT ceramics exhibited high values of piezoelectric charge coefficient (d33) as 115, 121, 129 and 100 pC/N, respectively.  相似文献   

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