共查询到20条相似文献,搜索用时 15 毫秒
1.
《Ceramics International》2019,45(12):14983-14990
Dielectric materials with high permittivity and low dielectric loss have a range of promising applications within electronic devices. Here, we report on Zr co-doped (Ga0.5Nb0.5)0.03Ti0.97O2 ceramics, fabricated using a solid-state reaction. The colossal permittivity (CP) of (Ga0.5Nb0.5)0.03-(ZrxTi1-x)0.97O2 ceramics was investigated (x = 0%, 1%, 4%, 6%, 10%, 20%). When the doping value of Zr was 4%, the dielectric loss was reduced to 0.098 and, at room temperature and at a frequency of 1000 Hz, the dielectric permittivity was recorded as 2420. In addition, the material's dielectric permittivity exhibited good stability at temperatures ranging from −50 °C to 200 °C. Using X-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy (SEM), we have observed that Zr doping reduces grain size and increases grain boundary regions. According to our XPS and impedance analysis, Zr doping also reduces the concentration of oxygen vacancies, which are considered to be the main cause of dielectric loss. We believe that the Zr doping is an effective method for reducing the dielectric loss of CP materials. 相似文献
2.
A series of Tl?+?Nb co-doped TiO2 ceramics ((Tl0.5Nb0.5)x%Ti1-x%O2 0.5?≤?x?≤?10.0) were prepared by a solid-state reaction method under N2 atmosphere. The evolution of their microstructures, and dielectric properties were systematically studied. The co-doped ceramics exhibited a tetragonal rutile structure wherein the Nb and Tl elements were homogeneously distributed. The cell volumes, grain size, and permittivity increased with doping x, whereas the impedance values of the grain and grain boundary decreased with an increasing x. The optimum dielectric performance (εr >?104, tanδ?<?0.05) in the range of 10–106 Hz was obtained for x?=?1.5 with a corresponding grain boundary active energy of 0.86?eV. Four types of dielectric relaxation were observed at different temperature ranges: 10–30?K, 30–200?K, 200–350?K and 350–475?K; those dielectric relaxtions were respectively caused by electron-pinned defect-dipoles, electron hopping, oxygen vacancy hopping, and Maxwell–Wagner polarization. The colossal permittivity is primarily a result of the electron-pinned defect-dipole polarization. 相似文献
3.
《Dyes and Pigments》2008,76(3):526-532
The electrical properties: DC-electrical conductivity (σDC), AC-electrical conductivity (σAC), dielectric permittivity (ɛ′) and dielectric loss (ɛ″) for pure polymethylmethacrylate (PMMA) and mixed with phthalocyanine, Ni-phthalocyanine and hematoporphyrin IX chloride laser dyes have been investigated. The conductivity values for all polymer–dye samples are higher than that of the pure PMMA. For all investigated samples, at the constant temperature, the frequency dependence of (σAC) was found to obey the relation (σAC) = Aωs. The results are discussed according to the correlated barrier hopping CBH mechanism from which the Coulomb well barrier of charge carriers (WM) was calculated. For the dye-doped samples, the hematoporphyrin IX chloride mixed sample showed the larger value of (WM) compared with the others. At all frequencies, ɛ′ values for doped samples are higher than that of pure one. This is due to a free volume enhancement offered by the large size of the dye molecule. Also, the addition of dyes to PMMA causes an increase in the intensity of the loss peak (ɛ″) accompanied by a shift in its position. The effect of chemical structure of investigated dyes on the electrical properties is discussed. 相似文献
4.
Graphene oxide (GO) was used to fabricated the highly homogenization reduced graphene oxide (RGO)/alumina (Al2O3) metacomposites with low percolation threshold and adjustable negative permittivity by spark plasma sintering method. Compared to the dry grinding method used for the graphene(GR)/Al2O3 and GR/AlN metacomposites reported in our previous work, the highly homogenization RGO/Al2O3 metacomposites were obtained based on freeze-drying. The microstructures and phase composition of the RGO/Al2O3 metacomposites were investigated by field emission scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The dielectric properties including permittivity (ε′ and ε′′), dielectric loss tangent (tan?δ), alternating current conductivity (σac) and reactance (Z′′) were discussed in detail. The percolation phenomenon of σac was observed when the content of RGO increased from 13.50 to 15.38?wt%, and the percolation threshold fitted by the power law was 14.31?wt%, which appeared earlier than the reported GR/Al2O3 and GR/AlN metacomposites. What's more, the negative permittivity behavior was observed when the content of RGO reached 13.50?wt%, which was ascribed to the formation of continuous three-dimensional RGO network among the metacomposites. The RGO13.50/Al2O3 and RGO15.38/Al2O3 metacomposites realized the ε′ transition from negative to positive at 501 and 299?MHz, corresponding to the capacitive-inductive conversion. 相似文献
5.
Rodrigo Espinoza-González Samuel Hevia Álvaro Adrian 《Ceramics International》2018,44(13):15588-15595
The extremely high dielectric constant of the cubic perovskite CaCu3Ti4O12 (CCTO) has attracted increasing attention for a variety of capacitive elements in microelectronic device applications. In this research, the influence of Sr and La replacing Ca and Cu, respectively, to simultaneously controlling the intrinsic properties of grain boundaries in a co-doped CCTO ceramic has been investigated. The preparation was done using high purity compounds milled and mixed by mechano-synthesis and further consolidated by reactive sintering without calcination. Characterization by XRD confirmed the formation of single-phase CCTO ceramic and a residual amount CaTiO3. The microstructure and composition analyzed by SEM/EDX showed a smaller grain size for the co-doped CCTO. Impedance measurements indicated the smallest dielectric loss for the co-doped ceramics compare to pure and single-doped CCTO, while reaching a higher dielectric permittivity than single-doped ceramics. The CCTO-SrLa sample also showed high thermal stability of the dielectric permittivity between 100 and 470?K, and the lowest loss between 200 and 300?K. This behavior was attributed to the lower bulk resistance exhibited by the co-doped sample. 相似文献
6.
Novel high temperature ceramic capacitors (1??x)(Na0.5Bi0.5TiO3 ??0.15Ba0.8Ca0.2Ti0.8Zr0.2O3)??xK0.5Na0.5NbO3 were synthesized in the solid-state reaction route. The influence of K0.5Na0.5NbO3 modification on dielectric behavior, energy-storage properties, ac impedance and temperature stable dielectric performance were systematically investigated. The reduced grain size and enhanced relaxor properties are obtained with the addition of KNN. The content of x?=?0.1 exhibits a stable permittivity (~ 1630) and dielectric loss (<?0.05) over a relatively broad temperature range (66–230?°C). A variation in permittivity within ±?15% can be observed over a pretty wide temperature range of 66–450?°C. Beyond that, this ceramic shows enhanced energy-storage properties with the density (Wrec) of 0.52?J/cm3 and efficiency (η) of 80.3% at 110?kV/cm. The possible contributions of the grain and the grain boundary to the ceramic capacitance are discussed by the ac impedance spectroscopy. 相似文献
7.
The correlations of the microstructures and the electrical properties of high reactive Ce0.8Sm0.2O1.9 (SDC) powders, synthesized via an optimal carbonate coprecipitation method, were investigated. Microstructure of the SDC ceramics sintered at 900-1400 °C showed uniform grain and small grain size, compared with those prepared with various methods under similar sintering conditions. These features may be related to high conductivity (σ600 °C = 0.022 S cm−1) and low activation energy for conduction (0.66 eV). AC impedance spectra were involved to resolve grain interior and grain boundary resistance. Grain boundary contribution to the total resistance showed the values below 1/2 at 200-450 °C, suggesting low grain boundary effect. The motion enthalpy for the grain interior conduction decreased while the association enthalpy increased with sintering temperature up to 1300 °C, which might be possibly originated from the increase in lattice parameters with the sintering temperature. 相似文献
8.
Manojit De Sugato Hajra Rashmi Tiwari Sushrisangita Sahoo R.N.P. Choudhary H.S. Tewari 《Ceramics International》2018,44(10):11792-11797
The paper mainly reports the effect of NaNbO3 (as a doping material) on the structural (crystal data and microstructure), dielectric (permittivity, dissipation of energy) and electrical (impedance, modulus, and conductivity) characteristics of BiFeO3 forming a solid solution of Bi.8Na.2Fe.8Nb.2O3. By analysis of the room temperature X-ray diffraction data, the formation of pure-phase material and its crystal data were obtained. The comprehensive studies of dielectric parameters (relative dielectric constant (εr), and tangent loss (tan δ) were measured in a wide range of temperature (25–450?°C) and frequency (1?kHz-1?MHz). The surface morphology, obtained with a gold-coated pellet sample, exhibits the high density of the sample. The frequency-temperature dependence of conductivity follows the Jonscher’s Universal Power law. The electrical behavior of the compound has been studied using complex impedance and modulus data. The effect of grain and grain boundary on the capacitive and resistive properties of the material has been studied from complex impedance spectroscopy. 相似文献
9.
We investigate the effects of doping and annealing on the dielectric properties of metal ions doped TiO2 ceramics. Colossal permittivity (CP) above 104 was observed in single Nb ion doped TiO2, which was dominated by electron transport related interfacial polarization. Moreover, the CP can be dropped to 120 when simultaneously introducing Mn ion into the sample. The disappearance of CP behaviors maybe due to the multivalence of Mn which would inhibit the reduction of Ti4+ to Ti3+, and thus reduce delocalized electrons. Interestingly, the CP was recovered for the (Nb+Mn) co-doped TiO2 after post-sintering heat treatment in N2 atmosphere. The recovery of CP in the sample after annealing can be ascribed to the semiconducting grain and the insulating grain boundary, according to impedance spectroscopy. We therefore believe that this work can help us understand the mechanism of CP from a new perspective. 相似文献
10.
《Ceramics International》2017,43(18):16580-16592
Structural phase transition from rhombohedral (space group: R3c) to orthorhombic (space group: Pnma) cell is observed in Bi1-xSmxFeO3 (x = 0 – 0.3) compounds. The evolution of non-ferroelectric Pnma phase reduces the dielectric strength and stabilizes the collinear antiferromagnetism. Temperature variations of dielectric permittivity and its loss component show the presence of Polomska transition and it is found to shift downward towards room temperature with increase in Sm concentration. The frequency dispersion of complex dielectric permittivity was best explained in terms of Havriliak-Negami equation and by invoking the conductivity contribution. The Cole-Cole plots of complex dielectric permittivity show two distinct semicircular arcs corresponding to dielectric relaxation due to grains and grain boundaries respectively. The relaxation dynamics is explained in terms of polaron hopping across Fe2+ and Fe3+ sites in grains and short range movement of oxygen vacancies at grain boundaries. The composition dependence of magnetization is explained in terms of evolution of weak ferromagnetism due to partial breaking of spiral spin structure and the growth of collinear antiferromagnetism driven by Pnma phase. We have also observed the exchange bias behavior in some of Sm substituted samples due to the exchange interaction at the interface of coexisting weak ferromagnetic (R3c) and collinear antiferromagnetic (Pnma) phases. 相似文献
11.
Dy substituted CCTO ceramics were synthesized using solid state reaction method. Effect of Dy on structural, microstructural, dielectric and electrical properties has been studied over a wide temperature (300–500 K) and frequency range (100 Hz–1 MHz). Rietveld refinement, carried out on the samples, confirmed single phase formation and indicated overall decrease in lattice constant. Microstructure showed bimodal distribution of grains in CCTO with bigger grains surrounded by smaller grains. Dy substitution reduced grain size. Dy substitution in CCTO reduces the dielectric constant which may be attributed to increase of the Schottky potential barrier. The dielectric constant remains nearly constant in temperature range 300–400 K. The AC conductivity obeys a power law, σac=A fn, where n is the temperature dependent frequency exponent. The AC conductivity behaviour can be divided into three regions, over entire temperature range, depending on conduction processes. The relevant charge transport mechanisms have been discussed. 相似文献
12.
Vasundhara Katari Sadequa J. Patwe Srungarpu N. Achary Avesh K. Tyagi 《Journal of the American Ceramic Society》2013,96(1):166-173
Orthorhombic InVO4 was prepared by solid‐state reaction method and characterized by powder X‐ray diffraction and scanning electron microscopy. The frequency‐dependent dielectric and conductivity properties were studied from 300 to 973 K by impedance spectroscopy. A significantly enhanced conductivity was observed at higher temperature whereas almost no conduction was observed below 723 K. Appreciable grain boundary conductivity was observed at higher temperature. The activation energies for grain and grain boundary conductivities are 0.87 and 1.28 eV, respectively. The relative permittivity of ~35 was observed in a wider range of frequencies and temperatures. The frequency dispersion dielectric studies indicated thermally activated hopping conduction process. The high temperature structural studies revealed no significant change in structural parameters except a gradual increasing trend in the unit cell parameters and amplitude of isotropic thermal parameters with increasing temperature. 相似文献
13.
Yanmin Huang Laijun Liu Danping Shi Shuangshuang Wu Shaoying Zheng Liang Fang Changzheng Hu Brahim Elouadi 《Ceramics International》2013
CaCu3Ti4O12 (CCTO) powder has been prepared by a molten salt method using the NaCl–KCl mixture. Crystal structure and microstructure of the powder and the resulting ceramics have been characterized by using X-ray diffraction (XRD) and scanning electron microcopy (SEM). Impedance analyzer and current–voltage meter were employed to analyze dielectric and nonlinear (I–V) properties of the CCTO ceramics with different sintering durations and subsequent cooling rates. The values of dielectric permittivity and nonlinear coefficient of the quenched sample were found to be higher than those of the slowly cooled sample. More specifically, the cooling methods (quenching and furnace-cooling) have allowed to adjust; (?) the breakdown voltage within a rather low range of 0.3–4.4 kV cm−1; (??) the nonlinear coefficient between 2 and 6 and (???) the giant dielectric permittivity for the ceramics within a range from 5000 to 20000. A double Schottky barrier can be evidenced from the linear behavior between the ln J and E1/2 in grain boundary regions. The relationship between the electrical current density and the applied electrical field indicates that the potential barrier height ΦB is holding time dependent. 相似文献
14.
Takao Sada Kosuke Tsuji Arnaud Ndayishimiye Zhongming Fan Yoshihiro Fujioka Clive A. Randall 《Journal of the European Ceramic Society》2021,41(1):409-417
Cold sintering process (CSP) offers a promising strategy for the fabrication of innovative and advanced high permittivity dielectric nanocomposite materials. Here, we introduce Ba(OH)2?8H2O hydrated flux as a new transient chemistry that enables the densification of BaTiO3 in a single step at a temperature as low as 150 °C. This remarkably low temperature is near its Curie transition of 125 °C, associated with a displacive phase transition. The cold sintered BaTiO3 shows a relative density of 95 % and a room temperature relative permittivity over 1000. This new hydrated flux permits the fabrication of a unique dense BaTiO3-polymer nanocomposite with a high volume fraction of ceramics ((1-x) BaTiO3 – x PTFE, with x = 0.05). The composite exhibits a relative permittivity of approximately 800, at least an order of magnitude higher than previous reports on polymer composites with BaTiO3 nanoparticle fillers that are typically well below 100. Unique high permittivity dielectric nanocomposites with enhanced resistivities can now be designed using polymers to engineer grain boundaries and CSP as a processing method opening up new possibilities in dielectric materials design. 相似文献
15.
《Journal of the European Ceramic Society》2002,22(4):579-583
Impedance spectroscopy is used to deconvolute the dc conductivity (σ) of undoped BaTiO3 ceramics (∼95% of the theoretical X-ray density) into bulk (σb) and grain boundary (σgb) components at two oxygen partial pressures, PO2 ∼10 Pa (N2) and ∼0.21 MPa (air). At 900°C, σ∼σb in both atmospheres, however, at lower temperatures Z1 plots are dominated by the grain boundary component and σ∼σgb. The temperature of the switch from σ∼σb to σ∼σgb is different in the two atmospheres and occurs at ∼850°C in air and ∼650°C in N2. Isothermal plots of log σb vs log PO2 in the temperature range 450–900°C show the expected oxygen partial pressure dependence with a gradient of +1/4. In contrast, σgb is relatively insensitive to PO2 and log σgb vs log PO2 plots have gradients < +1/4 with values as low as ∼+1/14.0. In general, isothermal log σ vs log pO2 plots have gradients <+1/4 as σ is dominated by the grain boundary component. This may explain the wide range of gradients (∼1/4–1/9) reported in the literature for isothermal dc conductivity measurements on polycrystalline BaTiO3 in the p-type regime. 相似文献
16.
Yüksel Köseoğlu 《Ceramics International》2013,39(4):4221-4230
MnxNi1?xFe2O4 (x=0.2, 0.4, 0.6) nanoparticles were synthesized by a polyethylene glycol (PEG)-assisted hydrothermal route. We present a systematic investigation on the structural, magnetic, electrical and dielectric properties of the products by using XRD, FT-IR, SEM, TGA, VSM and dielectric spectroscopy, respectively. Single phased cubic spinel structure was confirmed for all samples and the average crystallite size of the products was estimated using Line profile fitting and ranges between 6.5 and 11 nm. The nanoparticles have ferromagnetic nature with small coercivity. The samples showed semiconducting behavior which is revealed from temperature dependent conductivity measurements. Temperature and frequency dependent dielectric property; dielectric permittivity (ε) and ac conductivity (σAC) studies for the samples indicated that the dielectric dispersion curve for all samples showed usual dielectric dispersion confirming the thermally activated relaxation typical for Debye-like relaxation referring to it as the Maxwell–Wagner relaxation for the interfacial polarization of homogeneous double structure. The particle size, saturation magnetization, coercive field, conductivity and dielectric constant of the samples are strictly temperature dependent and increased with Mn concentration. 相似文献
17.
Ashok Kumar Baral 《Electrochimica acta》2010,56(2):667-675
This work presents the ionic transport properties in some nanocrystalline double doped cerias, i.e., Ce0.8Gd0.1Pr0.1O2−δ and Ce0.8Gd0.15Pr0.05O2−δ with various average grain sizes, in the intermediate temperature region. The correlations between electrical and dielectric properties of these materials have been established and variation of conductivity with respect to temperature has been thoroughly discussed. All the materials are found to be ionic in nature and show high value of ionic conductivity at intermediate temperatures. The nanocrystalline Ce0.8Gd0.1Pr0.1O2−δ material (irrespective of grain size), shows lowest association energy, i.e., 0.03 eV, which is close to the theoretically predicted lowest value (0.02 eV) in double doped ceria. A repulsive force is expected between the free oxygen vacancies at the grain boundary regions at higher temperatures, which restricts the rise in grain boundary conductivity and results in decrease in total conductivity. 相似文献
18.
Powders of gadolinium-doped ceria solid solutions, Ce1−xGdxO2−δ (x = 0.05, 0.1, 0.2, 0.3 and 0.4), were prepared by a freeze-drying precursor route. Dense ceramic pellets with average grain sizes in the range of several microns were obtained after sintering at 1600 °C. Cobalt nitrate was added to the powders to obtain dense ceramic samples with grain sizes in the submicrometer range at 1150 °C. The ionic conduction was analysed by impedance spectroscopy in air, to de-convolute the bulk and grain boundary contributions. The bulk conductivity at low temperature clearly decreases with increasing content of Gd whereas the activation energy increases. An alternative method is proposed to analyse the extent of defect interactions on conduction. For samples without addition of Co, the specific grain boundary conductivity increases with increasing Gd content. Addition of cobalt does not alter the bulk properties but produces an important increase in the specific grain boundary conductivity, mainly in samples with lower Gd-concentration (x = 0.05 and 0.1). Segregation of Gd and its strong interaction with charge carriers may explain the blocking effects of grain boundaries. 相似文献
19.
Jakkree Boonlakhorn Narong Chanlek Jedsada Manyam Sriprajak Krongsuk Prasit Thongbai Pornjuk Srepusharawoot 《Ceramics International》2021,47(16):22390-22396
CaCu3-xZnxTi4O12 ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu3Ti4O12 (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn2+ doping ions at Cu2+ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu3-xZnxTi4O12 decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu3-xZnxTi4O12 ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn2+ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu+/Cu2+ and Ti3+/Ti4+, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model. 相似文献
20.
Transparent and stable glasses in the chemical composition of Li2O–LiF–B2O3–MO (M = Zn and Cd) have been prepared by a conventional melt quenching method. For these glasses, absorption spectra, structural (XRD, FT-IR, and Raman spectra), thermal (TG–DTA and DSC), dielectric (?′, ?″, tan δ), ac conductivity (σac), and electric modulus (M′ and M″) have been investigated. Amorphous nature of these glasses has been confirmed from their XRD profiles. The LFB glasses with the presence of ZnO or CdO an extended UV-transmission ability has been achieved. The measured FT-IR and Raman spectra have exhibited the vibrational bands of B–O from [BO3] and [BO4] units and Li–O. The dielectric properties (tan δ, dielectric constant (?′), dielectric loss (?″)), electrical modulus and electrical conductivity (σac) of these glasses have also been studied from 100 Hz to 1 MHz at the room temperature. Based on the trends noticed in the ac conductivities, the present glasses could be found useful as battery cathode materials. 相似文献