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1.
The electrical properties of the (Na0.6Ag0.4)2PbP2O7 compound were studied using the complex impedance spectroscopy in the temperature range (502-667 K). Grain interior, grain boundary and electrode-material interface contributions to the electrical response are identified by the analysis of complex plan diagrams. The imaginary part of the modulus at several temperatures shows a double relaxation peaks, furthermore suggesting the presence of grains and grain boundaries in the sample. An analysis of the dielectric constants ?′, ?″ and loss tangent tan(δ) with frequency shows a distribution of relaxation times. The dc conductivity of the material is thermally activated with an activation energy about 0.8 eV which is in the vicinity of the that obtained from tan(δ) (E = 0.7 eV) and modulus (Em = 0.68 eV) studies. 相似文献
2.
Pure and Pr6O11-doped CaCu3Ti4O12 (CCTO) ceramics were prepared by conventional solid-state reaction method. The compositions and structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of Pr-ion concentration on dielectric properties of CCTO were measured in the ranges of 60 Hz-3 MHz and 290-490 K. The third phase of Ca2CuO3 was observed from the XRD of CCTO ceramics. From SEM, the grain size was decreased obviously with high valence Pr-ion (mixing valence of Pr3+ and Pr4+) substituting Ca2+. The room temperature dielectric constant of Pr-doped CCTO ceramics, sintered at 1323 K, was an order of magnitude lower than the pure CCTO ceramics due to the grain size decreasing and Schottky potential increasing. The dielectric spectra of Pr-doped CCTO were flatter than that of pure CCTO. The loss tangent of Pr-doped CCTO ceramics was less than 0.20 in 2 × 102-105 Hz region below 440 K. The complex impedance spectra of pure and Pr-doped CCTOs were fitted by ZView. From low to high frequency, three semicircles were observed corresponding to three different conducting regions: electrode interface, grain boundary and grain. By fitting the resistors R and capacitors C, the activation energies of grain boundary and electrode contact were calculated. All doped CCTOs showed higher activation energies of grain boundary and electrode than those of pure CCTO ceramics, which were concordant with the decreasing of dielectric constant after Pr6O11 doping. 相似文献
3.
In order to investigate the electrical transport in LaNi3/4Mo1/4O3 and LaNi3/4W1/4O3, the dc conductivity and dielectric properties in these polycrystalline materials are investigated in the temperature range from 163 K to 383 K and frequency range from 50 Hz to 1 MHz. The X-ray diffraction patterns of the samples show monoclinic phase at room temperature. The homogeneity of the samples is determined by energy dispersive analysis of X-ray (EDAX) attached with a scanning electron microscope. The temperature dependence of dc conductivity shows the semiconducting nature of the materials. The complex impedance plane plots show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The frequency-dependent electrical data are also analyzed in the framework of ac conductivity formalism. The ac conductivity spectra follow the universal power law. The activation energies required for bulk conduction is 0.143 and 0.165 eV for LNM and LNW respectively. The scaling behaviour of loss tangent suggests that the relaxation describes the same mechanism at various temperatures. 相似文献
4.
Devang D. Shah P.K. Mehta M.S. DesaiC.J. Panchal 《Journal of Alloys and Compounds》2011,509(5):1800-1808
The X-ray diffraction Rietveld refinement of Ba[(Fe1−xCox)1/2Nb1/2]O3 with 0 ≤ X ≤ 1 shows cubic structure formation with space group Pm3m. No distinct tilting of oxygen octahedron is observed. The dielectric measurement of such a cubic system exhibited giant values (?′ > 104) in the temperature range of 298-483 K and frequency range of 102-105 Hz. An analysis of the permittivity, electric modulus, and electrical conductivity properties in these systems confirmed the presence of oxygen vacancies induced dipolar relaxation. Our investigations show that the observed extremely high dielectric constant values are predominantly the result of oxygen vacancies induced dipoles produced at the grain boundaries. Additional significant intrinsic contributions to the permittivity comes from the directly doped electrons at the unit cell, as indicated by the enhancement in the observed values of the permittivity on replacement of Fe3+ (3d5) by Co3+ (3d6). The contributions of the doped free charges and the oxygen vacancy induced dipoles are separated using the Jump Relaxation Model. 相似文献
5.
Multiferroic ceramics based on BiFeO3 and Sr-doped BiFeO3 have been processed by high energetic milling and later thermal treatments at reduced temperatures to synthesize the perovskite structure. Single phase materials are obtained at 800 °C, reducing the temperature needed to complete the reaction in solid state method. Ceramics with densities higher than 94% were obtained at 1000 °C, and up to 98% at 1050 °C. All the ceramics were obtained in a single thermal treatment, where synthesis, grain growth and densification take place. The addition of Sr stabilizes the BiFeO3 perovskite structure, avoiding its decomposition. Ceramics with higher dielectric permittivity and conductivity than non-doped materials are obtained, due to the increase of the amount of oxygen vacancies. It is shown for the first time that the grain boundary conductivity is increased in BiFeO3 by doping with Sr. 相似文献
6.
High dielectric CaCu3Ti4O12 (CCTO) ceramics have been successfully prepared by a novel basic co-precipitation (BCP) method. Compared with the conventional solid-state and/or soft chemistry methods, the BCP method has many advantages such as relatively lower sintering temperature, shorter sintering time and lower costs. The XRD patterns confirm the formation of CCTO crystal phase in the as-prepared samples. Influences of initial ingredients and sintering condition on phase composition, microstructure and dielectric property have been investigated through series of trials. The correlation between the process of the grain growth and dielectric properties of final products has been explored. The final products exhibit the dielectric constants higher than 10,000 and the dielectric losses lower than 0.15 at 1 KHz. 相似文献
7.
K.P. Padmasree R.A. Montalvo-LozanoS.M. Montemayor A.F. Fuentes 《Journal of Alloys and Compounds》2011,509(34):8584-8589
In this work, we present the electrical conductivity and dielectric relaxation studies of 20 mol% yttria doped ceria (Ce0.8Y0.2O1.9) electrolyte prepared by mechanical milling technique. The ac conductivity was found to obey the universal dielectric response at low temperatures. At high temperatures, the conductivity value estimated from the high frequency plateau agreed with the bulk conductivity (σb) obtained form the impedance spectra and the low frequency plateau value agreed with the grain boundary conductivity (σgb). Temperature dependence of σb and σgb gives the activation energies for conduction in the bulk and grain boundary. Two relaxation peaks were observed in the tan delta spectra; the high frequency relaxation peak is due to the bulk conduction and the low frequency peak result from the grain boundary conduction. The migration energy EM and the energy required for the creation of free oxygen vacancies assisting oxide ion migration EO is estimated from the resonant frequency and maxima of the tan delta spectra of these relaxation peaks. The sums of these two values in the low and high frequency peaks are nearly equal to the activation energies obtained from the bulk and grain boundary conductivity plot. 相似文献
8.
S. Bhaskar Reddy K. Prasad RaoM.S. Ramachandra Rao 《Journal of Alloys and Compounds》2011,509(4):1266-1270
Pure and Gd-doped barium zirconate titanate (BaZr0.1Ti0.9O3, BZT) ceramics were prepared by solid state reaction method. Phase analysis showed the formation of the pyrochlore phase (Gd2Ti2O7) at about 5 mol% Gd doping in BZT. The microstructural investigation on the sintered ceramics showed that Gd doping significantly reduced the grain size of pure BZT ceramics, from about 100 μm to 2-5 μm. Change in the Gd concentration had minor influence on the grain size and on morphology. An increase in the Gd content decreased the Curie temperature (TC) of the BZT ceramics. The maximum dielectric constant at TC was observed for 2 mol% Gd and with further increase in Gd content the dielectric constant at TC decreased. The dielectric constant was significantly improved compared to that of pure BZT ceramic. Tunable dielectric materials with good dielectric properties can be prepared by doping BZT with Gd. 相似文献
9.
Muhammad Azwadi SulaimanSabar D. Hutagalung Julie J. MohamedZainal A. Ahmad Mohd Fadzil AinBakar Ismail 《Journal of Alloys and Compounds》2011,509(18):5701-5707
Impedance analyses was performed on undoped and Nb-doped CaCu3Ti4O12 (CaCu3Ti4−xNbxO12+x/2; x = 0, 0.01, 0.03, 0.05, 0.1) to investigate their electrical properties. The pellet samples were prepared using the solid state reaction method. Silver electrode was deposited on both pellets’ surfaces for electrical measurement. The thermally etched samples showed tiny bumped domains within the grains. The existence of both domain and grain boundaries are believed to strongly influence the dielectric constant of CaCu3Ti4O12 (CCTO). Undoped CCTO showed two arcs of impedance complex plane while Nb-doped samples have three arcs. Each arc represents the constituent elements of the CCTO. The highest frequency arc is evidence that CCTO consists of conductive domains which measure about 1 Ω and are insulated by two types of barriers, i.e. domain boundary and grain boundary. 相似文献
10.
《金属学报(英文版)》2017,(2)
To get a better understanding of the influence of rare-earth element doping,CaCu_3Ti_4O_(12)(CCTO) samples with a partial substitution of Ca with Eu with different compensation mechanisms were designed and prepared by solid-state reaction.All the ceramics were single phase,while the dielectric constants and thermally activated energy values for dielectric relaxation in Eu-doped ceramics were both lower than those of CCTO.Ca_(0.875)Eu_(0.1)Cu_3Ti_4O_(12)(CECT1)exhibited a slight decrease in both the permittivity and electric resistance of grain boundaries compared with CCTO,while Ca_(0.85)Eu_(0.1)Cu_3Ti_4O_(12)(CECT2) underwent a sharp decrease in permittivity associated with an abnormally large resistance.The different dielectric behavior indicates that the dielectric properties of CCTO are sensitive to the valence states of cations and defects.The variation of permittivity is related to the localization of carriers,which,according to the XPS results,should be caused by the presence of oxygen vacancies.The formation of defect complexes between cations and oxygen vacancies leads to the increase in resistance and prevents the hopping between Cu~+ and Cu~(2+),which is an important source of the polarization in grain boundaries. 相似文献
11.
K. Sambasiva Rao B. TilakK.Ch. Varada Rajulu A. SwathiHaileeyesus Workineh 《Journal of Alloys and Compounds》2011,509(25):7121-7129
Polycrystalline perovskite lead free material (Na0.5Bi0.5)0.91Ba0.090TiO3 was prepared by solid state reaction method. The crystal structure examined by X-ray powder diffraction indicates that the material was single phase with tetragonal structure. Dielectric studies exhibit a diffuse phase transition and characterized by a strong temperature and frequency dispersion of permittivity which relates cation disorder at A-site and exhibits relaxor behaviour. The dielectric relaxation has been modeled using the Vogel-Fulcher relationship, the calculated activation energy found to be Ea = 0.021 eV. Complex impedance analysis indicates the system undergoing a polydispersive non-Debye type relaxation. Also, used to characterize grain and grain-boundary resistivities of Ba substituted (Na0.5Bi0.5)TiO3 ceramic. The phenomenon was also interpreted by accounting for microstructural differences. The corresponding relaxation times were also used to confirm the interpretation of complex impedance spectra. Overlapping of grain boundary and electrode relaxation processes can be separated above about 4000 C. Electrical modulus spectroscopy studies have been performed. The conductivity parameters such as ion-hopping rate (ωp) and the charge carrier concentration (K1) have been calculated using Almond and West formalism. 相似文献
12.
Tao LiRenzhong Xue Junhong HaoYuncai Xue Zhenping Chen 《Journal of Alloys and Compounds》2011,509(3):1025-1028
CaCu3Ti4O12 (CCTO) ceramics are prepared by the traditional solid-state reaction method under the same sintering conditions. The effect of calcining temperatures for the powders before sintering on the microstructure and electric properties of CCTO ceramics has been investigated. The XRD patterns for the powder calcined at 950 °C show that some measure of second phases (CaTiO3, TiO2 and CuO) can be found except a considerable amount of CCTO phase in them and the content of second phases decrease markedly as the calcining temperature is raised to 1000 °C. The XRD patterns for the powder calcined at 1050 °C indicate that the powder has been basically formed into a single CCTO phase except a small quantity of CaTiO3 phase, which is attributed to CuO volatilizing in the calcining process. Furthermore, the XRD patterns for the CCTO pellets sintered at 1080 °C/10 h manifest that all the second phases have disappeared after the sintering process except that a very weak peak of CaTiO3 can still be seen in the XRD pattern for the pellets made of the powder calcined at 1050 °C. The electric properties measurement demonstrates that the lower calcining temperature for the raw powder is helpful to increase the values of permittivity and the higher calcining temperature is helpful to improve the non-ohmic properties. The non-ohmic characteristic has a behavior reverse to that of the permittivity, which can be ascribed to the change in the height of Schottky barriers. 相似文献
13.
Aurivillius SrBi2(Nb0.5Ta0.5)2O9 (SBNT 50/50) ceramics were prepared using the conventional solid-state reaction method. The obtained samples were thermally modified in high vacuum to study the influence of the formed defects on the dielectric and electrical properties of the samples. Scanning electron microscopy with an energy dispersion X-ray spectrometer was applied to investigate the grain structure and stoichiometry of the studied ceramics. Their dielectric properties were determined by impedance spectroscopy measurements. A strong low frequency dielectric dispersion was found to exist in this material which was controlled by thermal modification of the tested ceramics. This phenomenon can be ascribed to the presence of ionized space charge carriers such as oxygen and bismuth vacancies. The dielectric relaxation was defined on the basis of an equivalent circuit. Moreover the temperature dependence of various electrical properties was determined and discussed. 相似文献
14.
The Gd(Ni1/2Zr1/2)O3 (GNZ) ceramic is synthesized by the solid-state reaction technique. The X-ray diffraction pattern of the sample shows monoclinic phase at room temperature. The dielectric dispersion of the material is investigated in the temperature range from 303 K to 673 K and in the frequency range from 100 Hz to 1 MHz. The relaxation peak is observed in the frequency dependence of the loss tangent. The relaxation time at different temperatures is found to obey Arrhenius law having activation energy of 1.1 eV which indicates the hopping of ions at the lattice site and may be responsible for the dielectric relaxation of GNZ. The scaling behaviour of loss tangent suggests that the relaxation mechanism is temperature independent. The frequency dependent conductivity spectra follow the power law. In the impedance formalism, the Cole-Cole model is used to study the relaxation mechanism of GNZ. 相似文献
15.
The dielectric properties of Mg substituted Ni-Li spinel ferrites synthesized by sol-gel auto combustion process have been studied using impedance measurements in the frequency range from 10 Hz to 10 MHz and in the temperature range from 310 K to 473 K. The effect of frequency, temperature and composition on dielectric constant (?′), dielectric loss (tan δ) and conductivity (σ) has been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. The electrical modulus formulism has been employed to study the relaxation dynamics of charge carriers and the results indicate the presence of non-Debye type of relaxation in the present ferrites. Similar values of activation energies for dc conduction (Edc) and for conductivity relaxation (EM″) reveal that the mechanisms of electrical conduction and dielectric polarization are same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of dynamical process for charge carriers. The saturation magnetization and coercivity have been calculated from the hysteresis loop measurements and show striking dependence on the composition. 相似文献
16.
Alok Kumar RaiNitish Kumar Singh Sang-Kwon LeeK.D. Mandal D. KumarOm Parkash 《Journal of Alloys and Compounds》2011,509(36):8901-8906
CaCu2.9Fe0.1Ti4O12 (CCFTO) has been prepared by a novel semi-wet route and its dielectric properties have been studied in the temperature range 300-500 K. It is found that dielectric constant (?) decreases drastically in the frequency range 100 Hz to 1 MHz. Complex plane impedance and modulus analysis was done to understand this drastic decrease in ?. Oxidation state of various ions was studied using X-ray photoelectron spectroscopy (XPS). The decrease in the permittivity of CCFTO can be attributed to two factors: the suppression of the Ca/Cu disorder in CCFTO which is observed in CaCu3Ti4O12 (CCTO) and the absence of the grain boundary internal barrier layer capacitance mechanism. 相似文献
17.
Moti Ram 《Journal of Alloys and Compounds》2011,509(40):9659-9662
The electrical impedance and modulus properties of a LiCo3/5Fe1/5Cu1/5VO4 ceramic system were measured by impedance spectroscopy method in the frequency range 102-106 Hz and temperature range 22-250 °C. X-ray diffraction study reveals formation of the compound in a cubic crystal system with lattice parameters a = 8.2756 (3) Å. Field emission scanning electron microscopy is used to investigate the grain morphology of the material. Nyquist plots confirm the existence of bulk and grain boundary effects at 22 °C ≤ T ≤ 200 °C, and bulk, grain boundary and polarization effects at T ≥ 225 °C. Electrical modulus study indicates a non-Debye behavior of the material. A detailed study of bulk conductivity shows electric conduction in the material as a thermally activated process. 相似文献
18.
A.A. Yadav M.A. BaroteT.V. Chavan E.U. Masumdar 《Journal of Alloys and Compounds》2011,509(3):916-921
Polycrystalline indium doped CdS0.2Se0.8 thin films with varying concentrations of indium have been prepared by spray pyrolysis at 300 °C. The as deposited films have been characterized by XRD, AFM, EDAX, optical and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of indium doping concentration. AFM studies reveal that the RMS surface roughness of film decreases from 34.68 to 17.76 with increase in indium doping concentration up to 0.15 mol% in CdS0.2Se0.8 thin films and further it increases for higher indium doping concentrations. Traces of indium in CdS0.2Se0.8 thin films have been observed from EDAX studies. The optical band gap energy of CdS0.2Se0.8 thin film is found to decrease from 1.91 eV to 1.67 eV with indium doping up to 0.15 mol% and increase after 0.15 mol%. The electrical resistivity measurement shows that the films are semiconducting with minimum resistivity of 3.71 × 104 Ω cm observed at 0.15 mol% indium doping. Thermoelectric power measurements show that films exhibit n-type conductivity. 相似文献
19.
Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics
Chen Zhi-hui Ding Jian-ning Mei LinYuan Ning-yi Zhu Yuan-yuan 《Journal of Alloys and Compounds》2011,509(2):482-485
(Bi0.5Na0.5)0.94Ba0.06TiO3 + x wt% Dy2O3 with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy2O3 on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi0.5Na0.5)0.94Ba0.06TiO3 composition was not changed by adding 0.05-0.3 wt% Dy2O3. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy2O3 inhibits the grain growth of the ceramics. The addition of Dy2O3 shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy3+ ions substitute B-site Ti4+ ions, and increasing the properties for 0.15 < x < 0.3 when Dy3+ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d33 = 170 pC/N and the dielectric constant ?r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3. 相似文献
20.
Dong Xu Xiaonong ChengHongming Yuan Juan YangYuanhua Lin 《Journal of Alloys and Compounds》2011,509(38):9312-9317
Y(NO3)3·6H2O-doped ZnO-Bi2O3-based varistor ceramics were prepared using a solid reaction route. The microstructure, electrical properties, degradation coefficient (DV), and dielectric characteristics of varistor ceramics were studied in this paper. With increasing amounts of Y(NO3)3·6H2O in the starting composition, Y-containing Bi-rich, Y2O3, and Sb2O4 phases were formed, and the average grain size decreased. Results also showed that with the addition of 0.16 mol% Y(NO3)3·6H2O, Y(NO3)3·6H2O -doped ZnO-based varistor ceramics exhibit comparatively better comprehensive electrical properties, such as a threshold voltage of 425 V/mm, a nonlinear coefficient of 73.9, a leakage current of 1.78 μA, and a degradation coefficient of 1.7. The dielectric characteristics and lightning surge test also received the same additional content of Y(NO3)3·6H2O. The results confirmed that doping with rare earth nitrates instead of rare earth oxides is very promising route in preparing high-performance ZnO-Bi2O3-based varistor ceramics. 相似文献