Impedance spectroscopy and dielectric properties of Ce and La substituted Pb0.7Sr0.3(Fe0.012Ti0.988)O3 nanoparticles

We present the structural, microstructural, dielectric and impedance behavior of Pb_0.7Sr_0.3[(Fe_2/3Ce_1/3)_0.012Ti_0.988]O₃ (PSFCT) and Pb_0.7Sr_0.3[(Fe_2/3La_1/3)_0.012Ti_0.988]O₃ (PSFLT) nanoparticles. These nanoparticles were prepared by a chemical synthesis route using polyvinyl alcohol as surfactant. The X-ray diffraction pattern shows polycrystalline nature with coexistence of tetragonal and cubic phase in both PSFCT and PSFLT nanoparticles. The average particle size has been measured using Scherer's relation. The average particle sizes also measured by TEM are 10 and 11 nm, and by SEM 9 and 12 nm, respectively, of PSFCT and PSFLT nanoparticles. By measuring the value of relative permittivity (?′) and loss (tan δ) at lower frequency, the dielectric properties show Maxwell-Wagner type interfacial polarization. However, due to nano size effect of PSFCT and PSFLT, dispersionless dielectric response has been observed up to higher frequency of 15 MHz. The frequency dependent real (Z′) and imaginary (Z″) parts of impedance confirmed the variation which was observed in dielectric properties. The values of resistance of grain boundaries, R_gb is higher than grains, R_g indicates that the effect of grain boundaries is dominant on electrical properties when the size of nanoparticles is quite small.     

Impedance and modulus analysis of the (Na0.6Ag0.4)2PbP2O7 compound

The electrical properties of the (Na_0.6Ag_0.4)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 (E_m = 0.68 eV) studies.     

Electrical conduction and dielectric relaxation process in Ce0.8Y0.2O1.9 electrolyte system

In this work, we present the electrical conductivity and dielectric relaxation studies of 20 mol% yttria doped ceria (Ce_0.8Y_0.2O_1.9) 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 (σ_b) obtained form the impedance spectra and the low frequency plateau value agreed with the grain boundary conductivity (σ_gb). Temperature dependence of σ_b and σ_gb 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 E_M and the energy required for the creation of free oxygen vacancies assisting oxide ion migration E_O 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.     

Stress and defect induced enhanced low field magnetoresistance and dielectric constant in La0.7Sr0.3MnO3 thin films

Colossal magnetoresistive manganite La_0.7Sr_0.3MnO₃ (LSMO) films were prepared by pulsed laser deposition on three different single crystal substrates using different deposition parameters. Characterizations of their surface morphologies, structural, magnetic and magneto-transport properties show that films on MgO single crystal substrates contain higher amount of structural defects compared to those on SrTiO₃ (STO) and NdGaO₃ (NGO) substrates. Low deposition rate and thicker films give rise to polycrystallinity and grain boundaries. The films on MgO substrate showed a broad paramagnetic (PM) to ferromagnetic (FM) transition accompanied with metal-insulator transition (MIT) much below their Curie temperature (T_C) indicating growth of strained structures due to large lattice mismatch (9%) between the substrate and the film. The deposited films on STO and NGO show least effect of substrate induced strain exhibiting sharper PM-FM transition and metallic behavior below T_C. The magnetoresistance (MR) measured with 300 mT field clearly shows two contributions, one due to grain boundary tunneling and the other due to colossal MR effect. The highest low field MR effect of 17% was achieved for the film on MgO with the highest thickness and surface roughness indicating the presence of grain boundary related defects. Also a high dielectric constant was observed for the same film at room temperature up to 100 kHz frequency. Coexistence of defect induced large low-field MR and abnormally high dielectric constant can give rise to different exciting applications.     

High frequency response to the impedance complex properties of Nb-doped CaCu3Ti4O12 electroceramics

Impedance analyses was performed on undoped and Nb-doped CaCu₃Ti₄O₁₂ (CaCu₃Ti_4−xNb_xO_12+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.     

Dielectric relaxation behaviors of pure and Pr6O11-doped CaCu3Ti4O12 ceramics in high temperature range

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.     

Dielectric properties of Cu substituted Ni0.5−xZn0.3Mg0.2Fe2O4 ferrites

Dielectric properties of Cu substituted Ni-Zn-Mg ferrite samples having the general formula Ni_0.5−xCu_xZn_0.3Mg_0.2Fe₂O₄ (where x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) synthesized by Pramanik method are reported. The single phase formation of the ferrites was confirmed by XRD technique. The lattice parameter is found to increase with increase in Cu content. Average grain size, obtained from SEM micrographs, is found to increase with increase in Cu content. Dielectric parameters were measured as a function of frequency at room temperature as well as at higher temperatures. The variation in dielectric constant (?′) with temperature at four different fixed frequencies viz. 1 kHz, 10 kHz, 100 kHz, and 1 MHz was also studied. The room temperature dielectric constant (?′) and dielectric loss (tan δ) are found to decrease with increase in frequency. The ac conductivity (σ_ac) is found to increase with increase in the frequency.     

Dielectric properties of iron doped calcium copper titanate, CaCu2.9Fe0.1Ti4O12

CaCu_2.9Fe_0.1Ti₄O₁₂ (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.     

A diffuse phase transition study on Ba substituted (Na0.5Bi0.5)TiO3 ferroelectric ceramic

Polycrystalline perovskite lead free material (Na_0.5Bi_0.5)_0.91Ba_0.090TiO₃ 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 E_a = 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 (Na_0.5Bi_0.5)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 (ω_p) and the charge carrier concentration (K¹) have been calculated using Almond and West formalism.     

Fabrication and characterization of ceramic thin films by RF magnetron sputtering using Zn-enriched (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 as target

Dielectric ceramic thin film was fabricated on SiO₂ (1 1 0) substrates by radio frequency (RF) magnetron sputtering method using a Zn-enriched (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ target. The microstructure, components, and morphological properties of the thin films were characterized thoroughly. The results reveal that the main phases of the thin films are Ba_xSr_1−xNb₂O₆, which are of different compositions from that of the ceramic target due to Zn loss. The thin films are polycrystalline and of dense structure with uniform grain sizes and well-defined grain boundaries.     

Origin of giant dielectric constant in Ba[(Fe1−xCox)1/2Nb1/2]O3

The X-ray diffraction Rietveld refinement of Ba[(Fe_1−xCo_x)_1/2Nb_1/2]O₃ with 0 ≤ X ≤ 1 shows cubic structure formation with space group P_m3_m. 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.     

High permittivity and low dielectric loss of the Ca1−xSrxCu3Ti4O12 ceramics

The Ca_1−xSr_xCu₃Ti₄O₁₂ (CSCTO) giant dielectric ceramics were prepared by conventional solid-state method. X-ray diffraction patterns revealed that a small amount of Sr²⁺ (x < 0.2) had no obvious effect on the phase structure of the CSCTO ceramics, while with increasing the Sr²⁺ content, a second phase of SrTiO₃ appeared. Electrical properties of CSCTO ceramics greatly depended on the Sr²⁺ content. The Ca_0.9Sr_0.1Cu₃Ti₄O₁₂ ceramics exhibited a higher permittivity (71,153) and lower dielectric loss (0.022) when measured at 1 kHz at room temperature. The ceramics also performed good temperature stability in the temperature range from −50 °C to 100 °C at 1 kHz. By impedance spectroscopy analysis, all compounds were found to be electrically heterogeneous, showing semiconducting grains and insulating grain boundaries. The grain resistance was 1.28 Ω and the grain boundary resistance was 1.31 × 10⁵ Ω. All the results indicated that the Ca_0.9Sr_0.1Cu₃Ti₄O₁₂ ceramics were very promising materials with higher permittivity for practical applications.     

Influence of A-site Gd doping on the microstructure and dielectric properties of Ba(Zr0.1Ti0.9)O3 ceramics

Pure and Gd-doped barium zirconate titanate (BaZr_0.1Ti_0.9O₃, 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 (T_C) of the BZT ceramics. The maximum dielectric constant at T_C was observed for 2 mol% Gd and with further increase in Gd content the dielectric constant at T_C 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.     

Impedance analysis of thermally modified SrBi2(Nb0.5Ta0.5)2O9 ceramics

Aurivillius SrBi₂(Nb_0.5Ta_0.5)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.     

Mg-substituted ZnNb2O6-TiO2 composite ceramics for RF/microwaves ceramic capacitors

Microstructure and microwave dielectric properties of Mg-substituted ZnNb₂O₆-TiO₂ microwave ceramics were investigated. Mg acted as a grain refining reagent and columbite phase stabilization reagent. With an increasing Mg content, the amount of ixiolite (Zn, Mg) TiNb₂O₈ decreased, and the amount of (Zn_0.9Mg_0.1)_0.17Nb_0.33Ti_0.5O₂ and columbite increased. ZnO-Nb₂O₅-1.75TiO₂-5 mol.%MgO exhibited excellent dielectric properties (at 950 °C): ?_r = 35.6, Q × f = 16,000 GHz (at 5.6 GHz) and τ_f = −10 ppm/°C. The material was applied successfully to make RF/microwaves ceramic capacitor, whose self-resonance frequency was 19 GHz at low capacitance of 0.13 pF.     

Ferroelectric relaxor behavior and dielectric spectroscopic study of 0.99(Bi0.5Na0.5TiO3)-0.01(SrNb2O6) solid solution

0.99(Bi_0.5Na_0.5TiO₃)-0.01(SrNb₂O₆) was prepared by simple solid state reaction route. Material stabilized in rhombohedral perovskite phase with lattice constants a = 3.9060 Å, α = 89.86° and a_h = 5.4852 Å, c_h = 6.7335 Å for hexagonal unit cells. Density of material was found 5.52 g_m/cm³ (92.9% of theoretical one) in the sample sintered at 950 °C. The temperature dependent dielectric constant exhibits a broad peak at 538 K (?_m = 2270) at 1 kHz that shows frequency dependent shifts toward higher temperature - typical relaxor behavior. Modified Curie-Weiss law was used to fit the dielectric data that exhibits almost complete diffuse phase transition characteristics. The dielectric relaxation obeys the Vogel-Fulcher relationship with the freezing temperature 412.4 K. Significant dielectric dispersion is observed in low frequency regime in both components of dielectric response and a small dielectric relaxation peak is observed. Cole-Cole plots indicate polydispersive nature of the dielectric relaxation; the relaxation distribution increases with increase in temperature.     

Low-loss microwave dielectrics using rock salt oxide Li2MgTiO4

Rock-salt-structured Li₂MgTiO₄ ceramic was prepared by the conventional mixed oxide route and its microwave dielectric properties were investigated. The microstructures of the ceramics were characterized by SEM. The dielectric properties of the ceramics exhibited a significant dependence on the sintering condition and crystal structure. A new microwave dielectric material, Li₂MgTiO₄ sintered at 1360 °C has a dielectric constant (?_r) of ∼17.25, a Q × f of ∼97,300 GHz (where f = 9.86 GHz, is the resonant frequency) and a τ_f of ∼-27.2 ppm/°C. The microwave dielectric properties of the ceramic are reported for the first time.     

Structural impact of tungsten ions on ZnO-Sb2O3-As2O3 glass system

Five glasses in the quaternary system 5 ZnO-(50 − x) As₂O₃-45 Sb₂O₃: x WO₃ with the values of x ranging from 0 to 20 mol% (in steps of 5 mol%) are prepared. The samples are characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy (EDS) and differential thermal analysis (DTA) techniques. The DTA studies have indicated that the glass forming ability decreases with the increasing content of WO₃. A number of studies, like, spectroscopic (optical absorption, IR, Raman, ESR spectra) and dielectric studies (dielectric constant ?, loss tan δ, a.c. conductivity σ_a.c.) over a wide range of frequency and temperature and dielectric break down strength at room temperature, have been carried out and are analysed in the light of different oxidation states and environment of tungsten ions in these glasses. These glasses have potential photonic applications.     

Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + 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 (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ 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.     

Effect of CaTiO3 addition on microwave dielectric properties of Mg2(Ti0.95Sn0.05)O4 ceramics

The microwave dielectric properties of CaTiO₃-added Mg₂(Ti_0.95Sn_0.05)O₄ ceramics prepared by the mixed oxide route have been investigated. The combination of spinel-structured Mg₂(Ti_0.95Sn_0.05)O₄ and perovskite-structured CaTiO₃ forms a two-phase system (1 − x)Mg₂(Ti_0.95Sn_0.05)O₄-xCaTiO₃, which was confirmed by the XRD patterns and the EDX analysis and it also leads to a zero τ_f. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a new microwave dielectric material 0.91Mg₂(Ti_0.95Sn_0.05)O₄-0.09CaTiO₃ is suggested and it possesses a good combination of dielectric properties with an ?_r of ∼18.01, a Q × f of ∼92,000 GHz, and a τ_f of ∼0 ppm/°C, which makes it is a very promising candidate material for high frequency applications.