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.     

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.     

Correlation between the chemical composition and the conduction mechanism of barium strontium titanate thin films

Sol-gel barium strontium titanate thin films with different barium-to-strontium (Ba:Sr) values have been fabricated as MFM configurations. The Perovskite phase for the films is confirmed via XRD. In order to correlate the effect of the chemical composition of the films with the conduction mechanism, different AC electrical parameters have been addressed. The results show that the impedance and dielectric constant decrease as Ba content in the film increases, whereas the conductivity shows the opposite variation; this is attributed to the grain size and dipole dynamics. Complex impedance (Z*) and electric modulus (M*) planes show three overlapping regions as the response for the bulk, the grain boundaries and the film/electrode interface mechanisms. These mechanisms have been represented by an equivalent circuit. The imaginary component of electric modulus (M″) versus frequency plots, which reveal relaxation peaks that are not observed in the dielectric loss (?″) plots, and it is found that these peaks are of a non-Debye-type. Furthermore, the frequency dependent conductivity plot shows three regions of conduction processes.     

Transport mechanism in a ceramic system: LiCo3/5Fe1/5Cu1/5VO4

The electrical impedance and modulus properties of a LiCo_3/5Fe_1/5Cu_1/5VO₄ 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.     

A.c. conductivity of poly(N-methylpyrrole)

The dielectric constant ɛ′(ω) and measured a.c. conductivity σ_m(ω) of lightly doped poly (N-methylpyrrole) films have been investigated in the temperature range 77–350 K and in the frequency range 100 Hz–1 MHz. In the low-temperature region the measured a.c. conductivity can be described by the relation σ(ω) = Aω_s, where the exponent s is found to be less than unity. At high temperatures the conductivity remains strongly frequency dependent but the dependence becomes weak at low frequencies. The temperature and frequency dependences of a.c. conductivity σ(ω) can be qualitatively explained by the contributions from two mechanisms, one giving rise to a broad dielectric loss peak having a distribution of relaxation times, and the other giving a linear dependence of conductivity on frequency.     

Impedance and electric modulus analysis of Sm-modified Pb(Zr0.55Ti0.45)1−x/4O3 ceramics

The polycrystalline ceramic samples of Pb_1−xSm_x(Zr_0.55Ti_0.45)_1−x/4O₃ (x = 0.00, 0.03, 0.06 and 0.09) were prepared by solid-state reaction technique at high temperature. Electric impedance (Z) and modulus (M) properties of the materials have been investigated within a wide range of temperature and frequency using complex impedance spectroscopy (CIS) technique. The complex impedance analysis has suggested the presence of mostly bulk resistive (grain) contributions in the materials. This bulk resistance is found to decrease with the increase in temperature. It indicates that the PSZT compounds exhibit a typical negative temperature coefficient of resistance (NTCR) behavior. The bulk contribution also exhibits an increasing trend with the increase in Sm³⁺ substitution to PZT. The complex modulus plots have confirmed the presence of grain (bulk) as well as grain boundary contributions in the materials. Both the complex impedance and modulus studies have suggested the presence of non-Debye type of relaxation in the materials.     

Dielectric relaxation and conduction mechanism in LaNi3/4M1/4O3 (M = Mo, W) at low temperature

In order to investigate the electrical transport in LaNi_3/4Mo_1/4O₃ and LaNi_3/4W_1/4O₃, 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.     

Dielectric dispersion in Li2O–MoO3–B2O3 glass system doped with V2O5

Li₂O–MoO₃–B₂O₃ glasses containing different amounts of V₂O₅, ranging from 0 to 1.5 mol%, were prepared. The dielectric properties (viz., constant ′, loss tan δ, AC conductivity σ_ac over a wide range of frequency and temperature) have been studied as a function of the concentration of vanadium ions. The variation of AC conductivity with the concentration of V₂O₅ passes through a maximum at 0.8 mol% V₂O₅. In the high-temperature region, the AC conduction seems to be connected with the mixed conduction, viz., electronic and ionic conduction. The dielectric relaxation effects exhibited by these glasses have been analyzed quantitatively by pseudo Cole–Cole plot method and the spreading of relaxation times has been established. Further analysis of these results has been carried out with the aid of the data on ESR, IR and optical absorption spectra.     

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.     

Complex impedance analysis of (Y2O3 + CeO2)-YCr0.5Mn0.5O3 composite NTC ceramics

Ceramic compositions based on (aY₂O₃ + bCeO₂)-0.4YCr_0.5Mn_0.5O₃ (a + b = 0.6) were prepared by conventional solid state reaction at 1200 °C, and sintered under air atmosphere at 1600 °C. For 0 ≤ a < 0.6, XRD patterns have shown that the major phases presented in the calcined powders are Y₂O₃, CeO₂ and orthorhombic perovskite YCr_0.5Mn_0.5O₃ phase, respectively. SEM and EDAX observations confirm the YCr_0.5Mn_0.5O₃ phases mostly exist at the grain, whereas the Y₂O₃ and CeO₂ phases mainly exist at the grain boundaries. Complex impedance analysis shows that, for 0 < a ≤ 0.6, single semicircular arc whose shape does not show any change with temperature. Nevertheless, for a = 0, two overlapping semicircular arcs are observed at and above 300 °C. The grain boundary properties exhibit thermistor parameters with a negative temperature coefficient characteristic. The relaxation behavior and conduction for the grain boundary could be due to a space-charge relaxation mechanism and oxygen vacancies, respectively.     

Electrical characteristics of Li(Ni7/10Fe3/10)VO4 ceramics

The compound [Li(Ni_7/10Fe_3/10)VO₄] was produced by a solution-based chemical route whose electrical properties were investigated using complex impedance spectroscopy technique. X-ray diffraction study reveals an orthorhombic unit cell structure of the compound. Complex electrical impedance analysis exhibits: (i) grain interior, grain boundary and electrode-material interface contributions to electrical response and (ii) the presence of temperature dependent electrical relaxation phenomena in the material. Electrical conductivity study indicates that electrical conduction in the material is a thermally activated process.     

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.     

Charge compensation, electrical and dielectric behavior of lanthanum doped CaCu3Ti4O12

Mechanism of charge compensation on lanthanum, (La³⁺) substitution on Ca site in calcium copper titanate (CaCu₃Ti₄O₁₂), and its effect on resulting electrical and dielectric properties has been studied in the present investigation. For this purpose samples were prepared according to two stoichiometries viz. La_xCa_(1−3x/2)Cu₃Ti₄O₁₂ (x ≤ 0.09) and La_xCa_(1−x)Cu₃Ti₄O₁₂ (x = 0.03) by solid state ceramic route. The former represents ionic compensation while the later is in accordance with electronic compensation. Nature of charge carriers is identified by measuring Seebeck coefficient which is found to be negative in the entire range of measurement. In order to understand the mechanism of conduction, ac conductivity is measured as a function of temperature and frequency. Space charge polarization is the dominant polarization mechanism phenomenon at low frequency and high temperature while orientation polarization dominates at low temperature and high frequency. Impedance analysis confirms the formation of internal barrier layers which is responsible for high dielectric constant in these samples.     

Structural and electrical properties of Gd(Ni1/2Zr1/2)O3

The Gd(Ni_1/2Zr_1/2)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.     

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.     

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.     

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.     

AC conductivity and dielectric properties of GeSexTl0.3 amorphous thin films

AC conductivity and dielectric properties have been studied for amorphous thin films with different thicknesses of glassy system GeSe_xTl_0.3 with X = 3, 4 that prepared with thermal evaporation technique. The measurements are taken at temperature range (303-403 K) and frequency range (10²-10⁵ Hz).AC conductivity σ_ac(ω) is found to be proportional to ω^s where s < 1. The temperature dependence of the ac conductivity and the parameter s can be discussed with the aim of the correlated barrier-hopping (CBH) model.The dielectric constant ?′and the dielectric loss ?″ showed frequency and temperature dependence. The maximum barrier height W_M calculated from the dielectric measurements according to Giuntini equation are in good agreement with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott in the case of chalcogenide glasses.     

Enhanced thermoelectric performance via randomly arranged nanopores: Excellent transport properties of YbZn2Sb2 nanoporous materials

Fabricating nanoporous bulk thermoelectric (TE) materials with periodically arranged nanopores is highly challenging and expensive, although TE materials exhibit high power factors (α²σ) and low thermal conductivities (κ). Enhanced TE performance via randomly arranged nanopores is demonstrated with a YbZn₂Sb₂ nanoporous material (nPM) fabricated by a combination of melt quenching and two stage spark plasma sintering in less than 10 h. Measurement of the electrical conductivity, Hall mobility, Seebeck coefficient, and thermal conductivity show that simultaneously enhancing α²σ and reducing κ can realize in the YbZn₂Sb₂ nPM with randomly arranged nanopores about 50-200 nm in diameter. Compared with YbZn₂Sb₂ dense bulk materials (dBM) fabricated by a conventional method taking more than 180 h, α²σ at 300 K increases by 122%, κ at 300 K decreases by 29%, and the maximum ZT value at 775 K reaches 0.67, increasing by 46% for the nPM725 sample. This work shows that a periodic arrangement of nanopores is not essential for the fabrication of attractive TE materials, which offers a wider approach to nanostructure engineering to improve TE performance.     

Microstructures and electrical responses of pure and chromium-doped CaCu3Ti4O12 ceramics

Pure and chromium-doped CCTO (CaCu₃Ti₄O₁₂) ceramics were prepared by a conventional solid-state reaction method, and the effects of chromium doping on the microstructures and electrical properties of these ceramics were investigated. Efficient crystalline phase formation accompanied by dopant-induced lattice constant expansion was confirmed through X-ray diffraction studies. Scanning electron microscopy (SEM) results show that doping effectively enhanced grain growth or densification, which should increase the complex permittivity. The dielectric constant reached a value as high as 20,000 (at 1 kHz) at a chromium-doping concentration of 3%. The electrical relaxation and dc conductivity of the pure and chromium-doped CCTO ceramics were measured in the 300-500 K temperature range, and the electrical data were analyzed in the framework of the dielectric as well as the electric modulus formalisms. The obtained activation energy associated with the electrical relaxation, determined from the electric modulus spectra, was 0.50-0.60 eV, which was very close to the value of the activation energy for dc conductivity (0.50 ± 0.05 eV). These results suggest that the movement of oxygen vacancies at the grain boundaries is responsible for both the conduction and relaxation processes. The short-range hopping of oxygen vacancies as “polarons” is similar to the reorientation of the dipole and leads to dielectric relaxation. The proposed explanation of the electric properties of pure and chromium-doped CCTO ceramics is supported by the data from the impedance spectrum.