Complex Impedance Spectroscopy Research Articles

Electrical characterisation and analysis of dominant contributions in disordered semiconducting systems with an application to the pure bentonite material for civil engineering applications

Semiconductors and clay materials have significant applications in environmental, civil engineering and optoelectronic sectors. The application of an electric field to such systems is subject of many works. However, to understand the behaviour of such materials under the influence of an electric field, the perception of its electrical properties is essential. In the present study, the powerful technique of complex impedance spectroscopy (CIS) is introduced to illustrate the electrical characteristics of two types of disordered semiconducting materials. These are Cu5In9Se16, an ordered defect compound of the I-III-VI2 family and a novel bentonite clay system which is an insulator at room temperature and semiconductor above 400 °C. Na-bentonite has been studied extensively because of its strong adsorption capacity and complexation ability while Cu5In9Se16 is considered for its use in solar and phtovoltaique domain. Some of selenides have turned out to be leading materials for electro-optical devices and the tellurides for thermoelectric power generation. It is very likely that study of bentonite clay and other similar materials may lead to the technology of heterojunction and clay composite. The frequency dependence of conductivity of bentonite was investigated using an impedance analyzer in the frequency range (20 Hz–1 MHz). The experimental data of CIS are analyzed using some analytical methods that take into account the effect of the grains and grain boundaries. The impedance data confirm the non-Debye behavior in these systems. Some important parameters related to the identified dominant contribution such as relaxation time and activation energies are estimated for the studied materials in the considered temperature and frequency ranges

Complex Impedance Spectroscopy studies to unravel electrical properties and processes in Al+3-modified PLZT

Complex Impedance Spectroscopy studies to unravel electrical properties and processes in Al+3-modified PLZT

Onset of vacancy-mediated high activation energy leads to large ionic conductivity in two-dimensional layered Cs2PbI2Cl2 Ruddlesden-Popper halide perovskite

We report the dielectric properties of a two-dimensional layered Ruddlesden-Popper halide perovskite ${\mathrm{Cs}}_{2}{\mathrm{PbI}}_{2}{\mathrm{Cl}}_{2}$ synthesized via a simple mechanochemical process to explore fundamental aspects of ionic conduction and relaxation mechanism over a wide temperature and frequency range. Several experimental techniques, such as complex impedance spectroscopy, alternating current (AC) conductivity spectroscopy, and complex electric modulus spectroscopy, have been employed to investigate the nuances of ionic conduction and relaxation mechanisms, and the results have been corroborated using different theoretical models, such as the Maxwell-Wagner equivalent circuit model, the modified Jonscher power law, the Havrilliak-Negami (HN), and the Kohlrausch-Williams-Watts (KWW) model. The contribution of the grains and grain boundaries to the total impedance in the system is estimated by the analysis of the Nyquist plots. In temperature-dependent AC conductivity spectra, a critical temperature (413 K) is observed, beyond which the conductivity increases abruptly. This critical temperature also defines two distinct temperature ranges: the low-temperature (303--413 K) and the high-temperature (423--463 K) regimes, where the ionic transport mechanism switches from the normal ionic transport to a vacancy-mediated ionic transport mechanism. A substantially high activation energy $\ensuremath{\sim}1.82\phantom{\rule{0.16em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ is calculated from the Arrhenius plot of the ionic conductivity in the high-temperature region, while at the low-temperature region, the activation energy is found to be $\ensuremath{\sim}0.48\phantom{\rule{0.28em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$. The abrupt jump in the ionic conductivity beyond the critical temperature is attributed to the onset of the anionic vacancy-mediated enhanced ionic conductivity. Polaronic models have been used to interpret the AC conductivity and its power-law exponent. The activation energy obtained from ionic conductivity measurements is consistent with those calculated from relaxation time using the HN and KWW models. The presence of two master curves in time-temperature superposition scaling of AC conductivity and modulus loss spectra specifies the validity of two different conduction mechanisms.

Regulating ferroelectric polarization and dielectric properties of BT-based lead-free ceramics

The ternary system of BaTiO3 (BT) -based lead-free ceramics ((1-x)BaTiO3-x(0.94 Sr0.7Bi0.2TiO3-0.06BiMg0.5Ti0.5O3) are investigated on their structural, dielectric and ferroelectric properties. The structural evolution is identified from the tetragonal phase (P4mm) to the pseudocubic phase with increasing the dopant concentration x. The gradually diffusive dielectric peak and highly dispersive relaxor behaviors are recognized, indicating the transformation from ferroelectric to relaxor state. Meanwhile, the ceramics are characterized by the slim polarization hysteresis loops associated with polar nano-sized cluster formation. Complex impedance spectroscopy reveals the electrical inhomogeneities with enhanced boundary effect caused by the excessive addition, leading to the abnormally degraded electric breakdown strength. Combined with the X-ray photoelectron spectroscopy, the oxygen vacancy hopping mechanism is proposed for the high dopant concentration, contributing to the diffuse dielectric response. As a result, optimized energy-storage density and efficiency are simultaneously obtained at a relatively low electric field. All these features demonstrate an effective route in the composition modulation of BT-based dielectric capacitor ceramics that not only the formation of polar nano regions but also the electrical homogeneities can greatly influence the comprehensive dielectric performance.

A Very Low Temperature Growth of BaTiO3 Nanoparticles by Sol‐Hydrothermal Method

Low‐temperature intercessions are the most proficient technique to control the particle size in the nanometres range with low agglomeration. Herein, BaTiO3 (BT) nanoparticles (NPs) are prepared at low temperatures by using the sol‐hydrothermal technique. An X‐ray diffraction (XRD) pattern of the powder signifies the pure tetragonal phase, and the average crystallite size (43.2 nm) is calculated using different methods: Scherrer's, uniform deformation model (UDM), uniform stress deformation model (USDM), and uniform deformation energy density model (UDEDM) analysis, and the structure is refined by Rietveld refinement method with a good fit value (χ2 = 1.66). Spherical and uniform surface morphology is counted up for BT NPs. Under suitable conditions, BT NPs can be prepared with an average particle size of ≈115 ± 10 nm. However, after sintering, the average grain size (335 ± 10 nm) of the BaTiO3 nanopowder is found to increase with dense grain boundaries. The dielectric behavior of the sample is analyzed with the variation of frequency at different temperatures. The effect of grain and grain boundary on the electrical properties of the material is also investigated by using complex impedance spectroscopy (CIS).

(Digital Presentation) Reactive Magnetron Sputtering Deposition of La1.6Nd0.4NiO4 Coating As Cathode for Solid Oxide Fuel Cell

Ln2NiO4 (Ln=La, Pr, Nd, etc.) materials with K2NiF4 structures are interesting materials for intermediate temperature solid oxide fuel cell (IT-SOFC) due to Mixed Ionic and Electronic Conductivity (MIEC) [1-2]. The present work is focused on the elaboration of La1.6Nd0.4NiO4 coating obtained by Reaction Magnetron Sputtering (RMS). This compound is a promising oxygen electrode able to decrease the operating temperature of SOFC. After a presentation of the deposition operating conditions for obtaining the films, the structural and microstructural characterizations of the coatings were, respectively, determined by XRD and SEM. The electrical properties were studied as a function of temperature by the 4-probe method. Electrochemical properties were investigated in a symmetrical cell electrode / YSZ / electrode by complex impedance spectroscopy. Finally, a complete cell composed of a commercial anode, and YSZ electrolyte made by RMS and the cathode of this study was tested under hydrogen and air in single SOFC cell configuration.It appeared that the films are amorphous when processed and that they crystallize after an annealing treatment under air. According to this study, a correlation between crystalline structure, morphology and electrical properties will be presented and its last ones are completed by a thermogravimetry analysis.

Effects of LiF on the properties of (Ba, Ca)(Ti, Sn, Hf)O3‐based multilayer ceramics co‐fired with Ni at reduced atmosphere

AbstractIn this work, (Ba0.97Ca0.03)(Ti0.96Sn0.005Hf0.035)O3–0.03MnCO3–xLiF (BCTSH–0.03M–xL, x = 0–6 mol%) multilayer piezoelectric ceramics were prepared by the solid‐state synthesis technique. The microstructure and piezoelectric properties of the samples sintered at the reduced atmosphere and co‐fired with the Ni base metal inner electrode were studied. The results showed that 3 mol% LiF could effectively reduce the sintering temperature from 1350 to 1200°C. BCTSH–0.03M–3L ceramics exhibited excellent electrical properties with d33 = 277 pC/N, d31 = −132 pC/N, kp = 0.350, Qm = 315, and εr = 3387. Furthermore, the complex impedance spectroscopy (e.g., activation energy) was used to analyze the doping mechanism of these obtained ceramics sintered at reduced atmosphere. The results indicated when LiF was added in a small amount (x ≤ 3), the bulk density was enhanced, and thus, the activation energy was also increased. Moreorver, when x > 3, Li ions could partly enter the interstitial site of crystal structure resulting in the increase of activation energy. Rayleigh behaviors of reversible and irreversible domain wall contributions were analyzed. It was observed when x = 3, there was a larger Rayleigh coefficient, suggesting that this sample had the weaker pinning effect, and thus contributing to the higher d33 value due to the irreversible domain wall contribution. As x > 3, the Rayleigh coefficient was found to decrease with increasing x due to the formation of the second phase, which could inhibit the motion of extrinsic domain wall. Finally, five‐layer multilayer piezoelectric ceramics co‐fired with inner Ni electrode were fabricated, and the electrical properties of five‐layer multilayer piezoelectric ceramics were found to be d33 = 1468 pC/N, d33* = 2000 (at 20 kV/cm), and kp = 0.342. To the best of our knowledge, the (Ba, Ca)(Ti, Sn, Hf)O3‐based lead‐free multilayer piezoelectric ceramics co‐fired with Ni‐based metal was first reported by us and used as the alternative multilayer ceramics for piezoelectric device applications.

Effect of Alkaline earth oxides on the ionic conductivity of Boro-Tellurite glasses for solid state ion batteries

The complex impedance spectroscopy studies (electrical impedance, a.c. conductivity, dielectric constant, loss tangent) of the boro-tellurite glasses were measured as a function of the alkaline earth oxide content at broad range of frequencies and temperatures. Three series of boro-tellurite glasses containing BaO/SrO viz. BaO-TeO2-TiO2-B2O3 (BTTB), BaO-TeO2-B2O3 (BTB) and SrO-TeO2-TiO2-B2O3 (STTB) were prepared by the melt quenching method. The prepared glasses were characterized by XRD, DSC, density, FTIR and complex impedance spectroscopy experimental techniques. The XRD spectra exhibited no characteristic sharp peaks indicating the amorphous nature of the prepared glass samples. The glass transition temperature (Tg) values were evaluated from the DSC thermograms. The density values were found to increase with BaO content while they decreased with SrO content. This variation was attributed to the different density values of BaO and SrO. FTIR spectra revelated the presence of different structural units like BO3 and BO4. Impedance studies demonstrated that the replacement of TeO2 by the BaO content enhanced the ionic conductivity. The impedance plots of BTTB, BTB and STTB glasses exhibited nearlys semicircles. The bulk resistance (Rb) was calculated from the impedance plots. It was observed that the Rb values decrease with increasing BaO in BTTB and BTB glasses, while it increased with SrO in STTB glasses which may be attributed to the variation of mobile charge carriers. The Rb values vary as BTB > BTTB > STTB. The capacitance calculated from the impedance plots increased with increasing BaO mol% and decreasing SrO mol%. The capacitance also increased with increasing temperature. The power law exponent (k) values decrease with increasing temperature. Therefore, the ac conduction mechanism may follow correlated barrier hopping model. The real part of dielectric constant has high values at low frequencies, which decreased rapidly with surge of frequency. At high frequencies the contribution of charge accumulation is minimum resulting in constant

Analysis of frequency dependence of complex impedance and electrical characterization of Fe2O3/kaolin ceramics for civil engineering applications

The complex impedance spectroscopy (CIS) method is usually used in order to analyze the electrical response of different semiconducting disordered materials as a function of frequency at different temperatures. The real and imaginary parts of the complex impedance can show different semicircles in the complex plane that give evidence for the presence of both bulk and grain boundary contributions. Many parameters can be deduced from the analysis of CIS data, such as relaxation times and activation energies. There are some literature data concerning electrical properties of clays and (semiconductor, sand, cement,…)/clay mixtures. Most of the published works are related to the AC conductivity of rocks with the effect of water or oil content but there are no similar studies on the characterization of the microstructure of individual clays as ceramic materials by analyzing their temperature and frequency dependence of their electrical conductivities. Hence, this paper presents an analysis of electric complex impedance of the Fe2O3/Kaolin composite in the high temperature range up to 740 °C. Sinusoidal voltage with frequency in the range [100 Hz, 1 MHz] is applied to the material in order to measure the electrical conductivity for various concentrations of Fe2O3 from zero to 100 %. The activation energies for the conduction and for the relaxation processes are determined and their dependence on the density of Fe2O3 analyzed. Furthermore, let’s found that Fe2O3 have the effect to increase the electrical conductivity in our samples. From the Nyquist diagrams, only one semi-circle related to the contribution of the grains to the total electrical conduction is identified for all investigated samples.

Investigation of crystal structure, electrical and dielectric response of Zr4+ -Co2+ substituted Ba–Sr–Ni Y-type hexagonal ferrites synthesized by sol-gel route

A series of (Zr–Co) substituted Y-type polycrystalline hexaferrite with composition SrBaNi2(ZrCo)xFe12-2xO22 (x = 0.0, 0.25, 0.50, 0.75, 1.0) were fabricated by sol-gel auto combustion method. Pure Y-type single phase formation was achieved at a relatively lower temperature of 1150 °C for 5:30 h. The fabricated nano ferrites were examined by X-ray powder diffraction to confirm the pure single-phase formation of Y-type hexaferrites. An increase in lattice parameters (a& c) was observed by adding Zr4+-Co2+ metal cations. Crystallite size (D) measured in the 48-19 nm range. FTIR spectra clarified iron-oxygen vibrational bands at 417-487 cm−1, which approved the Y-type hexaferrites formation. DC electrical resistivity has an opposite trend at high and low temperatures with increasing Zr4+-Co2+ content (x). DC electrical resistivity values depend on grain size; they have an inverse relation. Activation energy, drift mobility, and Curie temperature were also determined. Conduction is due to the hopping of electrons below the Curie temperature, and polarons are responsible for hopping above the Curie temperature. Activation energy varies from 0.39 to 0.10 eV with the substitution of Zr4+-Co2+ ions. A wide frequency range of dielectric characteristics (1 MHz–6GHz) was observed, and these parameters revealed a considerable fluctuation with the substitution of Zr4+–Co2+ ions. Dielectric constant, dielectric loss and ac conductivity of nano ferrites materials increased with frequency and Zr4+-Co2+ content (x). Complex impedance spectroscopy formalism using the Cole-Cole plots indicated that most dielectric responses arise from grain boundary contributions.

Head-to-Tail and Head-to-Head Molecular Chains of Poly(p-Anisidine): Combined Experimental and Theoretical Evaluation.

Poly(p-anisidine) (PPA) is a polyaniline derivative presenting a methoxy (–OCH3) group at the para position of the phenyl ring. Considering the important role of conjugated polymers in novel technological applications, a systematic, combined experimental and theoretical investigation was performed to obtain more insight into the crystallization process of PPA. Conventional oxidative polymerization of p-anisidine monomer was based on a central composite rotational design (CCRD). The effects of the concentration of the monomer, ammonium persulfate (APS), and HCl on the percentage of crystallinity were considered. Several experimental techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), multifractal analysis, Nuclear Magnetic Resonance (13C NMR), Fourier-transform Infrared spectroscopy (FTIR), and complex impedance spectroscopy analysis, in addition to Density Functional Theory (DFT), were employed to perform a systematic investigation of PPA. The experimental treatments resulted in different crystal structures with a percentage of crystallinity ranging from (29.2 ± 0.6)% (PPA1HT) to (55.1 ± 0.2)% (PPA16HT-HH). A broad halo in the PPA16HT-HH pattern from 2θ = 10.0–30.0° suggested a reduced crystallinity. Needle and globular-particle morphologies were observed in both samples; the needle morphology might have been related to the crystalline contribution. A multifractal analysis showed that the PPA surface became more complex when the crystallinity was reduced. The proposed molecular structures of PPA were supported by the high-resolution 13C NMR results, allowing us to access the percentage of head-to-tail (HT) and head-to-head (HH) molecular structures. When comparing the calculated and experimental FTIR spectra, the most pronounced changes were observed in ν(C–H), ν(N–H), ν(C–O), and ν(C–N–C) due to the influence of counterions on the polymer backbone as well as the different mechanisms of polymerization. Finally, a significant difference in the electrical conductivity was observed in the range of 1.00 × 10−9 S.cm−1 and 3.90 × 10−14 S.cm−1, respectively, for PPA1HT and PPA16HT-HH.

High breakdown electric field in (Ta1−xPrx)0.03Ti0.97O2 colossal permittivity ceramics through defect chemistry optimization

In this work, a novel (Ta1−xPrx)0.03Ti0.97O2 (x = 0.3, 0.5, 0.7 and 0.9) ceramic was fabricated via a solid-state reaction (SSR) method using an efficient defect engineering strategy, and the microstructure, breakdown electric field and charge transport processes were investigated in detail. All co-doped ceramics exhibit a pure rutile structure and the grain size is effectively refined by Pr/Ta ion doping. Notably, the ceramic sample with x = 0.9 displays a low tanδ of 0.018 and a large ε' of 1.74 × 104, enhancing temperature stability from RT to 200 ◦C (Δε′(T)/ε′30 = 1.5%, at 1 kHz) and Eb of 2.07 kV/cm. XPS and complex impedance spectroscopy analyses show that the excellent electrical properties of (Ta1−xPrx)0.03Ti0.97O2 ceramics originate from grains with electron-pinned defect dipoles (EPDD) and insulating grain boundaries. The (Ta1−xPrx)0.03Ti0.97O2 ceramics possess enhanced breakdown field strength and excellent giant dielectric properties, making them potential candidates for capacitors.

Synthesis and characterization of non-stoichiometric Li1.1Co0.3Fe2.1O4 ferrite nanoparticles for humidity sensors

A humidity sensor plays a crucial role in determining the efficiency of materials and the precision of apparatuses. To measure and control humidity, a non-stoichiometric Li1.1Co0.3Fe2.1O4 mesopore sensor is synthesized by a modified citrate auto combustion technique. The XRD study confirms that prepared nanoparticles are cubic spinel structures having an Fd3m space group. The crystallite size is approximately 36 nm. Thermal analysis measurements show that samples become thermally stable at a temperature of 600 °C. Additionally, the kinetic studies of the prepared samples are calculated via a pseudo-first-order kinetic model. The temperature dependence of AC conductivity is found to increase with increasing temperature. These observations are explained in various models. The resistivity mechanism of humidity sensors is studied via complex impedance spectroscopy (CIS). Its impedance data are fitted to a corresponding circuit, to achieve a simulation of the sample under study. This fitting is detected by the Nyquist plot (Cole–Cole). The obtained data confirm that the studied samples are very sensitive to humidity and can be commercially used as a humidity sensing element.Graphical abstract

Impedance Spectroscopy of Pr-Doped BaBi2Nb2O9 Aurivillius Ceramics.

Herein this study, the polycrystalline nature of the Aurivillius type structure is studied; primarily, the main objective is to observe the influence of dopant Pr3+ at the Ba2+-site of BaBi2Nb2O9 (BBN) ceramics. The ceramics under investigation were fabricated via the conventional solid-state reaction method. Scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) techniques were used to analyse their morphological structure. It was found that the chemical composition of the ceramic samples corresponds well to the initial stoichiometry of the ceramic powders. An increase in praseodymium content caused a slight decrease in the average size of the ceramic grains. The obtained ceramic materials are described by a tetragonal structure with the space group I4/mmm. The electrical properties of the material have been studied using complex impedance spectroscopy methods in wide temperature and frequency ranges. The analysis of obtained results showed grains and grain boundaries contribute to conductive processes in the material. A possible ’hopping’ mechanism for electrical transport processes in the system is evident from the analysis of results based on Joncher law.

Temperature Dependence of the Electrical Properties of Na2Ti3O7/Na2Ti6O13/POMA Composites.

The temperature dependence of the electrical properties of composites formed by biphasic sodium titanate and poly(o-methoxyaniline) (Na2Ti3O7/Na2Ti6O13/POMA) with different concentrations of POMA (0%, 1%, 10%, 15%, 35% and 50%) in the ceramic matrix was determined from measurements of complex impedance. The structural details were studied by means of X-ray diffraction, confirming the formation of the Na2Ti3O7/Na2Ti6O13/POMA composites. The displacement of the (200) reflection from 2θ = 10.45° to 11.15° in the composites with 10 and 15% of POMA suggested the partial replacement of H+ for Na+ in the Na2Ti3O7 structure. The thermal properties were investigated by Thermogravimetry and Differential Thermal Analysis. The Thermogravimetry curves of the composites with POMA content of 1, 10 and 15% presented profiles similar to that of pure sodium titanate sample. The composites with 35 and 50% of POMA showed a process at temperatures around 60–70 °C, which was associated with water absorbed by the polymer. The analysis of the complex impedance spectroscopy measurements revealed that the electrical resistivity of the composites in the range from 0 to 35% increased by two orders of magnitude, with different values for each concentration. This positive temperature coefficient of resistivity was less noticeable in the composite with highest POMA mass content (50%). The rapid increase in resistivity caused an increase in the relaxation time calculated from the time domain. The electrical response of the 50% of POMA compound changes in relation to what was observed in the other compounds, which suggests that there is a saturation limit in the increase in resistivity with POMA content.

Thermal stable and ultralow dielectric loss in (Gd0.5Ta0.5)xTi1-xO2 giant permittivity ceramics by defect engineering

High dielectric loss and poor temperature stability are the current barriers to the application of dielectric materials. In present work, we synthesized a system of acceptor Gd3+ and donor Ta5+ co-doped (Gd0.5Ta0.5)xTi1-xO2 (GTTOx, x = 0, 0.01, 0.02, 0.04, 0.06) ceramics to enhance dielectric response. It was found that a colossal permittivity (CP, 2.65 × 104@1 kHz, 2.37 × 104@1 MHz), a very low dielectric loss (tanδ, 0.007@1 kHz, 0.03@1 MHz), good stability of frequency (20–106 Hz) and temperature (RT–250 °C, Δε′ (T)/ε′30 < ± 15%, at 1 kHz) were achieved simultaneously in GTTO0.01 ceramic. Complex impedance spectroscopy, XPS, SEM, and Raman spectroscopy were used to investigate the reasons for the improved dielectric properties. The result indicated that the main reasons for CP and low dielectric loss are the synergistic effect of the electron pinning defect-dipole (EPDD) model, the internal blocking layer capacitance (IBLC) mechanism, and electrode response. This work provides a promising approach for the design of defect-related high-performance giant dielectric ceramics.

Electrical transport properties of nanocrystalline and bulk nickel ferrite using complex impedance spectroscopy: a comparative study

In this work, the comparative study on the electrical transport properties of nanocrystalline nickel ferrite (NiFe2O4) and its bulk counterpart has been carried out in detail by using complex impedance spectroscopy in a wide range of frequencies (100 Hz–1 MHz) and temperatures (40 °C–320 °C). The dispersive nature of the dielectric constant and loss factor is explained by the Maxwell-Wagner model and Koop’s phenomenological theory. The value of the dielectric constant for nanocrystalline nickel ferrite is found to be more as compared to its bulk counterpart. The frequency variation dielectric permittivity is well fitted with the modified Debye formula, which suggests the presence of multiple relaxation processes. The temperature dependent ac conductivity follows Jonscher’s universal power law and reveals the presence of multiple transport mechanisms from small polaron hopping (SPH) to correlated barrier hopping (CBH) mechanism near 200 °C. The estimated values of Mott parameters are found to be satisfactory. Thermally activated relaxation phenomena have been confirmed by scaling curves of imaginary impedance () and modulus (). The comparison between the and spectra indicates that both long-range and short-range movement of charge carriers contribute to dielectric relaxation with short-range charge carriers predominating at low temperatures while long-range charge carriers are dominating at high temperatures. Analysis of the semicircular arcs of Nyquist plot indicates the presence of grain boundary contribution to the electrical conduction process for the nanocrystalline sample at high temperatures. The non-Debye type of relaxation has been examined by stretching exponential factor (β) which has been estimated by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary electric modulus curve. The value of β is found to be strongly temperature dependent and its value for the nanocrystalline sample is less than that of the bulk system which is explained on the basis of dipole-dipole interaction.

Electrical conductivity and relaxation phenomena in Li2O·B2O3 based glass and glass-ceramic: A comprehensive and comparative analysis

This work reports a detailed investigation on the electrical conductivity and dielectric relaxation phenomena in Li2O·B2O3 based glass and glass-ceramic materials. Measurements reveal that the electrical conductivity of glass-ceramic is lower than glass. This owes to occurrence of grain boundaries which impede the mobility of charge carriers in glass-ceramic as confirmed by FESEM micrographs. The frequency-dependent behavior of electrical conductivity, within the measured temperature range, is analysed using Jonscher's power law. It is found that the conductivity rises with an increase in temperature and the range of conductivity reveals the semiconducting behavior of the material. The ac conductivity mechanism of system is observed to follow the overlapping large polaron tunneling model. The conduction and relaxation mechanism studies are performed using electric modulus and impedance spectroscopy within the frequency and temperature ranges varied from 103 Hz to 107 Hz and 593 K–773 K, respectively. Analysis of the relaxation mechanism in both samples is performed employing Kohlrausch-William-Watts (KWW) model, which reveals that the charge carriers are following non-Debye type relaxation. To distinguish between the contribution of grain boundaries and grains in the relaxation mechanism, a combined analysis of complex electric module and impedance spectroscopy has been discussed.

Charge conduction mechanism and non-debye type relaxation in LaCrO3 perovskite orthochromite

The orthochromite LaCrO3 (LCO) was synthesized via the sol-gel auto-combustion route and sintered at 900 °C. The Rietveld refined XRD profile confirmed the single-phase perovskite structure of the compound crystallized in the orthorhombic unit cell with Pbnm space group symmetry. The electrical studies were conducted by complex impedance spectroscopy in 40-5 × 106 Hz and 133–363 K experimental ranges of frequency and temperature, respectively. The complex impedance data were modeled by (RGQG)(RGBQGB) equivalent circuit that revealed the contributions of grains and grain boundaries to the electrical transport mechanism of the material. The AC conductivity analysis proposed that the electrical conduction in the LCO perovskite was governed through Mott's variable range hopping (VRH) mechanism. The imaginary modulus spectra were fitted by the Kohlrausch–Williams–Watts (KWW) relaxation function that resolved the presence of two thermally activated relaxation phenomena. The dielectric permittivity followed the non-Debye relaxation model which characterized the nature of dielectric relaxation in the LCO chromite.

A high-k Cu-doped ZnO film formed via Ga-ion implantation: The acceptor-donor co-doping approach

Dielectric thin films having high permittivity (high-k) and low dielectric loss is essential for developing high performance capacitive devices like metal oxide field effect transistor or thin film transistor. Ga ion implantation performed on Cu-doped ZnO film fabricated by pulsed laser deposition with optimized doping concentrations and post-implantation annealing yielded film having high permittivity and low dielectric loss (ε = 87 and tan δ = 0.17 at the frequency of 1 kHz). Moreover, the permittivity exhibits good stability over a wide range of frequency from 20 Hz to 10 MHz. The high-k film was characterized by detailed dielectric studies, including frequency dependence of permittivity and dielectric loss, complex electrical modulus analysis, impedance spectroscopy and ac conductivity. The enhancement of the permittivity was attributed to the correlated potential barrier hopping of electrons between the neighboring acceptor-donor defect complex states in the band gap created by the co-doping, thus acting as electric dipoles polarizing the film. This work opens up future possibility for ‘dielectric engineering’. The three-dimensional dielectric spatial profile can be controlled via the selective area ion implantation with the depth controlled by the ion implantation energy. • A high-k Ga-Cu co-doped ZnO film formed via pulsed laser deposition and ion implantation method. • Optimized doping concentrations yielded high permittivity and low dielectric loss (ε=87 and tan δ=0.17 at 1 kHz). • Enhancement of permittivity was attributed to the correlated barrier hopping of electrons between neighboring defect complex.