Conductivity Relaxation Phenomena Research Articles

Synthesis and Electrical Characterization of Lead-Free Electronic Material: Bi(Co2/3Nb1/3)O3

A lead-free electronic compound with chemical composition Bi(Co2/3Nb1/3)O3 has been synthesized via classical solid state reaction based ceramic technology. The structure of the compound as well as the frequency and temperature field dependent resistive, conductive and dielectric properties of the specimen have been examined. The room temperature X-ray diffraction analysis exhibits the formation of the sample in orthorhombic crystal symmetry. The observed dielectric constant and tangent loss characteristics substantiate the prepared compound as a dielectric. The impedance spectra confirms the presence of negative temperature coefficient of resistance behaviour, grain and grain boundary effect in the fabricated compound. The compound modulus spectrum shows that the temperature dependent conductivity relaxation phenomenon is of non-exponential-type. The illustrated important characteristics props up the material for different device applications.

Bias dependent conduction and relaxation mechanism study of Cu5FeS4 film and its significance in signal transport network

Here we have reported the electric and dielectric properties of a Bornite (Cu5FeS4) film using non-destructive complex impedance spectroscopy (CIS) in the frequency range 40 Hz–20 MHz and bias voltage range 0–0.8 V. A typical hydrothermal reaction was carried out to obtain the Cu5FeS4 material. Thereafter, we fabricated the film of the synthesized material and analysed its various properties as a function of frequency and dc bias voltages. The CIS analysis at room temperature (303 K) for different forward dc bias voltages shows that the bulk resistance plays a predominant role in conduction mechanism. The complex impedance (Nyquist) plots are well modelled with grain and grain boundary resistance by introducing proper ac equivalent circuit. The impedance loss spectra showed that the relaxation peak shifts towards the higher frequency with increasing bias voltages, which implies the possibility of a charge hopping between the localized charge states. Furthermore, we find that dielectric constant ( $${\varepsilon ^\prime }$$ ), dielectric loss ( $${\varepsilon ^{\prime \prime }}$$ ), electrical modulus ( $${{\text{M}}^*}$$ ) and ac/dc conductivity of the Cu5FeS4 film are strongly frequency dependent. The values of $${\varepsilon ^\prime }$$ and $${\varepsilon ^{\prime \prime }}$$ decreases whereas ac conductivity increases with increasing frequency. High frequency and low frequency dielectric constant of the material are found to be 3.48 and in the order of 104 respectively. Electrical modulus study is introduced for better explanation of conductivity relaxation phenomenon. Finally, we investigated the variation of ac/dc conductivity with forward dc bias voltages. This confirmed the presence of a hopping mechanism for electrical transport in our system, which can be best explained on the basis of jump relaxation model. Overall, this extensive study based on complex impedance spectroscopy demonstrates the dielectric relaxation behaviour of Cu5FeS4 film and also shed light on hopping induced conduction mechanism.

Structural and electrical properties of (x)Mn0.45Ni0.05Zn0.50Fe2O4 + (1 − x)BaZr0.52Ti0.48O3 multiferroic materials

Multiferroic (x)Mn0.45Ni0.05Zn0.50Fe2O4 + (1 − x)BaZr0.52Ti0.48O3 materials (where x varies from 0.0 to 0.8 in steps of 0.20) were prepared by the standard solid state reaction method. X-ray diffraction patterns verify the development of tetragonal perovskite structure for ferroelectric and cubic spinel structure for ferrite phase. The frequency and temperature dependent electrical parameters have been investigated to understand the conduction mechanism in these multiferroic materials. The grain effect contributes to the conduction mechanism for the sample containing 0–60% ferrite and both the grain and grain boundary effect contribute to the conduction mechanism for the composite containing 80% ferrite at high temperature. The ac conductivity increases with increasing frequency for the sample x = 0. This is due to the small polaron hopping. For the sample containing 20% ferrite, the frequency independent dc conductivity is observed at low temperature and dominates over a wide frequency range at high temperature region for the sample containing higher percentage of ferrite. The frequency independent dc conductivity is shifted to the frequency dependent ac conductivity, indicating the beginning of the conductivity relaxation phenomenon. This is attributed to the translation of long range polaron hopping to the small range charge carriers. The temperature dependence conductivity indicates that the impurities present in these multiferroic materials are almost minimized and polaron hopping type of conduction mechanism is valid.

Influence of Bismuth Content on Complex Immittance Characteristics of Pressureless Sintered BiNbO4 Ceramics

Abstract Goal of the present research was to study immittance properties of BiNbO4 ceramics fabricated by the solid state reaction route followed by pressureless sintering. Four sets of samples were examined, namely the one fabricated from the stoichiometric mixture of oxides, viz. Bi2O3 and Nb2O5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. The immittance properties were studied by impedance spectroscopy. Measurements were carried out within the frequency range ν =20Hz-1MHz and temperature range T =RT-550°C. The Kramers-Kronig data validation test was employed in the impedance data analysis. It was found that complex impedance first increases with an increase in Bi2O3 content and decreases for 10mol% excess of Bi2O3. Two relaxation phenomena manifested themselves at elevated temperature (T>267°C) within the measuring frequency range. The conductivity relaxation phenomenon (M″(ν) spectra) took place at higher frequency than the phenomenon with dominant resistive component (Z″(ν) spectra).

Low Frequency AC Conduction in Polyaniline/Zinc Tungstate (PANI/ZnWO4) Composites

In the present paper, we report low frequency ac conductivity and dielectric studies on the composites of conducting polyaniline (PANI) with crystalline zinc tungstate (ZnWO4) powder. These composites have been synthesized by single step in situ polymerization technique by placing fine grade powder of ZnWO4 during the polymerization of aniline. The composites thus formed were characterized by FTIR spectra and scanning electron microscopy (SEM), which conforms the presence of ZnWO4 in polyaniline matrix and the formation of the composite. AC conductivity and dielectric response of these composites were investigated in the frequency ranging from 50 Hz to 5 MHz. it was found that the ac conductivity obeyed the power law index, where the ac conductivity increases with frequency. PANI/ZnWO4 composites have shown high dielectric constant, which could be related to conductivity relaxation phenomenon. It is observed that both dielectric constant and dielectric loss have decreased with increase in frequency. Variations in measured parameters of AC response with increase frequency of the composites follow systematic trends that are similar to those observed with decreasing temperature and level of doping.

AC conductivity and dielectric behavior of polyaniline/sodium metavenadate (PANI/NaVO3) composites

The conducting polyaniline/sodium metavenadate (PANI/NaVO 3 ) composites were synthesized by single step in situ polymerization technique by placing finely grinded powder of NaVO 3 during the polymerization of aniline. The formation of mixed phases of the polymer together with the conducting emeraldine salt phase was confirmed by spectroscopic techniques like FTIR. SEM images indicated a systematic morphological variation of particles aggregated in the composite matrix as compared to the pristine PANI. AC conductivity and dielectric behavior of these composites were investigated in the frequency range 50 Hz to 5 MHz. It is found that AC conductivity obeyed the power law index and the variation of conductivity with wt% of NaVO 3 could be related to conductivity relaxation phenomenon. These composites have shown high dielectric constant, which is related to polarization. It is seen that both dielectric constant and dielectric loss decrease with increase in frequency. Variations in measured parameters of AC response with increasing frequency of these composites are found to follow systematic trends that are similar to those observed with temperature and doping.

Oxide ion conductivity and relaxation in CaREZrNbO 7 (RE = La, Nd, Sm, Gd, and Y) system

CaREZrNbO 7 (RE = La, Nd, Sm, Gd and Y) system changed from fluorite (F)-type to pyrochlore (P)-type structure when the ionic radius ratios, r(Ca 2+–RE 3+) av/ r(Zr 4+–Nb 5+) av were larger than 1.34. Thus, the La, Nd, and Sm compounds have a cubic P-type structure and the Gd and Y ones have a defect F-type structure. The electrical conductivity was measured using complex-plane impedance analysis over a wide temperature (300–750 °C) and frequency (1 Hz–1 MHz) ranges. The conductivity relaxation phenomenon was observed in these compounds and the relaxation frequencies were found to show Arrhenius-type behavior and activation energies were in good agreement with those obtained from high temperature conductivity plots. These results support the idea that the relaxation process and the conductivity have the same origin. The ionic conductivity of CaREZrNbO 7 (RE = La, Nd, Sm, Gd and Y) system showed the maximum at the phase boundary between the F-type and P-type phases. On the other hand, the activation energy for the conduction decreased in the F-type phase and increased in the P-type phase with increasing ionic radius ratio. Among the prepared compounds, CaGdZrNbO 7 showed the highest ionic conductivity of 9.47 × 10 − 3 S/cm at 750 °C which was about twice as high as that observed in Gd 2Zr 2O 7 (4.2 × 10 − 3 S/cm at 800 °C). The grain morphology observation by scanning electron microscope (SEM) showed well-sintered grains. AC impedance measurements in various atmospheres further indicated that they are predominantly oxide ion conductors at elevated temperatures (> 700 °C).

Synthesis, characterization and low frequency AC conduction of polyaniline/niobium pentoxide composites

New types of conducting polyaniline–niobium pentoxide (PANI/Nb 2O 5) nanocomposites have been synthesized by in situ deposition technique by placing fine grade powder of Nb 2O 5 during in situ polymerization of aniline. The composites formed were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). XRD and TEM indicated the dominant role-played by Nb 2O 5 particles, whereas XPS indicated incomplete protonation of imine moieties. SEM images indicated a systematic morphological variation of particles aggregated in the composite matrix as compared to the pristine PANI. Three step decomposition patterns were observed for PANI and its composites. AC conductivity and dielectric response of the composites were investigated in the frequency range, 10 2–10 6 Hz. AC conductivity obeyed the power law index, which decreased with increasing wt.% of Nb 2O 5. PANI showed high dielectric constant, which could be related to conductivity relaxation phenomenon. Both dielectric constant and dielectric loss decreased with increasing wt.% of Nb 2O 5. Variations in measured AC response parameters with increasing Nb 2O 5 contents of the composite followed systematic trends that are similar to those observed with decreasing temperature and level of doping.

Conductivity relaxation phenomena of the oxide ion conductor Zn 2−2 xTi 1+ xO 4

Impedance measurements were carried out on the oxide ion conductor Zn 2−2 x Ti 1+ x O 4 in the frequency range between 20 Hz and 10 6 Hz below 600°C. The frequency dependence of the electric modulus M″ shows the double peak shape in the cubic structure. These results are different from the previously studied Zn 2− x/2 Ti 1− x Ta x O 4 system where the single and double peaks have been observed for cubic and tetragonal phases, respectively. The M″ profile of the present system was not significantly varied with the composition and activation energies could be obtained from both lower- and higher-frequency peaks. The lower-frequency relaxation was supposed to be related to the long-range ion hopping, since the activation energy obtained from the lower frequency peak is close to that from the conductivity

Conductivity Relaxation Study of the Cubic and Tetragonal Zn2 − x / 2Ti1 − xTax O 4

Conductivity relaxation phenomena have been investigated in the oxide ion conductor with an inverse‐spinel‐type structure. The frequency dependencies of the imaginary part of the electric modulus M″ for the cubic and the tetragonal phases were found to be observed as the single and double peaks, respectively. The contribution of the tantalum substitution to the phase transition was confirmed together with the conduction properties of the compounds. © 2000 The Electrochemical Society. All rights reserved.

Conductivity Relaxation Study on (Bi 2O 3) 1−x(Y 2O 3) x and (Bi 2O 3) 1−x(Gd 2O 3) x with the Defect Fluorite Structure

In order to investigate the conductivity phenomena below 400°C in high-temperature-type oxide ion conductors of (Bi 2O 3) 1−x(Y 2O 3) x and (Bi 2O 3) 1−x(Gd 2O 3) x, impedance spectra were measured in the frequency range between 20 Hz and 1 MHz. The conductivity relaxation phenomena observed were studied in terms of the electric modulus formula. The relaxation frequencies were found to show Arrhenius-type behavior and the activation energies were in good agreement with those obtained by high temperature electric conductivity.

Fast ionic conduction in Na2S+B2S3 glasses: Compositional contributions to nonexponentiality in conductivity relaxation in the extreme low-alkali-metal limit.

The conductivity relaxation phenomenon in glassy and crystalline ionic conductors has been known for many years to be a highly nonexponential process. The stretched exponential function exp-(t/\ensuremath{\tau}${)}^{\mathrm{\ensuremath{\beta}}}$ has been used with varying levels of success to describe this relaxation. Whether the nonexponentiality is due to parallel conducting processes acting independently of each other and having a distribution of relaxation times or to serial processes strongly coupling the ionically conducting species and constraining each other's relaxation, the exact nature of this process is still unknown. If coupling is the active mechanism responsible for the nonexponentiality, then there should be a relationship between the extent of the nonexponentiality and the average ion separation distance; the greater the ion-ion separation, the smaller the coupling between the ions. To test this hypothesis, wide composition, frequency, and temperature range conductivity measurements have been performed on the fast-ion-conducting glass series, ${\mathrm{Na}}_{2}$S+${\mathrm{B}}_{2}$${\mathrm{S}}_{3}$. For x(${\mathrm{Na}}_{2}$S)=0.001, the relaxation is nearly exponential. As the ${\mathrm{Na}}_{2}$S concentration increases, the estimated ion-ion separation distance decreases; so do both the dc conductivity activation energy and the \ensuremath{\beta} parameter in the stretched exponential. The \ensuremath{\beta} parameter, however, shows a much stronger dependence to the ion-ion separation distance. It is also found that for nearly all of the glasses studied to date, the composition dependencies of the \ensuremath{\beta} parameter can be cast onto a master plot of \ensuremath{\beta} versus average ion-ion separation distance. In this way, we provide a universal trend for the compositional dependence of the nonexponentiality in glass.