Polaron Tunneling Research Articles

Colossal dielectric constant and non-debye type relaxor in Ca0.85Er0.1Ti1-x Co4x/3O3 (x=0.15 and 0.2) ceramic

We, herein, report on the structural, dielectric and electrical properties of Ca0.85Er0.1Ti1-xCo4x/3O3 ceramic prepared by sol-gel method. The XRD patterns of the samples at room temperature showed a perovskite phase having an orthorhombic structure with a Pbnm space group. The addition of cobalt (x > 0.1) improved the feature of electrical conductivity and dielectric constant. The DC-conductivity measurements show a semiconductor behavior with increasing Co rate and the Arrhenius plots of the direct current conductivity confirmed the existence of two anomalies refer to singly and doubly ionized oxygen vacancies. The (AC) electrical conduction was supported by two theoretical models of conduction that can be attributed to the correlated barrier hopping (CBH) mechanism and the non-overlapping small polaron tunneling (NSPT) model. Excellent dielectric properties were observed in the samples when we studied the dielectric constant and dielectric loss as a function of frequency [10–107 Hz] at different temperatures [460–700 K]. The dielectric constant exceeded 105 which is a colossal permittivity and it is one of the most giant values reported for ceramic capacitors. In the thermal study, we observed a dielectric anomalies, corresponding to relaxor-like behavior attributable to Maxwell-Wagner relaxation and conduction relaxation associated with doubly ionized oxygen vacancy.

Synthesis, electrical properties, and conduction mechanism of [N(CH3)4]2PdCl4 compound

[N (CH3)4]2 PdCl4hybrid compound was synthesized and studied by X-ray powder diffraction patterns, differential scanning calorimetry (DSC), and impedance spectroscopy. It is crystallized at room temperature in the tetragonal system with P4/mmm space group and the refined unit cell parameters are a = b = 8.831 Å, c = 11.415 Å. Four phase transitions at T1 = 348 K, T2 = 398 K, T3 = 462 K and T4 = 472 K were detected by DSC measurements and confirmed by the variation of fp, σg and σdc as a function of temperature. The equivalent circuit was attributed based on the Z-View software, and the (AC) electrical conduction in [N(CH3)4]2PdCl4 was determined by two processes based on Elliot’s theory: non-overlapping small polaron tunneling model (NSPT) in phase I and IV and the correlated barrier hopping model (CBH) in phase II and III.

Investigation of structural and electrical transport properties of nano-flower shaped NiCo2O4 supercapacitor electrode materials

Nickel cobaltite nano-flower was synthesized via temperature dependent co-precipitation techniques and its single phase formation, vibrational spectra and nanostructured with flower-like morphology were confirmed by XRD, FTIR, Raman and TEM micrographs. The electrical transport properties and conduction mechanism of NiCo2O4 were studied first time using complex impedance spectroscopy in frequency range 100 Hz-1 MHz and wide temperature range 25 °C-300 °C. Poor grain relaxation was observed from RT to 75 °C whereas interface (both grain boundary and electrode effect) plays a dominant role above 75 °C are ascertained from Nyquist plot of impedance and modulus spectra. The utmost dielectric constant (6.8 × 102) and loss (540) was observed at high temperature (300 °C) and low frequency (100 Hz) regime and gradually diminished with high-frequency evolution and low-temperature approach. Finally, the ac and dc conduction mechanism were examined individually in details by the help of hooping relaxation model and overlapping large polaron tunneling (OLPT) concept for supercapacitor application. The calculated value of activation energy for dc conduction (0.63 eV) is larger than ac conduction (0.36 eV) as the ac conductivity is thermally activated.

Electrical Conduction Mechanism and Dielectric Properties of Spherical Shaped Fe₃O₄ Nanoparticles Synthesized by Co-Precipitation Method.

On the basis of dielectric measurements performed in a wide temperature range (173–373 K), a comprehensive analysis of the dielectric and electrical properties of magnetite nanoparticles electrical conduction mechanism of compressed spherical shaped Fe3O4 nanoparticles was proposed. The electrical conductivity of Fe3O4 nanoparticles was related to two different mechanisms (correlated barrier hopping and non-overlapping small polaron tunneling mechanisms); the transition between them was smooth. Additionally, role of grains and grain boundaries with charge carrier mobility and with observed hopping mechanism was described in detail. It has been confirmed that conductivity dispersion (as a function of frequencies) is closely related to both the long-range mobility (conduction mechanism associated with grain boundaries) and to the short-range mobility (conduction mechanism associated with grains). Calculated electron mobility increases with temperature, which is related to the decreasing value of hopping energy for the tunneling of small polarons. The opposite scenario was observed for the value of electron hopping energy.

Multifunctional polyaniline/chloroplatinic acid composite material: Characterization and potential applications

Polyaniline/chloroplatinic acid (PANI/H2PtCl6.H2O) composite is synthesized viain situoxidative polymerization method. Fourier transform infrared, ultraviolet‐visible, energy‐dispersive X‐ray, and Thermogravimetric techniques are used for the characterization studies. The surface morphology of the samples is investigated by scanning electron microscopy and atomic force microscopy. Dielectric measurements are carried out depending on the temperature. The dispersion process increases the thermal degradation temperature of PANI by about 60°C, while reducing the optical energy gap of PANI from 1.99 to 1.76 eV. Chloroplatinic acid significantly increases the agglomeration and grain size (up to 10 μm) on the surface of the PANI. Gas sensor measurements show that Polyaniline/chloroplatinic acid composite can be a candidate for ethanol detection. With the dispersion process, the electrical conductivity of PANI increases almost 2.5 times. The charge transport mechanism of the samples is consistent with electron tunneling model up to 97°C and with small polaron tunneling model at higher temperatures. The hopping distance of the charge carriers reduced to 4.82 from 5.30 nm with dispersion process. Experimental results reveal that PANI/chloroplatinic acid composite can be a rather suitable multifunctional material for various applications such as gas sensors, optoelectronic and semiconductor devices. POLYM. ENG. SCI., 59:66–73, 2019. © 2018 Society of Plastics Engineers

Phase transition, impedance spectroscopy and conduction mechanism of Li0.5Na1.5WO4 material

In order to better characterize the tungsten-based samples, and to get better inside into this field, we synthesized the Li0.5Na1.5WO4 compound and identified its purity by X-ray diffraction which showed that it crystallizes in the orthorhombic system with the Pmmm space group. Accordingly we used Raman spectroscopy, differential scanning calorimetry and impedance spectroscopy as to distinguish its properties. All WO42− tetrahedral vibration modes appear in the Raman spectra. The calorimetric study displays two phase transitions at 498 K and 567 K. Impedance spectroscopy reveals the contribution of two electrically active regions corresponding to the bulk mechanism and distribution of grain boundaries which allows us to use two cells mounted in series each one of them is composed of the combination in parallel of a resistance R and a fractal capacitance CPE. The variation σdc as a function of the inverse of temperature confirms the presence of three phases for each one of them the conductivity is ensured by a specific conduction mechanism. It has been pointed out that the first phase is described by the correlated barrier hopping model (CBH), the second one by the over loping polaron tunneling model (OLPT) and the third one by the non small polaron tunneling model (SPT). A comparison with the compound of Li1.5Na0.5WO4 confirms that the transport is dominated by the motion of the monovalent cations (Li+ and Na+) in the investigated material.

Effect of dilute concentrations of Sm on the temperature‐dependent electrical and dielectric properties of ZnO

AbstractCompounds of undoped and samarium (Sm) doped ZnO have been prepared by standard solid‐state reaction method. X‐ray diffraction (XRD), Williamson‐Hall (W‐H) analysis, Transmission Electron Microscopy (TEM), temperature‐dependent electrical and dielectric studies have been done to characterize these materials. Inclusion of Sm as dopant in hexagonal wurtzite ZnO changes the lattice parameters to a small extent with some Sm aggregation at higher concentration. Also, the mean particle sizes of ZnO:Sm compounds showed an inter‐correlation with the Scherrer method, W‐H analysis as well as with TEM results. The electrical resistivity depicts an exponential decay and metal‐semiconductor transition (MST) at ~300 K for the pristine sample whereas there is large decrement in the resistivity with Sm doping. The analysis of σac of ZnO suggests that the power law is obeyed and indicated an increase in the ac conductivity with Sm content. The mechanism behind this type of conductivity is elucidated by small polaron tunneling (SPT) model of conductivity. The dependence of ln dc on the temperature inverse shows that the traps of electrons are thermally activated such that low and high temperature activation energies confirm the presence of vacancies and interstitials of both O and Zn ions. Thus, a high value of dielectric constant makes these materials suitable for high frequency and charge storage device applications.

Temperature and frequency response of conductivity in Ag2S doped chalcogenide glassy semiconductor

The electric conductivity of chalcogenide glassy semiconductor xAg2S-(1-x)(0.5S-0.5Te) has been presented here as a function of temperature and frequency. Formation of different nanocrystallites has been confirmed from X-ray diffraction study. It is also noteworthy that average size of nanocrystallites decreases with the increase of dislocation density. Dc conductivity data have been interpreted using Mott's model and Greaves's model in low and high temperature regions respectively. Ac conductivity above the room temperature has been analyzed using Meyer-Neldel (MN) conduction rule. It is interestingly noted that Correlated Barrier Hopping (CBH) model is the most appropriate conduction mechanism for x = 0.35, where pairs of charge carrier are considered to hop over the potential barrier between the sites via thermal activation. To interpret experimental data for x = 0.45, modified non–overlapping small polaron tunnelling (NSPT) model is supposed to be appropriate model due to tunnelling through grain boundary. The conductivity spectra at various temperatures have been analyzed using Almond-West Formalism (power law model). Scaling of conductivity spectra reveals that electrical relaxation process of charge carriers (polaron) is temperature independent but depends upon the composition of the present chalcogenide glassy system.

Synthesis, crystal structure, thermal analysis, dielectric properties and electrical conduction mechanisms of the new mixed solid solution of thallium rubidium sulfate selenate tellurate

The new mixed compound Tl1.90Rb0.10(SO4)0.92(SeO4)0.08Te(OH)6 (TlRbSSeTe) has been synthesized in order to determine the temperature transitions and to specify the electrical properties as well as the conduction mechanism. It is obtained by slow evaporation at room temperature and prove to crystallize in the monoclinic system with P21/c space group using X-ray diffractometer data. The basic property of these atomic arrangements is the coexistence of three different anions (SO42−, SeO42− and TeO66− groups) in the unit cell, related by O−H…O hydrogen bonds building up the crystal. Thermal analysis (DSC, DTA and TG) of the title compound confirms the presence of the phase transitions and the temperature of the decomposition of the studied salt. In order to characterize the phase transitions, Raman spectra have been recorded at various temperatures in the wavenumber range from 50–1200 cm−1. Detailed dielectric and electrical properties of the material have been analyzed as a function of frequency (100 Hz–10 MHz) and temperature (383–518 K). Besides, the analysis of Nyquist plots were well fitted to an equivalent circuit consisting of a series of combination of grains and grain boundary elements. The variation of the DC and AC conductivity confirms all the transitions of our sample. Furthermore, The frequency dependence of alternative current (AC) conductivity is interpreted in terms of Jonscher's law (developed). The alternative current (AC) electrical conduction in TlRbSSeTe material is accounted for in terms of two processes that can be assigned to a hopping transport mechanism. These processes are the correlated barrier hopping (CBH) model in some regions, as well as the non-overlapping small polaron tunneling (NSPT) model in the other regions. The conduction mechanism for each phase is determined with the help of Elliot's theory.

Effect of annealing temperature on structural, morphology and dielectric properties of La0.75Ba0.25FeO3 perovskite

The effect of annealing temperature on the structure, morphology and dielectric properties of La0.75Ba0.25FeO3 compound prepared by the sol-gel method was investigated. The increase of the annealing temperature from 900 to 1100 °C, promotes an increase of the average grain size value. Two dielectric relaxations are detected using the dielectric modulus formalism, attributed to grain and grain boundary relaxations. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance and Modulus results at different measuring temperatures. The ac conductivity could be described by Jonscher's power law revealing the presence of both overlapping large polaron tunneling and non-overlapping small polaron tunneling mechanisms.

AC electrical conduction mechanisms and dielectrical studies of DD3 kaolin sintered at high temperature

In this study, DD3 kaolin, as a raw material, was thermally treated at a temperature ranging from 1000 °C to 1600 °C. The X-ray diffraction (XRD) patterns show the appearance of cristobalite and mullite phases at sintered temperature less than 1300 °C. Moreover, they revealed the formation of mullite at a higher temperature (1600 °C). The surface of mullite sample (DD3 at 1600 °C) is showed roughly with prismatic grains having an average size in the range of 32–42 nm. The FTIR spectrum is dominated by the stretching Si-O modes and Al-O at the wave number ranging from 443 to 1257 cm−1. The dielectric and electrical properties were investigated in a wide frequency (0.1–10 MHz) and at a temperature ranging from 0 to 200 °C. A strong dispersion of permittivity constants was observed at a low frequency, which can be attributed to interfacial Maxwell–Wagner–Sillar (MWS) relaxation. It is found that the ac conductivity depends on frequency and temperature with the Joncher power law A(T) ωs. Temperature analysis showed that the electron conductivity is controlled by both the small polaron tunneling (SPT) and the hopping correlated barrier (CBH) models.

Theoretical and experimental study of AC electrical conduction mechanism in the low temperature range of p-CuIn3Se5

In the present work, an attempt has been made to study theoretically and experimentally the AC electrical conduction mechanism in disordered semiconducting materials. The key parameter considered in this analysis is the frequency exponent s(ω,T)=(∂ln(σAC(ω,T))∂ln(ω))T, where σAC is the AC electrical conductivity that depends on angular frequency ω and temperature T. In the theoretical part of this work, the effect of the barrier hopping energy, the polaron radius and the characteristic relaxation time is considered. The theoretical models of Quantum Mechanical Tunneling (QMT), Non overlapping Small Polaron Tunneling (NSPT), Overlapping Large Polaron Tunneling (OLPT) and Correlated Barrier Hopping (CBH) are considered to fit experimental data of σAC in p-CuIn3Se5 (p-CIS135) in the low temperature range up to 96 K. Some important parameters, as the polaron radius, the localization length and the barrier hopping energies, are estimated and their temperature and frequency dependence discussed.

Effect of doping of alkaline metal ions on structural and electrical properties of Bi0.8M0.2FeO3-modified Na0.5Bi0.5TiO3 ceramics (M=Ca, Sr, and Ba)

In the present work the electrical properties of polycrystalline 0.9(Na0.5Bi0.5TiO3)–0.1(BiFeO3) and Bi0.8M0.2FeO3-modified Na0.5Bi0.5TiO3, (where M = Ca, Sr, and Ba) lead-free ceramics were investigated through impedance spectroscopy. X-ray diffraction analyses indicate the incorporation of alkaline earth metal ions at A-site of perovskite type ceramics revealing the conservation of crystal structure (rhombohedral structure with R3c space group) in the synthesized compositions. The substitution of alkaline earth metal ions at the A-site in perovskite-structured ceramics led to an enlargement of unit cell. The appearance of depressed semicircle arcs in Nyquist plots suggests non-Debye nature of relaxation occurring in studied samples. An equivalent circuit model comprising of parallel combination of resistance and constant phase element was used for the simulation of Nyquist plots. The mismatching of peaks in the combined spectroscopic plots of Z″ and M″ versus frequency also confirms the occurrence of non-Debye relaxation in BBFO sample. The ac conductivity studies show that the conduction mechanism changes from correlated barrier hopping model (CBH) to overlapping large polaron tunneling, when alkaline metal ions are substituted in place of Bi3+ ions. Activation energy values calculated from conductivity data suggest the presence of oxygen vacancies. The dielectric, impedance and conductivity behaviors are significantly influenced by the distortion of Ti/FeO6 octahedron.

Theoretical Study of the AC Conduction in β-In2S3

β-In2S3 is of great interest in photovoltaic applications and presents a certain number of vacant sites allowing the displacement of indium atoms by hopping from one site to another. Recently, it has been shown that it exhibits ionic behavior. Experimental works have been carried out in order to study the alternating current (AC) conductivity in β-In2S3, showing the validity of the hopping model (correlated barrier hopping; CBH) in the frequency range not exceeding \( \omega \) = 104 Hz. For \( \omega \) > 104 Hz, the transport mechanism was dominated by small polaron tunneling (SPT). The theoretical model developed in this work in order to study the AC conductivity is based on the hopping model adapted to the case of β-In2S3 by considering the jump of indium ions from one site to another. We report the frequency and temperature dependence on β-In2S3 AC conductivity. An examination of the experimental results shows a qualitative compatibility of our model. Indeed, our theoretical simulations are in agreement with the experimental data in the same frequency range where the CBH model was dominant. A quantitative discrepancy between theory and experiment has been observed beyond this frequency range where the SPT has been dominant. This discrepancy increases by raising the temperature. A FORTRAN program based on the Lenvenberg–Marquardt method was established to determine the fitting curve of the theoretical model to the experimental. This program allowed us to deduce the vibration frequencies about the equilibrium of indium atoms in the case of β-In2S3 which are parameters of fundamental importance in solid-state physics. The vibration modes obtained from the numerical simulation are in agreement with the orders of magnitude found in the literature.

Dielectric relaxation, protonic defect, conductivity mechanisms, complex impedance and modulus spectroscopic studies of pure and L-threonine-doped ammonium dihydrogen phosphate

Ammonium dihydrogen phosphate (ADP) has a wide range of applications in integrated and nonlinear optics. The dopant-like L-threonine has hydrogen-bonded side chain that causes defects in ADP. The pure and L-threonine-doped ADP crystals are grown using slow evaporation technique. The powder XRD patterns show the single-phase nature of pure and doped ADP. The dielectric constant and dielectric loss have shown the usual behaviour with respect to frequency and temperature. The protonic conduction is prevailing for electric transport, and from Jonscher’s plot, the correlation barrier hopping (CBH) and non-overlapping small polaron tunnelling (NSPT) conduction mechanism is confirmed. The Nyquist plot and modulus spectra show the presence of grain and grain boundary. The stretch exponent exhibits non-Debye-type relaxation. The activation energy of relaxation time for all samples is calculated. The modulus master curve and variation of Z″ and M″ versus angular frequency confirmed the proposed conduction. The nonlinear optical counterpart is in accordance with dielectric results.

Dielectric and electrical study along with the evidences of small polaron tunnelling in Gd doped bismuth ferrite lead titanate composites

The phase formation of the polycrystalline samples of 0.6BiGdxFe1−xO3–0.4PbTiO3 (x = 0.05, 0.10, 0.15 and 0.20) was studied by X-ray diffraction technique prepared by using solid state reaction route. From analysing the X-ray diffraction pattern, the appearance of morphotrophic phase boundary between rhombohedral and tetragonal phase was observed in some of these composites at room temperature. The dielectric parameters are measured in a frequency range between (102–106) Hz at different temperatures. The nyquist plot (Z′ vs. Z″) fit confirmed the contribution of bulk and grain boundary effect in the materials. Impedance, ac and dc conductivity showed the negative temperature co-efficient of resistance behavior. The temperature dependence of dc conductivity and relaxation time followed Arrhenius equation. The ac conductivity followed by the power law showed that the dynamics of charge carrier arises due to translational hopping motion for x = 0.10–0.20 and localised one for x = 0.05. The increasing behaviour of frequency exponent (n) with temperature strongly suggests that the small polaron tunnelling is the dominant conduction mechanism for the studied samples except for x = 0.05 composition.

Electrical, dielectric properties and study of AC electrical conduction mechanism of Li0.9□0.1NiV0.5P0.5O4.

In this paper, we report the measurements of impedance spectroscopy for a new olivine-type lithium deficiency Li0.9□0.1NiV0.5P0.5O4 compound. It was synthesized by the conventional solid-state technique. All the X-ray diffraction peaks of the compound are indexed, and it is found that the sample is well crystallized in orthorhombic olivine structure belonging to the space group Pnma. Conductivity and dielectric analyses of the sample are carried out at different temperatures and frequencies using the complex impedance spectroscopy technique. The electrical conductivity of Li0.9□0.1NiV0.5P0.5O4 is higher than that of parent compound LiNiV0.5P0.5O4. Temperature dependence of the DC conductivity and modulus was found to obey the Arrhenius law. The obtained values of activation energy are different which confirms that transport in the title compound is not due to a simple hopping mechanism. To determine the conduction mechanism, the AC conductivity and its frequency exponent have been analysed in this work by a theoretical model based on quantum mechanical tunnelling: the non-overlapping small polaron tunnelling model.

An investigation into the dielectric and electrical properties of LaErO3 and LaHoO3 rare earth perovskites

We have investigated the electrical and dielectric properties of rare earth perovskites-type oxide (LaErO3 and LaHoO3) by using impedance spectroscopy, respectively, over a frequency and temperature range of [0.6 kHz–8 MHz] and [673–973 K]. Both oxides crystallize in the orthorhombic structure but exhibit difference in lattice distortions. A correlation between structural properties and dielectric anisotropies is carried out. The analysis of Nyquist semicircles confirms the presence of bulk effects and non-Debye relaxation processes for both compounds. The activation energy, calculated using relaxation time and direct current conductivity models, was found to follow the Arrhenius law. The frequency dependence of alternative current conductivity is described by Jonscher's universal power law and shows that the conduction mechanism follows the non-overlapping small polaron tunneling model. The investigation of dielectric properties revealed that at low frequencies the dielectric constant was higher for LaHoO3 oxide than that for LaErO3. Modulus formalism examination demonstrates that the relaxation process of studied materials takes place via the hopping mechanism.

Frequency and temperature dependent electrical and dielectric properties of LaCrO3 and Ir doped LaCrO3 perovskite compounds

Perovskite oxide materials, especially perovskite lanthanum chromium oxide, LaCrO3 (LCO) have taken considerable attention among the scientists due to the changing optical, electrical, dielectric and magnetic properties depending on doping via various elements. In this study, the LCO and iridium (Ir) doped LCO (LaCr1-xIrxO3) (x = 0.10) compounds were synthesized using solid-state reaction method. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) have been employed to study particle morphologies and oxidation states of synthesized powders, respectively. Frequency-depended electrical/dielectric properties of perovskite oxide samples were performed in wide range frequency (1Hz-10 MHz) and temperature (−100 °C to +100 °C) using dielectric/impedance spectrometer. Electrical measurements have underscored that the dielectric constant of LCO compound dramatically decreased after doped with Ir. Furthermore, it was observed that ac conductivity and capacitance value of LCO decreased while impedance increased after Ir doping due to i) Ir occupation in Cr sites and ii) lattice distortion owing to doping larger ion Ir4+ into smaller Cr3+ ion in the LCO lattice. Finally, overlapping large polaron tunneling (OLPT) and quantum mechanical tunneling (QMT) conduction mechanisms were suggested for LCO while the correlated barrier hopping (CBH) and QMT conduction mechanisms were observed for Ir doped LCO compound. Moreover, the activation energy values have been calculated by employing both fmaxvs. 1/T and σdcvs. 1/T plots. It has been shown those energy values are in good agreement with each other for LCO and Ir doped LCO samples at various temperature ranges.

Dielectric relaxation and conduction mechanism of complex perovskite Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 ceramic

In this work, Sr and Zn co-doped calcium copper titanate having nominal formula Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 has been synthesized and systematically studied for structure, dielectric and electrical properties. The phase purity of the prepared composition has been confirmed by X-ray diffraction (XRD) pattern and various structural parameters are presented here with Rietveld refinement data. The Scanning electron microscopy (SEM) image revealed the presence of homogeneous fine-grained microstructure investigated in the prepared ceramic. The impedance data well fitted with 2 R-CPE model confirmed the non-ideality of the system. Dielectric studies have shown the existence of two relaxation processes in low and high frequency domains. Low frequency dielectric response proposed as a combination of Maxwell-Wagner relaxation and intrinsic defect (Vo++) while high frequency behavior has been interpreted in terms of polaronic relaxation caused by hopping process of an electron between Ti3+ and Ti4+ states. The frequency dependent behavior of conductivity has been well fitted to Dong’s model and interpreted in term of Overlapping Large Polaron Tunneling (OLPT) mechanism. The various parameters; relaxation angular frequency (ω1) of Debye process, ionic hopping frequency (ω2), dc conductivity (σo), cole- cole parameter (α) and frequency exponent (s) have been determined by Dong’s Model fitting.