Small Polaron Tunneling Research Articles

Studies of structural, dielectric, conductivity, leakage current mechanism, and efficiency of complex electroceramic

Bismuth ferrites are quite interesting because of their high conductivity and dielectric constant. Recent times now need innovative materials with high mechanical strength, minimal energy loss, and cost effective. The analysis of X-ray diffraction pattern/data and scanning electron micrograph provides the formation of complex bismuth ferrite containing lithium and tungsten of a composition Bi1/2Li1/2Fe1/2W1/2O3, with monoclinic symmetry. The relation between the electrical and dielectric characteristics was examined in the frequency region from 1 kHz to 1 MHz at different temperatures (25–500 °C). The electrical conductivity experiments on the compound containing lithium and tungstate produced some exciting findings. As the frequency increases, the ac resistivity showing decreasing trend with small resistance and large conductivity. With the help of non-overlapping small polaron tunneling (NSPT) and overlapping large polaron tunneling (OLPT) models, temperature-frequency dependent conduction mechanisms have been explained. When electrical characteristics are examined using impedance spectroscopy (non-Debye relaxation), the contributions of grain and grain boundaries effect in the material are observed in the material. The Ohmic and Space Charge Limited Current conduction mechanism (SCLC) were found at low and high electric field (voltage) under forward bias current-voltage situations. The energy storage efficiency of the material is 61.80 %, obtained at room temperature with an applied electric field (−3 to +3 kV/cm) at a frequency of 50 kHz from the hysteresis loop. It implies that the material is promising for pulsed power energy storage capacitors.

Structure, optical, charge transport mechanism, dielectric properties and leakage current analysis of Sm2MgMnO6 double perovskite

Structure, optical, dielectric, charge transport properties, and leakage current density of Sm2MgMnO6 prepared via auto–combustion method have been investigated in this study. The stoichiometry of the constituent elements in the prepared sample agrees with the expected values. The sintered sample exhibits a monoclinic crystal structure with space group P21/n. The crystal structure is distorted and tilted. The grains are irregular in shape and size and distributed non–uniformly. The average crystallite and grain size are 151 nm and 176.49 nm, respectively. The direct optical band gap (1.41 eV) is associated with octahedral distortion. The tangent of dielectric loss increases beyond ∼300 °C rapidly. The Havriliak–Negami formalism has been used to explain the dielectric properties. The material is relaxor ferroelectric in nature. The conduction of charge carriers follows non–overlapping small polaron tunneling (NSPT) conduction model. The ac activation energy decreases with frequency. The leakage current conduction is Ohmic in nature. The sample exhibits 1.53 × 10−6 Acm−2 leakage current density at 5.11 Vcm−1 and 150 °C, which follows the Schottky emission relation. The obtained results have been compared with the literature.

Investigating the temperature and frequency dependence of dielectric response using AC impedance spectroscopy on SnO2

In this investigation, we explored tin oxide's dielectric properties and impedance spectroscopy, focusing on its temperature dependence across a frequency range of 20 Hz to 2 MHz. We analyzed the x-ray diffraction pattern using Rietveld refinement and established that the sample has a tetragonal phase with P42/mnm space group. Afterward, the surface structure of the SnO2 was examined using (FESEM) and Raman spectroscopy. Through FESEM, we analyzed the morphology of the prepared sample, which were nanospheres in structure. In contrast, we discovered the non-degenerated A1g and B2g modes through Raman spectroscopy, which matches well with the literature and displays the contraction and expansion of Sn-O bonds. We performed dielectric studies at varying frequencies and temperatures to further analyze the properties. We discovered that the ac conductivity increased as temperature and frequency increased. The activation energy was calculated using dc electrical conductivity measurement. The DC conductivity exhibits a temperature dependence that can be described by the Arrhenius equation, which reveals that the tin oxide has to conduct behavior with an estimated activation energy of 0.025 eV, 0.035 eV, and 0.082 eV for three temperature ranges of 80–120 K, 120–175 K, and 175–270 K, respectively. Additionally, the AC conductivity data conforms to Jonscher's universal power law. The frequency-dependent parameter “s” increases as the temperature elevates. A transition from the QMT (Quantum mechanical tunneling) model to NSPT (non-overlapping small polaron tunneling) was employed to analyze the data.

Investigation of electric transport in mixed conducting Na2O modified zinc borate glasses for electrode material using broadband dielectric spectroscopy.

The electrical conductivity of Na2O substituted zinc borate glasses has been studied in the frequency range of 10 mHz to 1MHz and in the temperature range from 313 to 573K. The conduction mechanism has been ascertained using the values of the frequency exponent (s) extracted from the fitting of experimental data of the real part of electric conductivity in light of the Almond-West equation. Depending on the glass composition, the ac conduction in the glasses happened via correlated barrier hopping and non-overlapping small polaron tunneling conduction models. The electric modulus studies support the assertion of composition dependent conduction mechanisms. Furthermore, electronic conduction and ionic conduction have been studied from impedance investigations. Equivalent circuit models were used to fit the Nyquist and Bode plots of each sample at the temperatures under consideration. It has been found that the activation energy values calculated from conductivity, electric modulus, and impedance measurements are more or less the same.

Assessment of Conductivity through Impedance Analysis of CuO:Ho2O3 Modified BaZr0.05Ti0.95O3

The solid state reaction method was used to prepare 2 wt% of BaZr0.05Ti0.95O3 doped by (CuO:Ho2O3) in different ratios. The variation in the ratio of CuO:Ho2O3 was fixed at 1:1, 1:2, 1:3, 2:1 and 3:1. The dielectric data and impedance analysis confirmed the non-Debye nature of all the samples. Conductivity results show the Non-overlapping Small Polaron tunnelling conduction mechanism up to 240 °C and the Co-related Barrier Hopping conduction mechanism after 240 °C in the selected temperature range for all the samples. For the Co-related Barrier Hoping model, a sample with a ratio of 1:3 has shown the maximum binding energy value for the charge carrier and a comparatively lesser value of conductivity.

Crystal structure, thermal behavior and electric properties of a new semiconductor cobalt-based hybrid material

The crystals of the new organic-inorganic hybrid material, (C5H12N)2[CoBr2.73Cl1.27], were successfully synthesized by the slow evaporation method and characterized by single-crystal X-ray diffraction, thermal analysis, UV–Vis absorption and electrical measurements. This compound crystallizes in the centrosymmetric space group P21/n of the monoclinic system with unit cell parameters: a = 9.7724 (6) Å, b = 12.3920 (6) Å, c = 15.0307 (9) Å, β = 100.864(6) °, V = 1787.59(18) Å3 and Z = 4. The IR spectrum of the compound is studied, especially for the cationic vibrational part. The thermal analysis indicates that (C5H12N)2[CoBr2.73Cl1.27] is stable up to 270 °C and that it undergoes two reversible phase transitions at 152 and 187 °C and at 141 and 128 °C on heating and cooling, respectively. From UV visible gap energy value of 3 eV it can be concluded that the new mixed halide compound is a semiconductor material. The electrical behavior of (C5H12N)2[CoBr2.73Cl1.27] was studied using impedance spectroscopy in the temperature range of 323 to 403 K. According to a study on the frequency dependence of ac conductivity, the material follows Jonscher's universal dynamic law with an increase in the frequency exponent (s) as temperature increases. This behavior reveals that the conduction mechanism is the nonoverlapping small polaron tunneling (NSPT) model.

Comprehensive studies on the electrical transport of some chalcogenide semiconductors: frequency- and temperature-dependent AC conductivity

The AC conductivity of chalcogenide semiconductors doped with Ag2S was extensively studied, not only for applications in devices but also for academic interests. X-ray diffraction studies reveal the presence of GeS, Ag2S, Se5.1S1.9, Se2.57S5.43, Ag2Se, S3Se5, Se4.7S3.3, and Ag8S nanocrystallites. The characteristic vibration that appeared in the range 500–600 cm−1 is due to the Ag–S bond, and the vibrations at 3,700 and 1600 cm−1 can be assigned as the bending and stretching vibrations of the O–H bond, which may be formed due to the adsorption of H2O molecules on the Ag2S surface. DC electrical conductivity can be increased by optical phonon frequency, which may be involved in the enhancement of structural vibrations. At low temperatures, the “density of states” increases from 3.337 × 1019 to 2.396 × 1021 eV−1 cm−3, and at high temperatures, it enhances from 3.417 × 1028 to 1.1356 × 1031 eV– 1 cm−3. The correlated barrier hopping model explores the maximum barrier height for composition, x = 0.1 as 0.0292 eV. The modified non-overlapping small polaron tunnelling model reveals the polaron transfer activation energy for x = 0.2 as 0.09110 eV. The independence of the electrical relaxation process of the system on temperature and its dependence on composition were exhibited by the scaling of the conductivity spectra.

Low-frequency electrical response related to oxygen vacancies in Al3+ substituted M-type hexaferrite

The presence of oxygen vacancies is unavoidable in many complex metal oxide materials such as hexaferrites. This article investigates the role of crystal defects, such as oxygen vacancies, and different oxidation states of Fe ions, on the electrical conduction behaviors of Al3+ substituted Ba0.4La0.1Sr0.5Al x Fe12−x O19 hexaferrites by analyzing the temperature dependent AC impedance and AC conductivity. The optimal substitution of La3+ ions and high-temperature sintering is responsible for forming oxygen vacancies while reducing Fe from Fe3+ to Fe2+ cations, as observed in structural and XPS analysis, which affects electrical conduction behaviors. The departure from ideal Debye-type relaxation behavior is also one of the effects of crystal defects. Temperature variation of relaxation time shows a sharp change at around 403 K. This may be due to different electrical entities influencing the mode of electron hopping with temperature. The activation energy calculated from the temperature dependent relaxation time confirmed the presence of electron hopping through the bridging effects of the first ionization of oxygen vacancies Fe2+––Fe3+ below a temperature of 403 K. Above 403 K, electron hopping through different oxidation states of Fe3+ + e− → Fe2+ and migration of oxygen vacancies toward the bulk surface are responsible for the conduction mechanism. The DC resistivity and AC conductivity show that the bridging effects of oxygen defects can also induce Coulomb interaction between the defect sites resulting in Efros–Shklovskii variable range hopping and correlation barrier hopping below 403 K. Above 403 K, polaron-assisted electron hopping is more desirable, as confirmed by the non-overlapping small polaron tunneling model.

Study of the structural, electrical, dielectric properties and transport mechanisms of Cu0.5Fe2.5O4 ferrite nanoparticles for energy storage, photocatalytic and microelectronic applications

Cu0.5Fe2.5O4 nanoparticles were synthesized by the self-combustion method whose XRD and FTIR analyzes confirm the formation of the desired spinel phase. The thermal evolution of conduction shows a semiconductor behaviour explained by a polaronic transport mechanism governed by the Non-overlapping Small Polaron Tunnelling (NSPT) model. DC conductivity and hopping frequency are positively correlated. The scaling of the conductivity leads to a single universal curve where the scaling parameter α has positive values, which testifies to the presence of Coulomb interactions between the mobile particles. Conduction and relaxation processes are positively correlated by similar activation energies. Nyquist diagrams are characterized by semicircular arcs perfectly modeled by an equivalent electrical circuit (R//C//CPE) indicating the contribution of the grains. The dielectric behaviour shows a strong predominance of conduction by the phenomenological theory of Maxwell-Wagner. The low values of electrical conductivity and dielectric loss and the high value of permittivity, make our compound a promising candidate for energy storage, photocatalytic and microelectronic applications.

Consistency between theoretical conduction models and experimental conductivity measurements of strontium-doped lanthanum manganite

La0.9Sr0.1MnO3 nanoparticles are elaborated using the citrate-gel route. The X-ray patterns show that the prepared sample crystallizes in the rhombohedral symmetry. Interesting results were obtained from the electrical conductivity measurements of the lanthanum manganite doped low strontium content. Indeed, numerous conduction models are used to analyze the electrical conductivity response. It is found that transport properties are governed by hopping processes at different temperature ranges. Such mechanisms explain the evolution of the DC-conductivity as well as the displacement of charge-carriers with temperature excitation. Then, thermal activation of the charge-carriers is confirmed. The temperature dependence of the frequency exponents reveals the contribution of Non-overlapping Small Polaron Tunneling (NSPT), Quantum Mechanical Tunneling (QMT), Over-lapping Large Polaron Tunneling (OLPT) and Correlated Barrier Hopping (CBH) to the transport properties. Conductivity spectrum shows a significant increase with frequency in the temperature range [80–500 K]. The frequency dependence of the AC-conductivity obeys to the "Double Jonscher Power Law" in the temperature range [80–300 K]. From 340 to 500 K, it is governed by the "Single Jonscher Power Law". Moreover, a high frequency plateau is observed presenting a percolation behavior in the conductivity spectrum. The deduced values of the disorder and hopping energies show the impact of hopping distance and polaron radius on the charge-carriers transport.

Structural study and temperature dependent relaxation and conduction mechanism of orthorhombic tungsten bronze Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic

In this study, the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic was prepared using the solid-state technique. The X-ray diffraction technique was used in this study to investigate the Ba/La order in the solid solution Ba4La28/3(Zr0.05Ti0.95)18O54. We have developed a structural model, to represent the order within the structure. The formula of model [Ba4−a□a]A2[La8+2b3□2−2b3]A1,A1′(Zr0.05Ti0.95)18O54 is described as perovskite layers with a thickness of 3 octahedral parallel to the xOz plane. Scanning electron microscopy (SEM) showed that Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic exhibits a typical columnar grain with a heterogeneous distribution over the entire surface. Complex impedance spectroscopy was used to analyze the dielectric and electrical properties of Ba4La28/3(Zr0.05Ti0.95)18O54 materials over a frequency range of 10 Hz to 1 MHz and a temperature range of 350°C to 400°C. An appropriate equivalent electrical circuit was also used to investigate the contributions of grains and grain boundaries. The AC-conductivity data was analyzed using Jonscher's universal power law. The thermal behavior of the exponent parameter "s" indicates that the dominant conduction mechanism in our compound is the non-overlapping small polaron tunneling (NSPT) model. The activation energies calculated from the conduction and relaxation mechanisms are nearly identical for the Ba4La28/3(Zr0.05Ti0.95)18O54 ceramic.

Temperature-driven complex dielectric and polaron-hopping mediated electrical conduction in aurivillius Gd2MoO6

In this work, aurivillius gadolinium molybdate (Gd2MoO6) was synthesized by the conventional solid-state route which was accompanied by cutting-edge characterization i.e., structural, and electrical, to give insight into the material characteristics required for possible high-temperature applications. The single-phase crystalline nature with monoclinic symmetry (C2/c, Space group-15) of Gd2MoO6 was confirmed by the X-ray diffraction (XRD) pattern. The average particle size was obtained to be ∼0.495 µm. The electrical conductivity and dielectric properties of a Gd2MoO6 plate capacitor were investigated in the frequency range between 10 Hz and 1 MHz and temperature from 473 to 773 K. A high dielectric constant (ε') of ∼3272 and low dielectric loss (δ) of ∼200 was observed at the low frequency and high-temperature regions, respectively. The Maxwell–Wagner interfacial polarization was found to be responsible for the decrease of the dielectric constant with increasing frequency. The behavior with the temperature of the frequency exponent (n) from the fitted conductivity spectra by Jonscher power law corresponds to the non-overlapping small polaron tunneling model between 473–673 K and correlated barrier hopping model at/over 673 K. The non-exponential Kohlrausch Williams-Watts function was introduced to fit the imaginary modulus (M′′) spectra and the activation energy was obtained to be 0.81 eV for grain and 0.94 eV for grain boundary conduction. The Nyquist plots(Z′vs.Z′′) differentiate the grain and grain boundary contribution and were fitted with the combinations of resistance (R), capacitance (C), and constant phase element (Q) in an equivalent circuit model(RC)(RCQ). Typical negative temperature coefficient of resistance behaviors of Gd2MoO6 suggest its possible application as thermistors in modern electronics circuits.

Effects of the substitution by copper on structural, optical and dielectric properties of the spinel LiFe2O4

Spinel lithium ferrites are of great importance in fields of technological applications. Their characteristics are subject to several studies to investigate the involved mechanisms. We prepared the spinel Li0.2Cu0.8Fe2O4-d ferrite by the solid-state method and we studied the effect of copper incorporation. X-ray diffraction confirms the Li0.2Cu0.8Fe2O4-d compound crystallizes with a cubic spinel structure with space group Fd3‾m. The morphology micrograph shows that the grains are agglomerated in asymmetrical formations. Nyquist plots exhibits significant contribution of grains and grain boundaries. Both modulus and impedance results confirm that Li0.2Cu0.8Fe2O4-d sample exhibits a Cole-Cole relaxation type. The AC conductivity variation shows a dispersive behavior governed by the jump relaxation model. Hopping conduction is explained by two theoretical models. The first is attributed to the correlated barrier-hopping model at low temperature, and the second corresponds to the non-overlapping small polaron tunneling mechanism at high temperature. The dielectric behavior shows a polarization effect. Optical properties show that the band gap value is equal to 1.47 eV. Finally, the magnetization curve indicates that our sample present a phase transition and evidences the presence of ferromagnetic behavior.

Crossover from small polaron tunneling to correlated barrier hopping and its evolution with thermal instability of SnO surface

In this paper, we have studied the surface and bulk stoichiometry and its effect on DC-AC conductivity measurements by x-ray photoelectron spectroscopy (XPS) as well as Raman spectroscopy depth profiling respectively. The SnO surface sheets are readily oxidized to Sn3O4phases and partially SnO2. The temperature dependence of DC resistance shows three-dimensional variable range hopping (VRH) below 200 K and Nearest Neighbor Hopping (NNH) between 200 and 300 K and undergoes a crossover to the thermally activated band conduction above 300 K till it decomposes at 600 K. This crossover temperature increases beyond 300 K during the subsequent heating cycles. In the frequency and temperature dependent conductivity, the bulk SnO throughout 300–600 K shows the frequency exponent of 0.8 which is ascribed to tunneling mechanism. Whereas, the surface progressively changes from correlated barrier hopping, CBH (band conduction) to a crossover of non-overlapping small polaron tunneling to CBH in samples in 300 to 400 K range after a thermal cycling. The oxidized phases bring about the polaronic sites which tunnel below 400 K. The energy of hopping reveals that the pristine sample has band like transport due to shallow Sn vacancies acceptors and the oxidized surface repositions fermi level to midgap due to oxygen vacancy donors.

Electrical characterization of AgNPs-PVA nanocomposites thin film-based heterojunction diode

The purpose of this work is to study the results of electrical measurements carried out of nano metal-semiconductor heterojunctions based on Poly Vinyl Alcohol (PVA)to examine the possibilities of either an Ohmic contacts or rectifying behavior like a Schottky junction. The PVA doped silver nanoparticles (AgNPs-PVA)were confirmed and characterized by using x-ray Diffraction (XRD),Fourier-Transform Infrared Spectroscopy (FT-IR), Thermogravimetric analysis (TG) and Differential Scanning Calorimeter (DSC). A thorough investigation of the predominant conduction mechanism, dielectric relaxation, and current-voltage behavior of a polyvinyl alcohol (PVA)–Silver nanoparticles (AgNPs) nanocomposite film has been presented. With two activation energies, Ag nanoparticles have been demonstrated to improve the conductivity and dielectric permittivity of films. In the sample, a non-Debye type asymmetric behavior has been found, which may be analyzed using a modified Cole-Cole model. The temperature dependence of the a.c. conductivity σ ac and power law exponent s is reasonably interpreted by the Correlated Barrier Hopping (CBH) and Small Polaron Tunnelling (SPT) models at low and high frequency ranges, respectively. The junctions were created by spin coating and characterized of evaluated according to their I-V characteristics. Non-Ohmic electrical behavior was observed. The phenomenon supposed to be partly responsible for such nonlinearity is existence of thin barrier layer on the surface of dried polymer nanocomposites, through which charge carriers could pass by tunneling. This Schottky diode manufactured of an AgNPs-PVA nanocomposite was electrically characterized and investigated. However, deeper discussion will be necessary to illuminate all the circumstances leading to understand this behavior.

Optimisation of electrical conductivity and dielectric properties of Sn4+-doped (Na0.5Bi0.5)TiO3 perovskite

The structural, microstructural, dielectric, and conductivity properties of Tin modified Sodium Bismuth Titanate (Na0.5Bi0.5)(Ti1-xSnx)O3, where x (mol%) = 0%, 1%, 3% (labeled as NBT, NBTS1, and NBTS3, respectively) were experimentally investigated in this paper. In this regard, the solid-state reaction process was used to prepare polycrystalline materials, where sintering was performed at 1100 °C for 3 h under atmospheric air. As a result, X-ray diffraction confirms, as it seems, the presence of a rhombohedral phase (R3c) in all compositions at room temperature. The electrical properties of the compositions are also studied using complex impedance spectroscopy (CIS). Subsequently, at room-temperature, doping 1% of Sn4+ in the NBT perovskite reduces the dielectric loss from 4.4 × 10−2 to 3.43 × 10−2 at 1 MHz. Moreover, it is around 3.05 × 10−2 at 93.6 °C and 1 MHz for NBTS3. Sn4+ significantly doping improved electrical conductivity. Therefore, at 10 Hz and 450 °C, the electrical conductivity of NBTS3 (σac = 8.76 × 10−3 S.m−1) is 61.26 times that of pure NBT (σac = 1.43 × 10−4 S.m−1). Joncher's power law investigates the conduction mechanism's nature; (i) the decreasing variation of the exponent s1 with temperature suggests that the NBT compound is characterized by the CBH (Correlated Barrier Hopping) model. On the other hand, for NBTS1 and NBTS3 (ii), the increase in s1 and s2 parameters under temperature indicates that the NSPT (non-overlapping small polaron tunneling) model is the most dominant. In this work, all tested compounds exhibit a sort of ferroelectric relaxation behavior. Our results demonstrate that doped materials can be applied to solid oxide fuel cells.

Complex permittivity and predominance of non-overlapping small-polaron tunneling conduction process in copper indium selenide compound

Abstract This paper presents a study of the complex permittivity of n-type copper indium selenide semiconductor compound at low temperatures down to −175 °C. Alternating current with frequency varying between 20 Hz and 1 MHz is applied to the material in order to measure the dielectric constant ɛ′ and dielectric loss D = ɛ″/ɛ′. ɛ′ is found to decrease with temperature and frequency, whereas D decreases with frequency and increases with temperature. The experimental data of ɛ″ agree with the expression ε ″ = A ω m ω , T ${\varepsilon }^{{\prime\prime}}=A{\omega }^{m\left(\omega ,T\right)}$ , where the frequency exponent m(ω, T), calculated through the relation m ω , T = ∂ ⁡ ln ε ″ / ∂ ⁡ ln ⁡ ω T $m\left(\omega ,T\right)={\left.\left(\partial \mathrm{ln}{\varepsilon }^{{\prime\prime}}/\partial \mathrm{ln}\omega \right.\right)}_{T}$ , shows a frequency and temperature dependence. The data are analyzed in light of existing theoretical models.

The effect of transition metal substitution on the structural, elastic, optical, electrical and dielectric properties of M0.5Fe2·5O4 (M=Co and Mg) synthesized by the auto combustion method

Spinel nanoparticles M0.5Fe2.5O4 (M = Co,Mg) were elaborated by the auto-combustion method using glycine as a fuel. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy have been invested to investigate the structural and morphological properties of these compounds. The optical study reveals that these samples exhibit a strong absorption in the visible range. They possess intermediate gap energies 2.91 eV for Co0.5Fe2.5O4 and 3.16 eV for Mg0·5Fe2·5O4 which makes them good candidates in terms of photovoltaic applications. Electrical analysis demonstrates a semiconductor [300–520 K] - metallic [540–660 K] transition at 540 K. Correlated Barrier Hopping (CBH) and No Overlap Small Polaron Tunneling (NSPT) models dominate the conduction mechanisms in both compounds. The Nyquist diagrams are modelled by two series-connected circuits reflecting grain (Rg//Cg) and grain boundary effects (Rgb//CPEgb). Quantitative analysis of the dielectric constant is indicative that these compounds are promising at the level of electronic systems industry, LTCC devices and super capacitor applications.

Lead-free double perovskite Cs2MBiCl6 (M = Ag, Cu): insights into the optical, dielectric, and charge transfer properties.

Recently, double perovskites have shown excellent potential considering the instability and toxicity problems of lead halide perovskites in optoelectronic devices. Here, the double perovskites Cs2MBiCl6 (M = Ag, Cu) were successfully synthesized via the slow evaporation solution growth technique. The cubic phase of these double perovskite materials was verified through the X-ray diffraction pattern. The investigation of Cs2CuBiCl6 and Cs2AgBiCl6 utilizing optical analysis showed that their respective indirect band-gap values were 1.31 and 2.92 eV, respectively. These materials, which are double perovskites, were examined using the impedance spectroscopy technique within the 10-1 to 106 Hz frequency and 300-400 K temperature ranges. Jonncher's power law was utilized to describe AC conductivity. The outcomes of the study on charge transportation in Cs2MBiCl6 (where M = Ag, Cu) suggest that the non-overlapping small polaron tunneling mechanism was present in Cs2CuBiCl6, whereas the overlapping large polaron tunneling mechanism was present in Cs2AgBiCl6.

Summerfield scaling model and electrical conductivity study for understanding transport mechanisms of a Cr3+ substituted ZnAl2O4 ceramic.

Solid-state and sol-gel procedures were used to prepare ZnAl1.95Cr0.05O4 nanocrystal spinels. From the results obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM), it can be concluded that the samples prepared by sol-gel synthesis are better crystallized than the ones resulting from the solid-state method. Studies by spectroscopy of impedance were done in function of frequency (40-107 Hz) and temperature (540-680 K) in the sample prepared by sol-gel synthesis. The electrical conductivity spectra obey Jonscher's law and two models were observed studying the variation of the exponent 's' as a function of temperature, Correlated Barrier Hopping (CBH) and Non-overlapping Small Polaron Tunnelling (NSPT). The predominant conduction mechanism is bipolaron hopping. The scaling behavior of conductivity spectra was checked by Summerfield scaling laws. The time-temperature superposition principle (TTSP) points to a common transport mechanism working for the low and middle frequency ranges. The scaling mechanism fails in the high-frequency ranges suggesting that conduction dynamics, and the usual hopping distance of mobile species, have changed. The values obtained for the activation energy from the hopping frequency, conductivity σ dc, bulk resistance R gb, and relaxation (f max), in the temperature range of 540-680 K, are very close. A higher and negative temperature coefficient of resistivity (TCR coefficient) equal to -2.7% K-1 is found at 560 K. This result shows that our compound is suitable for uncooled infrared bolometric applications and infrared detectors.