Temperature Dependence Of Dc Conductivity Research Articles

Study of conduction mechanisms of InSeSb nano-chalcogenide alloys

The electrical conduction mechanisms for bulk samples of In0.1Se0.9−x Sb x (x = 0, 0.04, 0.08 and 0.12) nano-chalcogenide system, synthesized by the melt-quenching technique are investigated through current–voltage (I–V) characteristics. For the detailed study of conduction mechanism pellets of bulk samples are prepared. A thorough examination of electrical conductivity is done in the temperature range of 295–318 K and 0–50 V voltage range. From I–V measurements it is observed that samples are showing ohmic nature at lower field and non-ohmic nature at relatively higher field values. The temperature dependence of DC conductivity is analyzed using the Arrhenius relationship which is found to increase with Sb content. The value of activation energy and pre-exponential factor are calculated, which revealed that the conduction is due to the hopping of charge carriers among the localized states. Different parameters of Mott’s variable range hopping such as degree of disorder T 0, density of localized states N(E F), hopping distance (R hop), and hopping energy (W) are calculated. For the high field conduction process Poole–Frenkel, and Schottky processes are studied.

Effect of La, Zr Doping on the Structural and Electrical Conduction Behaviour of BiFeO<sub>3</sub>-BaTiO<sub>3</sub> Ceramics

<p>This study presents a comprehensive investigation of the crystal structure and DC conduction mechanism of [(Ba<sub>0.7-x</sub> La<sub>x</sub>) Bi<sub>0.3</sub>][(Ti<sub>0.5</sub> Zr<sub>0.2</sub>) Fe<sub>0.3</sub>]O<sub>3</sub> with x = 0.00, 0.01, 0.03, 0.05 employing X-ray diffraction (XRD) and electrical conductivity measurements. Various compositions were synthesized through the solid-state ceramic route. XRD was used to investigate phase formation. Analysis of XRD data suggested a structural transition from cubic to tetragonal for x ≥ 0.01. The average crystallite size first increases for x = 0.01 and then decreases for x ≥ 0.03. The temperature-dependent electrical conductivity measurements were investigated over a wide temperature range which revealed distinct conductivity mechanisms governing the material's transport properties. The activation energy (E<sub>a</sub>) has been estimated from temperature-dependent DC conductivity. Overall, this study provides valuable insights into the correlation between crystal structure and electrical properties in [(Ba<sub>0.7-x</sub> La<sub>x</sub>) Bi<sub>0.3</sub>][(Ti<sub>0.5</sub> Zr<sub>0.2</sub>) Fe<sub>0.3</sub>]O<sub>3</sub>, offering significant implications for its potential applications in electronic and optoelectronic devices requiring tailored conductivity characteristics.</p>

Investigation of structural, temperature and frequency dependent dielectric behavior of Zn2SnO4@amorphous SiO2 core shell nanocomposites

Herein, the detailed investigation of frequency and temperature dependent dielectric behavior of Zn2SnO4@SiO2 core shell nanocomposites (CSNs) is reported. Powder XRD analysis and FTIR spectral analysis were employed to comprehend the structure. The chemical and valence states are analyzed using XPS which confirms the existence of Zn, Sn, and SiO2, each with their distinctive Zn 2p, Sn 3d, and Si 2p valence states. The core shell formation is confirmed from their distinct color contrast in the TEM micrographs. The electrical response was investigated using impedance spectroscopy in the frequency range 1Hz-1 MHz at various temperatures. Positive temperature coefficient of resistance type behavior was established from impedance and modulus formalism. The total conductivity values were well fitted by the universal Jonscher law σtotal = σdc+ Aωn, and the temperature dependence of dc conductivity was discussed.

Temperature and frequency dependent response of electrical conduction and dielectric relaxation mechanism in CuCr2O4 tetragonally distorted spinel chromite

Herein, the polycrystalline CuCr2O4 (CCO) electro-ceramic was prepared via the sol-gel self-combustion route. The X-ray powder diffraction analysis at room temperature revealed that the CCO chromite was synthesized in a single phase tetragonally distorted normal spinel structure with I41/amd space group. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigated the polycrystalline nature of the compound. The microstructural analysis by field emission scanning electron microscopy (FESEM) explored the surface morphology of micron-sized grains (Gs) distinguished by well-pronounced grain boundaries (GBs) available for electrical response of the material. The color mapping images of elements by energy-dispersive X-ray spectroscopy (EDS) divulged the homogeneous distribution of elements in the compound. The surface chemistry of the compound was studied by X-ray photoelectron spectroscopy (XPS). This information helped in understanding the electronic states of the ions contributing to the electrical networks and mechanisms responsible for the charge transport within the CCO system. The dielectric relaxation and electrical transport properties were analyzed using complex impedance spectroscopy (CIS) over the experimental range of frequency and temperature from 40 Hz to 1 MHz and 243–493 K, respectively. The experimental complex impedance data were analyzed by RGQGRGBQGB equivalent circuit model which resolved the electro-active contributions of bulk and interface of the CCO spinel to its electrical dynamics. The dispersion in AC conductivity was explained by Jonscher's double power law which provided evidence of small polaron hopping (SPH) as a dominant transport mechanism governing electrical conduction in the compound. The temperature-dependent DC conductivity pattern exhibited an Arrhenius-like behavior that followed Mott and Davis's model of SPH. The analysis of complex electrical modulus M*(ω,T) professed the localized and de-localized movements of the charge carriers. The dielectric permittivity response of CCO followed Havriliak-Negami (HN) phenomenology that divulged the existence of non-Debye type dielectric relaxation processes. The interfacial polarization was observed to be accountable for the dispersion in dielectric loss spectra.

Analysis of structural and electrical properties of Sn modified Ca0.6Sr0.4TiO3 ceramics

In this study, we synthesized Ca0.6Sr0.4Ti1-xSnxO3 ceramics using the solid-state reaction technique, varying the Sn compositions from x = 0.0 to 0.08. X-ray diffraction analysis revealed a slight modification in the crystallographic structure of calcium strontium titanate (CST) as the Sn content increased, while confirming the formation of single-phase ceramics. Parameters such as crystallite size, lattice strain, stacking fault, and dislocation density were estimated based on the XRD data. Crystallite size generally increased with higher tin concentrations, except for x = 0.08 where a decrease was observed. The FTIR spectra exhibited a broad band, and deconvolution using a Gaussian distribution was employed to identify structural units. Density measurements demonstrated densification with increasing Sn content. The activation energy values increased from 0.76 eV for undoped CST to 0.95 eV for x = 0.06, except for x = 0.08, which measured 0.89 eV, indicating the role of Sn in modifying the structure. Activation energy was determined through linear fitting of experimental data, revealing that the reciprocal temperature dependence of DC conductivity followed Arrhenius behaviour. These findings contribute novel insights into the synthesis and characterization of Ca0.6Sr0.4Ti1-xSnxO3 ceramics, highlighting the impact of Sn on the structural and electrical properties of CST.

Field and temperature assisted DC/AC conduction measurements of PS/ZnO nanocomposite films

Electrical, optical and morphological properties of polymer nanocomposite materials are quite interesting to investigate due to their innovative characteristics and applications. Temperature dependent dc conductivity using different charge transport mechanisms like ionic hopping, Schottky and Poole-Frankel emissions has been investigated for pristine PS and PS/ZnO (at different wt% of ZnO) nanocomposite films in this research report. Non-ohmic conduction behaviour of these films developed an interest to carry out bulk and electrode limited conduction mechanisms. Ionic jump distance ‘a’ and conduction coefficient ‘βexp’ values for these films were calculated at various temperatures from the slopes of log I vs E and log I vs E1/2 plots respectively. The increase in dc conductivity of an order of 108 was observed by increasing the doping concentration up to 20 wt% of ZnO. The change in their ac conductivity was observed from 10−9 S/m to 10−6 S/m by varying the frequency from 1 to 300 kHz.

Formation of silver particles in [PVA:CS:PEG]-AgNO3 based biopolymer electrolyte membranes: Structural and electric transport properties study

[Chitosan (CS)-poly(vinyl) alcohol (PVA)-polyethylene glycol (PEG-200)]+xwt% silver nitrate (AgNO3) (x = 0, 10, 20, 30, 40) based biopolymer blend electrolytes (BPBEs) were prepared using solution casting method. FTIR results show the interaction of Ag+/NO3− with the constituents of polymers CS/PVA. XRD results reveal that the amorphousness increases with increasing AgNO3 concentration. Optical morphological (OM) images show that the silver, Ag(o) particles are agglomerated on the surface of the membrane. Temperature dependent dc conductivity (σdc) and dielectric relaxation frequency (fr) for BPBEs follow the Arrhenius type behavior and the sample containing 30 wt% salt has optimum dc conductivity, σdc∼1.7×10−4 S/cm at 30oC with lowest activation energy∼ 0.16 eV. The ac conductivity spectra follow the Jonscher's power law (JPL) with power law exponent, s > 1. The scaling of AC conductivity and loss tangent (tanδ) spectra were performed with respect to temperatures/concentrations of salt. The dielectric permittivity study reveals that the electrode polarization effect predominates at low frequencies. The Ionic Transference Number (ITN) measurement was used to determine the nature species of charge carrier, either ionic or electronic. The linear sweep voltammetry (LSV), result shows that 30% AgNO3containing sample has the electrochemical stability window (ESW) ∼+1.5 to -1.5 V.

Investigation of electrical conduction and optical properties of amorphous Se88Zn10Bi2 chalcogenide thin film

Thin film of Bi incorporated SeZn with a chemical composition of Se88Zn10Bi2 was deposited using the thermal evaporation technique. X-ray diffraction shows the amorphous nature of the film. The optical investigation revealed a wide absorption band in the range of 400–700 nm and the optical bandgap of the film is found to be 1.78 eV. Raman spectrum of the as-synthesized film has been analyzed to confirm the phase purity of the sample. In order to understand the conduction mechanism, the temperature dependence of dc conductivity is investigated in the temperature range 298–380 K.

Polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2 for excellent and stable high-temperature microwave absorption (up to 900 °C)

Microwave absorbing materials for high-temperature harsh environments are highly desirable for aerodynamically heated parts and engine combustion induced hot spots of aircrafts. This study reports ceramic composites with excellent and stable high-temperature microwave absorption in air, which are made of polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2. The fabricated ceramic composites have a crystallized t-ZrO2 interface between ZrB2 and SiOC domains. The ceramic composites exhibit stable dielectric properties, which are relatively insensitive to temperature change from room temperature to 900 °C. The return loss exceeds − 10 dB, especially between 28 and 40 GHz, at the elevated temperatures. The stable high-temperature electromagnetic (EM) absorption properties are attributed to the stable dielectric and electrical properties induced by the core–shell nanophase structure of ZrB2/ZrO2. Crystallized t-ZrO2 serve as nanoscale dielectric interfaces between ZrB2 and SiOC, which are favorable for EM wave introduction for enhancing polarization loss and absorption. Existence of t-ZrO2 interface also changes the temperature-dependent DC conductivity of ZrB2/SiOC ceramic composites when compared to that of ZrB2 and SiOC alone. Experimental results from thermomechanical, jet flow, thermal shock, and water vapor tests demonstrate that the developed ceramic composites have high stability in harsh environments, and can be used as high-temperature wide-band microwave absorbing structural materials.

Mechanism of Polaronic Conduction in Olivine Phosphates: An Influence of Crystallite Size

We report the polaronic conduction mechanism in transition-metal phosphate with different crystallite sizes by performing broadband ac conductivity measurements. The conductivity spectra exhibited a frequency-independent dc conductivity at low frequencies, and the conductivity becomes frequency-dependent above the characteristic frequency. The temperature-dependent dc conductivity has been analyzed within the framework of Mott’s model of polaronic conduction, which exhibits non-Arrhenius behavior within the hopping conduction region. The apparent non-Arrhenius behavior is divided into three different regions depending on the type of lattice phonons associated with the bound charge carrier. Interestingly, at high temperatures, the dc conductivity is primarily determined by the polaron concentration, and it varies with temperature. To ascertain the temperature-dependent polaron concentration variation at high temperatures, the frequency-dependent conductivity spectra have been analyzed by scaling procedure individually on three distinct regions. The application of the Summerfield scaling law on the ac conductivity spectra at low- and intermediate-temperature regions follows the time–temperature superposition principle (TTSP). On the other hand, at high temperatures, the scaling of the ac conductivity spectra with the Summerfield scaling law was found to exhibit pronounced deviations. The scaling of the ac conductivity spectra at high temperatures was improved significantly using the random barrier model. We suggest that at high temperatures, the number density of polarons performing a long-range hopping process becomes a temperature-dependent quantity and increases with temperature.

A New Zn(II) Metal Hybrid Material of 5-Nitrobenzimidazolium Organic Cation (C7H6N3O2)2[ZnCl4]: Elaboration, Structure, Hirshfeld Surface, Spectroscopic, Molecular Docking Analysis, Electric and Dielectric Properties.

The slow solvent evaporation approach was used to create a single crystal of (C7H6N3O2)2[ZnCl4] at room temperature. Our compound has been investigated by single-crystal XRD which declares that the complex crystallizes in the monoclinic crystallographic system with the P21/c as a space group. The molecular arrangement of the compound can be described by slightly distorted tetrahedral ZnCl42- anionic entities and 5-nitrobenzimidazolium as cations, linked together by different non-covalent interaction types (H-bonds, Cl…Cl, π…π and C-H…π). Hirshfeld's surface study allows us to identify that the dominant contacts in the crystal building are H…Cl/Cl…H contacts (37.3%). FT-IR method was used to identify the different groups in (C7H6N3O2)2[ZnCl4]. Furthermore, impedance spectroscopy analysis in 393 ≤ T ≤ 438 K shows that the temperature dependence of DC conductivity follows Arrhenius' law. The frequency-temperature dependence of AC conductivity for the studied sample shows one region (Ea = 2.75 eV). In order to determine modes of interactions of compound with double stranded DNA, molecular docking simulations were performed at molecular level.

A novel double perovskite BaKFeWO6: Structural, Microstructural, Dielectric and optical properties

• The synthesis of a stable BaKFeWO 6 double perovskite from BaWO 4 & KFeO 2 two non-perovskites materials. • Semiconducting property and NTC thermistor applications. • The study of I-V characteristics confirms the Ohmic nature with a low leakage current. • The study of UV visible spectrum provides the energy bandgap of 3.16 eV; which was found suitable for some optoelectronic devices. In this paper, the synthesis (solid-state reaction) and characterization (structural, electrical, and optical) of K + /Fe +3 co-doped inorganic BaWO 4 (i.e., BaKFeWO 6 ) double perovskite are reported. The x-ray diffraction (XRD) profile suggests an orthorhombic crystal symmetry with an average crystallite size of 95 nm and a lattice strain of 0.145 %. The incorporation of the potassium/iron ions on both sides of the barium tungstate is confirmed from RAMAN while microstructure (grain/grain boundary) analysis by scanning electron microscopy (SEM). The study of energy-dispersive X-ray spectroscopy (EDX) confirms the presence of all constituent elements with both weight and atomic percentage. The study of dielectric as a function of both frequency (1 kHz −1 MHz) and temperature (25 °C – 500 °C) insights into the structure, grain, grain boundary, transport properties and charge storage capacities. Modulus study suggests a non-Debye relaxation mechanism while impedance analysis suggests a negative temperature of coefficient of resistance (NTCR) behavior. The temperature-dependent dc conductivity follows Arrhenius's relation while frequency-dependent ac conductivity obeys Jonscher's power law and confirms the presence of the thermally activated conduction mechanism. The variation of the resistance with temperature confirms the character of the NTC thermistor. The I-V study supports the low leakage current and Ohmic character of the sample. The study of UV visible spectrum provides band-gap energy of 3.16 eV for some device applications.

Fortified relaxor ferroelectricity of rare earth substituted 4-layered BaBi3.9RE0.1Ti4O15 (RE = La, Pr, Nd, and Sm) Aurivillius compounds

In this report, the effect of rare-earth (RE3+) ion substitution on structural, microstructural, and electrical properties in barium bismuth titanate (BaBi4Ti4O15) (BBTO) Aurivillius ceramics has been investigated. The Rietveld refinements on X-ray diffraction (XRD) patterns confirm that all the samples have an orthorhombic crystal system with A21am space group. Meanwhile, temperature dependent synchrotron XRD patterns reveal that the existence of dual phase in higher temperature region. The randomly oriented plate-like grains are experimentally strived to confirm the distinctive feature of bismuth layered Aurivillius ceramics. The broad band dielectric spectroscopic investigation signifies a shifting of ferroelectric phase transition (Tm) towards low temperature region with a decrease of the RE3+-ionic radii in BBTO ceramics. The origin of diffuse ferroelectric phase transitions followed by stabilization of the relaxor ferroelectric nature at high frequency region is explained using suitable standard models. The temperature dependent ac and dc conductivity results indicate the presence of double ionized oxygen vacancies in BBTO ceramics, whereas the dominance of single ionized oxygen vacancies is observed in RE-substituted BBTO ceramics. The room temperature polarization vs. electric field (P–E) hysteresis loops are shown to be well-shaped symmetric for BBTO ceramics, whereas slim asymmetric ferroelectric characteristics developed at RE-substituted BBTO ceramics.

On Molecular Dynamics and Charge Transport in a Flexible Epoxy Resin Network.

An epoxy based on diglycidyl ether of bisphenol A was reacted with a long-chain poly(oxypropylene diamine) hardener in the presence of an accelerator, resulting in a flexible epoxy network. Tensile properties were tested as a function of accelerator concentration. All systems exhibited high levels of extensibility, with strain at failure values in excess of 65%. Molecular dynamics in a formulation containing 10 phr of accelerator were then examined using dielectric spectroscopy over the temperature range of 103–433 K. At low temperatures, a molecular relaxation process (γ relaxation) was observed and shown to conform well to both the Arrhenius equation and activated tunnelling. A stronger relaxation appeared (203–303 K) just before the onset of charge transport, which dominated the behaviour at higher temperatures. The former takes an unusual bimodal form, which we consider a result of overlapping β and α relaxations, consequently termed αβ mode. Analysis of this mechanism revealed a Vogel–Fulcher–Tammann (VFT) behaviour. The temperature-dependent DC conductivity, σDC (deduced from the low-frequency charge transport contribution to εr″), also revealed VFT behaviour with an onset statistically equivalent to that of the αβ mode, therefore suggesting that charge transport, at this temperature regime, is strongly affiliated with cooperative molecular motion.

Anomalous dielectric relaxation peak in Nb-doped SrTiO3 single crystals

Anomalous dielectric relaxation appears in Nb-doped SrTiO3 (SNT) single crystal with relaxation rate displaying unusual slowing down with increasing temperature. Dielectric measurements show that the resistivity increases with temperature. Raman spectrum and the spherical aberration-corrected transmission electron microscope (STEM) show the existence of polar nano regions (PNRs) in the crystal. The temperature-dependence of DC conductivity and current-voltage (I–V) curves suggest that this anomalous behavior happens at the interfaces of PNRs. The evolution of the anomalous relaxation peak in the annealed samples indicates that this effect is simultaneously affected by the carrier concentration and the interface structure. The anomalous dielectric relaxation is reminiscent of the positive temperature coefficient of resistance (PTCR) effect in a polycrystalline material. The resistive switching effect makes such materials to have potential application value in switches, sensors, and device miniaturization.

Structural, morphological, electrical, and magnetic characteristics of 20MnFe2O4-80SiO2 nanocomposite synthesized by the one-pot auto-combustion route

We report an investigation of the structural, morphological, the ac-dc electrical, magnetic, and Mössbauer spectroscopy properties of 20MnFe2O4-80SiO2 nanocomposite prepared using a one-step and facile auto-combustion approach. XRD pattern shows the formation of MnFe2O4 nanocrystallite without any crystallization of the SiO2 phase. However, the presence of a secondary phase of the nanosized α-Fe2O3 particles was also detected. The morphological analysis showed aggregation of polygonal magnetic nano-crystallites dispersed non-uniformly in a silica matrix. The dc electrical measurements performed on a wide range of temperatures from 120 to 400 K showed the semiconducting nature of the nanocomposite. The temperature dependence of dc conductivity could be perfectly fitted to the nearest neighborhood hopping model with activation energy, ΔENNH, of 0.45 eV. The Nyquist plots demonstrated a nonmonotonous thermally activated trend and non-Debye relaxation behavior. An equivalent circuit was successfully fitted to the complex impedance spectra. The variation of both grain and grain boundary conductivities as a function of temperature exhibited three distinct regions, semiconducting-metallic-semiconducting with different activation energies over the measured temperature window. The provided description of such behavior is further advocated by the ac conductivity and dielectric modulus studies. VSM measurements revealed that the nanocomposite magnetic behavior deviates from the ideal non-interacting superparamagnetic picture, due to the presence of α-Fe2O3 nanocrystalline impurities and relatively intensive exchange interactions between ions. Mössbauer spectra showed the presence of Fe3+ ions with sixfold environment and also confirmed the existence of a sextet related to α-Fe2O3 with a quantity of about 20% out of magnetic components. Fe3+ superparamagnetic doublets were also found within the fitting procedure.

Structural characteristics, impedance spectroscopy, ac-conductivity and dielectric loss studies on RF-magnetron sputtered F doped ZnO (FZO) thin films

The manuscript demonstrates the structural characteristics, impedance spectroscopy, ac-conductivity and dielectric loss studies on F-doped ZnO films grown by RF-magnetron sputtering at TS ∼50 and 125 °C. The electrical impedance spectroscopy enables separately recognizing the contributions of grain and grain-boundary on the electronic properties. The relaxation time distribution on temperature results in the asymmetric and depressed nature of the semi-circular arcs in the Cole-Cole plot and endorses a non-Debye type response under changing electric fields. The negative temperature coefficient of resistance behaviour indicates the semiconducting characteristics. A parallel equivalent circuit model (R || CPE) is designed to fit the semi-circular arc. The grain boundary being more resistive than ZnO-grain, its activation energy appears more significant because of the dynamic disorder characteristics. The ac-conductivity obeys Jonscher power law, and frequency exponent n < 1 suggests hopping of charge carriers with translation motion under ac electric field. The temperature-dependent dc-conductivity follows the Arrhenius behaviour. Sample deposited at higher TS has a greater carrier lifetime due to the improved crystalline structure and lesser defects. Although, the dielectric loss in the form of conduction loss is higher for the low temperature grown sample owing to the relatively effortless movement of charge carriers and formation of dipoles due to its elevated dc conductivity consequent to increased doping.

Synthesis of x[La0.67Sr0.33MnO3] – (1-x)[0.5Ba0.7Ca0.3TiO3-0.5BaZr0.2Ti0.8O3] multiferroic composite with its dielectric, magnetodielectric, magnetic and electrical conductivity studies

The present paper studies the synthesis and characterization of x[La0.67Sr0.33MnO3] – (1-x)[0.5Ba0.7Ca0.3TiO3-0.5BaZr0.2Ti0.8O3] multiferroic composite for x = 0.1 and 0.175. Parent materials of ferroelectrics Ba0.7Ca0.3TiO3 (BCT) and BaZr0.2Ti0.8O3 (BZT) and ferrite La0.67Sr0.33MnO3 (LSMO) have been prepared via hydroxide co-precipitation method while its composite x[LSMO] – (1-x)[0.5 BCT -0.5 BZT] was synthesized by ceramic route. The presence of ferroelectric and ferrite phases were confirmed by structural studies of composites. Microstructure shows the dense and closely packed LSMO particles over BCT-BZT ferroelectric phase. The dielectric properties of composites were studied in frequency range of 1KHz-1MHz and from room temperature to 500OC. P-E hysteresis loops of composites shows noticeable values of saturation polarization (Ps) and remnant polarization (Pr). Significant value of magnetoelectric (ME) coupling coefficient (α) of 2.15mV/cmOe was observed for the composite 0.175LSMO – 0.825(0.5BCT-0.5BZT) at 1 KHz frequency. Magnetodielectric (MD) properties of the composites were investigated by measuring the magnetocapacitance up to 1 T magnetic field. MD effect can be explained on the basis of contribution of dielectric constant due to interfacial polarization which depends on magnetic field and changes due to induced stress. Frequency dependent ac conductivity was confirmed by Jonscher's Universal Power law. Temperature dependent dc conductivity of the materials shows the Arrhenius behavior. As the ferrite content of LSMO increases in the composite saturation magnetization increases which can be studied by the hysteresis plot.

Electrical properties of amorphous Ge26InxSe74-x chalcogenide thin films

Amorphous Ge26InxSe74-x (1 ≤ × ≤ 5) chalcogenide thin films have been deposited by thermal evaporation technique. The temperature-dependence of DC conductivity and the temperature and frequency dependence of AC conductivity have been studied in the temperature range 295–523 K and in the frequency range 4–8 MHz. The study of the temperature-dependent of DC conductivity refers to the presence of two distinct conduction mechanisms; the activation energies for each were calculated and it was observed that their values decrease by increasing In content. Besides, in the low-temperature region, the variation of the conductivity against temperature was further analyzed according to the variable-range hopping model based on Mott’s relation, whereby the hopping parameters were evaluated. For all investigated compositions, the variation of the AC conductivity against frequency at the studied temperatures was interpreted according to the correlated barrier hopping (CBH) model which based on Jonscher’s power law, whereby the potential barrier height, WM, and the theoretical optical bandgap, Eg, were calculated.

Electrical and electrochemical properties of nanostructured Ni and Zn substituted Co3O4 spinels for thermistors and supercapacitor applications

Cobalt oxide-based spinels in the form of Co3O4, NiCo2O4 and ZnCo2O4 are synthesized by the co-precipitation technique. Powder X-ray diffraction studies confirm the arrangement of ions in spinel structure with minor secondary phases of native oxides. Scanning electron micrographs of spinels show the formation of fine nanostructures with an overall grain size below 90 nm for Co3O4 and ZnCo2O4. However, the grain size of NiCo2O4 varied from 100 to 250 nm. Dielectric measurements of all spinels exhibit low dielectric loss in lower temperature regions indicating superior dielectric behavior. Almost stable dielectric loss at lower temperatures confirms the usability of these spinels in supercapacitor applications. The dielectric loss increases with temperature due to the dominance of conductive grains and thereby demonstrates improved electrical conductivity. Temperature-dependent dielectric constant studies show the dominance of space charge polarization in lower temperature regions and orientation polarization in higher temperature regions, respectively. The temperature-dependent dc-conductivity of all spinels exhibits NTCR behavior and the same is confirmed by the Cole-Cole plots. The cyclic voltammettry measurement shows highest specific capacitance of 767 F/g for NiCo2O4 spinel followed 600 F/g for ZnCo2O4 and 439 F/g for Co3O4 coated electrodes. Electrochemical impedance measurement shows no sign of a semicircle along with low internal resistance for Ni and Zn-substituted Co3O4 spinels. This endorses the significance of substitution in improving the electrochemical behavior of Co3O4 spinel and their use in supercapacitor applications.