Activation Energy Of Dc Conductivity Research Articles

Study of EPR, optical properties and dc conductivity of VO2+ ion doped TiO2⋅R2O⋅B2O3 (R = Li and K) glasses

Electron paramagnetic resonance (EPR), optical properties and dc conductivity of xTiO2⋅(30−x)R2O⋅70B2O3 and xTiO2⋅(70−x)B2O3⋅30R2O (R=Li, K; 0⩽x⩽7, in mol%) glasses containing 2mol% V2O5 have been studied. Spin Hamiltonian parameters, g‖, g⊥, A‖, A⊥, the dipolar hyperfine coupling parameter (P) and the Fermi contact interaction parameter (K) have been evaluated. Decrease in Δg‖/Δg⊥ ratio with increase in TiO2 content in TiO2⋅Li2O⋅B2O3 glasses show that the octahedral symmetry of V4+O6 complex is improved; whereas in TiO2⋅K2O⋅B2O3 glasses, it is reduced with increase in x. The decrease in P, in both systems, indicates that the 3dxy orbit expands with increase in mol% of TiO2. The molecular orbital coefficients, α2 and γ2 have been calculated by recording the optical transmission spectra in the range 400–850nm. α2 and γ2 increase with increase in x in all glasses expect KB glasses, which indicate that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity (σ) decreases and activation energy (W) increases with increase in TiO2:R2O ratio in TiO2⋅R2O⋅B2O3 glasses whereas with increase in TiO2:B2O3 ratio in TiO2⋅B2O3⋅R2O glasses the variation in σ and W is within experimental error.

Influence of SiO2 on conduction and relaxation mechanism of Li+ ions in binary network former lead silicate glasses

Ion conducting glasses having composition 30Li2O·(70−x)PbO·xSiO2 were prepared by the normal melt quench technique. The compositional variations in density, molar volume and glass transition temperature confirm the dual role of PbO acting as a network modifying oxide as well as a network forming oxide. Conduction and relaxation mechanisms in these glasses were studied using impedance spectroscopy in the frequency range from 1Hz to 7MHz and in a temperature range below glass transition temperature. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency were extracted from the impedance spectra. Similar values of activation energy for dc conduction and for conductivity relaxation time indicate that the ions have to overcome the same energy barrier while conducting and relaxing. The increase in dc conductivity for silica rich compositions is attributed to the presence of mixed former effect in the studied glasses. The study of conductivity spectra reveals a transition from non-random to random hopping motion of lithium ions on successive replacement of PbO by SiO2 in glass matrix. The conduction and relaxation mechanism in the studied glasses are well explained with the concept of mismatch and relaxation (CMR) model.

Impedance Spectroscopy Models for X5R Multilayer Ceramic Capacitors

High capacitance X5R MLCCs based on BaTiO₃ ceramic dielectric layers exhibit a single broad, asymmetric arc shape impedance and modulus response over the wide frequency range between 1 MHz to 0.01 Hz. Analysis according to the conventional brick-layer model for polycrystalline conductors employing a series connection of multiple RC parallel circuits leads to parameters associated with large errors and of little physical significance. A new parametric impedance model is shown to satisfactorily describe the experimental spectra, which is a parallel network of one resistor R representing the DC conductivity thermally activated by 1.32 eV, one ideal capacitor C exactly representing bulk capacitance, and a constant phase element (CPE) Q with complex capacitance A(iω) α?1 with α close to 2/3 and A thermally activated by 0.45 eV or ca. 1/3 of activation energy of DC conductivity. The feature strongly indicate the CK1 model by J. R. Macdonald, where the CPE with 2/3 power-law exponent represents the polarization effects originating from mobile charge carriers. The CPE term is suggested to be directly related to the trapping of the electronic charge carriers and indirectly related to the ionic defects responsible for the insulation resistance degradation.

Dielectric properties and relaxation behavior of the indium doped cadmium zinc telluride single crystal

Low frequency dielectric dispersion behavior of the indium doped cadmium zinc telluride single crystal has been investigated. The temperature dependent of dielectric loss shows a broadening peak at high temperatures, which is attributed to thermally activated relaxation process. The large dielectric permittivity can be attributed to the influence of the dc conductivity and the predominance of the dc conduction in low frequency region overshadows the true behavior of the imaginary part of dielectric permittivity. The contribution of dc conduction and ac conduction has also been studied. A polaron theory indicates that the dielectric relaxation of the indium doped cadmium zinc telluride crystal at high temperature is associated with the hopping localized cadmium vacancies and telluride antisites defects. The hopping energy increases from 1.204 eV at 499 K to 1.267 eV at 534 K monotonically, which is close to the thermal activation energy 1.541 eV and dc conductivity activation energy 1.239 eV.

Dielectric loss, conductivity relaxation process and magnetic properties of Mg substituted Ni–Cu ferrites

The dielectric properties, dc and ac electrical resistivities of Mg substituted Ni–Cu ferrites with general formula Ni0.5Cu0.5−xMgxFe2O4 (0.0≤x≤0.5) have been investigated as a function of frequency, temperature and composition. ac resistivity of all the samples decreases with increase in the frequency exhibiting normal ferrimagnetic behavior. The frequency dependence of dielectric loss tangent showed a maximum in between 10Hz and 1kHz in all the ferrites. The conductivity relaxation of the charge carriers was examined using the electrical modulus formulism, and the results indicate the presence of the non-Debye type of relaxation in the prepared ferrites. Similar values of activation energies for dc conduction and for conductivity relaxation reveal that the mechanism of electrical conduction and dielectric polarization is the same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the distribution of relaxation time is temperature independent. The saturation magnetization and coercivity as calculated from the hysteresis loop measurement show striking dependence on composition.

Thermoelectric properties and impedance spectroscopy of polycrystalline samples of the beta-gallia rutile intergrowth, (Ga,In)4(Sn,Ti)5O16

Polycrystalline samples of Ga3In(Sn1−yTiy)5O16, y≤0.3 were prepared by solid-state synthesis and characterized to determine their optical properties, thermoelectric properties and electrical impedance. Using diffuse reflectance data and assuming a direct band gap, the band gap of the material ranges from 3.58eV for y=0 to 3.74eV for y=0.2. The dc conductivity decreased with increasing Ti content and was thermally activated, ranging from ≤10−5S/cm at 300°C to 0.03S/cm at 1000°C for Ga3InSn5O16. The Seebeck coefficient was negative indicating n-type conduction. The activation energies for dc conduction and thermopower were similar, ranging from 1.4±0.1eV for y=0 to 1.8±0.2eV for y=0.2, suggesting band conduction. The thermal conductivity of Ga3InSn5O16 ranged from 1.1W/mK at 500oC to 0.75W/mK at 800°C. The highest figure of merit measured was 2×10−4 at ∼900°C, which is much lower than desired for thermoelectric materials. A comparison of dc conductivity and impedance data indicated a substantial ionic contribution for samples containing titanium.

Preparation, characterization and electromagnetic properties of polyaniline/carbon nanotubes/nickel ferrite nanocomposites

AbstractNew electromagnetic nanocomposites were prepared from polyaniline (PANI)/oxidized single‐walled carbon nanotubes (OxSWCNTs)/NiFe2O4 by in situ polymerization of aniline using hexanoic acid as a soft template. OxSWCNT and NiFe2O4 were prepared first so as to be used in the formulation of PANI composites. Transmission electron microscope (TEM) results revealed the formation of PANI nanoparticles of 60 nm diameter, OxSWCNT of 24 nm, and NiFe2O4 of 54 nm. Also, TEM image of the ternary composite indicated agglomerative coating of PANI appearing as a gray shells and black core of NiFe2O4 with widening the diameter of OxSWCNT to be around 66 nm. Dc conductivity was measured as a function of temperature. Magnetic susceptibility was measured as a function of temperature and magnetic field intensity. All samples revealed NiFe2O4‐dependent ferromagnetism. The activation energies for dc conductivity suggest that the conductivity is owing to hopping conduction mechanism. A synergistic effect between NiFe2O4 and PANI/OxSWCNT is observed. POLYM. COMPOS.,, 2012. © 2012 Society of Plastics Engineers

Electrical Behavior of CeP2O7 Electrolyte for the Application in Low-Temperature Proton-Conducting Ceramic Electrolyte Fuel Cells

The proton conducting electrolyte cerium pyrophosphate was synthesized by digesting cerium oxide with 85% H3PO4. The crystal structure and phase stability of the material were analyzed by X-ray diffraction and thermogravimetric analysis/differential thermal analysis (TGA/DTA), and the microstructure was analyzed by scanning electron microscopy (SEM). The electric conductivity behavior of CeP2O7 sintered pellets was analyzed by electrochemical impedance spectroscopy (EIS) and modulus spectroscopy. The activation energies for migration (Eω) and dc conduction (Eσ) calculations indicates that the charge carriers responsible for conductivity and relaxation are same and the concentration of charge carries is independent of temperature. The variation of conductivity with temperature was studied in dry and humid atmosphere for the possible application as electrolyte in proton conducting ceramic electrolyte fuel cells (PCFCs) in the temperature range of 100–220°C, which showed that the conductivity of CeP2O7 was mainly due to the incorporation of water and the maximum conductivity was found to be 2.1 × 10−4 S cm−1 at 175°C and PH2O = 0.06 atm. The presence of water in CeP2O7 matrix increases the number of jump sites and facilitates the hopping of protons, leading to an increase in the conductivity.

Influence of SiO 2 on dispersive conductivity and absorption edge of calcium bismuthate glasses

The dynamics of Ca 2+ ions and the optical properties of calcium bismuth silicate glasses were investigated using relaxation spectroscopy and optical absorption spectra. These glasses were prepared by normal melt quench technique. Density, molar volume and glass transition temperature (T g) have been measured. A large difference in the values of T g and crystalline temperature (T C) suggests the thermal stability of these glasses. The ac and dc conductivities, activation energy for dc conduction (E dc) and for relaxation frequency (E τ) were extracted from the impedance spectra. The compositional variation in conductivity has been attributed to the presence of mixed glass former effect in these glasses. Both electric modulus and the conductivity formalism have been employed to study the relaxation dynamics of charge carriers in these glasses. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the dynamic processes for ions in these glasses are temperature independent. Similar values of E dc and E τ indicate that the ions have to overcome the energy barrier of same height in their conduction as well as relaxation. The observed conductivity spectra follows power law with exponent ‘s’ which increases regularly with frequency and approaches unity at higher frequencies. It has been observed that the position of the absorption edge and cutoff wavelength shift towards blue as Bi 2O 3/SiO 2 ratio decreases. The compositional variation in optical band gap (E g) has been attributed to the influence of the CaO and SiO 2 on conduction band. The values of Urbach energy confirm the existence of phonon-assisted indirect transitions in the present glass system. The average electronic polarizability of oxide ion (α O 2−) and the optical basicity (Λ th) have been estimated from the calculated values of the optical band gap and were found to be dependent directly on Bi 2O 3/SiO 2 ratio.

Physical and electrical properties of combustion synthesized NASICON type Na 3Cr 2(PO 4) 3 crystallites: Effect of glycine molar ratios

Thermally stable Na 3Cr 2(PO 4) 3 nano-crystallites are synthesized through novel solution combustion technique using glycine fuel in three molar ratios. Effects of fuel molar ratio on structural and electrical properties are investigated. Reaction parameters like fuel molar ratio, flame temperature and number of moles of gases evolved, play a major role in deciding physical and electrical properties. Out of the synthesized samples, one which contains fuel in 1:1 molar ratio shows highest grain conductivity of 2.35 × 10 −6 S cm −1. Improved conductivity is elucidated by least size and highest density of the crystallites, which in turn is decided by the flame temperature. Ac electrical properties are investigated using complex impedance spectroscopy. Activation energies for dc conduction and relaxation are determined and the results are reported.

Microstructures and electrical responses of pure and chromium-doped CaCu 3Ti 4O 12 ceramics

Pure and chromium-doped CCTO (CaCu 3Ti 4O 12) ceramics were prepared by a conventional solid-state reaction method, and the effects of chromium doping on the microstructures and electrical properties of these ceramics were investigated. Efficient crystalline phase formation accompanied by dopant-induced lattice constant expansion was confirmed through X-ray diffraction studies. Scanning electron microscopy (SEM) results show that doping effectively enhanced grain growth or densification, which should increase the complex permittivity. The dielectric constant reached a value as high as 20,000 (at 1 kHz) at a chromium-doping concentration of 3%. The electrical relaxation and dc conductivity of the pure and chromium-doped CCTO ceramics were measured in the 300–500 K temperature range, and the electrical data were analyzed in the framework of the dielectric as well as the electric modulus formalisms. The obtained activation energy associated with the electrical relaxation, determined from the electric modulus spectra, was 0.50–0.60 eV, which was very close to the value of the activation energy for dc conductivity (0.50 ± 0.05 eV). These results suggest that the movement of oxygen vacancies at the grain boundaries is responsible for both the conduction and relaxation processes. The short-range hopping of oxygen vacancies as “polarons” is similar to the reorientation of the dipole and leads to dielectric relaxation. The proposed explanation of the electric properties of pure and chromium-doped CCTO ceramics is supported by the data from the impedance spectrum.

Characterization of chitosan/PVA blended electrolyte doped with NH 4I

The (chitosan–PVA)–NH 4I electrolytes have been prepared by the solution casting method. The prepared electrolytes are analyzed using Fourier transform infrared (FTIR) spectroscopy in order to determine the interaction between salt and the polymer blend hosts which can be deduced from the band shifting. From infrared spectra, shifts are observed at the amine, carboxamide, carbonyl and hydroxyl bands of chitosan and PVA. These shifts indicate that complexation has occurred. The crystallinity/amorphousness of the blended electrolytes has been examined by X-ray diffraction (XRD). XRD pattern shows that the crystallinity of chitosan–NH 4I electrolyte increases with PVA concentration. Impedance of the electrolytes has been measured using electrochemical impedance spectroscopy (EIS) over the frequency range from 50 Hz to 1 MHz. The highest conducting sample 55 wt.% (chitosan–PVA)–45 wt.% NH 4I has conductivity of 1.77 × 10 − 6 S cm − 1 . The chitosan:PVA ratio is 1:1. This is higher than the conductivity for the unblended electrolyte 55 wt.% chitosan–45 wt.% NH 4I which is 3.73 × 10 − 7 S cm − 1 . From ln τ versus 10 3/ T plot, the activation energy for relaxation process is 0.87 eV. This is different from activation energy for dc conductivity which is 0.38 eV. Ion conduction is by hopping.

Dielectric relaxation, conductivity behaviour and magnetic properties of Mg substituted Ni–Li ferrites

The dielectric properties of Mg substituted Ni–Li spinel ferrites synthesized by sol–gel auto combustion process have been studied using impedance measurements in the frequency range from 10 Hz to 10 MHz and in the temperature range from 310 K to 473 K. The effect of frequency, temperature and composition on dielectric constant ( ɛ′), dielectric loss (tan δ) and conductivity ( σ) has been discussed in terms of hopping of charge carriers between Fe 2+ and Fe 3+ ions. The electrical modulus formulism has been employed to study the relaxation dynamics of charge carriers and the results indicate the presence of non-Debye type of relaxation in the present ferrites. Similar values of activation energies for dc conduction ( E dc) and for conductivity relaxation ( E M″) reveal that the mechanisms of electrical conduction and dielectric polarization are same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of dynamical process for charge carriers. The saturation magnetization and coercivity have been calculated from the hysteresis loop measurements and show striking dependence on the composition.

Effect of Sb Substitution on the Structural and Electrical Properties of Bi4Ti3−2xNbxTaxO12 Ceramics

Bi4Ti3−2xNbxTax−ySbyO12 (BTNTS) ceramics were investigated as a potential candidate of lead-free piezoelectric ceramics. X-ray diffraction results indicated that all samples have monoclinic structure. Scanning electron microscopic studies revealed that the addition of Sb2O3 did not cause a suppressed grain growth for their morphological behavior. The Bi4Ti2.98Nb0.01Ta0.002Sb0.008O12 (8BTNTS) ceramics possess a dielectric constant of 1328 at 100 kHz, a piezoelectric constant (d33) of 35 pC/N and Curie temperature (Tc) of 664°C. The electrical properties of the investigated compositions exhibited a significant dependence on the content of Sb2O3 addition. The electrical conductivity for 8BTNTS ceramics was lower than that of other investigated compositions. Dielectric and electrical transport properties have been carried out over a wide range of frequency and temperature in order to explore the conduction mechanism in the investigated samples. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.0±0.03 eV, close to that of the activation energy for DC conductivity (1.08±0.02 eV). It suggests that the movements of oxygen ions are responsible for both the ionic conduction as well as relaxation process.

Characterization of zinc telluride thin films deposited by two-source technique and post-annealed in nitrogen ambient

ZnTe thin films were deposited by the two-source evaporation technique on amorphous glass substrate. The deposited films were annealed under nitrogen ambient pressure. The resistivity of the film annealed under nitrogen pressure of 100 mbar was found to be less than that of as-deposited film by more than four orders of magnitude. The films structures were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The films' thickness and the optical properties such as refractive index, absorption coefficient and optical band gap of the films were determined from transmittance spectra in the wavelength range of 400–2000 nm. The dark electrical conductivity of the films was studied as a function of temperature to determine the DC conductivity activation energy of the films.

Electrical, optical, and mechanical properties of amorphous hydrogenated carbon obtained under various deposition conditions

Activation energy of dc conductivity, refractive index, and microhardness of amorphous hydrogenated carbon films a-C:H have been studied. The films are produced from a methane-argon mixture under various deposition conditions on quartz and silicon substrates: E/p = 40–180 V/mPa (E is the electric-field strength in the space between the electrodes, and p is the gas mixture pressure in the chamber) and substrate temperature Ts = 50–300°C. In these deposition conditions, diamond-like, polymer-like, and graphite-like a-C:H films can be obtained with widely varying activation energy of conductivity, microhardness, and refractive index.

Dielectric relaxation, conductivity behavior and magnetic properties of Mg substituted Zn–Li ferrites

Spinel ferrites having compositions Zn 0.5Li 1−2 x Mg x Fe 2O 4 (0 ≤ x ≤ 0.5) have been prepared by sol-gel auto combustion technique. The dielectric properties of these ferrites have been studied using impedance measurements in the frequency range 10 Hz–10 MHz and in the temperature range 310–473 K. The effect of temperature, frequency and composition on dielectric constant (ε′), dielectric loss (tanδ) and conductivity ( σ) have been discussed in terms of hopping of charge carriers (Fe 2+↔Fe 3+). The occurrence of peak in the dielectric loss (tanδ) spectra is found to be temperature and composition dependent. The electrical modulus formulism has also been employed to study the relaxation dynamics of charge carriers and the results indicate the presence of non-Debye type of relaxation in these ferrites. Identical values of activation energy for dc conduction ( E dc) and for conductivity relaxation ( E M″) reveal that the charge carriers have to overcome the same energy barrier while conducting and relaxing. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of dynamical process for charge carriers in the present ferrites. The absence of hysteresis and non-attainment of saturation magnetization (even at 8 kOe) suggests the super paramagnetic behaviour of these ferrites.

Ion dynamics in combustion synthesized Na 3Cr 2(PO 4) 3 crystallites

Phase pure Na 3Cr 2(PO 4) 3 crystallites of 41 nm are synthesized by novel solution combustion technique. Characterization methods like X-ray diffraction, Fourier transform infrared spectroscopy, UV–vis spectroscopy, Thermo gravimetric, differential thermal analysis and scanning electron microscopy with energy dispersive X-ray analysis are utilized to validate the structure and phase purity. These crystallites are stable in room temperature rhombohedral phase of R 3 ¯ c symmetry. Fascination of the material is because of its structural stability and high conductivity. Due to its structural stability, present study depicts the ion dynamics in the crystal lattice by analyzing the conductivity relaxation process. Interpretations from impedance representation fortify these conclusions and the dc conductivity activation energy is found to be 0.70 ± 0.02 eV. Almost same value of activation energy for conductivity relaxation from modulus and conductivity representations show that while conducting and relaxing, ion has to overcome the same energy barrier. The conductivity and modulus isotherms are shown to be collapsed to a master curve upon appropriate scaling of the axes; indicating the temperature independent relaxation mechanism. It is evident that the scaling of conductivity and modulus spectra provides the same information on ion dynamics of this material.

On the origin of electrical relaxation in tellurite glasses

The dielectric properties of ternary silver vanadium tellurite and titanium vanadium tellurite glasses of the form [0.5[xAg2O-(1−x)V2O5]–0.5TeO2, x=0.1–0.8mol] and [0.5[xTiO2-(1−x)V2O5]–0.5TeO2, x=0.1–0.6mol] are investigated as a function of frequency (10Hz–1MHz) and temperature (70–425K). Electrical relaxation is analyzed in terms of dielectric modulus and Kohlrausch–Williams–Watts (KWW) stretched exponential distribution function. The composition dependence of the stretched exponential parameter (β) is explained according to the variation of activation energy for dc conductivity and inter-charge separation in the two glass series. From the transition of polaronic to ionic conduction in silver vanadium tellurite glass series, it is established that ion–ion correlations are more effective in slowing down the electrical relaxation than the interactions between electronic charge carriers.

Effect of CaO on the conductivity and dielectric properties of novel Fe 2O 3·CaO·Bi 2O 3 glasses

Iron calcium bismuthate glasses having composition 0.05Fe 2O 3·0.95{ xCaO·(100− x)Bi 2O 3} ( x=30, 35 and 40 mol%) were prepared using normal melt quench technique. Complex impedance spectra of these glasses have been recorded in the temperature range 523–633 K and in the frequency range 20 Hz–1 MHz. The complex impedance data have been analyzed using the conductivity as well as electric modulus formalisms. The dc conductivity increases and activation energy decreases when CaO content increases. The modification of the glass network, due to the increase in CaO content, is responsible for the increase in conductivity. The frequency dependence of ac conductivity is found to obey the Jonscher power law. At low frequencies, dispersion was investigated in terms of dielectric loss. Significant changes in the values of the non exponential parameter ( β) and the power law exponent ( s) of the ac electrical properties have been observed as a function of CaO in the present glasses. A single ‘master curve’ for the normalized plots of all the modulus isotherms observed for a given composition indicates that the conductivity relaxation is temperature independent. The overlapping of the normalized peaks corresponding to impedance ( Z″) and electric modulus ( M″) suggests the same thermal activation energy for conduction and relaxation, which further suggests a single mechanism for the dynamic processes in the present glasses.