The effect of non-bridging oxygen on the electrical transport of some lead borate glasses containing cobalt

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Fatma B. M. Ahmed ◽  
Ali Badawi ◽  
Fouad Abdel-Wahab
Keyword(s):  
Electrical Transport ◽  
Ac Conductivity ◽  
Gradual Increase ◽  
Glass Network ◽  
Chloride Ions ◽  
Dc Conductivity ◽  
Oxidation States ◽  
Frequency Exponent ◽  
Cobalt Ions ◽  
Oxygen Ions

Abstract The effect of reducing oxygen in glass network on the electrical conductivity of system 50 B2O3 − 20 Pb3O4 − 10 Co3O4 − (20 − x)CaO − xCaCl2 (0 ≤ x ≤ 20 mol%) has thoroughly been investigated. This reduction was created by substituting oxygen ions with chloride ions. The measurements were conducted in the temperature range 320–560 K for fixed frequencies 0.1, 1, 10 and 100 kHz. It was found that at low temperatures, the dc conductivity (σ dc) is lower than the measured ac conductivity σ(ω), whereas σ(ω) and σ dc became equal at high temperature for all frequencies. The ac, dc conductivity as well as dc activation energies decrease with the gradual increase of CaCl2 content. The ac conductivity and the frequency exponent data showed that the correlated barrier hopping of electrons between both of oxidation states of cobalt ions (Co2+ and Co3+) is the most probable mechanism. The dielectric constant and the dielectric loss of the present glass system can be fitted to the Cole–Cole equation for all frequencies and temperatures.

AC CONDUCTION PHENOMENON OF Li2O–WO3–B2O3 GLASSES DOPED WITH V2O5

2013 ◽  
Vol 06 (03) ◽  
pp. 1350032 ◽  
Author(s):  
LINGANABOINA SRINIVASA RAO ◽  
NALLURI VEERAIAH ◽  
TUMU VENKATAPPA RAO
Keyword(s):  
High Temperatures ◽  
Ac Conductivity ◽  
Conduction Mechanism ◽  
Glass Composition ◽  
Melt Quenching ◽  
Frequency Exponent ◽  
Spreading Factor ◽  
Cbh Model ◽  
Tan Δ ◽  
Ac Conduction

The glass composition 40 Li 2 O –5 WO 3–(55−x) B 2 O 3: x V 2 O 5 for x = 0.2, 0.4, 0.6 and 0.8 is chosen for the present study. The glass samples were synthesized by conventional melt-quenching technique. The dielectric properties such as constant (ε′), loss (tan δ) and ac conductivity (σac) are carried out as a function of temperature (30–270°C) and frequency (102–105 Hz). The glass sample (at x = 0.6) exhibited highest ac conductivity (σac) and spreading factor (β) among all the samples. All glasses exhibited mixed conduction (both electronic and ionic) at high temperatures. The frequency exponent s denotes the ac conduction mechanism is associated with both QMT model (at low temperatures) and CBH model (at high temperatures).

Electrical and Dielectric Spectroscopic Characterization of Polycrystalline Dy2Si2O7

2012 ◽  
Vol 510-511 ◽  
pp. 194-200 ◽  
Author(s):  
Shahid Ameer ◽  
Asghari Maqsood
Keyword(s):  
High Temperature ◽  
Electrical Transport ◽  
Ac Conductivity ◽  
Orthorhombic Phase ◽  
Theoretical Models ◽  
Spectroscopic Characterization ◽  
Dielectric Parameters ◽  
Triclinic Phase ◽  
Electrical Conductivities ◽  
Phase Type

The compound Dy2Si2O7exists in two polymorphs, the low temperature triclinic phase (type B) and a high temperature orthorhombic phase (type E).The dc and ac electrical conductivities of E-Dy2Si2O7are measured in the temperature range 290-510 K and frequency range 1 kHz to 1 MHz . The dc electrical transport data are analyzed according to Motts variable-range hopping model. The disorder parameter (To) and density of states at fermi level are obtained. The ac conductivity σac(ω) is obtained through the dielectric parameters. The ac conductivity can be expressed as σac(ω) =B ωs, where s is slope and it decreases with increase in temperature. The conduction mechanism in the compound is discussed in low and high temperature regions in the light of theoretical models.

Dielectric and ac Conductivity Studies on Nanocrystalline Mn Modified Cobalt Ferrite

2018 ◽  
Vol 24 (8) ◽  
pp. 5629-5632 ◽  
Author(s):  
Sweety Supriya ◽  
Sunil Kumar ◽  
Manoranjan Kar
Keyword(s):  
Dielectric Constant ◽  
Frequency Response ◽  
Electrical Transport ◽  
Ac Conductivity ◽  
Cobalt Ferrite ◽  
Electrical Transport Properties ◽  
Arrhenius Behavior ◽  
Temperature Dependent ◽  
Two Layer Model ◽  
Frequency Temperature

The ac conductivity and dielectric properties on CoFe2−xMnxO4 for x = 0.00, 0.10, 0.15 and 0.20 have been studied in detail. All the samples were prepared in nanocrystalline size. These materials are found to be crystallized to Fd <mml:math display="block"> <mml:semantics> <mml:mover accent="true"> <mml:mi>3</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:semantics> </mml:math> m space group in cubic spinel structure. The dielectric constant and ac conductivity has been discussed as a function of frequency, temperature and composition. The relation between dielectric constant and ac conductivity has been analyzed and the results validate each other. The frequency response of ac conductivity (σac) obeys Johnschers power law and the parameters obtained, explain the sources of ac and dc electrical conductivity in the material. The frequency response of σac follows Maxwell–Wagner two-layer model. The influence of frequency as pumping force on activation energy has been determined. The temperature dependent ac conductivity shows the Arrhenius behavior. The σac observed to be enhanced with increase in frequency as well as temperature. The semiconducting behavior (NTCR) was also evident from temperature dependent electrical transport properties study. The low value of ac conductivity suggests a possible use of this material in dielectric applications.

AC conductivity and dielectric relaxation of Se80−xTe20Bix (x=6, 12) glasses

2019 ◽  
Vol 60 (6) ◽  
pp. 222-230
Author(s):  
Deepika Deepika ◽  
Hukum Singh
Keyword(s):  
Dielectric Relaxation ◽  
Ac Conductivity ◽  
Lower Energy ◽  
Dielectric Relaxation Time ◽  
Frequency Exponent ◽  
Dielectric Parameters ◽  
Cbh Model ◽  
Increase With Increase ◽  
Different Temperatures ◽  
Frequency Temperature

The present paper reports the ac conductivity and dielectric relaxation of Se80−xTe20Bix (x=6, 12) glasses at various temperatures and frequencies. It was found that ac conductivity increases on increase of frequency, temperature as well as Bi content. The increase in conductivity is due to the formation of lower energy Se–Bi and Te–Bi bonds which takes the system to a stable lower energy configuration. The values of frequency exponent (s) were calculated and it was found that samples obey CBH model of conduction. Density of states (N(Ef)) near the fermi level were calculated at different temperatures and it was found that addition of Bi increases the number of localised states in the tails which leads to increase in ac conductivity. Further, it was found that dielectric parameters increase with increase in temperature. However, a decrease in both dielectric constant (ε′) and dielectric loss ((ε″) was observed with increase in frequency. Beside this, dielectric relaxation time (τ) and activation energy of relaxation (∆Eτ) were also determined for both the samples under study and was found to be lower for Se68Te20Bi12 glass.

Transport properties of impurity-doped VO2

1976 ◽  
Vol 54 (4) ◽  
pp. 413-423 ◽  
Author(s):  
J. M. Reyes ◽  
M. Sayer ◽  
A. Mansingh ◽  
R. Chen
Keyword(s):  
Density Of States ◽  
Ac Conductivity ◽  
Energy Gap ◽  
Dc Conductivity ◽  
Total Conductivity ◽  
Total Density ◽  
Impurity Doped ◽  
Impurity Sites ◽  
Total Density Of States ◽  
Band Conduction

The temperature dependence of the DC conductivity in the semiconducting phase of undoped and Al, Cr, and Ti-doped VO2 has been interpreted with the aid of AC conductivity and thermopower measurements down to 77 K. A hopping conductivity is shown to be dominant for T < 180 K and to make up about 10% of the total conductivity at the metal–semiconductor transition temperature. The frequency dependence of the AC conductivity, σ~fs, is shown to be sensitive to crystalline disorder through the parameter s; s ~0.5 for 'good' crystals and 0.7–0.9 for highly doped or nonstoichiometric material. For the best crystals, a phonon drag contribution is found to exist in the thermopower. The hopping component of the DC conductivity is analyzed in terms of variable range hopping within a nonuniform density of states. For a total density of states between 1018–1020 this leads to a localization radius of 3–11 Å and the conclusion that the position of the Fermi level within the gap strongly influences the relative contributions of hopping and band conduction. A model for the density of states within the energy gap for both pure and doped VO2 is presented on the basis of localized correlations between electrons on pairs of vanadium or vanadium–impurity sites.

IMPEDANCE MEASUREMENTS ON PZT ANDLa0.75Bi3.25Ti3O12CERAMICS

2009 ◽  
Vol 23 (19) ◽  
pp. 3881-3893 ◽  
Author(s):  
N. V. PRASAD ◽  
J. SUBRAHMANYAM ◽  
P. NARAYANA MURTY ◽  
S. KARMAKAR ◽  
S. M. GUPTA
Keyword(s):  
Temperature Coefficient ◽  
Ac Conductivity ◽  
Figure Of Merit ◽  
Room Temperature ◽  
Spectroscopic Analysis ◽  
Dc Conductivity ◽  
Ferroelectric Ceramics ◽  
Frequency Range ◽  
Impedance Measurements ◽  
Different Temperatures

Impedance measurements were made on technological important ferroelectric ceramics, namely PZT and La0.75Bi3.25Ti3O12(BLT), in the frequency range of 100 Hz to 1 MHz, from room temperature to 500°C. Combined impedance and modulus spectroscopic analysis along with the detailed conductivity (ac and dc) data was used to understand the heterogeneity of the ceramics and the results were corroborated with temperature coefficient of dc-conductivity (figure of merit) data for the further understanding. AC-conductivity plots against frequency at different temperatures for PZT and BLT suggest the response of obeying Jonscher's and modified Jonscher's law, respectively.

scholarly journals The Electrochemical Reduction Mechanism of ZnFe2O4 in NaCl-CaCl2 Melts

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 925
Author(s):  
Chang Liu ◽  
Jinglong Liang ◽  
Hui Li ◽  
Hongyan Yan ◽  
Sijia Zheng ◽  
...  
Keyword(s):  
Electrochemical Reduction ◽  
Thermodynamic Analysis ◽  
Irreversible Process ◽  
Gradual Increase ◽  
Reduction Process ◽  
Reduction Mechanism ◽  
Reversible Process ◽  
Electrochemical Tests ◽  
Oxygen Ions ◽  
One Step

The electrochemical reduction process of ZnFe2O4 in NaCl-CaCl2 melts was studied. Thermodynamic analysis shows that the reduction process of ZnFe2O4 is carried out in multiple steps, and it is difficult to reduce Fe3+ to Fe in one step. Electrochemical tests revealed that the reduction process of ZnFe2O4 includes three steps: First, Fe3+ is reduced to Fe in two steps, then Zn2+ is reduced to Zn in one step. The reduction of Fe3+ on the Mo electrode is a reversible process controlled by diffusion, while the reduction of Zn2+ is an irreversible process controlled by diffusion. The influence of electrolysis voltage and temperature on the process of electric deoxidation has also been studied. It is indicated that properly increasing the temperature is conducive to the diffusion of oxygen ions, thereby increasing the deoxidation rate. With the gradual increase of voltage, the reduction process of ZnFe2O4 is ZnFe2O4 → FeO + ZnO → Fe + ZnO → Fe + Zn.

Theoretical and experimental studies on DC conductivity and temperature-dependent AC conductivity of poly(butyl methacrylate)/Nd-TiO2 nanocomposites

2019 ◽  
Vol 33 (8) ◽  
pp. 1061-1077 ◽  
Author(s):  
K Suhailath ◽  
MT Ramesan
Keyword(s):  
Ac Conductivity ◽  
Volume Fraction ◽  
Experimental Studies ◽  
Dc Conductivity ◽  
Butyl Methacrylate ◽  
Temperature Dependent ◽  
Exponential Factor ◽  
Structural Regularity ◽  
Uniform Dispersion ◽  
Xrd Patterns

Electrically conductive nanocomposite system based on poly(butyl methacrylate) (PBMA) with different contents of neodymium-doped titanium dioxide (Nd-TiO2) was prepared by in situ free radical polymerization method. The effect of Nd-TiO2 on the morphology and structural properties of the composites was carried out by scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). The temperature-dependent AC conductivity and DC electrical conductivity of PBMA/Nd-TiO2 nanocomposites were studied with respect to the different volume fraction of Nd-TiO2 nanoparticles. SEM and XRD patterns revealed the uniform dispersion and structural regularity of nanoparticles in the polymer matrix. The AC conductivity of PBMA and its composites were found to be increased with an increase in temperatures and frequencies. The activation energy and exponential factor were analyzed from AC conductivity and both results indicate the hopping conduction mechanism present in PBMA/Nd-TiO2 nanocomposite, which is responsible for the variation of conductivity with temperature also. The DC conductivity of nanocomposites was higher than pure PBMA and the conductivity increases with increase in the concentration of Nd-TiO2 nanoparticles. Experimental and theoretical investigations based on McCullough, Bueche, Scarisbrick, and Mamunya modeling were carried out to observe the DC conductivity differences induced by the addition of Nd-TiO2 nanoparticles in PBMA matrix. Among the various modeling studied here, Mamunya model shows better agreement with the experimental conductivity.

Alternating current conductivity of the interfacial phase in copper oxide–silica gel nanocomposites

2001 ◽  
Vol 16 (4) ◽  
pp. 1047-1051 ◽  
Author(s):  
D. Das ◽  
D. Chakravorty
Keyword(s):  
Ac Conductivity ◽  
Alternating Current ◽  
Angular Frequency ◽  
Conductivity Measurements ◽  
Frequency Exponent ◽  
Oxidation Treatment ◽  
Copper Particles ◽  
Effective Barrier ◽  
Interfacial Phase ◽  
Tunneling Mechanism

A nanocomposite structure was induced in gel of composition 60CuO · 40SiO2 (mol%) by first of all precipitating nano-sized copper particles by a reduction treatment and subsequently subjecting these to a controlled oxidation treatment. The particle size was of the order of 6.8 nm. Alternating current (ac) conductivity measurements were carried out on different specimens in the temperature range 300 to 630 K covering a frequency spectrum 0.1 kHz to 2 MHz. The ac conductivity was found to have a variation with frequency given by ωs, ω being the angular frequency and s the frequency exponent. The analysis of the variation of s as a function of temperature led to the conclusion that an overlapping large polaron tunneling mechanism was operative in this system. The effective barrier height for polaron transfer for infinite intersite separation was found to be almost twice in the case of the precursor gel as compared to that for the composite with the interfacial amorphous phase.

ELECTRICAL PROPERTIES OF RARE EARTH SUBSTITUTED Bi6Fe2Ti3O18 COMPOUND

2002 ◽  
Vol 16 (16) ◽  
pp. 2231-2246 ◽  
Author(s):  
N. V. PRASAD ◽  
G. PRASAD ◽  
G. S. KUMAR
Keyword(s):  
Rare Earth ◽  
Electrical Properties ◽  
Ac Conductivity ◽  
Dc Conductivity ◽  
Polycrystalline Materials ◽  
Conductivity Measurements ◽  
Conductivity Data ◽  
Ac Conductivity Measurements ◽  
Lower Temperature

The Ac conductivity measurements of polycrystalline materials of rare earth substituted Bi 6 Fe 2 Ti 3O18 compound at different frequencies (1 kHz–1 MHz) and temperatures (30–550°C) are reported. The dc conductivity, ionic hoping rate as well as carrier densities have been extracted from the ac conductivity data. The results show that hoping mechanism dominates at lower temperature. The results are discussed.

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