AC Conduction Mechanism Research Articles

Electrical conduction and dielectric properties of Bi2O3–B2O3–TeO2 glass

Amorphous bulk bismuth boron tellurium glass system of compositions (Bi2O3) x (B2O3)0.5−x (TeO2)0.5 with x = 0.05, 0.1, 0.2, 0.3 and 0.4 is prepared using melt quenching method. The ac and dc conductivities (σ ac and σ dc) of as-prepared samples are measured in the temperature range 303–373 K and displayed dielectric dispersion in the frequency range 100 Hz–5 MHz. The ac conductivity versus frequency plots were analyzed by considering a power law: σ ac α ω s(s ≤ 1). A comparison between values of the index s with those numerically calculated from different conduction models revealed that correlated barrier hopping is a fairly good model to describe the dominant ac conduction mechanism in the studied compositions. Besides, results of the real dielectric constant (e′), loss factor (e″), and loss tangent (tan δ) together with the optical (e ∞) and static (e s) dielectric constants, estimated from Cole–Cole diagrams, for the studied samples are given and discussed. Temperature dependence of the frequency exponent s for the studied amorphous bulk samples obtained from slopes of the relation ln σ ac = f(T). The solid curves represent the values calculated using the models: QMT, NSPT, and OLPT. The dashed curve represents the CBH model, which gives a fairly good fit with the experimental results (symbols) .

AC conduction mechanism and battery discharge characteristics of (PVC/PEO) polyblend films complexed with potassium chloride

New K+ ion-conducting polymer blend electrolyte films based on amorphous polymer poly(vinyl chloride) (PVC) and semicrystalline polymer poly(ethylene oxide) (PEO) complexed with KCl salt were prepared using a solution-cast technique. The maximum value of ionic conductivity of a PVC/PEO:KCl (42.5:42.5:15) system is 8.29×10−6S/cm at 303K. The absorption edge was found at 4.30eV for undoped film, while it was observed at 4.03 and 3.93eV for 10 and 15wt% KCl doped films, respectively. The direct band gaps for these pure and salt doped PVC/PEO films were found to 4.10, 3.86 and 3.74eV, respectively, whereas the indirect band gaps were determined as 4.15, 3.72 and 3.64eV. Transference number values showed that the charge transport in this electrolyte system is predominantly due to ions (tion=0.97). The discharge capacity for PVC/PEO:KCl (42.5:42.5:15) polymer blend electrolyte system is 11μA/h.

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

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).

Conduction Mechanism by Using CBH Model in Fe3+ and Mn3+ Ion Modified Pb(Zr0.65−xAxTi0.35)O3 (A = Mn3+/Fe3+) Ceramics

Polycrystalline samples of manganese and iron substituted lead zirconium titanate (PZT) with general formula Pb(Zr0.65−xAxTi0.35)O3 (A = Mn3+ and Fe3+) ceramics have been synthesized by high temperature solid state reaction technique. X-ray diffraction (XRD) patterns were recorded at room temperature to study the crystal structure. All the patterns could be refined by employing the Rietveld method to R3c space group with rhombohedral symmetry. Microstructural properties of the materials were analyzed by scanning electron microscope (SEM), and compositional analysis was carried out by energy dispersive spectrum (EDS) measurements. All the materials exhibit ferroelectric to paraelectric transition. The variation of dielectric constant and loss tangent with temperature and frequency is investigated. The decrease of activation energy and increases of AC conductivity with the Fe3+ or Mn3+ ion concentration have been observed. The AC conductivity has been analyzed by the power law. The frequency exponent with the function of temperature has been analyzed by assuming that the AC conduction mechanism is the correlated barrier hopping (CBH) model. The conduction in the present sample is found to be of bipolaron type for Mn3+ ion-doped sample. However, the conduction mechanism could not be explained by CBH model for Fe3+ ion-doped sample.

Thermistor behaviour and electric conduction analysis of Ni-doped niobate ferroelectric: the role of multiple β parameters

A new engineered non-stoichiometric niobate ceramic with a tetragonal tungsten bronze (TTB)-type structure is prepared by non-isovalent substitution at the niobium backbone. The compound's formula is KSr2(Ni0.75Nb4.25)O15−δ, with space group equal to P4bm (#100), a polar group. Electrical properties of this new ferroelectric-semiconductor ceramic are investigated by impedance spectroscopy in the temperature range from 453 up to 953 K. The curve of the resistance as a function of temperature presents further characteristics of a temperature sensor with a negative temperature coefficient (NTC). At high temperatures, the analysis of electrical parameters shows an NTC behaviour ceramic with three distinct thermistor characteristic parameters, β. The values of the β parameter change from 9.82 × 103 to 1.29 × 104 K, while the temperature coefficient of resistance α changes from −0.047 to −0.023 K−1. The NTC behaviour of KSr2(Ni0.75Nb4.25)O15−δ is compared with the behaviour of some dielectric and other ferroelectric semiconductors. β dependence with dc or the ac conductivity mechanism and its correlation with β quality are discussed.

Structural and transport properties of nanocrystalline MnFe2O4 synthesized by co-precipitation method

Nanocrystalline MnFe2O4 has been synthesized by co-precipitation methods. X-ray diffraction studies were carried out for the determination of phase purity, crystal structure and average crystallite size. X-ray Absorption Fine Structure spectroscopy has been used to determine the valence state and cationic distribution; these results show that nanocrystalline MnFe2O4 has cubic symmetry with 80% inversion. The electrical transport properties were investigated by employing impedance spectroscopy; it has been observed that the dielectric constant decreases with the increase in frequency, the effects of frequency on dielectrical properties are more prominent in the low frequency region, where dielectric constant increases as temperature is increased. However, the ac conductivity is independent of frequency in the low frequency region, <100 Hz, but increases with frequency above 500 Hz. For ac conduction mechanism two models have been presented: in the lower temperature region (233 K–278 K) the small polaron (SP) model has been suggested, whereas for higher temperature regions (above 278 K) the correlated barrier hopping (CBH) mechanism has been proposed.

Mechanism of ac and dc conduction in chalcogenide glasses

We have investigated the dc and ac conduc- tivities of Se75Te20Sn5 glass from 80 to 290 K in the frequency range 40 to 10 6 Hz. The behavior of the ac conductivity with temperature, T, is similar to that observed in many chalcogenide glasses. In this frequency range the ac conductivity r(x) is proportional to x s . The frequency exponent shows a T dependence. The experi- mental data have been analyzed using the modified bi- polaron correlated barrier hopping model, which assumes that the relaxation time should contain a Meyer-Neldel rule term. It is observed that this model is consistent with temperature dependent dc conductivity, rdc, ac conductiv- ity, rac, and s, for activation energies above 0.1 eV. At high frequency, that is, low activation energy, the behavior changes. We suggest that in this regime, the carriers may tunnel rather than hopping. We also present a correlation between the residual ac prefactor r00(x) and the Meyer- Neldel temperature (TMN), similar to that previously reported for dc conductivity. This similarity points strongly to the dc and ac conduction mechanisms being the same.

Electrical and NO2 sensing properties of liquid crystalline phthalocyanine thin films

Abstract In this study, the electrical and nitrogen dioxide (NO2) sensing properties of a series liquid-crystalline octakisalkylthiophthalocyanine (C6S)8PcM [M = 2H, Ni, Cu, Zn] thin film were investigated. The thin films were coated on to the Interdigital Transducer (IDT) with gold electrodes, using jet-spray technique in an inert ambient from a solution of phthalocyanines in chloroform. The electrical properties of liquid-crystalline phthalocyanines were studied within wide temperature range from 293 to 423 K under the high purity nitrogen (N2) flow and in the frequency range from 500 Hz to 1 MHz for ac electrical measurements. It was observed that the I–V curves of all phthalocyanines showed a significant hysteresis at low temperature and the maximum dc conductivity obtained for (C6S)8PcZn thin film. The ac conduction mechanism of all thin films could be explained with quantum-mechanical tunneling (QMT) model. The NO2 gas sensing measurements were done in the concentration range of 1–10 ppm at the temperatures of 100 °C and 150 °C. The maximum sensor response (%) was obtained as approximately 10,000 and the response time was observed to be a few seconds for (C6S)8PcH2 thin film at 150 °C.

Dielectric Properties and AC Conductivity of Ag(Ta,Nb)O3 Ceramics

The ac conductivity and relaxation mechanism in Ag(Ta,Nb)O3 ceramics have been investigated systematically. The formation of the ceramics was checked by an X-ray diffraction (XRD) technique analysis. The dielectric permittivity and the loss tangent of the Ag(Ta,Nb)O3 specimen were measured in a frequency range from 1 to 100 kHz at the various temperature ranges (30–110°C). A study on dielectric properties reveals the electrical relaxation phenomenon occurs in the material. Studies on the frequency and temperature dependence of ac conductivity of the Ag(Ta,Nb)O3 ceramics suggest that conduction process in the material is thermally activated process. In this paper, we will discuss the dielectric properties and the ac conductivities of Ag(Ta,Nb)O3 ceramics in relation to the electrical conduction process.

Analyses of the Leakage Current Characteristics of Lead Lanthanum Titanate-Cobalt Iron Oxide Multiferroic Composite Thin Film

We have investigated the leakage current characteristics of polycrystalline lead lanthanum titanate (PLT) - cobalt iron oxide (CFO) composite multiferroic thin films. The dc conductivity is found to increase monotonically with the increase of CFO volume contents. From the measurement of both field and temperature dependence of leakage current, Schottky emission is found to be the dominant current conduction mechanism in these composite films. The frequency dependence of ac conductivity obeys Jonscher power law. Probing the temperature dependence of ac conductivity the plausible ac conduction mechanism in these films is discussed.

Change in AC conduction mechanism together with conversion of submicron to nanoparticles in polyaniline and its poly(vinyl pyrrolidone) blends on heating-induced water elimination

The present work is an investigation of AC impedance behaviors of polyaniline (PANI) and its poly(vinyl pyrrolidone) (PVP) blends. The materials were prepared by polymerization of aniline hydrochloride without/with PVP using FeCl 3 oxidant. PANI–PVP blends have greater AC conductivities than that of PANI in proportion to the amount of PVP incorporated. At lower frequencies (10 Hz – critical frequency f c) conductivity remains independent but at frequencies > f c, conductivity raises with frequency. In the entire range, however, the universal power law σ ac( ω) = Aω s holds good. In fresh condition PANI exhibits an increase in bulk resistance ( R b) and frequency exponent s up to 373 K and blends up to 423 K beyond which they show a decrease. The trend in conduction could be explained by the operation of small polaron tunneling up to 373/423 K and afterwards correlated barrier hopping (CBH) conduction mechanisms. Studied PANI, PANI–PVP blend materials and a fresh but annealed (463 K) PANI all display only a decrease in R b and s values in the entire temperature range of study and hence they follow only CBH mechanism. The fresh samples, together with change of conduction mechanism with temperature also undergo submicron to nanoparticles conversion and changes in other physico-chemical properties. All these changes have the origin on elimination of occluded water from the fresh materials on heating.

Tuning A-site ionic size in R0.5Ca0.5MnO3 (R = Pr, Nd and Sm): robust modulation in dc and ac transport behavior

Structural investigations on Pr0.5Ca0.5MnO3, Nd0.5Ca0.5MnO3 and Sm0.5Ca0.5MnO3 display a systematic tuning in orthorhombic distortion which appears due to a change in A-site ionic size. Comprehensive investigations on dc conduction using various models indicate strong correlation with structural changes. Careful analysis of the ac conductivity mechanism as a function of frequency and temperature brings out a pronounced effect of structural modifications on the polaron conduction mechanism. Contrary to typical manifestations, dc conductivity and relaxation of charge carriers reveal non-Arrhenius behavior. This work provides a detailed and systematic addition to the phase diagram of electronic transport in the rare-earth manganite system doped with a divalent alkali atom.

Acoustic studies of ac conductivity mechanisms inn-GaAs/AlxGa1−xAs in the integer and fractional quantum Hall effect regime

For the heterostructure $n$-GaAs/Al${}_{x}$Ga${}_{1\ensuremath{-}x}$As with a sheet density $n=2\ifmmode\times\else\texttimes\fi{}{10}^{11}$cm${}^{\ensuremath{-}2}$ and mobility $\ensuremath{\mu}\ensuremath{\approx}2\ifmmode\times\else\texttimes\fi{}{10}^{6}$ cm${}^{2}$/V$ $s with integer and fractional quantum Hall effects (IQHE and FQHE, respectively) we demonstrate the wide applicability of acoustic methods for determining the general conduction parameters of a two-dimensional electron gas. We also examine the mechanisms of low-temperature conductivity in the minima of oscillations of high-frequency conductivity in the IQHE and FQHE regimes. In the magnetic field region where electrons are delocalized, the parameters determined by the acoustic technique do not differ from those determined by a direct current. However, the acoustic measurements do not require Hall bars and electrical contacts to be fabricated. In the minima of IQHE and FQHE oscillations, electrons are localized, and ac conductivity occurs via hopping. An analysis of the high-frequency conductivity in the QHE regime has been carried out within a ``two-site'' model. Furthermore, measurements of acoustoelectric effects in a tilted magnetic field were used to determine how the activation energy of the $\ensuremath{\nu}=2/3$ fractional quantum Hall effect gap varies with magnetic field.

Frequency dependent electrical transport properties of 4,4′,4″-tris(N-3-methylphenyl-N-phenylamine)triphenylamine by impedance spectroscopy

The frequency dependent ac conduction mechanism in 4,4′,4″-tris(N-3-methylphenyl-N-phenylamine)triphenylamine (m-MTDATA) has been studied as a function of applied bias and temperature. The Cole–Cole plot shows a slightly depressed semicircle indicating Debye type relaxation. This result has been explained by an equivalent circuit of the device designed as a two parallel resistor and capacitance network in series with contact resistance. The ac conduction studies under dc bias for hole only devices shows an increase in device conductivity with the increase in bias. The variation of bulk resistance with applied bias indicates Space Charge Limited Conduction (SCLC) mechanism for hole conduction. The hole mobility of the material has also been evaluated from SCLC as 8.859 × 10 −6 cm 2/V s. The temperature dependent impedance studies show two activation energies indicating two different phase of the material with a phase transition at 235 K.

Electrical conduction and dielectric properties of lithium aluminum silicate glasses doped with Cr 3+ ions

Amorphous lithium aluminum silicate glass system (LAS) implanted with chromium ions are prepared. The ac and dc conductivities ( σ ac and σ dc) of as-prepared bulk samples are measured under vacuum in the temperature range 373–153 K and displayed dielectric dispersion in the frequency range 50 Hz–80 kHz. The ac conductivity versus frequency plots were analyzed by considering a power law: σ ac ∝ ω s ( s ⩽ 1 ) . A comparison between values of the index s with those numerically calculated from different conduction models reveals that correlated barrier hopping (CBH) is a fairly good model to describe the dominant ac conduction mechanism. The concept of the Meyer–Neldel (MN) rule in the expression of the relaxation time is considered for both ac and dc experimental data. The validity of the CBH model based on the MN (normal and inverted) rule is studied and discussed. Besides, results of the real dielectric constant ( ε′), loss factor ( ε″) and loss tangent (tan δ) together with the Cole–Cole diagrams and the optical ( ε ∞) and static ( ε s) dielectric constants for the studied samples are given and discussed.

Ac conductivity and relaxation mechanism in Ba 0.9Sr 0.1TiO 3

The ac conductivity and relaxation mechanism in Ba 0.9Sr 0.1TiO 3 ceramics have been investigated systematically. A high-temperature solid-state reaction technique was used to synthesize the compound. The formation of the compound was checked by an X-ray diffraction (XRD) technique. The dielectric permittivity and the loss tangent of the sample were measured in a frequency range from 1 kHz to 1 MHz at different temperatures (30–500 °C). A study on dielectric properties reveals the electrical relaxation phenomenon occurs in the material. The activation energy was calculated from the temperature variation of dc conductivity. Studies of frequency and temperature dependence of ac conductivity of the compound suggest that conduction process in the material is thermally activated.

Dielectric properties and AC conduction mechanism for 5,7-dihydroxy-6-formyl-2-methylbenzo-pyran-4-one bis-schiff base

The dielectric properties and the electrical conductivity of the tetradentate Schiff base, derived from the condensation of 5,7 dihydroxy-6- formyl-2-methylbenzo-pyran-4-one with ethylenediamine has been studied in the temperature range 300 K< T<420 K and the frequency range 0.1–20 KHz. At T>350 K, both the dielectric constant, ε ′ , and the dielectric loss, ε ″ , showed a decrease with increasing frequency and increasing temperature. The broad loss peak anomalies observed are attributed to intrinsic lattice dipoles in the hydrogen bonded Schiff base investigated. The discontinuity observed in the DC conductivity-temperature dependence behavior is correlated with structural changes in the network. The AC conductivity measurements as function of temperature exhibit a frequency dependent, temperature dependent behavior. Protonic conduction prevails at temperatures below 350 K. Decrease in the AC conductivity above 350 K is also indicative of structural changes within the hydrogen-bonded conjugated system. The frequency dependent-conductivity of the Schiff base is found to be proportional to ω s . Analysis of the AC conductivity experimental data obtained, and the frequency exponent s with theoretical models reveals that the correlated barrier hopping (CBH) model is the appropriate mechanism for conduction in the Schiff base system. The barrier height, W m , between charged defect states is calculated and its value is in good agreement with the theory of hopping of charged carriers over a potential barrier.

Effects of the molar mass of the matrix on electrical properties, structure and morphologyof plasticized PANI–PMMA blends

The effects of the molar mass of polymethylmethacrylate (PMMA) on electrical, structuraland morphological properties of conductive polyaniline–polymethylmethacrylateblends have been studied. We have plasticized the PMMA matrix by using dioctylphthalate (DioPh). Three different molar masses of PMMA, 15 000, 120 000 and350 000 g mol−1, have been used. The x-ray diffraction analysis showed amorphous structure for all our studiedPANI–PMMA blend films. The SEM micrographs showed more aggregation with the lowestmolar mass of PMMA matrix. The direct current (dc) and alternating current (ac) electricalconductivities have been investigated in the temperature range 20–300 K and frequency range7–1 × 108 Hz. The results of this study indicate an increase of the conductivity whenthe molar mass of PMMA decreases. With the lowest molar mass of PMMA(15 000 g mol−1), we obtained the lowest percolation threshold(pc≈0.3%). The dc conductivity is governed by Mott’s three-dimensional variablerange hopping (3D VRH) model; different Mott’s parameters have beenevaluated. At high frequencies, the ac conductivity follows the power lawσ(ω,T) = A(T)ωs(T,ω), which is characteristic for charge transport in disordered materials by hoppingor tunnelling processes. The observed decrease in the frequency exponents with increasing temperature suggests that the correlated barrier hopping (CBH) model bestdescribes the ac conduction mechanism. All our blends are well described by the scaling lawσ(ω)/σdc = 1+(ω/ωc)n with n≈0.51–0.52.

The electrical properties of boron‐containing poly(vinyl alcohol) derived ceramic organic semiconductor

AbstractThe direct and alternating current conductivity, space charge limited current, and thermoelectrical properties of boron‐containing poly(vinyl alcohol)‐derived ceramic have been investigated. The electrical conductivity of the sample increases with increase in temperature and the room temperature conductivity of the sample was found to be 3.82 × 10−5 S/cm. The electrical conductivity and thermoelectric power results suggest that the PVAB polymer has p‐type electrical conductivity. The current–voltage characteristics indicate that at higher voltages, the space charge limited conductivity mechanism is dominant in the PVAB sample. The electronic parameters such as the position of the Fermi level bottom of the conduction band, EF, the density of states in conduction band Nc, effective mass of holes ms were found to be 0.44 eV, 2.12 × 1025 m−3, and 0.59 mo, respectively. Alternating current conductivity results suggest that the correlated barrier hopping conductivity is dominant in AC conductivity mechanism of the sample. The imaginary part of the dielectrical modulus at different temperatures shows a relaxation peak, indicating a temperature‐dependent non‐Debye relaxation. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

AC conduction mechanisms of Gd1/3Sr2/3FeO3 ceramic

Abstract In this study, the AC conductivity of insulating Gd 1/3 Sr 2/3 FeO 3 was analyzed within the framework of the quantum-mechanical tunneling mechanism (QMT) and the hopping of barrier mechanism (HOB). Experimental data were taken from 20 Hz to 1 MHz and from 80 to 300 K. Observation revealed that the small polaron QMT model is the more suitable mechanism for modeling the AC conductivity of Gd1/3Sr2/3FeO3 at low temperatures.