Activation Energy For Ac Conduction Research Articles

Enhanced mechanical, electrical, thermal, and optical properties of poly(methyl methacrylate)/copper oxide nanocomposites for flexible optoelectronic devices via in‐situ polymerization technique

AbstractPolymethyl methacrylate (PMMA) with varied compositions of copper oxide (CuO) nanoparticles was synthesized using in‐situ free radical polymerization. UV–visible, FT‐IR, XRD, FE‐SEM, DSC, and TGA were employed to examine their structure, morphology, and thermal properties. The broadening and intensification of UV absorption, as well as the shift in IR peaks of PMMA with the addition of CuO, confirm their interactions. The reduction in optical bandgap values with the reinforcement of nanofillers confirms the existence of intermediate energy bands in nanocomposites. XRD indicated that polymerization with CuO reduced the amorphous nature of PMMA. The FE‐SEM image revealed that the dispersion of CuO altered the nonporous, rough surface of PMMA into a homogeneous shape. The reinforcement of CuO enhanced the thermal stability and glass transition temperature of PMMA. The mechanical strength, modulus, impact strength, and rigidity of PMMA were significantly improved through in‐situ polymerization. The electrical property analysis revealed that the AC conductivity increased with frequency, temperature, and filler content. The reduction in activation energy of AC conductivity with temperature points toward their semiconducting nature. PMMA/CuO nanocomposites with higher tensile strength, lower bandgap energy, higher conductivity, and thermal properties can be used to make flexible optoelectronic devices.Highlights A series of PMMA/CuO nanocomposites were synthesized and characterized. Enhanced optical property, thermal stability, and glass transition temperature. Possess excellent dielectric constant and AC conductivity. Mechanical strength and impact resistance of PMMA were greatly enhanced. A promising material for flexible optoelectronic and power storage applications.

Electrical conductivity and significant radiation shielding properties of B2O3.Pb3O4.ZnO.Y2O3 glasses

The electrical properties and radiation shielding characteristics are investigated for a glass system of the configuration 60% B2O3-35% Pb3O4-(5-x)%ZnO - x%Y2O3 with x from 0 to 3 mol%. Frequencies from 100 Hz to 5 MHz were applied to measure the ac conductivity in a temperature range between 310 and 700K. The values of ac conductivity (σac) are found in the range from 2×10−9 S.cm−1 to 5×10−2 S.cm−1, while the activation energy for ac conductivity (Eac) is found to fluctuate between 0.4 and 1.43 eV. The dc conductivity (σdc) and dc activation energy (Edc) are discussed according to thermal activation and small polaron hopping mechanisms. An alternation from mainly electronic to mainly ionic conduction mechanism is evidenced for the samples greater than 2% mol of the Y2O3. The radiation shielding characteristics are studied in wise of mass attenuation coefficient, μ/ρ, effective atomic number, Zeff, half value layer (HVL), and mean free path (MFP). The values of μ/ρ are obtained experimentally and theoretically by Phy-X/PSD software. The obtained relative deviation between theoretical and experimental results lies in the range from 0 to 3.8%. All the shielding factors demonstrate an inverse reliance on the Y2O3 content in the glasses. The MFP and HVL magnitudes of the glasses are compared with other traditional shielding materials and presented better attenuation ability. The relation between the shielding parameters and the electrical properties is discussed and it is also found that both properties are strongly affected by the interionic separations between the Pb ions in the glasses.

Electrical conduction mechanism and dielectric relaxation of bulk disodium phthalocyanine

AC conductivity and dielectric characteristics of disodium phthalocyanine (Na2Pc) in a pellet form were investigated in a frequency range from 45 Hz to 3.12 MHz and a temperature range from 303 to 423 K. The charge carrier transport mechanism was determined according to the correlated barrier hopping model (CBH). Also, the electrical parameters were estimated in light of this model. The thermal activation energy of AC conductivity decreases with increasing frequency. The behavior dependence of dielectric loss and dielectric constant on temperature and frequency was discussed. The behavior of dielectric loss was explained based on the Giuntini model. The maximum value of barrier height, was obtained to equal The results showed that the type of relaxation mechanism is a non-Debye one. The activation energy is calculated for dielectric relaxation to be

Electromechanical coupling, AC and DC resistivity simulation studies on [Ba(Nd0.075Ti0.85Nb0.075)O3]0.30 [(Na0.5Bi0.5)TiO3]0.70 piezoelectric ceramic

In the present study, we have prepared the [Ba(Nd0.075Ti0.85Nb0.075)O3]0.30–[(Na0.5Bi0.5)TiO3]0.70 ceramic through solid-state double sintering route. New equations which were proposed by us earlier were used to describe and model the electromechanical, AC and DC resistivity data. The activation energy for resonance and anti-resonance at 300 K is 30.28 and 30.11 meV; whereas the value is 38.32 and 38.91 meV at 448 K. The higher activation energy for AC conduction when compared to DC conduction is attributed to the fast vibration of charged polar and conducting species in response to the applied frequency, which requires more temperature.

The grain size effect in dielectric diffusion and electrical conduction of PZnTe-PZT ceramics

This study investigates systematically the microstructure, dielectric diffusion and electrical conduction behavior in xPb(Zn0.5Te0.5)O3-(1-x)Pb(Zr0.5Ti0.5)O3 (PZnTe-PZT) ceramics. The grain size has an obvious drop in PZT and PZnTe-PZT system. EDS reveals that the Te element segregates at the grain boundary, which can inhibit grain growth during the sintering process and result in the difference of element contents between grain and grain boundary. The permittivity peak become broaden when the PZnTe add in and this phenomenon is explained by the brick-wall model, which is due to the difference in grain size. The diffusion behavior is described by the empirical expression and the W2/3M-H parameter and it shows that the co-action of the grain size effect and the doping effect influence the dielectric diffusion of PZnTe-PZT ceramics. The electrical conduction characteristics in different temperature and frequency show the difference of activation energy for ac conductivity between the PZT and the PZnTe-PZT, which are related to the grain size and the element segregation in grain boundary.

Conducting polymers IX: Optical properties, dielectric constants and conduction mechanism of poly(N,N′-Bis-salphinyl 2,6-diaminipyridine-3,5-diamini-1,2,4-trizole)

Poly(N,N′-Bis-salphinyl 2,6-diaminipyridine-3,5-diamini-1,2,4-trizole) (PBDPT) is synthesized starting with 2,6-diamino-pyridine using thionyl chloride (SOCl2) as an oxidizing agent and then is polymerized with 3,5-diamino-1,2,4-triazole. The chemical structure of the produced PBDPT is confirmed by spectroscopic analyses techniques. The average molecular weight of PBDPT is determined using 1H NMR technique. The optical investigations of PBDPT showed two absorption peaks and two remarkable emission peaks. The oscillator strength of the absorption peaks is calculated and is found to be 4.4×1012 and 1.96×1012 for the peaks at 9.19×1014 and 7.54×1014Hz, respectively. The energy gap (Eg) is found to be 2.66eV. Direct current electrical conductivity (σDC), alternating current electrical conductivity (σAC) and conduction mechanisms are investigated in the temperature range 298–373K. The thermal activation energy for DC conductivity, ΔEDC, is determined and found to be 0.54eV while the thermal activation energy for AC conductivity, ΔEAC, is found to be in the range 0.09–0.17eV; depending on the test frequency. The semi-circle behavior of the impedance spectra confirmed that the equivalent circuit of the sample can be represented by a resistor Rp in parallel with a capacitor Cp.

Electrical and thermal properties of bisphenol A propoxylate diglycidyl ether-piperazine copolymer/functionalized MWCNT composites

In this work, bisphenol A propoxylate diglycidyl ether?piperazine copolymer functionalized MWCNTs (oxidized MWCNT + aminated MWCNT) composites were prepared and structurally characterized using FTIR and NMR spectroscopy. The composites were investigated in terms of their electrical and thermal properties. The surface morphology of the composites was examined by SEM. It was observed that thermal stability decreased while the ac conductivity and dielectric constant (relative permittivity) increased with increasing functionalized MWCNT content (2, 5, 10 and 15 mass %) of the composites. The electrical conductivity increased with increasing temperature and the activation energy of ac conductivity was determined and discussed.

Low Temperature Broad Band Dielectric Spectroscopy of Multiferroic Bi6Fe2Ti3O18 Ceramics

AbstractIn the present research the tool of broadband dielectric spectroscopy was utilized to characterize dielectric behavior of Bi6Fe2Ti3O18(BFTO) Aurivillius-type multiferroic ceramics. Dielectric response of BFTO ceramics was studied in the frequency domain (Δν=0.1Hz – 10MHz) within the temperature range ΔT=-100°C – 200°C. The Kramers-Kronig data validation test was employed to validate the impedance data measurements and it was found that the measured impedance data exhibited good quality justifying further analysis. The residuals were found to be less than 1%, whereas the “chi-square” parameter was within the range χ2~10−7−10−5. Experimental data were analyzed using the circle fit of simple impedance arc plotted in the complex Z”-Z’ plane (Nyquist plot). The total ac conductivity of the grain boundaries was thus revealed and the activation energy of ac conductivity for the grain boundaries was calculated. It was found that activation energy of ac conductivity of grain boundaries changes from EA=0.20eV to EA=0.55eV while temperature rises from T=-100°C up to T=200°C. On the base of maxima of the impedance semicircles (ωmτm=1) the relaxation phenomena were characterized in terms of the temperature dependence of relaxation times and relevant activation energy was calculated (EA=0.55eV).

Aliovalent Ba2+ doping: A way to reduce oxygen vacancy in multiferroic BiFeO3

This paper demonstrates the impact of Ba2+ substitution on the structural, dielectric relaxation and AC conductivity properties of Bi1−xBaxFeO3(0≤x≤0.25) ceramics. Ba doping incorporates rhombohedral to tetragonal structural transformation in perovskite BFO. XPS data shows change in oxygen vacancy concentration with Ba doping and it also suggests that schoimetry of the doped compounds is not maintained by creating mix valance state of Fe. Reduction in oxygen vacancy (OVs) in the doped samples is explained by Kroger–Vink notation. Arrhenius plot shows activation energy for dielectric relaxation of the doped samples lies between ~1.16 and 1.44eV. AC conductivity of material decreases as Ba ion substitution increases in the parent compound. Electrical conductivity is attributed to the correlated barrier hopping (CBH) motion of the oxygen vacancies in the samples. Coulombic potential barrier (WM) height, calculated from Elliott model for CBH motion of charge carriers shows correlation with the activation energy of AC conductivity at low temperature. Activation energy value obtained from the impedance measurements of the samples implies short range migration of oxygen vacancies dominates the frequency dependent conductivity while the frequency independent part of conductivity is the result of long range migration of oxygen vacancies.

Activation behavior and dielectric relaxation of nanocrystalline zinc ferrite

We report the ac conductivity and dielectric relaxation studies of nanocrystalline zinc ferrite prepared by the ball milling. The real part of the complex ac conductivity is found to follow the universal dielectric response σ′(f)∝Tnfs and values of both s and n show an anomalous behavior. Both the magnitude of the temperature exponent ‘n’ and thermal activation energy for ac conduction strongly depends on frequencies. The dielectric constant exhibits strong temperature dependence at higher temperature and lower frequencies. The dielectric properties of the samples have been analyzed in terms of electric modulus vector. The complex impedance has also been modeled by an ideal equivalent circuit consisting of grain and grain boundary resistances and capacitances. Considering the formation of Schottky diode at the metallic electrode and semiconductor junction, the diode parameters like built in voltage and space charge density have been extracted from the capacitance-voltage characteristics.

Charge transport and electrode polarization in epoxy resin at high temperatures

Complex permittivity spectra were measured for epoxy resin at various temperatures and numerically fitted to theories of electrode polarization (EP) and ac conduction. Complex permittivity at high temperatures fits the Cole–Cole relation for EP well, with the shape parameter relating to the electrode blockage coefficient for ions. The Debye length, ion density and mobility, hopping rate and distance, and other parameters controlling the charge transport can be obtained. Both the density and mobility of ions are thermally activated, and the sum of their activation energies is nearly the same as the activation energy of ac conductivity. It is indicated that the theory of power-law frequency response as a result of short-range hopping of ions is an extension of the EP theory above its peak frequency. On the other hand, the relaxation of ac conduction revealed by electric modulus and that of EP appearing at low frequencies are due to long-range hopping of ions. It is demonstrated that data fitting of complex permittivity to the theories of EP and ac conduction in combination with the electric modulus analysis is effective to estimate various characteristic parameters of charge transport.

Dielectric and electrical conductivity studies of bulk lead (II) oxide (PbO)

The dielectric properties, the impedance spectroscopy and AC conductivity of bulk PbO have been investigated as a function of frequency and temperature. The measurements were carried out in the frequency range from 40 to 5×106 Hz and in temperature range from 313 to 523K. The frequency response of dielectric constant, ε1, and dielectric loss index, ε2, as a function of temperature were studied. The values of ε1 and ε2 were found to decrease with the increase in frequency. However, they increase with the increase in temperature. The presence of a single arc in the complex modulus spectrum at different temperatures confirms the single-phase character of the PbO. The AC conductivity exhibited a universal dynamic response: σAC=Aωs. The AC conductivity was also found to increase with increasing temperature and frequency. The correlation barrier hopping (CBH) model was found to apply to the AC conductivity data. The calculated values of s were decreased with temperature. This behavior reveals that the conduction mechanism for PbO samples is CBH. The activation energy for AC conductivity decreases with increasing frequency. This confirms that the hopping conduction to the dominant mechanism for PbO samples.

Effect of Process Parameter Optimization in Reducing Sintering Temperature in the Synthesis and Characterization of Ba(Zn1/3Nb2/3)O3

Controlling the cooling rate during calcination and sintering, phase pure perovskite Ba(Zn1/3Nb2/3)O3 has been prepared by simple solid state reaction route with density >93% at relatively low sintering of 1175°C making it compatible for microwave dielectric applications. The samples are characterized by X-ray diffraction analysis and scanning electron microscopy. The X-ray diffraction shows pure perovskite phase with cubic structure. The lattice constants were obtained a = 4.1032 Å. Detailed studies of ε′ and ε′′ show that the compound exhibits dielectric anomaly at 430°C. Material shows distributed relaxation at higher temperature. Impedance analysis revealed that the impedance is mainly due to the grains. AC conduction activation energies are estimated from Arrhenius plots, and conduction mechanism is discussed.

Dielectric Studies on Alkali Borate Glasses Mixed with Iron Oxide

Glass system of composition Li2O-Na2O-B2O3: Fe2O3with replacing alkali oxides one by another have been prepared via melt quenching. Further, the samples were characterized by X-ray diffraction. XRD studies have indicated that the prepared samples were amorphous in nature. Dielectric properties (constant ε , loss tan δ, a.c. conductivity σacover a wide range of frequency and temperature) of these glasses have also been explored. The activation energy for ac conduction is estimated to be the lowest for glass F25and the highest for glass F0. Finally the study on dielectric properties indicated that the ac conduction is predominantly ionic in nature in the samples containing high content of Li2O.Keywords:Borate glasses; dielectric properties; alkali effect

Electrical charge conductivity behavior of electrodeposited Cu2O/ZnO heterojunction thin films on PET flexible substrates by impedance spectroscopy analysis

The bottom-up self-assembly Cu2O/ZnO heterojunction thin films electrodeposited on indium tin oxide flexible substrate (polyethylene terephthalate, PET) have been investigated by impedance spectroscopy. It is used to study the electric conductivity of the Cu2O/ZnO heterojunction thin films combined electric modulus and impedance plots. The electric modulus and impedance as a function of the frequency analysis show the distribution of the relaxation times due to the hopping of charge carriers among defects in the Cu2O/ZnO heterojunction thin films. The values of activation energies derived from the electric modulus and impedance are found to be 0.42 and 0.40 eV, respectively, which is close to the activation energy (0.28 eV) of dc electrical conductivity and activation energy of ac conductivity (0.45–0.14 eV at the range of 100 Hz–1 MHz) in the temperature range over 303–423 K.

Fabrication, Structural and AC Impedance Studies of Layer-Structured Bi4Ti3O12 Ceramics

Fabrication, Structural and AC Impedance Studies of Layer-Structured Bi4Ti3O12 Ceramics In the present research bismuth titanate Bi4Ti3O12 (BiT) ceramics was synthesized by the standard solid-state reaction method from the mixture of oxides, followed by free sintering at temperature T=1000°C. BiT ceramics was studied in terms of its chemical composition (EDS), crystalline structure (X-ray), microstructure (SEM) and dielectric properties (ac technique of complex impedance spectroscopy) over a range of frequency (ƒ=100Hz to ƒ=1MHz) and temperature (T=200-500°C). Experimental results confirmed the phase formation. It was found that BiT ceramics crystallized in orthorhombic symmetry, best described with Fmmm space group and the following elementary cell parameters: a=5.409(6)°A, b=5.449(2)°A and c=32.816(2)°A. It was also found that BiT ceramics exhibited the plate-like microstructure and stoichiometric chemical composition. Impedance spectroscopy measurements showed contribution of three overlapping relaxation processes (three semicircles in the complex impedance diagrams were observed) ascribed to bulk, grain boundary and electrode/interface polarization phenomena. Impedance data were fitted to the corresponding equivalent circuit using the complex nonlinear least squares (CNLS) method. The ac conductivity for grains, grain boundaries and electrode processes was calculated from CNLS fit of the impedance data and thus the activation energy of ac conductivity (σAC) and relaxation (τ) was calculated for the three revealed components of the impedance spectra from the slopes of σAC and τ versus 1000/T plots (semi log scale) in the range of ΔT=200-500°C.

DIELECTRIC RELAXATION AND ELECTRICAL STUDY OF BaNb2O6 PREPARED BY SOL–GEL ROUTE

A gel was formed when an aqueous solution of BaCl 2, NbF 5 and citric acid in stoichiometric ratio is heated on a water bath at 100°C. This gel on decomposition at 700°C yielded the nano phase of BaNb 2 O 6 as confirmed by X-ray diffraction study. The crystal structure is orthorhombic with unit cell parameter a = 12.2136 Å, b = 10.2413 Å, c = 7.8831 Å. The estimated grain size is 88 nm. Dielectric studies reveal the dielectric relaxation mechanism. Conducting charges and free charges both contribute to the dielectric relaxation in this material. Electrical properties of the material were studied using impedance spectroscopy technique. Detailed analysis of impedance spectrum suggested that the electrical properties are strongly temperature-dependent. The relaxation is polydispersive and conduction is mainly through grains. AC conduction activation energies are estimated from Arrheneus plots and conduction mechanism is discussed.

Dielectric relaxation and ac conductivity study of Ba(Sr 1/3Nb 2/3)O 3

Single phase perovskite Ba(Sr 1/3Nb 2/3)O 3 ceramics was prepared using the columbite precursor method. X-ray diffraction (XRD) technique is used to verify the single phase formation. It stabilizes in hexagonal phase with lattice constants a=12.1243 Å and c=15.3747 Å. Impedance analysis shows distributed relaxation time. Single semicircular arc observed in complex impedance plot confirms that only semiconducting grains are contributing to the polarization. The scaling behavior of both Z″ and M″ infers that the dynamical processes are temperature independent. Comparison of the impedance and electrical modulus data shows that the bulk response has contributions from both localized, i.e. defect relaxation, and non-localized conduction, i.e. ionic or electronic conductivity. The ac conductivity of the ceramics at higher temperatures indicates NTCR (negative temperature coefficient of resistance) behavior like semiconductors. The ac conduction activation energies are estimated from Arrhenius plots and conduction is largely due to hopping process.

Dielectric Relaxation in Pure Columbite Phase of SrNb<sub>2</sub>O<sub>6</sub> Ceramic Material: Impedance Analysis

Controlling the heating rate during calcination and cooling rate during sintering, pure columbite like phase of SrNb2O6 is synthesized. By optimizing the sintering temperature, ceramic with density (>92%) is achieved for material calcined at 11250C and sintered at 12000C. The ceramic shows orthorhombic structure with lattice parameters a = 11.011 Å b = 7.7136 Å, c = 5.5969Å having average grain size ≈ 1.03 μm. The temperature dependent dielectric response shows a peak at temperature 300.90C, which shows significant dielectric dispersion towards high temperature side of the peak with almost dispersion free low temperature side; an effect observed in relaxors. Dielectric dispersion in the material is fitted with the Jonscher’s relation. Impedance analysis suggests strongly temperature dependent relaxation. The dielectric relaxation is polydispersive and conduction is mainly through grains. The equivalent circuit model for the impedance response is proposed and the temperature dependence of circuit elements deduced. The frequency dependent ac conductivity at different temperatures indicated that the conduction is governed through thermally activated processes. AC conduction activation energies are estimated from Arrhenius plots and conduction mechanism is discussed.

Charge migration in Pb(Zr,Ti)O3 ceramics and its relation to ageing, hardening, and softening

The dielectric response of hard (Fe-doped) and soft (Nb-doped) rhombohedral Pb(Zr0.58Ti0.42)1−xMexO3 (Me=Fe or Nb) ceramics was studied at subswitching conditions over a wide range of temperatures (50–450 °C) and frequencies (10 mHz to 10 kHz). The results show qualitative differences in the behavior of the acceptor- and donor-doped samples. Hard materials exhibit a steep increase in the complex permittivity with decreasing frequency. The onset of the dispersion is thermally activated with activation energies of about 0.6–0.8 eV and is attributed here to oxygen vacancy hopping. The activation energy for ac conductivity observed in soft materials is estimated to be about 1.7 eV, corresponding to half of the energy gap of Pb(Zr,Ti)O3 and is thus consistent with electronic conduction. The relevance of ionic hopping conductivity in hard materials to ferroelectric aging/deaging and hardening is analyzed. Strong ionic conductivity in hard samples and its absence in soft samples agree well with the dipolar mechanism of aging in hard materials and the absence of significant aging in soft materials.