Dominant Conduction Process Research Articles

Mixed Ionic and Electronic Conduction in TeO2-ZnO-V2O5 Glasses towards Good Dielectric Features.

The melt-quenching technique was used to synthesize tellurite glasses of the chemical composition 80TeO2-(20-x) ZnO-xV2O5. X-ray diffraction (XRD) patterns indicate the amorphous nature of the prepared glasses. Raman and FTIR measurements demonstrate a progressive substitution of the Te-O-Te linkages by the Te-O-V bridges and the formation of VO4 and VO5 units by a change of the vanadium coordination due to the higher number of oxygens incorporated by further addition of V2O5. The AC conductivity was investigated in the frequency range of 40 Hz to 107 Hz between 473 K to 573 K. A good coherence of the AC conductivity was found using a model correlating the barrier hopping (CPH) and the dominant conduction process changes from ionic to polaronic with the addition of V2O5. The dielectric constant exhibits high values in the range of lower and medium frequencies. Both variations of the electric modulus and the dielectric loss parameters with frequency and temperature showed a relaxation character mainly assigned to the vanadate phases. The electric modulus displays a non-Debye dielectric dispersion and a relaxation process. The present results open the door to future zinc-tellurite glasses-doped vanadium exploitation as a potential electrolyte-based material for solid-state batteries.

Study of electrical properties and conduction mechanisms in La0.4Bi0.3Sr0.2Ba0.1MnO3 Ceramic elaborated by sol gel method

Using the sol gel method, we will incorporate Bi, Sr and Ba in site A into the LaMnO3 matrix to get La0.4Bi0.3Sr0.2Ba0.1MnO3 compound. Our aim is to explore the structural and the electrical properties of this compound. X-ray diffraction study indicates that the investigated compound exhibits a rhombohedral crystalline phase with R3̅c space symmetry. Temperature dependence of the electrical conductivity indicates that the investigated sample exhibits a semiconductor behavior in the explored temperature range [80–400 K]. Then a saturation region appears at ambient temperature. For ac-conductivity, the spectra obey to the double Jonscher response in the temperature range [80–135 K], the single Jonscher power law for [140–210 K] and to the classical Drude model for [220–400 K]. At elevated temperatures, the conduction is governed by the thermally activated hopping of small polaron (SPH). However, the most appropriate conduction mechanism at low temperatures is the Variable Range Hopping process (VRH). In the intermediate temperature range, the transport properties are described by Greaves variable range hopping model. Then, the correlated barrier hopping (CBH) and the Jump relaxation Model (JRM) were used to explain the dispersion region. Moreover, the value of the extracted activation energies is strongly dependent on frequency suggesting that the hopping mechanism is the dominant conduction process. Also, the disorder energy decreases with increasing frequency indicating that the separation path between jump centers is modified. Indeed, the contribution of various processes to the conductivity makes our system as good candidate in the solid oxide fuel cells (SOFCs) applications.

Optical and electrical studies on MgTiO3– Ba5Nb4O15 composite thin films for integrated microwave circuit applications

A correlative study on optical and electrical properties of MgTiO3 (MTO) -Ba5Nb4O15 (BNO) composite thin films (MTBN) with respect to film thickness (260–450 nm) is reported. The optical bandgap energy of MTBN composite thin films (3.76 eV–3.65 eV) are found to be intermediate to MTO (3.44 eV) and BNO (3.85 eV) monoliths. Further, the optical dispersion in MTBN composite thin films can be defined by Cody-Lorentz dispersion law. Higher photoluminescence (PL) emission intensity and shorter carrier lifetime (0.8376 ns) ascribed to local symmetry break is observed for 450 nm film. Moreover, the Mott's variable range hopping mechanism was dominant conduction process in the MTBN composite films. Further, density of states near the Fermi level were found to be around 7.85×1018 eV−1cm−3 - 3.478×1019 eV−1cm−3 for 260 nm–450 nm MTBN films. The obtained optical and electrical properties prospect a potential application of the MTBN composite thin films in integrated microwave circuits.

Electrical transport of 0.3Bi1-xYxFeO3-0.7Ba0.8Sr0.2TiO3 ceramics

Polycrystalline sample of 0.3Bi1-xYxFeO3-0.7Ba0.8Sr0.2TiO3 (0.05 < x < 0.15) are prepared via solid state route. The analysis of x-rays diffraction shows that the prepared ceramics crystallize in a tetragonal structure. Moreover, Raman measurement confirms the tetragonal structure of all samples. From the temperature dependence of dielectric constant, we deduced that the samples show a relaxor behavior. So as to look into the electrical properties a complex impedance spectroscopy is highlighted. The conductivity spectrum exhibits a semi conducting behavior. At low frequency the dominant conduction process is the small polarons jump mechanism while for high frequency the charges carriers moves according to the correlated barrier hopping model. Nyquist plots show that the most adequate equivalent circuit is composed by a grain resistance in series with a parallel combination between a grain boundary resistance and capacitance.

Electrical conduction mechanism and dielectric characterization of MnTPPCl thin films

The AC conductivity and dielectric properties of MnTPPCl sandwich structure as Au/MnTPPCl/Au were studied. The conductivity of the MnTPPCl thin films have been interpreted by the correlated barrier hopping (CBH) model. The dominant conduction process have found to be the single polaron hopping conduction. The values of the hopping distance, Rω, barrier height, W, and the localized-state density, N, are estimated at different frequencies. The behavior of dielectric constant and dielectric loss was discussed as a function of temperature and frequency. The dielectric constant was described in terms of polarization mechanism in materials. The spectral behavior of dielectric loss is interpreted on the basis of the Giuntini et al. model [1]. The value of WM is obtained as 0.32 eV. A non-Debye relaxation phenomenon was observed from the dielectric relaxation mechanism.

Effects of Electrode Materials on Charge Conduction Mechanisms of Memory Device Based on Natural Aloe Vera

ABSTRACTResistive switching behaviors in Aloe vera films are being explored for nonvolatile memory applications. A simple structure in which the Aloe vera films sandwiched in between a top and bottom electrode are used. The switching behaviors of the devices in which the Aloe vera film is dried at different temperatures and the roles of top electrode materials (Al and Ag) are investigated. Current density–voltage measurements reveal that filamentary conduction is the dominant conduction process inducing resistive switching characteristics in Aloe vera films. Device with Al-top electrode requires a forming voltage higher than devices with Ag-top electrode, due to the tendency of oxide formation of these materials. The resistive switching behaviors are highly reproducible, as demonstrated by the data retention performance over an interval of 104 s and endurance capability of over 100 cycles.

Dominant conduction mechanism in NiO-based resistive memories

The conduction characteristics of Pt/NiO/Pt resistive switching cells were investigated systematically through DC and AC conductance measurements in each of three resistance states: the initial state, the low resistance state (LRS), and the high resistance state (HRS). In the initial state, two different conduction processes are dominant, although this dominance is temperature-dependent. The activation energy (Ea) of the DC conductance was approximately 4.3 meV below 170 K. In addition to the low Ea, the frequency and temperature dependence of the AC conductance confirmed that the conduction originated from hopping between isolated sites. However, above 170 K, the Ea of the DC conductance was 330 meV, and this conductance was independent of frequency at low frequencies. The dominant conduction process above 170 K was found to be band conduction from analysis of the AC conductance. The resistance in the LRS varied linearly with temperature and was almost independent of frequency, thus representing the characteristics of metallic band conduction of conductive filaments. In the HRS, the DC conductance exhibited an Ea of 16 meV, which was higher than that in the initial state (4.3 meV), thus indicating that the dominant conduction mechanism in the HRS is different to the mechanism in the initial state. From discussions based on a filament model, it was concluded that filament conduction is dominant in the HRS. As a result, it is proposed that the resistive switching originates from changes in the conduction properties of the filaments themselves rather than from their rupture and formation.

Conduction processes in metal–insulator–metal diodes with Ta2O5 and Nb2O5 insulators deposited by atomic layer deposition

Metal–insulator–metal diodes with Nb2O5 and Ta2O5 insulators deposited via atomic layer deposition are investigated. For both Nb2O5 and Ta2O5, the dominant conduction process is established as Schottky emission at small biases and Frenkel–Poole emission at large biases. Fowler–Nordheim tunneling is not found to play a role in determining current versus voltage asymmetry. The dynamic dielectric constants are extracted from conduction plots and found to be in agreement with measured optical dielectric constants. Trap energy levels at ϕT ≈ 0.62 and 0.53 eV below the conduction band minimum are estimated for Nb2O5 and Ta2O5, respectively.

Carrier Transport Mechanisms in Metal-Insulator–Metal Au/Ba0.8Sr0.2TiO3/ ZrO2/ Ba0.8Sr0.2TiO3/Pt Thin Film Heterostructures

ABSTRACTBa0.8Sr0.2TiO3/ZrO2 heterostructured thin films are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel process. The current versus voltage (I-V) measurements of metal-insulator-metal (MIM) devices using the above multilayered thin film as the dielectric have been taken in the temperature range of 310 to 410K. The electrical conduction mechanisms contributing to the leakage current at different field regions have been studied in this work. Various models are used to know the different leakage mechanisms contributing to the conduction current in these devices. It is observed that Poole-Frenkel mechanism is the dominant conduction process in the high field region with a deep trap level energy (φt) of 1.31 eV whereas space charge limited current (SCLC) mechanism and Ohmic conduction process are contributing to the leakage current in the medium and low field regions respectively. The estimated shallow trap level (Et) for SCLC mechanism is 0.26 eV whereas the activation energy (Ea) for the electrons in the Ohmic conduction process is about 0.07 eV. An energy band diagram is given to explain the various leakage mechanisms in different field regions for these heterostructured thin films.

Field Dependent Carrier Transport Mechanisms in Metal-Insulator–Metal Devices with Ba0.8Sr0.2TiO3/ ZrO2 Heterostructured Thin Films as the Dielectric

ABSTRACTBa0.8Sr0.2TiO3/ZrO2 heterostructured thin films with different individual layer ZrO2 thicknesses are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel process. The current versus voltage (I-V) measurements of the above multilayered thin films in metal-insulator-metal (MIM) device structures are taken in the temperature range of 310 to 410K. The electrical conduction mechanisms contributing to the leakage current at different field regions have been studied in this work. Various models are used to know the different conduction mechanisms responsible for the leakage current in these devices. It is observed that Poole-Frenkel mechanism is the dominant conduction process in the high field region with deep electron trap energy levels (φt) whereas space charge limited current (SCLC) mechanism is contributing to the leakage current in the medium field region with shallow electron trap levels (Et). Also, it is seen that Ohmic conduction process is the dominant mechanism in the low field region having activation energy (Ea) for the electrons. The estimated trap level energy varies from 0.2 to 1.31 eV for deep level traps and from 0.08 to 0.18 eV for shallow level traps whereas the activation energy for electrons in ohmic conduction process varies from 0.05 to 0.17 eV with the increase of ZrO2 sub layer thickness. An energy band diagram is given to explain the dominance of the various leakage mechanisms in different field regions for these heterostructured thin films.

Field Dependent Electrical Conduction in Metal-Insulator-Metal Devices using Alumina-Silicone Nanolaminate Dielectrics

ABSTRACTHybrid alumina-silicone nanolaminate films were synthesized by plasma enhanced chemical vapor deposition (PECVD) process. PECVD allows digital control over nanolaminate construction, and may be performed at low temperature for compatibility with flexible substrates. These materials are being considered as dielectrics for application such as capacitors in thin film transistors and memory devices. In this work, we present the temperature dependent current versus voltage (I-V) measurements of the nanolaminate dielectrics in the range of 200- 310 K to better asses their potential in these applications. Various models are used to know the different conduction mechanisms contributing to the leakage current in these nanolaminate films. It is observed that space charge limited current (SCLC) mechanism is the dominant conduction process in the high field region whereas Ohmic conduction process is contributing to the leakage current in the low field region. The shallow electron trap level energy (Et) of 0.16 eV is responsible for SCLC mechanism whereas for Ohmic conduction process the activation energy (Ea) for electrons is about 0.22 eV. An energy band diagram is given to explain the dominance of various conduction mechanisms in different field regions in these nanolaminate films.

Leakage current mechanisms in high performance alumina-silicone nanolaminate dielectrics

Alumina-silicone nanolaminates deposited by plasma-enhanced chemical vapor deposition were explored as dielectrics in metal-insulator-metal capacitors. Temperature-dependent current versus voltage (I-V) measurements were used to investigate the conduction mechanisms contributing to the leakage current in these structures. It is observed that space charge limited current mechanism is the dominant conduction process in the high field region. The estimated shallow trap level energies (Et) are 0.16 eV and 0.33 eV for 50% and 83.3% Al2O3 nanolaminates, respectively.

Ultrasonic attenuation of CdSe at low temperatures

The ultrasonic attenuation of a single crystal of CdSe has been investigated over the temperature range from 1.2 to 300 K at frequencies of 10, 30 and 90 MHz. We report here the temperature dependence of the attenuation in the range 1.2–30 K for piezoactive and non-piezoactive acoustic waves. A temperature-induced relaxation for two piezoactive waves, which scale with frequency towards higher temperatures, was found. A modified Hutson and White model with a new parameter γ is proposed to explain the relaxation maxima of our data and others in the literature. In this model the parameter γ, which seems to be closely related to the compensation, takes into account the impurities-sound wave piezoelectric coupling. By inverting the proposed expression for the sound attenuation to obtain the electrical conductivity from the relaxation, it is found that impurity conductivity of the hopping type is the dominant conduction process at low temperatures.

High-Temperature Poly(phthalazinone ether ketone) Thin Films for Dielectric Energy Storage

The synthesis and characterization of poly(phthalazinone ether ketone) (PPEK) for high-temperature electric energy storage applications is described. It was found that PPEK displayed excellent stability of the dielectric properties over a broad frequency and temperature range. Little change in the breakdown field and discharge time has been observed in PPEK with the increase of temperature up to 190 degrees C. A linear correlation between the AC conductance and the angular frequency implied that the hopping as a dominant conduction process contributed to the dielectric loss. Superior energy densities, remarkable breakdown strengths, and fast discharge speeds have been demonstrated in PPEK at various temperatures.

Dielectric characteristics of poly(ether ketone ketone) for high temperature capacitive energy storage

The dielectric constant and loss of poly(ether ketone ketone) have been investigated over a range of frequency and temperature. A linear correlation between the ac conductance and the angular frequency implies that the hopping as a dominant conduction process contributes to the dielectric loss. The energy density and discharged efficiency of the polymer were measured at various temperatures. High dielectric strengths (&amp;gt;400 MV/m) at temperatures up to 150 °C have been achieved. The increase of the dielectric loss and reduction in the breakdown field with increasing temperature could be attributed to thermally enhanced conduction of charge carriers in the polymer.

Effect of deuterium-hydrogen exchange on the electrical conduction in lysozyme

The H2O and D2O sorption isotherms have been measured for lysozyme powders, as well as the extent of the deuterium-hydrogen exchange as a function of D2O partial pressure. D2O appears to bind more strongly to lysozyme than H2O. There is a significant reduction in the steady-state conductivity of lysozyme when sorbed water molecules are replaced by the same number of sorbed D2O molecules. This effect is taken as strong evidence that the dominant conduction process in lysozyme powder involves the transport of protons.

Electrical transport and morphological study of PLD-grown nanostructured amorphouscarbon thin films

Nanostructured carbon thin films have been actively investigated recently for theirelectroresistance (ER) properties. Furthermore, carbon films with nonlinear current–voltage(I–V) characteristics have potential application in field-emission devices. This hasmotivated us to study the effect of various growth parameters on the physical andmorphological properties of carbon films grown by pulsed laser deposition (PLD). Carbonfilms have been deposited using a graphite target at different partial pressures ofargon. The morphology of film surfaces deposited at various growth conditionswas monitored using an atomic force microscope (AFM). AFM studies showednanostructured grain growth with average grain size of about 80–90 nm. As thedeposition time was decreased down to 1 min, the grain size was also found to decreasecorrespondingly. From Raman spectroscopic measurements an increase in theI(D)/I(G) ratio and a decrease in FWHM (G) clearly revealed the promotion ofsp2 hybridization as the substrate temperature increased. All the films showsemiconducting behaviour with the dominant conduction process being thethree-dimensional (3D) variable range hopping (VRH) mechanism. NonlinearI–V curves were obtained for carbon films deposited on p-type Si indicating diode-likebehaviour. The most significant result of this study was the observation of a largeelectroresistance value.

Proton mobility in oligomer-bound proton solvents: imidazole immobilization via flexible spacers

A completely new approach for obtaining high proton conductivity in polymers based on proton solvating heterocycles covalently bound via flexible spacers is presented. Imidazole-terminated ethyleneoxide (EO) oligomers as model materials have been characterized with respect to their conductivity by ac impedance spectroscopy and with respect to 1H- and 19F-diffusion coefficients by pulsed magnetic field gradient-NMR (PFG-NMR). Comparison of conductivity and NMR diffusion coefficients of pure and acid doped materials shows ‘structure diffusion’ (intermolecular proton transfer and structural reorganization by hydrogen bond breaking and forming processes) to be the dominant conduction process, which gives rise to proton conductivities of up to 5×10 −3 S cm −1 at 120°C in completely waterfree materials.

Structure and electrical properties of boron-added (Ba,Sr)TiO3 thin films fabricated by the sol-gel method

Thin films of BaxSr1−xTiO3 (BST, with x=0.5) were fabricated on a RuO2/Ru/SiO2/Si substrate by the spin coating of the multicomponent sol prepared using metal alkoxides. Boron alkoxide was intentionally introduced to establish a better microstructure and to reduce the leakage current. AFM indicated that a crack-free uniform microstructure having a smooth surface was gradually developed with increasing boron content. The relative dielectric permittivity of the 250-nm thick BST thin films fired at 700°C decreased with increasing content of boron, from 420 for the undoped film to 190 for the 10 mol% boron-added film at 1 MHz. This observation was interpreted in terms of a serial capacitance composed of the perovskite BST grain and the interfacial B2O3 glassy phase having a low dielectric permittivity. The leakage current density (J) also decreased with the amount of boron added. The leakage current for the applied voltage greater than 1 V showed a linear variation of logJ with E1/2 at room temperature, suggesting that the interface-controlled Schottky emission was the dominant conduction process for the BST thin films fabricated on the RuO2 electrode.

Electrical and magnetic properties of LiPc and LiPcI

We studied the ac electrical (20 Hz ≤ v ≤ 1GHz) and magnetic properties of the molecular semiconductors lithium phthalocyanine (LiPc) and lithium phthalocyanine iodide (LiPcI) at temperatures 1.5 K ≤ T ≤ 300 K. The frequency and temperature dependence of the complex ac conductivity suggest polarons as the dominant species of charge carriers. The higher conductivity of the iodine salt can be attributed to an enhanced mobility of the polaronic charge carriers due to a better overlap of the π-orbitals along the stacking direction of the molecules. Up to 300 K the dc conductivity can be described by σ dc α exp( −( T 0/ T) 1/2), i. e. quasi one-dimensional tunneling of charge carriers is the dominant conduction process in both compounds. Preliminary electron spin resonance (ESR) experiments were performed on LiPc. A single narrow, lorentzian shaped line is observed. Below 30 K a significant decrease in linewidth appears which may indicate the onset of magnetic order or dimerization.