Impedance spectroscopy and investigation of conduction mechanism in BaMnO3 nanorods

BaMnO₃ nanorods were synthesized at 200 °C and atmospheric pressure using the composite-hydroxide mediated method. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to investigate the structure, size, morphology, phase purity and elemental composition of BaMnO₃ nanorods. Electrical characterization of BaMnO₃ pellet was performed at 300-400 K and in the frequency range 200 Hz-2 MHz. Temperature dependence of AC conductivity suggests that the BaMnO₃ pellet behaves as a semiconducting material and conduction across the pellet can be explained by the correlated barrier hopping model. Impedance analysis was performed using the equivalent circuit model (R₁Q₁C₁)(R₂C₂) and it suggests a single relaxation process in the BaMnO₃ pellet at a particular temperature. The analysis reveals that the BaMnO₃ pellet behaves like an n-type semiconductor material due to the presence of oxygen vacancies and some disorder. Modulus spectroscopy also supports the impedance results.     

Impedance-based interpretations in 2-dimensional electron gas conduction formed in the LaAlO3/SrxCa1−xTiO3/SrTiO3 system

Frequency-dependent impedance spectroscopy was applied to the 2-dimensioanl conduction transport in the LaAlO₃/Sr_xCa_1−xTiO₃/SrTiO₃ system. The 2-dimensional conduction modifies the electrical/dielectric responses of the LaAlO₃/Sr_xCa_1−xTiO₃/SrTiO₃ depending on the magnitude of the interfacial 2-dimensional resistance. The high conduction of the 2-dimensional electron gas (2DEG) layer can be described using a metallic resistor in series with two parallel RC circuits. However, the high resistance of the 2-dimensional layer drives the composite system from a finite low resistor in parallel with the surrounding dielectrics composed of LaAlO₃ and SrTiO₃ materials to a dielectric capacitor. This change in the resistance of the 2-dimensional layers modifies the overall impedance enabled by the presence of the interfacial layer due to Sr_xCa_1−xTiO₃, which alters the charge transport of the 2-dimensional layer from metallic to semiconducting conduction. A noticeable change is observed in the capacitance Bode plots, indicating highly amplified dielectric constants compared with the pristine SrTiO₃ substrates and Sr_xCa_1−xTiO₃ with a greater Ca content.     

Analysis of electro-active regions and conductivity of BaMnO3 ceramic by impedance spectroscopy

Polycrystalline BaMnO₃ ceramic powders were prepared using the conventional mixed oxide route accompanied with several milling processes. Single phase formation was verified by recording the X-ray diffraction pattern of the powder as well as sintered pellet at room temperature. Scanning electron micrograph and energy dispersive X-ray spectrum of cross-sectional view have shown that sintered pellet is highly porous and contains only Ba, Mn and O elements, respectively. Analysis of impedance spectroscopy was carried out via the complex impedance and complex modulus formalisms. These results have shown that BaMnO₃ behave as semiconducting material. Furthermore, as a consequence of electrically inhomogeneous nature of the sample, it was observed that the electroactive regions (such as grain, grain boundary and sample-electrode interface) are overlapped in the applied frequency domain with dominant grain boundary effect. An equivalent circuit model (R _g C _g)(R _gb Q _gb)(R _e Q _e) was employed to fit the temperature dependent impedance spectroscopy data. Study of grain and grain boundary conductivities suggest that grains are more conductive than grain boundaries and conduction mechanism followed correlated barrier hopping (CBH) model.     

Study of density of localized states in Cd4Se96−xSx (x=0, 4, 8, 12) chalcogenide semiconductor

Thin films of Cd₄Se_96−xS_x (x=0, 4, 8, 12) chalcogenide semiconductor were deposited by the thermal evaporation technique on glass substrates. XRD pattern of CdSeS alloys show that the grain size decreases with the concentration of Sulfur (S). The surface morphology changes due to the addition of sulfur content. The effect of sulfur on the DC conductivity has been investigated, which show that the DC conductivity is a thermally activated process. The Mott parameter shows that dominate conduction is in the localized states, also the addition of sulfur in Cd–Se results an increase in electrical conductivity, which may be due to shift of Fermi level. Current–voltage (I–V) measurements at different fixed temperatures show two regions; Ohmic conduction at low bias having a unit slope, and non ohmic conduction at high bias. Observation of the data shows that conduction is dominated by trap limited space charge limited conduction (SCLC), from where the density of state has been calculated using SCLC measurement data. The increase in the density of states with sulfur concentration may be due to the increase in the defect states.     

Transport mechanisms in tris(8-hydroxyquinoline)aluminium (Alq3) electronic layers: a study by photodipolar absorption

This paper describes the role of traps in the electronic conductivity of tris(8-hydroxyquinoline)aluminium (Alq3) in a conventional sandwich structure with indium tin oxide and aluminium electrodes. New results obtained by photodipolar absorption techniques and impedance spectroscopy are presented. The former method acts as a probe to highlight the role of traps. It is shown that optical pumping of electrons to trap levels gives a clear increase in dielectric absorption due to the reorientation of dipoles associated with trapped charges. The trap depth is estimated to be around E _t?=?0.19?eV, a value in good agreement with theoretical calculations and thermoluminescence measurements. The latter method permits a representation of the sample in terms of a circuit composed of a parallel capacitor (C _p) and resistor (R _p) both in series with a resistor R _s?≈?50?Ω located on the anode side. A logarithmic plot of R _p as a function of the dc bias voltage gives a linear law that is recognized, for the first time, to be a consequence of a trapped charge limited (TCL) current. The linearity can be improved by the introduction of a field-dependent mobility.     

Use of fat suppression in R₂ relaxometry with MRI for the quantification of tissue iron overload in beta-thalassemic patients

Purpose

To assess the performance and results of R₂ relaxometry using a fat-suppressed (FS) multiecho sequence and compare these to conventional R₂ relaxometry in estimating tissue iron overload.

Materials and Methods

Relaxation rate values (R₂=1/T2) of the liver, spleen, pancreas and vertebral bone marrow (VBM) were estimated in 21 patients with β-thalassemia major, using a respiratory-triggered 16-echo Carr-Purcell-Meiboom-Gill (CPMG) spin-echo sequence before (R₂) and after (R₂ FS) the application of chemically selective fat suppression.

Results

Hepatic and splenic R₂ FS values correlated with respective R₂ values (r=0.98 and r=0.96, P<.001), whereas correlations between R₂ FS and R₂ values for pancreas and VBM were not statistically significant. Bland–Altman plots show disagreement between R₂ and R₂ FS values, particularly for pancreas and VBM. Hepatic, pancreatic and VBM R₂ FS values correlated with serum ferritin (r=0.88, P<.001; r=0.51, P<.003; and r=0.75, P<.002, respectively). Hepatic R₂ FS values correlated with splenic R₂ FS (r=0.77, P<.03), pancreatic R₂ FS (r=0.61, P<.006) and VBM R₂ FS values (r=0.70, P<.001), whereas pancreatic R₂ FS values correlated also with VMB R₂ FS values. On the contrary, among the R₂ values of the above tissues, obtained without fat suppression, only hepatic R₂ values correlated with serum ferritin, whereas no correlation was documented between hepatic and pancreatic or VBM R₂ values. The application of fat suppression did not improve breathing or flow artifacts.

Conclusion

Application of fat suppression in the standard CPMG sequence improved the capability of MRI in noninvasive quantification of iron, particularly in lipid-rich tissues, such as vertebral bone marrow (VBM) and pancreas.     

Vitreous solid state electrolytes in the system of RNO3–Zn(NO3)2–KHSO4–P2O5

The structure and electric conductivity of glasses in the system RNO₃–Zn(NO₃)₂–KHSO₄–P₂O₅ (R = Na, K) obtained at different temperatures were investigated by IR and impedance spectroscopy. Glasses fused at 250–350 °C demonstrated an increase of their ionic conductivity in 10³ times in comparison with the same compositions fused at 550 °C. The influence of the chemical composition on the structure and properties of the obtained glasses was analyzed. It is proposed that the high ionic conductivity of glasses obtained at low temperatures is related to the incorporation of the nitrate ions between long (PO₃)_n chains, similar to the iodide ions; this resulted in a maximal coordination of the local conduction space for the cation associated with a disordered glass network.     

Assessment of interstitial water content of articular cartilage with T1 relaxation

The interstitial water content typically increases in the early degeneration of articular cartilage. Previously, T₂ relaxation has been related to water content, yet it is known to be strongly affected by the collagen orientation. Articular cartilage plugs from the bovine patella, femur and tibia (N=20) were mapped for T₁ and T₂ at 9.4 T to test the ability of T₁ relaxation to reflect cartilage water content. As a reference, water and proteoglycan (PG) contents were determined. Significant (P<.01) linear associations were demonstrated between the relaxation rates and tissue water content (R₁: r=−.81, R₂: r=−.60) and PG content (R₁: r=.75). After adjustment for the tissue water content, partial correlation analysis did not show significant associations between the relaxation rates and tissue PG content. After the effect of PGs was removed, significant (P<.05) linear correlation between the relaxation rates and tissue water content (R₁: r=−.48, R₂: r=−.50) was observed. Thus, the spin-lattice relaxation rate is proposed to provide a biomarker for water content in articular cartilage.     

Modification of Au surfaces using new ferrocene derivatives

Gold surfaces have been modified by self-assembled techniques. Here the adsorption time of diasteroisomers (1R, 3S)-1-ferrocenyl-3-methyl-4,4-diphenyl-2,5-dioxacyclopentane and (1S, 3S)-1-ferrocenyl-3-methyl-4,4-diphenyl-2,5-dioxacyclopentane (Scheme 1, 3a and 3b) at a Au surface in ethanol solution was controlled. This study was followed by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) analysis. The method used for the surface modification was the control of exposure time of a Au surface in the modifier/ethanol solution. It was demonstrated by EIS and XPS that the Au surface was modified with mixture of compounds 3a + 3b, avoiding the electron transference in the interface. It was also observed that the organometallic molecule indeed had been adsorbed on the Au surface. In addition, evidence seems to conclude that the molecule-Au interaction is through the electrons of cyclopentadienyl moiety, where the oxygen atoms are near the air-molecule interface and the iron atom is near the Au surface. This type of interaction of the ferrocene derivatives with gold surfaces has not been reported by any other author.     

Thermodynamic properties and application of CBH model in the ac conductivity of LiNi1.5P2O7 ceramic

The LiNi_1.5P₂O₇ compound was prepared by the solid-state reaction method at 923 K and characterized through XRD and Raman spectroscopy techniques. The impedance spectroscopy measurements were performed in the frequency and the temperature range (300 Hz–5 MHz) and (633–729 K), respectively. The ac conductivity for grain contribution is interpreted using the universal Jonscher’s power low. The exponent n decreases with increasing temperature which reveals that the conduction inside the studied material is insured by the correlated barrier hopping (CBH) model. The parameters of CBH model were determined showing that the ac conduction is realised by single-polaron hopping mechanism. Thermodynamic parameters such as the free energy for dipole relaxation ΔF, the enthalpy ΔH, and the change in entropy ΔS have been calculated.     

Electrical analysis of a newly synthesized rare earth double perovskite oxide: Sr2CeNbO6

A polycrystalline rare earth double perovskite oxide, strontium cerium niobate, Sr₂CeNbO₆ (SCN) is synthesized by solid state reaction technique for the first time. Impedance spectroscopy is employed to determine the electrical parameters (resistance (R), capacitance (C) and relaxation time (τ)) of SCN in a temperature range from 303 to 703 K and in a frequency range from 100 Hz to 1 MHz. The spectrum of imaginary part of complex impedance (Z″) at each temperature exhibits one relaxation peak. The modified Cole-Cole equation is used (experimental data is fitted with this model) to describe these relaxation peaks. Scaling behaviour of Z″ suggests that the relaxation describes the same mechanism at the entire temperature range. Impedance data of SCN that have capacitive and resistive components is represented by Nyquist diagram. The experimental impedance data is fitted using equivalent RC circuit at various temperatures. The grain conduction and τ follow an Arrhenius law associated with activation energy 0.87 and 0.88 eV, respectively.     

Feasibility of using limited-population-based average R10 for pharmacokinetic modeling of osteosarcoma dynamic contrast-enhanced magnetic resonance imaging data

Retrospective analyses of clinical dynamic contrast-enhanced (DCE) MRI studies may be limited by failure to measure the longitudinal relaxation rate constant (R₁) initially, which is necessary for quantitative analysis. In addition, errors in R₁ estimation in each individual experiment can cause inconsistent results in derivations of pharmacokinetic parameters, K^trans and v_e, by kinetic modeling of the DCE-MRI time course data. A total of 18 patients with lower extremity osteosarcomas underwent multislice DCE-MRI prior to surgery. For the individual R₁ measurement approach, the R₁ time course was obtained using the two-point R₁ determination method. For the average R₁₀ (precontrast R₁) approach, the R₁ time course was derived using the DCE-MRI pulse sequence signal intensity equation and the average R₁₀ value of this population. The whole tumor and histogram median K^trans (0.57±0.37 and 0.45±0.32 min⁻¹) and v_e (0.59±0.20 and 0.56±0.17) obtained with the individual R₁ measurement approach are not significantly different (paired t test) from those (K^trans: 0.61±0.46 and 0.44±0.33 min⁻¹; v_e: 0.61±0.19 and 0.55±0.14) obtained with the average R₁₀ approach. The results suggest that it is feasible, as well as practical, to use a limited-population-based average R₁₀ for pharmacokinetic modeling of osteosarcoma DCE-MRI data.     

Electrical properties and conduction mechanism in the sodium nickel diphosphate

The Na_3.6Ni_2.2(P₂O₇)₂ compound was obtained by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction and vibrational and impedance spectroscopy. The AC electrical conductivity and the dielectric relaxation properties of this compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 209 kHz–1 MHz and 564–729 K, respectively. Dielectric data were analyzed using complex electrical modulus M* at various temperatures. The peak positions ω _m of M″ spectra shift toward higher frequencies with increase in temperature. The AC conductivity data fulfill the power law. Application of the correlated barrier hopping model revealed that the ionic conduction takes place by single-polaron and bipolaron hopping processes.     

Electrical properties and conduction mechanism of [N(C2H5)4][N(CH3)4]CuCl4 compound

The [N(CH₃)₄][N(C₂H₅)₄]CuCl₄ single crystal has been synthetized in order to determinate the temperatures transition and to study the electrical properties and the conduction mechanism. At room temperature, this compound crystallizes in the tetragonal system with P-42₁m space group. The calorimetric study shows three anomalies at 248, 284 and 326 K. Electrical conduction and dielectrical relaxation mechanisms at various frequencies and temperatures were analyzed by impedance spectroscopy and the equivalent circuit based on the Z-View-software was proposed. The variation of f_p relaxation determinate by the modulus study and σ_dc specific to the AC conductivity as a function of temperature and confirm the all transitions for our sample. The values of the activation energy are determined and compared by those, which are found in the similar compound. Frequencies dependence of alternative current (AC) conductivity is interpreted in terms of Jonscher's law and the conduction mechanisms for each phase are determined with the Elliot's theory.     

Complex impedance spectroscopy studies of (La0.70−xNdx)Sr0.30Mn0.70Cr0.30O3 (x≤0.30) perovskite compounds

The transport properties of Nd-doped perovskite materials (La_0.7−xNd_x)Sr_0.3Mn_0.7Cr_0.3O₃ (x≤0.30) were investigated using impedance spectroscopy techniques over a wide range of temperatures and frequencies. AC conductance analyses indicate that the conduction mechanism is strongly dependent on temperature and frequency. The DC conductance plots can be described using the small polaron hopping (SPH) model, with an apparent reduction of the polaron activation energy below the Curie temperature T_C. Complex impedance plots exhibit semicircular arcs described by an electrical equivalent circuit. Off-centered semicircular impedance plots show that the Nd-doped compounds obey to a non-Debye relaxation process. The conductivity of grains and grain-boundaries has been estimated. The activation energies calculated from the conductance and from time relaxation analyses are comparable. This indicates that the same type of charge carriers is responsible for both the electrical conduction and relaxation phenomena.     

Dielectric relaxation and ac conduction in multiferroic TbMnO3 ceramics: Impedance spectroscopy analysis

Polycrystalline samples of Tb_1−xAl_xMnO₃ (x = 0, 0.1, 0.2) have been synthesized by means of standard high-temperature solid-state reaction technique. Detailed studies on the effect of compositional variation of aluminum (Al) on the electrical behavior (complex impedance Z*, complex modulus M*, and relaxation mechanisms) of the parent TbMnO₃ have been performed by using the nondestructive complex impedance spectroscopy technique at temperatures above room temperature. In the temperature range covered, the impedance plots signalize that the grains are the unique responsible for the conduction mechanism of the concerned material. The impedance spectra are well modeled in terms of electrical equivalent circuit with a grain resistance (R_g) and constant phase element impedance (Z_CPE). The conductivity data of the undoped and Al-doped samples are well fitted by the universal Jonscher's power law. The resulting fitting parameters indicate that for the studied samples, the hopping process occurs between neighboring sites. Activation energy values for dc conductivity are calculated for undoped and Al-doped samples and found to decrease when Al is incorporated. In turn, the emergence of single arc in the complex modulus spectrum for all the compositions of Al suggests that for the studied samples only one type of relaxation behavior is present at the selected temperatures. A non-Debye-type relaxation is clearly verified. The relaxation process in the present samples seems to be composition and temperature dependent, particularly at higher frequencies.     

A comprehensive study of polysilicon resistors for CMOS ULSI applications

The characteristics of polysilicon resistors for CMOS ULSI applications have been investigated. Based on the presented sub-quarter micron CMOS borderless contact, both n⁺ and p⁺ polysilicon resistors with Ti- and Co-silicide self-aligned process are used at the ends of each resistor. A simple and useful model is proposed to analyse and calculate some important parameters of polysilicon resistors including electrical delta W(ΔW), interface resistance R_interface, and pure sheet resistance R_pure. Furthermore, the characteristics of voltage-coefficient resistor, temperature-coefficient resistor, and resistor mismatching are also studied. An interesting sine-wave voltage-dependent characteristic due to the strong relation to the R_interface has been modelled in this paper. This approach can substantially help engineers in designing and fabricating the precise polysilicon resistors in sub-quarter micron CMOS ULSI technology.     

Electrical conductivity of BaTi4O9 film prepared by laser chemical vapor deposition method

A BaTi₄O₉ film was prepared on a Pt/Ti/SiO₂/Si substrate by a laser chemical vapor deposition method and was investigated by impedance spectroscopy over ranges of temperature (300–1073 K) and frequency (10²–10⁷ Hz). Plots between real and imaginary parts of the impedance (Z′ and Z′′) suggest the presence of two relaxation regimes, which were attributed to grain and grain boundary responses. The conduction of both grains and grain boundaries obeys the Arrhenius format with activation energies of respectively 1.45 and 1.24 eV. The close activation energies indicate that the conduction in BaTi₄O₉ film is mainly by oxygen vacancies.     

Frequency domain measurements on Na2B4O7−V2O5 semiconducting glass

Summary Dielectric measurements on Na₂B₄O₇(99.5%)−V₂O₅(0.5%) glass system, in the frequency range 10⁻³ to 10⁴ Hz and temperature range 300 to 500 K, have been carried out. The normalized plots of complex capacitance have shown a single mechanism responsible for conduction for both volume and surface measurements with their close values of activation energies (0.67±0.03) eV and (0.64±0.03) eV, respectively. The low-frequency dispersion (LFD) behaviour has been observed to be perturbed by the presence of more than one competing process. The impedance plots have shown a parallel combination of a capacitor (C) and a resistor (R), with some contribution of a dispersive element due to charge accumulation in the vicinity of the electrodes. The values ofR andC were found to be of the same order of magnitude, for both surface and volume measurements. The observedR has shown a decrease with an increase in temperature due to an increase in mobility of Na⁺ ions, whereasC remains practicaly constant. The complex capacitance surface behaviour is dominated by volume, due to hygroscopy of this glass system.     

Verification and application of a finite-difference model for quasi-electrostatic scanning impedance imaging

We have previously introduced liquid-contact scanning impedance imaging (SII) as a high resolution, high contrast method for imaging electrical impedance. This technique has shown its potential to measure the impedance distribution of biological tissues. In this paper, a numerical model is developed to describe the SII system based on the finite difference method. Good correspondence can be observed when comparing data simulated using the model with experimental data. The relationships between measurable resolution and system parameters such as height are shown in both simulation results and measurements. It is shown that the numerical model provides a good explanation for experimental results and can also assist in the design of the dual-conductor impedance probe used in this imaging method. Model predictions on both the conductor spacing and the resistor R used in the system have been made indicating their relationships to an empirical notion of resolution. The simulation result of the conductor spacing also gives an insight to the function of the dual-conductor probe. Based on this model, an optimum probe design can be obtained by balancing ultimate resolution with the signal-to-noise ratio by adjusting spacing and resistor values.