Application of small amplitude cyclic voltammetry for the investigation of Naβ-alumina/metallic electrode interface electric properties

The use of small amplitude cyclic voltammetry for investigation of the β-alumina/metallic electrode interface is proposed. Voltammetric curve analysis is based on the electric circuit consisting of three elements. The plots of the reciprocal of capacity determined from voltammograms versus the reciprocal of voltage sweep period square root are extrapolated to obtain the limiting value of capacity. This limit corresponds to C_LF obtained in the ac impedance technique. This method can be mostly useful when the low frequency limit in impedance measurements is insufficient for exact determination of capacitive components of the electric equivalent circuit.     

Bounded diffusion in solid solution electrode powder compacts. Part I. The interfacial impedance of a solid solution electrode (MxSSE) in contact with a m+-ion conducting electrolyte

The transient and ac electrical response of electrochemical systems containing a solid solution electrode is derived using Laplace transform methods. First, the operational impedance of the electrolyte/solid solution electrode interface is derived, for both asymmetrical and symmetrical cell systems. From the operational impedance the current, voltage and ac impedance response is calculated. By combination of semi-infinite and bounded diffusive behaviour, both the chemical diffusion coefficient of the inserted ions and the thermodynamic factor (? ln a/? ln c) can be obtained from kinetic data only.     

Qualitative estimation of the contents of seeping water and estimation of the flow velocity in clay barriers by impedance spectroscopy

In this work, the flow of different kinds of liquids (differences in polarity, aromaticity, molecular size) through a layer of Friedland clay and the interaction of these liquids with the clay particles are investigated by means of electrical impedance measurements. The instationary flow can be described by data obtained from complex impedance plots. The gradient of the ohmic part of the impedance gives information about the strength of the driving force and the speed of flow/diffusion of the liquid through the clay. Different kinds of liquids lead to completely different impedance spectra. From time-dependent impedance measurements on a layer of defined thickness, information can be gained about the contents of the liquid flowing or diffusing through the clay. The impedance spectroscopy could be a powerful method for the development of an in situ monitoring system in waste disposal sites having clay barriers. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Temperature dependence of AC-photoconductivity of HgI2 crystal

An ac impedance method has been used to study the electrical properties of an illuminated HgI₂ crystal as a function of temperature [10–350 K] and frequency [1–10₄ Hz]. The complex impedance plane plots enabled us to determine the bulk resistance of the crystal as a function of temperature. Activation energies of [0.08±0.005 eV] and [0.25 ±0.01eV] are then found; they are attributed to acceptor and donor trapping levels, respectively. At temperatures lower than 230 K, a weak temperature dependence of the bulk resistance is observed. This weak dependence is supposed to be due to photoconductivity.     

Dielectric relaxation and ac conductivity study of Ba(Sr1/3Nb2/3)O3

Single phase perovskite Ba(Sr_1/3Nb_2/3)O₃ 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.     

Complex impedance analysis and ionic conductivity studies of NaBaPO4

The NaBaPO₄ compound was obtained by conventional solid-state reaction. The sample was characterized by X-ray powder diffraction and electrical impedance spectroscopy. The impedance plots show semicircle arcs at different temperatures, and an electrical equivalent circuit has been proposed. The circuits consist of the parallel combination of bulk resistance R _p and constant phase elements CPE. The dielectric relaxation is described by a non-Debye model. The frequency dependence of the conductivity is interpreted in term of the well-known universal dynamic response $ {\sigma_{\mathrm{ac}}}={\sigma_{\mathrm{dc}}}\left[ {1+{{{\left( {{\omega \left/ {{{\omega_h}}} \right.}} \right)}}^n}} \right] $ . The near value of activation energies obtained from the analyses of M″, conductivity data and equivalent circuit confirms that the transport is through ion hopping mechanism dominated by the motion of the Na⁺ ions in the structure. The better properties obtained for NaBaPO₄ can be attributed to the Ba derivatives’ larger size of the bottlenecks along the channels.     

Effect of melt compounding temperature on dielectric relaxation and ionic conduction in PEO–NaClO<Subscript>4</Subscript>–MMT nanocomposite electrolytes

Polymer nanocomposite electrolytes (PNCEs) of poly(ethylene oxide) and sodium perchlorate monohydrate complexes with montmorillonite (MMT) clay up to 20 wt.% MMT concentration of poly(ethylene oxide) (PEO) are synthesized by melt compounding technique at melting temperature of PEO (∼70 °C) and NaClO₄ monohydrate (∼140 °C). Complex dielectric function, electric modulus, alternating current (ac) electrical conductivity, and impedance properties of these PNCEs films are investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The direct current conductivity of these materials was determined by fitting the frequency-dependent ac conductivity spectra to the Jonscher power law. The PNCEs films synthesized at melting temperature of NaClO₄ monohydrate have conductivity values lower than that of synthesized at PEO melting temperature. The complex impedance plane plots of these PNCEs films have a semicircular arc in upper frequency region corresponding to the bulk material properties and are followed by a spike in the lower frequency range owing to the electrode polarization phenomena. Relaxation times of electrode polarization and ionic conduction relaxation processes are determined from the frequency values corresponding to peaks in loss tangent and electric modulus loss spectra, respectively. A correlation is observed between the ionic conductivity and dielectric relaxation processes in the investigated PNCEs materials of varying MMT clay concentration. The scaled ac conductivity spectra of these PNCEs materials also obey the ac universality law.     

The effect of potential of impedance in the pulsed-laser-deposited SrBi2Ta2O9 thin film

Ferroelectrics SrBi₂Ta₂O₉ (SBTO) thin films were grown on a highly oriented Pt/Ti/SiO₂/Si substrates using the pulsed laser ablation. The ac impedance of SBTO thin films have been measured at room temperature both in the frequency range from 10⁻¹ to 10⁶ Hz and bias voltage range from −6 to 6 V. The ac impedance dispersion was observed at low frequency with increasing bias voltage, which was interpreted based on a blocked charge. We can explain that the blocking interface gives rise to constant phase element (CPE) response, and we give an impedance model function that can fit data along the low frequency range when such a CPE is found. The low frequency dispersion phenomena of SBTO thin film are related to a charge diffusion process at the surface of thin film.     

Broad range frequency – temperature response of Ba2Zn2Fe12O22

Ba₂Zn₂Fe₁₂O₂₂ was synthesized by solid state reaction technique. The temperature and frequency dependent electrical properties and complex impedance spectroscopy were analysed. Complex modulus formalism shows the existence of high resistance and small capacitance of the material for the short range relaxation. The presence of non-Debye type relaxation is revealed from Nyquist plots and enabled to separate the contribution from bulk and grain boundary effect in the material. Further, the ac electrical conductivity of the material was well agreed with the Jonscher's universal power law.     

The effect of domain wall motion on the nondiagonal impedance component in amorphous wires with circular magnetic anisotropy

The effect of the domain wall motion on the nondiagonal impedance component in amorphous ferromagnetic wires with circular anisotropy was theoretically studied. The frequency spectrum of the electromotive force (emf) induced in the pick-up coil wound around the wire is analyzed. For sufficiently small amplitudes of the ac current passing in the wire, the emf frequency equals doubled frequency of the current. For the ac current amplitudes exceeding certain threshold value, all even harmonics appear in the frequency spectrum of the signal. The emf strongly depends on the longitudinal component of the applied magnetic field at any value of the ac current amplitude. These results can be important for developing frequency transducers controlled by magnetic field.     

Impedance spectroscopy study of Na<Subscript>1/2</Subscript>Sm<Subscript>1/2</Subscript>TiO<Subscript>3</Subscript> ceramic

Complex impedance analysis of a valence-compensated perovskite ceramic oxide Na_1/2Sm_1/2TiO₃, prepared by a mixed oxide (solid-state reaction) method, has been carried out. The formation of single-phase material was confirmed by X-ray diffraction studies, and it was found to be an orthorhombic phase at room temperature. In a scanning electron microscope, grains separated by well-defined boundaries are visible, which is in good agreement with that of impedance analysis. Alternating current impedance measurements were made over a wide temperature range (31–400 °C) in an air atmosphere. Complex impedance and modulus plots helped to separate out the contributions of grain and grain boundaries to the overall polarization or electrical behavior. The physical structure of the samples was visualized most prominently at higher temperatures (275 °C) from the Nyquist plots showing inter- and intragranular impedance present in the material. The frequency dependence of electrical data is also analyzed in the framework of the conductivity and modulus formalisms. The bulk resistance, evaluated from the impedance spectrum, was observed to decrease with rise in temperature, showing a typical negative temperature coefficient of resistance-type behavior like that of semiconductors. The modulus mechanism indicates the non-Debye type of conductivity relaxation in the materials, which is supported by the impedance data. PACS 77.22.Ch; 77.22.Ej; 77.22.Gm; 77.22.Jp; 77.84.Bw     

Structural and electrical properties of Na1/2La1/2TiO3 ceramics

Na_1/2La_1/2TiO₃ (NLT) ceramic was prepared by a high-temperature solid-state reaction technique. A preliminary structural analysis (XRD) suggested the formation of a single-phase orthorhombic structure. SEM micrograph of the material showed uniform grain distribution on the surface of the sample. The dielectric permittivity and the loss tangent of the sample were measured in a frequency range from 1 kHz to 1 MHz and a temperature range 28 °C to 525 °C. Electrical properties of the material were studied using an ac impedance spectroscopic technique. Detailed analysis of the impedance spectrum suggested that the electrical properties of the material are strongly temperature dependant. The Nyquist plots clearly showed the presence of both bulk and grain boundary effect in the compound. The activation energy was estimated to be 1.1 eV from the temperature variation of dc conductivity. The a.c. conductivity spectrum suggests a typical signature of ion conducting system. PACS 77.22.Ch; 77.22.Gm; 77.80.Bh; 77.22.Ej     

Automatic spectroscopy of solids in the low-frequency range

An automatic low frequency spectrometer is described, which gives plots of impedance, admittance and dielectric data versus the logarithm of the frequency as well as complex-plane plots of these data in the frequency range 100 Hz to 10 MHz and in the temperature range from 220 to 470 K. The development of this spectrometer was started in 1975 using a processor-controlled synthesizer and gain/phase-meter. Some typical applications are summarized.     

Synthesis, electrical and electromechanical properties of a tungsten-bronze ceramic oxide: Pb0.68K0.64Nb2O6

A tungsten-bronze ceramic oxide, Pb_0.68K_0.64Nb₂O₆, has been prepared by a standard solid-state reaction technique. Compound formation and phase identification has been confirmed by X-ray diffraction (XRD) studies. The dielectric permittivity and the loss tangent of the sample have been measured in a frequency range 45 Hz–5 MHz and a temperature range 35–590 °C. Electrical properties of the material were studied using an impedance spectroscopic technique. Detailed analysis of the impedance spectrum suggested that the electrical properties of the material are strongly temperature dependent. The Nyquist plots clearly showed the presence of bulk and grain boundary effect in the compound. The imaginary part of modulus at different temperatures shows a relaxation peak and its position shifts to higher frequency with increase in temperature. This suggests a temperature-dependent relaxation. The frequency dependent ac conductivity at different temperatures indicated that the conduction process is thermally activated process.     

Automated multifrequency measurements of the complex impedance of fast ion conductors

An automated apparatus based on phase synchronous detection has been assembled for measurements of the complex impedance of fast ion conductors. Procedures for calibration and for data acquisition and analysis are described. The relative advantages and disadvantages of this method are compared with ac bridge and pulse methods. The method is illustrated with measurements of the sodium beta-aluminas.     

Sol–gel synthesis,structural and ion transport studies of lithium borosilicate glasses

Lithium borosilicate (LBS) glasses of different modifier to formers (m/f) ratios were synthesized through sol–gel process. Structural characterisation of LBS glasses were made using XRD, FTIR and DSC techniques. XRD pattern of LBS samples showed amorphous phase for gels heat treated between 573 and 698 K and further heat treatment above 698 K showed the formation of crystalline multiphases. FTIR spectra for dried LBS gels between 338 and 443 K showed the presence of hydroxyl group on the surface of silicate and borates matrix and on heat treatment, the FTIR spectra revealed the formation of silicate and borate linkages in LBS glassy matrix. DSC curve confirmed the presence of adsorbed water molecules in LBS glassy matrix. Impedance measurements were carried out on LBS samples of different m/f ratios as a function of temperature and data were analyzed using Boukamp equivalent circuit software. The conductivity of LBS glasses at different temperatures was calculated from analyzed impedance data. Activation energy (E_a) is obtained from Arrhenius plots of the dc conductivity and it is found to be 0.64 (±0.02) eV for high conducting sample. ac conductivity is calculated from impedance data and analyzed using Jonscher's power law (JPL) exponent (s) for m/f ratios of LBS samples at different temperatures. The power law exponent s of LBS glasses exhibited a non-linear behavior with temperature. The electric modulus data were fitted with Kohlraush–William–Watts (KWW) stretched exponential function and the modulus formalism is used to study the ionic relaxation behavior in LBS samples.     

Determination of the magnetic transition temperature of dilute ferromagnetic alloys - the Pd(Gd) case

The determination of T_c in dilute alloys is examined. As an example, magnetization vs field data in a Pd_0.95Gd_0.05 alloy are presented. For this alloy, it was not possible to determine a value of T_c using Arrott-Belov-Kouvel (ABK) plots; the conditions for the applicability of ABK plots were not satisfied. Results of very-low-field ac and dc magnetization vs T, which depend mainly on the demagnetization factor, yield a more precise measure of T_c. We conclude that the latter procedures are more useful than ABK plots for determination of T_c in dilute alloys.     

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 spectroscopy and confirmation of ion conduction mechanism in direct melt compounded hot-press polymer nanocomposite electrolytes

Solid-type polymer nanocomposite electrolyte (PNCE) comprising poly(ethylene oxide) (PEO), lithium perchlorate (LiClO₄) and montmorillonite (MMT) nano-platelets were synthesized by direct melt compounded hot-press technique at 70 °C under 3 tons of pressure. The spectra of complex dielectric function, electric modulus and alternating current (ac) electrical conductivity, and complex impedance plane plots of these materials were investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The variation of electrode polarization and ionic conduction relaxation times with MMT concentration up to 20 wt.% confirms their strong correlation with direct current ionic conductivity. The predominance of exfoliated MMT structures in PEO matrix and their effect on cation conduction mechanism and ion pairing were discussed by considering a supramolecular transient cross-linked structure. The normalized ac conductivity as a function of scaled frequency of these PNCE materials obey the universal time–concentration superposition behaviour alike the disordered solid ionic conductors.