Real Part Of Complex Conductivity Research Articles

Structural, Magnetic, and Dielectric Spectroscopy Investigations of Multiferroic Composite Based on Perovskite–Spinel Approach

Multiferroic composite materials with the nominal composition (La0.8Gd0.2FeO3)1−x(Mn0.5Cu0.5Fe2O4)x, x = 0.0≤x≤1 were prepared using the co-precipition method. XRD, FTIR and Raman were utilized to investigate the structure phase, microstructural characteristics, vibrational bands. The optical properties were analyzed; the VSM was used to investigate the magnetic properties of the composites. Broadband dielectric spectroscopy is employed to investigate the dielectric and electrical performance of the prepared multiferroic composites. Rietveld refinement of the XRD patterns confirmed the orthorhombic phase for lanthanum gadolinium iron oxide (La0.8Gd0.2FeO3) and cubic phase for manganese copper ferrite (Mn0.5Cu0.5Fe2O4). The crystallite size of LGFO phase pointed out that it increases with increasing the MCFO phase, while the microstrain found to decline. The FTIR results elucidated the tetrahedral and octahedral bands. The deduced optical properties revealed that the samples have optical energy gap in the range 4.18 −4.5 eV. The magnetic properties revealed that the composites exhibit typical ferromagnetic hysteresis loops, indicating the presence of ordered magnetic structure. The frequency dependence of permittivity ε′(f) and real part of complex conductivity, σ′(f) exhibits a development of a net of micro-capacitors like behavior that stores charge carriers.

The interplay between molecular structure and dielectric propertiesin ionic liquids: A comparative study

In this work, C2-Methylated [C3DMIM+][I−] versus C2-Protonated [C3MIM+][I−] Imidazolium-Based Ionic Liquids containing iodide anion, have been synthesized and characterized using 1H and 13C NMR spectroscopy methods. In order to investigate the methylation effect on thermal properties, we rely to three additional thermal analysis techniques. The thermal behavior confirmed that the methylated [C3DMIM+][I−] IL is more stable than the protonated one [C3MIM+][I−].The conductivity and dielectric relaxation properties of both ILs have been investigated in the frequency range [10−2, 107 Hz] and the temperature ranging between −30 °C and 60 °C. Dielectric permittivity studies show that the substitution of the hydrogen atom by a methyl group has a significant impact in both the realε′ and imaginary ε′′ parts. In addition, the analysis of the observed relaxation times for the protonated IL [C3MIM+][I-] showed Arrhenius-type temperature dependence for the temperatures ranging between 20 °C and 60 °C − and VFT temperature dependence for the temperatures ranging between −20 °C and 20 °C−, while, the methylated IL [C3DMIM +][I−] showed Vogel-Fulcher-Tamman-type temperature dependence in the entire investigated temperature range − 30 °C to 60 °C. The representation of σ″ (ν, T) shows the buildup of the electrochemical double layer and interfacial effect. However the real part of complex conductivity follows the empirical Jonscher equation. The determined dc-conductivity of both investigated Ionic liquids present a new behavior regarding the thermal activation an anomalous thermal activation behavior. It follows an Arrhenius relation at lower temperatures and then reach a steady state values at higher temperatures.

An insight into the structure, conductivity and ion dynamics of Sr-Sm co-doped ceria oxygen ion conductors: Effect of defect interaction

In this work, we investigate the structure, conductivity and ion dynamics of mixed di and tri-valent doped Ce0.8Sm0.2-xSrxO2-δ (x = 0–0.2) oxygen ion conductors. The lattice parameter and root mean square strain are significantly affected by the ionic radius of dopants and their solubility into ceria lattice. Due to the solubility limit of Sr2+ ions, SrCeO3 phase increases with the doping concentration of Sr2+. The increase of Sr2+ ions into ceria lattice promotes the formation of large defect clusters by expense of formed oxygen vacancies. The coulombic interaction between oxygen vacancies with substituted dopant cations enhances with Sr2+ ions due to decrease of the value of dielectric constant of the compositions. The defect interaction significantly affects the conductivity values by means of increase of SrCeO3 phase and defect clusters. The conductivity values are found to be consistent with the migration and association energy. The scaled spectra of dielectric tangent loss and real part of complex conductivity confirm the temperature and defect interaction independent nature of hoping mechanism in the compositions.

Field-scale electrical geophysics over an olive oil mill waste deposition site: Evaluating the information content of resistivity versus induced polarization (IP) images for delineating the spatial extent of organic contamination

We performed 2D resistivity and IP measurements over a known olive oil mill waste plume at a site in western Crete, Greece. The objectives of the survey were: (1) to determine whether IP is more diagnostic in delineating the spatial extent of the plume relative to resistivity measurements alone; (2) to evaluate whether the additional information content obtained from IP is worth the effort given longer data acquisition times and higher measurement errors that inevitably characterize field IP data acquisition. Complex conductivity inversion of the field IP dataset revealed that the organic plume is characterized as a region of high electrical conductivity (real part of complex conductivity) consistent with the conceptual model for the electrical structure of a biodegraded LNAPL contaminant plume. The plume is also characterized by a region of high polarizability (imaginary part of complex conductivity) that is more localized to the known plume location (based on conventional monitoring) relative to the high conductivity region in the electrical conductivity image. This observation is attributed to the fact that electrical conductivity is more strongly controlled by hydrogeological and geological characteristics of the site that mask the response from the biodegraded plume. This result encourages the use of field IP to improve the spatial delineation of organic contamination in the subsurface. However, more laborious field procedures are required to acquire reliable field IP data and the inversion of field IP data remains more challenging than resistivity data alone.

Electrical conductivity and relaxation in poly(3-hexylthiophene)

We studied the complex conductivity of regioregular poly(3-hexylthiophene) (P3HT) in the temperature range between 193--333 K ($\ensuremath{-}80\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ to $60\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$) and in the frequency range from the direct current (dc) to 12 GHz. The identified relaxation process was investigated by quasielastic neutron scattering (QENS). The dielectric loss peak extracted from complex conductivity corresponds to local molecular motions having an activation energy of about 9 kJ/mol, which agrees well with the QENS results. The molecular motions of the hexyl side groups in poly(3-hexylthiophene) contribute to this relaxation process in P3HT, which is coupled with a cooperative charge transport along the P3HT chains. In the cutoff frequency range, the real part of complex conductivity $({\ensuremath{\sigma}}^{\ensuremath{'}})$ gradually transitions to a frequency-independent conductivity $({\ensuremath{\sigma}}_{\ensuremath{\propto}}^{\ensuremath{'}})$, which is thermally activated. The activation energy of ${\ensuremath{\sigma}}^{\ensuremath{'}}$ at 50 MHz is about 80 meV. In comparison, the activation energy of the dc conductivity, ${\ensuremath{\sigma}}_{0}$, is larger, about 280 meV, while the value of ${\ensuremath{\sigma}}_{0}$, is many orders of magnitude smaller than ${\ensuremath{\sigma}}_{\ensuremath{\propto}}^{\ensuremath{'}}$ We conclude that the local relaxation of the hexyl side groups contribute to a topological disorder in the polymer structure. As a consequence the energy barriers of the charge transport increase and the conductivity decreases. At 190 K the conductivity decreases from the disorder-free ${\ensuremath{\sigma}}_{\ensuremath{\propto}}^{\ensuremath{'}}$ of approximately $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{S}/\text{m}$ to ${\ensuremath{\sigma}}_{0}$ of about $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{S}/\text{m}$.

Superconducting gap anisotropy ofLuNi2B2Cthin films from microwave surface impedance measurements

Surface impedance measurements of LuNi2B2C superconducting thin films as a function of temperature have been performed down to 1.5 K and at 20 GHz using a dielectric resonator technique. The magnetic penetration depth closely reproduces the standard B.C.S. result, but with a reduced value of the energy gap at low temperature. These data provide evidence for an anisotropic s-wave character of the order parameter symmetry in LuNi2B2C. From the evaluation of the real part of complex conductivity, we have observed constructive (type II) coherence effects in the electromagnetic absorption below Tc.

A collective excitation on the slightly hole-doped ladders of Sr 14− xCa xCu 24O 41 in the microwave and millimeter wave regions

We measured the temperature- and the frequency dependence of the real part of complex conductivity σ 1(T, ω) along the ladder direction of Sr 14− x Ca x Cu 24O 41 between 10 and 100 GHz. For slightly hole-doped compounds ( x=0 and 3), σ 1(T, ω) shows a strongly frequency-dependent behavior at low temperatures, forming a clear peak in the conductivity spectra. In particular, the conductivity peak of x=0 was quite asymmetric and remained up to 150 K. The origin of this mode and the change with Ca doping are discussed in terms of the charge dynamics on Cu 2O 3 ladders.

Electrical relaxation of superionic conducting glasses AgX-AgPO3 (X=I, Br, Cl)

The complex impedance of superionic conducting glasses (AgX)0.3-(AgPO3)0.7 (X = I, Br, Cl) was measured in the frequency range 5 Hz–500 kHz and temperatures between 299 K and 348 K. The frequency dependence of Σ′ (the real part of complex conductivity) shows two regions: low and high frequencies. The first is attributed to the electrode-electrolyte polarization, while the second is attributed to the bulk conduction. The replacement of AgCl by AgBr or Agl at the same molar fraction is found to improve the bulk conductivity of the studied glasses. The electrical conductivity spectra exhibit one relaxation peak associated with dielectric loss which arises from the thermally activated jumps of Ag+ ions. The dependence of the relaxation time upon the halogen type is discussed in terms of the structural aspects, where the silver halides tend to form microdomains. The special characteristic of fast ionic conduction depending upon halide type is emphasized.