DC Conductivity Analysis Research Articles

Effect of sintering temperature and grain size on the electrical transport properties of La0.67Sr0.33MnO3 manganite

The effect of sintering temperature and grain size on the electrical transport properties of lanthanum-based manganite, La0.67Sr0.33MnO3, was investigated by impedance spectroscopy technique. The sintering temperature was varied from 600°C to 1000°C. From dc-conductivity analysis, it is found that increasing sintering temperature improved the electrical conductivity and does not change the value of the temperature of metal–semiconductor transition. Such results have been explained in terms of core–shell model. The presence of relaxation phenomenon in the material was detected by complex impedance analysis. Also, such analysis confirms the contribution of grain boundary in the electrical properties of the lanthanum–manganite.

Structural and electrical properties of Zn1-xNixFe2O4 ferrite

The phase purity, the homogeneity, lattice structure and cell parameters of the Zn1−xNixFe2O4 was checked by XRD technique. The Ni doping effects on the electrical properties in Zn1−xNixFe2O4 was investigated using conductance spectroscopy. When introducing nickel in Zn ferrite, the conductivity of the material increases. This effect disappears at high temperature (T>600K). The conductivity spectra can be splitted in three regions. In the first one, the conductivity is frequency independent. In the second region, the conductivity can be described by the ωn law. It decreases with increasing frequency in the third region. DC conductivity analysis proves that electronic conduction was dominated by thermally activated Hopping of Small Polaron (SPH) at high temperature and Variable Range Hopping (VRH) at low temperature. For T>Ts, where Ts is the temperature at which appears a change in the slope of σdcT(1000/T) curves, the activation energy decreases when increasing Ni content (from Ea=665meV for x=0 to Ea =283 for x=0.5). For all Ni compositions, the activation energy is equal to 280meV when temperature is lower than Ts. From AC-conductivity study, it is found that activation energy decreases with increasing Ni concentration and varies significantly when increasing frequency. Also, the variation of the exponent “n” confirms that hopping model is the dominating mechanism in the system.

Synthesis, Spectral, Thermal and Biological Studies of Mn(II), Co(II), Ni(II) and Cu(II) Complexes with 1‐(((5‐Mercapto‐1H‐1,2,4‐triazol‐3‐yl)imino)‐methyl)naphthalene‐2‐ol

AbstractMn(II), Co(II), Ni(II) and Cu(II) complexes of 5‐mercapto‐1,2,4‐triazol‐3‐imine‐2′‐hydroxynaphthaline have been synthesized and characterized by elemental analysis, IR, 1H NMR, EI‐mass, UV‐Vis, and ESR (electron spin resonance) spectra, molar conductance, magnetic moment measurements, DC conductivity and thermogravimetric analysis. IR spectra confirm that the ligand molecule existed in both thione and thiole forms. The molar conductance values indicate the complexes are nonelectrolyte. The magnetic moment values of the complexes display paramagnetic behavior. All studies confirm the formation of an octahedral geometry for complex 1 and the other complexes have tetrahedral geometrical structures. The structures of the complexes have also been theoretically studied by using the molecular mechanic calculations by the hyperchem. 8.03 molecular modeling program which confirm the proposed structures. The Schiff‐base ligand and its metal complexes have also been screened for their antimicrobial activities.

Physical characterizations of three phase polycarbonate nanocomposites

Zinc oxide–Barium titanate–Polycarbonate (ZnO−BaTiO3−PC) nanocomposites were prepared to investigate effect of ZnO–BaTiO3 mixed nanoparticles on the optical, electrical, and thermal properties of polycarbonate (PC). The UV-visible absorption spectra was measured for the nanocomposites at room temperature between 200 and 800 nm and the optical energy gap was determined from the measured absorption coefficient data. Optical results reveal that BaTiO3 ceramic has a strong absorption below 300 nm while ZnO has a strong absorption peak at 367 nm and the UV absorption in these regions depends on the ZnO and BaTiO3 concentration. This indicates that the PC UV shielding region can be controlled through the mixed BaTiO3-ZnO nanoparticle weigh ratios. Also, 10 wt% BaTiO3 nanoparticles in PC insignificantly affects the optical energy gap whereas 10 wt% ZnO nanoparticles in PC decreases the optical gap from 4.14 to 3.9 eV. Results obtained from DC conductivity and thermal analysis reveal that adding BaTiO3 nanoparticles into PC will decrease DC conductivity, restrict chain mobility, and increase thermal stability while, adding ZnO nanoparticles to PC increases DC conductivity, enhances chain mobility, and decreases the thermal stability. The optical, electrical, and thermal properties of these nanocomposites can be controlled by adjusting the ZnO to BaTiO3 nanoparticles weight ratios in the PC matrix.

Effects of ZnO on the dielectric, conductive and piezoelectric properties of low-temperature-sintered PMnN-PZT based hard piezoelectric ceramics

The ZnO-doped Pb 0.98Ca 0.01Sr 0.01[(Mn 1/3Nb 2/3) 0.06–(Zr 0.52Ti 0.48) 0.94]O 3 + 0.15 wt.% CuO for varying amounts of ZnO ( x wt.%) ceramics were prepared. Their structure evolutions and electrical properties were systematically investigated. A dc and ac conductivity analysis was conducted. It demonstrated that the probability of ZnO dopants entered the A and/or B-site of the perovskite structure, which affected the dielectric relaxation, activation energy, and piezoelectric properties. Experimental results showed that the tetragonality of the perovskite structure and electro-mechanical energy transformation ratio ( k 2 value) were increased with increasing the ZnO contents for 0.1 ≦ x ≦ 0.5. As ZnO contents increased for 0.1 ≦ x ≦ 2, the diffused phase transition (DPT) characteristic was gradually disappeared. And, the ac activation energy calculated was also decreased due to the conduction mechanism. In addition, the frequency dependence of the ac conductivity was complied with the Jonscher power law, for x = 0.5, 1, and 1.5 at measured temperature.

Time and frequency domains dc conductivity analysis in thin dielectric films at high temperature

Electrical conductivity of a thin dielectric film has been analysed at high temperature in both time and frequency domains (TD/FD). Two disturbing ionic space-charge phenomena have been highlighted in two different temperature ranges and a correlation of their electrical signature between TD and FD is carried out. These two phenomena were related to the thermal activation of ions coming from two different trap levels (shallow and deep traps). We validate here also the fact that the FD method is a powerful way to estimate the dc conductivity in dielectric solids at high temperature thanks to a better discrimination of ionic contributions and injection phenomena.

Studies on the synthesis and characterization of Zn1− x Cd x S and Zn1− x Cd x S:Mn2+ semiconductor quantum dots

Quantum dots (3–4 nm) of Zn1− x Cd x S (both free of Mn2+ and with Mn2+ incorporated) were synthesized through a novel solvothermal-microwave irradiation technique. Detailed structural analysis of the Zn1− x Cd x S and Zn1− x Cd x S:Mn2+ (x = 0, 0.25, 0.5, 0.75 and 1) materials was carried out using powder X-ray diffraction technique. For all the compositions, the crystallite size was controlled to less than 1.5 nm. The optical energy gap for Zn1− x Cd x S was found to vary from 3.878 to 2.519 eV and for Zn1−x Cd x S:Mn2+ it varies from 3.830 to 2.442 eV when x is increased from 0 to 1. Overall, the optical energy gap could be tuned from a minimum of 2.442 eV to a maximum of 3.878 eV. DC conductivity analysis (from 40°C to 150°C) and electrical energy gap analysis for all the compositions were also performed. The dc conductivity for Zn1− x Cd x S solid solutions varies from 0.3840 × 10−10 to 8.7782 × 10−10 mho/m at 150°C and for Zn1− x Cd x S:Mn2+ it varies from 0.5751 × 10−10 to 9.8078 × 10−10 mho /m at 150°C (for x = 0 to x = 1). The method of synthesis and the results observed in this investigation may assist in the fabrication of optical devices when the required operational performance falls under the range observed in the study.

Characterization of YSr 2Fe 3O 8 − δ as electrode materials for SOFC

YSr 2Fe 3O 8 − δ was prepared by traditional solid state reaction method and characterized by X-ray diffraction, ac impedance, dc conductivity, dilatometry and thermogravimetric analysis for possible use in solid oxide fuel cells (SOFCs). YSr 2Fe 3O 8 − δ crystallizes with tetragonal symmetry in the space group P4/mmm and found to be stable at high temperatures under H 2 and air. Four probe dc electrical conductivity measurements show that the conductivity increases up to 745 K and then decreases with temperature; the highest conductivity σ 745K = 43.5 S cm − 1 . The n-type conductivity at low oxygen partial pressure (pO 2) changes to p-type at high pO 2. Polarization behavior was investigated measuring the ac impedance response in symmetrical cell arrangements in air with YSZ and GDC electrolytes. Cathodic area specific resistance (ASR) varies with firing temperature. The lowest area specific resistance was observed with a GDC electrolyte fired at 1000 °C. In case of YSZ, ASR increases and in case of GDC, ASR decreases in air when electrode firing temperature decreases. At 800 °C ASRs are 0.20 Ω cm 2 and 0.65 Ω cm 2 with GDC and YSZ electrolytes, respectively, in air. Fuel cell measurements with symmetrical electrodes were performed using a thin YSZ electrolyte under H 2 at anode and air at cathode, show that the power density is about 0.035 W/cm 2 at 900 °C.

Synthesis, characterization, electrical transport and magnetic properties of PEDOT–DBSA–Fe 3O 4 conducting nanocomposite

Electrical transport and magnetic properties of newly synthesized conducting polymer nanocomposites involving poly(3,4-ethylenedioxythiophene) (PEDOT) and Fe 3O 4 nanoparticles are studied. Nanocomposite samples of varying proportions of inorganic to organic components were synthesized by adding EDOT monomer stabilized in miceller solution of DBSA (dodecylbenzene sulphonic acid) to aqueous colloidal dispersion of Fe 3O 4 nanoparticles, followed by oxidative polymerization using ammonium peroxodisulphate (APS). Transmission electron microscopic (TEM) photographs show presence of distinct spherical Fe 3O 4 naonparticles having diameter range of 20–40 nm and they are incorporated within the polymer chain in the nanocomposite samples. Temperature-dependent DC conductivity analysis indicates a smooth cross-over of the charge conduction from the high temperature 3D Mott's variable range hopping (VRH) mechanism to the 2D ES (Efros and Shklovoskii)-VRH behaviour at low temperature. Temperature-dependent DC magnetization studies reveal enhancement of blocking temperature ( T B ) in the nanocomposite samples compared to that of bare Fe 3O 4 nanoparticles. Core shell morphology of the nanoparticles seems to be the cause for lowering the value of saturation magnetization of the Fe 3O 4 nanoparticles. Estimated magnetic domain sizes are comparable to those of grain sizes for the nanocomposite samples having lower content of nanoparticles (P 50 and P 100). Temperature-dependent AC-susceptibility data also supports the superparamagnetic behaviour.

AC and DC conductivity analysis of hydroxyapatite and titanium calcium phosphate formed by dry ball milling

In this paper, we present the preparation and electrical properties of nanocrystalline powders of hydroxyapatite (HAP) bioceramics, produced using the starting materials Ca(H2PO4)2, Ca(OH)2 and a high energy dry ball milling technique. Titanium calcium phosphate (CaP–Ti) was also prepared, the raw materials Ca(H2PO4)2 and TiO2, and examined. The HAP was obtained of milling 5, 10 and 15h while in the reaction with CaP–Ti, the CaTi4P6O24 phase was obtained after 5, 10 and 15h of milling. The HAP and the ceramic calcium phosphate with titanium (CaP–Ti) were studied by X-ray powder diffraction, DC and AC conductivity and dielectric constant measurements.

Phase transformation and percolation effect in [formula omitted] system

The structure and electronic transport properties have been investigated for composite PbO2–112Ag2O–xC (0≤x≤2) materials prepared by mechanical milling in an O2 atmosphere. The solid-state reactions result in the occurrence of abundant phase transformations, when the graphite content increases. With the phase transformations occurring, the percolation effect is observed for the electronic transport of PbO2–112Ag2O–xC system, while its conductivity undergoes an insulator–metal transition. The percolation threshold is determined by DC conductivity measurement and analysis of X-ray diffraction patterns.

The Metallic State of Conducting Polymers: Microwave Dielectric Response and Optical Conductivity

ABSTRACTRecent advances in processing of polyaniline and polyacetylene have resulted in a new generation of conducting polymers with higher dc conductivities. We present the temperature (T) dependent microwave frequency dielectric constant, dc conductivity, and Kramers-Kronig analysis of conducting polyaniline and polyacetylene. The low temperature dielectric constant, ε, increases with the square of the x-ray crystalline domain length for preparations of HCl protonated polyaniline. For the highest crystalline polyaniline samples, ε increases dramatically with increasing T, supporting formation of three-dimensional (3-D) coupled “mesoscopic” Metallic regions. A “metallic” negative ε is observed for d,1-camphor sulfonie acid doped polyaniline prepared in m-cresol. Optical studies show a linear increase in reflectivity below 7000 cm-1. Below 600 cm-1 the reflectance increases rapidly. Kramers-Kronig analysis of the ir-visible results are presented. Highly conducting polyaniline is shown to have two plasma frequencies, one at ∼ 1.1 eV involving all the conduction band electrons, and one at ∼0.015 eV (120 cm-1) that is suggested to arise from the most delocalized electrons. The concept of inhomogeneous disorder is introduced. The results for polyaniline are compared to those of highly doped polyacetylene which also show metallic negative ε demonstrating the intrinsic metallic nature of the new generation of conducting polymers.

Synthesis of novel polyaniline colloids using chemically grafted poly( N-vinylpyrrolidone)-based stabilizers

We report the synthesis of polyaniline colloids using a new polymeric steric stabilizer based on a poly( N-vinylpyrrolidone) copolymer. This copolymer stabilizer contains pendant aniline groups which are believed to participate in the in situ aniline polymerization, leading to the chemical grafting of the stabilizer onto the surface of the polyaniline particles. The stabilizer is compatible with both (NH 4) 2S 2O 8 and KIO 3 oxidants and so represents an improvement over our earlier work. Our electron microscopy studies have confirmed that the polyaniline colloid morphology depends on the oxidant used for the aniline polymerization. Thus the (NH 4) 2S 2O 8 oxidant produces spherical particles while the KIO 3 leads to the formation of “rice-grain”-shaped particles. The mass ratio of grafted stabilizer/polyaniline has been indirectly determined by assaying postreaction supernatant solutions by colorimetry using congo red dye as a complexing agent. The polyaniline colloids were further characterized by a wide range of techniques including FTIR and visible absorption spectroscopy, microanalysis, dc conductivity, and thermogravimetric analysis.