MAGNETORESISTANCE OF FeS1.14 SINGLE CRYSTALS FOR B // c

Measurements of the transverse magnetoresistance on natural single crystals of pyrrhotite FeS1.14 revealed a phenomenon of the order 10-3. The shape of the curves Δρ/ρ(0) vs. B for different temperatures is explained and the magnitude of the magnetoresistance can be adequately forseen by the s-d model

Metal to insulator transition in conducting polyaniline/graphene oxide composites

Broadband dielectric spectroscopy measurements of polyaniline/graphene oxide composites were conducted for an as-prepared and a thermally annealed specimen, respectively, from 15 K to room temperature. The electrical conductivity values of the annealed composite display a very modest rise denoting the important contributions of the graphene oxide component to achieving electrical stability of the polymer. Patterns of the dc conductivity as a function of temperature also reveal a metal to insulator transition at around 75 K. The transition is dominated by two key factors: temperature and annealing process. Metal-like and insulating features are subsequently detected, as well, and accordingly described to provide a qualitative inspection of the charge transfer mechanisms involved. © 2019 Author(s)

Interfacial and space charge dielectric effects in Polypyrrole/ZnO composites

Polypyrrole/zinc oxide composites were studied by Broadband Dielectric Spectroscopy in the frequency range 10 mHz–1 MHz for temperatures ranging from 15 K to room temperature. Lowering temperature, the dc conductivity was suppressed revealing underlying dielectric relaxation mechanisms. For 20, 30 and 40 wt.% ZnO composites, a relaxation was detected in the vicinity of range 104–10­5 Hz. Its typical mean relaxation time and its concentration dependence are compatible with Sillar's model for interfacial polarization in heterogeneous matter. At high ZnO concentrtion, a low-frequency relaxation also appeared around 0.01–10 Hz, stemming from space charge polarization. The shift of the relaxation upon temperature provides an insight to the dynamics of relaxing charge entities. Composites consisting of 10 wt.% ZnO are most suitable optoelectronic material, as they combine good electrical conduction, low capacitance effects and ohmic sample-electrode contacts. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Conductivity Degradation Study of polypyrrole and polypyrrole/5% w/w TiO2 nanocomposite under Heat Treatment in Helium and Atmospheric Air

The thermal aging of the d.c. electrical conductivity sigma in pure polypyrrole (PPy) and in the nanocomposite PPy/5%w/w TiO2 was investigated for thermal treatment times from 0 to 50 hours at different temperatures Tau = 100, 300 and 380 K under atmospheric air and inert He gas. In both materials the fluctuation induced tunneling of charge carriers was followed revealing a granular metal structure. The isothermal variation of sigma with time under atmospheric air and inert He indicates the coexistence of two antagonistic mechanisms, the one increasing and the other decreasing sigma. In XRD patterns from PPy and PPy/5%w/w TiO2 the sharp peaks of rutile and anatase crystallographic types of TiO2 coexist with the broad peak of amorphous PPy. The latter shifts to smaller angles with the addition of TiO2 indicating a greater separation of pyrrole rings, which turns up to be about equal to the diameter of O2- indicating the diffuse of oxygen from TiO2 into PPy. SEM pictures confirm the removal of Cl- in the form of HCl during thermal aging, a process which decreases the conductive part of the polymer and at the same time rearranges the chains. These represent two antagonistic mechanisms the first decreasing, the second increasing conductivity.nbspnbs

Interfacial and space charge dielectric effects in Polypyrrole/Zinc Oxide composites

Polypyrrole/zinc oxide composites were studied by broadband dielectric spectroscopy in the frequency range 10 mHz to 1 MHz for temperature ranging from 15 K to room temperature. Lowering temperature, the dc conductivity was suppressed, revealing underlying dielectric relaxation mechanisms. For pristine polypyrrole and 10 wt% ZnO composites, no dielectric relaxation is detectable. For 20, 30 and 40 wt% ZnO composites, a relaxation was detected in the vicinity of range 104–105 Hz. Its typical mean relaxation time and its concentration dependence are compatible with Sillar's model for interfacial polarization in heterogeneous matter consisting of inclusions dispersed within a dielectric matrix. At high ZnO concentration, a low-frequency relaxation also appeared around 0.01–10 Hz, stemming from space charge polarization. The shift of the relaxation upon temperature provides an insight to the dynamics of relaxing charge entities. © 201