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The influence of the mechanical activation of ZnO nanoparticle fillers on the structural and electrical properties of the matrix of poly(vinylidenefluoride)-ZnO (PVDF-ZnO) films was investigated. Transmission electron microscopy and scanning electron microscopy analyses showed that mechanical activation in a high energy planetary ball mill reduces the size of ZnO particles. X-ray diffraction and Raman spectroscopy revealed that PVDF crystallized predominantly as the -phase. Non-activated ZnO filler reduces the degree of the crystallinity of the matrix and promotes crystallization of α-phase of PVDF in the film, while the fillers activated for 5 and 10 min induce crystallization of -phase, indicating that mechanical activation of the filler can be used as a general method for fabrication of PVDF composites with increased content of piezoelectric -phase crystals.Dielectric spectroscopy measurements show that polymer composite with the high content of -phase (with ZnO filler activated for 5 min) exhibits the highest value of dielectric permittivity in 150-400 K range of temperatures. Kinetic analysis shows combined effects of increased surface area and increased concentration of surface defects on the interactions between polymer chains and activated nanoparticles.

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In this work the DC resistivity of sintered nickel manganite NiMn2O4 (NTC thermistor material) was studied as a function of additional powder activation time in a planetary ball mill (0, 5, 15, 30, 45 and 60 min). The activated powders and non-activated powder were sintered at different temperatures (900, 1050 and 12000C) for an hour. Structural changes were analyzed using XRD. Sample density, porosity and DC resistivity were measured on the same sintered samples. Correlations between sample density, porosity, and intrinsic DC resistivity vs. additional powder activation time and the sintering temperature were made. It was noticed that the resistivity falls with the increase of sample density (or increase of the sintering temperature)

The effects of Zn-doping on the dielectric behavior and electrical properties of bulk ?-Fe2O3 have been studied. X-ray diffraction analysis revealed the presence of two phases in all samples: hematite and spinel ZnFe2O4, with the amount of spinel phase increasing with increasing Zn content. Scanning electron microscopy analysis combined with energy dispersive X-ray spectroscopy showed that the Zn-bearing phase occurred in the form of individual spinel ZnFe2O4 grains in a hematite matrix. DC conductivity was measured in the temperature range 25-225oC (298-498 K). Impedance spectroscopy measurements in the same temperature range were carried out in the frequency range 100Hz to 10 MHz. Increase in the Zn content resulted in increased electrical conductivity and higher values of the dielectric constant. The resistance and capacitance of grains and grain boundaries were analyzed by modeling the experimental results using an equivalent circuit. [Projekat Ministarstva nauke Republike Srbije, br. III 45014]

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