Zeynep Güven Özdemir

Polypropylene/basalt thick film composites: structural, mechanical and dielectric properties

Abstract In this work, polypropylene/volcanic basalt rock (PP/VBR) thick film composites with different VBR powder mass ratio varying from 0.5 wt.% to 20.0 wt.% were prepared by using the hot press technique. The effects of VBR powder doping on mechanical, structural and dielectric properties of PP were investigated by stress-strain measurements, Fourier transform infrared analysis, thermal gravimetric analysis, scanning electron microscopy and dielectric spectroscopy methods. The highest tensile strength, percentage strain and energy at break were achieved for 0.5 wt.% VBR powder doped PP composite. According to the stress-percentage strain curves of the samples, it was observed that 0.5 wt.% VBR powder doping increases the mechanical performance of PP polymer. In addition, regardless of the doping concentration level of basalt powder, the real part of complex dielectric function (ε′) of all PP composites display approximately frequency independent behavior between 100 Hz and 1 MHz. On the other hand, 0.5 wt.% VBR powder doped PP composite has also the lowest dielectric constant at the vicinity of 2.7 between 100 Hz and 1 MHz. The composite also has considerably low dielectric loss which has a crucial importance for technological applications. For these reasons, PP/0.5 wt.% VBR composite with the highest tensile strength can be considered as a suitable candidate for microelectronic devices. Furthermore, the alternative current conductivity mechanism was determined as nearly constant loss due to approximately constant dielectric loss between 10 Hz and 1 MHz.

CALCULATION OF MICROWAVE PLASMA OSCILLATIONS IN HIGH TEMPERATURE SUPERCONDUCTORS

It has been determined that the superconducting system, that consists of copper oxide based mercury oxide, behaves as if an oscillating cavity with the plasma frequency of 10 12 Hz under particular amount of magnetic field at space temperature of 100 K. Moreover, plasma frequency of superconducting system (mercury based superconductors) were found to be varying from infrared to microwave region by increasing the temperature from liquid helium of 4.2 K to space temperature of about 100 K. Furthermore, by dealing with calculations of Lawrance-Doniach Model it was found that the plasma frequency versus temperature relation satisfies the sigmoidal distribution whereas the anisotropy factor coincides with the polynomial fitting function.

Effect of borax additive on the dielectric response of polypyrrole

The main aim of this study is to produce added polypyrrole (PPy) borax composites with high dielectric properties for technological applications. For this purpose, PPy–borax composites with different borax concentrations varying from 10 to 50 wt% have been prepared. To reveal their structural and morphological attributes, the composites have been characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy. The real and imaginary parts of complex dielectric function, the imaginary component of complex electrical modulus and ac conductivity have been investigated at room temperature as a function of frequency in the range 100 Hz–15 MHz. It has been found that addition of borax increases the dielectric constant of pure PPy. In this respect, PPy–borax composites with the highest dielectric constant at low frequency may be utilized in charge storing devices. On the other hand, the dielectric loss is also very high in low-frequency region for the composites with high borax content. Exploiting this property, the material may also be used in decoupling capacitor applications. The relaxation mechanisms of the samples have also been determined as non-Debye type. The Nyquist curves of the samples have been analysed for calculating the grain and grain boundary resistance and capacitance values. In conclusion, borax has a promising potential to be used as a cheap and effective filler for improving the dielectric properties of PPy polymer.

Sodium meta silicate doped PPy and PT composites with giant dielectric constant

In recent years, scientists have focused on searching new dielectric materials due to increasing necessity of high dielectric constant materials for microelectronic applications. Especially, developing a new high dielectric constant materials with low cost and weight has a crucial role in power electronic systems. From this point of view, conducting polymer/mineral composites have been prepared for achieving high dielectric constant material in this work. The dielectric and ac conductivity properties of the polypyrrole/sodium metasilicate (PPy/Na2SiO3) and polythiophene/sodium metasilicate (PT/Na2SiO3) composites have been determined by impedance spectroscopy measurements performed between 100 Hz-15 MHz. The highest dielectric constants have been obtained as 105 and 107 for PPy and PT composites with weight percentages of 10% and 50% Na2SiO3 doping, respectively. The relaxation mechanism of the composites have also been analyzed by the frequency dependence of imaginary component of complex electrical modulus. In addition, ac charge carrier transport mechanism of the samples have been investigated.

Structural and dielectric properties of Europium based copper oxide layered perovskite material

ABSTRACT In this study, EuBa2Cu3O7+x (coded as Eu-123) material was synthesized by solid state reaction method and its chemical and physical properties were determined by FTIR, XRF, TGA and DTA techniques. The dielectric and impedance properties of Eu-123 were determined by HP-4194A Impedance Analyzer at room temperature. Eu-123 displays negative dielectric constant (NDC) property, which has a crucial importance for producing metamaterials. Moreover, the relaxation process of the material was also determined as pure conduction. In addition, it was revealed that application of magnetic field does not affect the NDC property of the sample but slightly changes the values of ϵ ′.

Molecular orientation of nickel phthalocyanine doped nematic liquid crystal composite under magnetic field

ABSTRACT The electrical and dielectric properties of the nematic liquid crystal (E63) and Nickel Phthalocyanine (NiPc) doped E63 composite have been investigated by dielectric spectroscopy under 0–0.4 T magnetic field. It has been observed that NiPc doping and external magnetic field, B decrease threshold voltage. Moreover, conductivity of the composite has an increasing tendency with magnetic field. Furthermore, a significant decrease in relaxation frequency with B has been interpreted as the simplification of molecular orientation. Hence, NiPc doping enhances the magnetic sensitivity of E63 and increases molecular orientation ability and conductivity.

The impact of NiPc additive and laser light dielectric properties of E63 nematic liquid crystal

ABSTRACT In this work, the electrical properties of the pure nematic liquid crystal (E63) and different concentrations Nickel Phthalocyanine (NiPc) doped (E63+1%NiPc, E63+3%NiPc and E63+5%NiPc) E63 have been investigated by means of dielectric spectroscopy measurements under laser light illumination. The variations of the real () and imaginary () parts of dielectric constant with frequency have been studied. According to versus voltage graphics, threshold voltage, Vth has been calculated. It has been observed that while NiPc doping increases the Vth, the application of laser light has a remarkable decreasing effect on threshold voltage, Vth. The absorption coefficients, , and relaxation times, , have also been calculated for determining the relaxation mechanism. It has been revealed that the relaxation type of these materials is nearly-Debye type regardless of the laser illumination. Moreover, the dielectric strength has been analysed both Debye and Cole-Cole models. Furthermore, conductivity mechanisms of these composites under dark and laser illumination have been investigated for four frequency regions. It has been shown that conductivity mechanism of the composites are not affected by application of laser light above .

Chiral Liquid Crystal-Based Sensor for the Detection of Low Humidity

The humidity sensing capability of a film of (S)-5-octyloxy-2-[{4-(2-methylbuthoxy)-phenylimino}-methyl]-phenol liquid crystal (LC) was studied. The experimental results show that LC thin film offers a promising perspective as a sensing material for the detection of relatively low humidity levels at even room temperature. It was observed that the operating temperature has a considerable effect on humidity sensing performance of the sensor. A comparison of kinetic models applied to the adsorption of water molecules on the LC film was evaluated for the Ritchie and Elovich kinetic models. Linear regression analysis results show that Elovich equation provides the best correlation for the water molecule adsorption processes.

Correlation Between The Anisotropy and The Effective Mass of The Quasi‐Particles in Oxide Superconductors

Determination of Josephson penetration depth has a crucial importance in calculation of both anisotropy factor and the effective mass of quasi‐particles (m*) in high temperature copper oxide superconductors. In this study, the effective mass values of the quasi‐particles have been determined via third derivative of phase differences of quantum wave function that represents the superconducting state of the system. According to our calculations, the anisotropy factor and m* have been affected by temperature varying from 5 to 90 K for over‐doped sample. Moreover, the anisotropy factor and m* of the superconducting media are found to be changed by temperature, applied magnetic field and the oxygen annealing procedures. Furthermore, the quantum vertex which corresponds to the quantum gravity that has been already determined for optimally oxygen doped mercury cuprate superconductors has not showed up in over‐doped samples investigated.