The nonlinear properties and frequency characteristics of ZnO-polypyrrole composites were investigated at 200 Hz-5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press metho...The nonlinear properties and frequency characteristics of ZnO-polypyrrole composites were investigated at 200 Hz-5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press method at 130 ℃. Results show an optimum point for breakdown voltage at ZnO content of 70%. Breakdown voltage decreases from 590 to 380 V and after that tends to increase from 450 to 740 V due to the absence of polypyrrole at grain boundaries. No matter how breakdown voltage behaves, nonlinear coefficient increases from 4.2 to 9 by increasing ZnO content because of the increase in acceptor-like states at grain boundaries by increasing ZnO content. The electrical parameters such as dielectric constant, dielectric loss and series resistance of samples show a strong dependence on frequency especially below 1 k Hz. These parameters fall off by increasing frequency up to 1 k Hz, which is related to charge transportation through the Schottky barrier at grain boundaries. The high dielectric constant of samples below 1 k Hz is related to the Maxwell-Wagner polarization at grain boundaries. The presence of different anomalies at different frequency intervals is related to interfacial polarization because of different structures of grains and intergranular layer with a huge difference in conductivity.展开更多
The effect of changes in sintering temperature on electrical properties and microstructure of ZnO?polyaniline?polyethylene composite ceramics,prepared in disk form at the pressure of 60 MPa and at five different tempe...The effect of changes in sintering temperature on electrical properties and microstructure of ZnO?polyaniline?polyethylene composite ceramics,prepared in disk form at the pressure of 60 MPa and at five different temperatures,has been investigated.Increasing sintering temperature from 30 to 120°C noticeably reduces breakdown voltage from 830 to 610 V.Further increase in sintering temperature causes breakdown voltage to increase.Interface voltage barrier height behaves differently when sintering temperature increases,which is in contrast to breakdown voltage behavior.These samples have a very low leakage current,a factor which indicates low degradation.Then again,the higher the sintering temperature gets,the less the nonlinear coefficient becomes.In addition,each sample has hysteresis which decreases through increase of sintering temperature up to 120°C.Further increase in sintering temperature,however,causes the hysteresis loop to spread.Regarding UV spectra of the samples,it is revealed that there are three impurity levels whose behaviors against sintering temperature are subtractive.Analysis of composite samples by scanning electron microscopy indicates that their microstructure consists of grains and grain boundaries.Resistivity of grain boundaries is the main responsible factor for these changes in varistor characteristic as a function of sintering temperature.展开更多
文摘The nonlinear properties and frequency characteristics of ZnO-polypyrrole composites were investigated at 200 Hz-5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press method at 130 ℃. Results show an optimum point for breakdown voltage at ZnO content of 70%. Breakdown voltage decreases from 590 to 380 V and after that tends to increase from 450 to 740 V due to the absence of polypyrrole at grain boundaries. No matter how breakdown voltage behaves, nonlinear coefficient increases from 4.2 to 9 by increasing ZnO content because of the increase in acceptor-like states at grain boundaries by increasing ZnO content. The electrical parameters such as dielectric constant, dielectric loss and series resistance of samples show a strong dependence on frequency especially below 1 k Hz. These parameters fall off by increasing frequency up to 1 k Hz, which is related to charge transportation through the Schottky barrier at grain boundaries. The high dielectric constant of samples below 1 k Hz is related to the Maxwell-Wagner polarization at grain boundaries. The presence of different anomalies at different frequency intervals is related to interfacial polarization because of different structures of grains and intergranular layer with a huge difference in conductivity.
文摘The effect of changes in sintering temperature on electrical properties and microstructure of ZnO?polyaniline?polyethylene composite ceramics,prepared in disk form at the pressure of 60 MPa and at five different temperatures,has been investigated.Increasing sintering temperature from 30 to 120°C noticeably reduces breakdown voltage from 830 to 610 V.Further increase in sintering temperature causes breakdown voltage to increase.Interface voltage barrier height behaves differently when sintering temperature increases,which is in contrast to breakdown voltage behavior.These samples have a very low leakage current,a factor which indicates low degradation.Then again,the higher the sintering temperature gets,the less the nonlinear coefficient becomes.In addition,each sample has hysteresis which decreases through increase of sintering temperature up to 120°C.Further increase in sintering temperature,however,causes the hysteresis loop to spread.Regarding UV spectra of the samples,it is revealed that there are three impurity levels whose behaviors against sintering temperature are subtractive.Analysis of composite samples by scanning electron microscopy indicates that their microstructure consists of grains and grain boundaries.Resistivity of grain boundaries is the main responsible factor for these changes in varistor characteristic as a function of sintering temperature.
