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Microstructure and electrical properties of ZrTiO4 ceramics

Microstructure affects the properties of ceramics. Since size and distribution of grains in microstructure determine the properties of ceramics, it is important to find out the relationship between grains and grain boundaries. The correlation between microstructure and electrical properties has been investigated by Scanning Electron Microscopy (SEM) and Impedance Spectroscopy (IS). The impedance spectra usually contain features that can be related to the microstructure. The purpose of the present research was to study electrical properties of ZrTiO4 ceramics prepared by sintering at the different temperatures and sintering times. The ceramics were prepared by sintering of the high-energy ball milled powder precursor. The sintering was performed at 1100 and 1400 °C and for 1, 4 and 8 h. The morphology and sizes of sintered grains in ceramics specimens were studied by SEM, JEOL T300, operated at 25 kV. For SEM measurements gold electrode was sputtered onto flat surface. Electrical properties of ZrTiO4 ceramics were investigated by impedance spectroscopy in the wide frequency range from 0, 01 Hz to 4 MHz, and over the temperature range from 303 to 473 K. The SEM micrographs indicated that the time and temperature of sintering are crucial for evaluation of microstructure. The ceramics sintered at 1100 &ordm ; ; ; ; C is porous while with increasing sintering temperature to 1400 &ordm ; ; ; ; C, there is corresponding enhancement of grain growth. Moreover, an increase of sintering time from 1 to 8 hours reduces the number of pores suggesting a formation of connected grains. Each ceramics exhibit a different shape of impedance spectra that follows observed changes in microstructure. Ceramics sintered at 1100 &ordm ; ; ; ; C show low electrical conductivity, which causes a large dispersion at low frequency region. Such a behavior is attributed to the electrical polarization appeared on highly porous ceramic surface. The impedance spectrum for ceramics sintered at 1400 &ordm ; ; ; ; C for 1 hour consists of single semicircle related to more compact ceramic structure. It was expected that ceramics sintered for 4 hours at 1400 &ordm ; ; ; ; C, also, shows impedance full semicircle because of lower pore fraction. However that was not observed. Although this ceramics is more compact with grains better connected over the grain boundaries, the SEM micrographs indicated that the grain boundaries have imperfect shapes. Therefore, such imperfect grain boundaries have blocking effect on charge carrier flow causing a decrease in electrical conductivity. On the other hand, impedance spectrum of ceramics sintered for 8 hours at 1400 °C contains two poorly resolved semicircles indicating two conducting mechanisms. Low frequency semicircle is related to conduction through grain boundaries whereas high frequency semicircle is related to conduction through grain interior. Accordingly, SEM images for these ceramics indicated well-shaped grains and grain boundary.

ceramics; microstructure; electrical properties

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