Wpływ warunków technologicznych na właściwości tytanianu sodowo-bizmutowego Na0,5Bi0,5TiO₃

Abstract

The purpose of the work was to investigate the influence of conditions in which sodium - bismuth titanate Na0.5Bi0.5TiO3 (NBT) was obtained on its properties. The thesis was put forward that various technological conditions for obtaining this material can significantly affect its properties, including in particular ferroelectric, relaxor and depolarization properties. Increasing the depolarization temperature, and thus expanding the temperature range of the ferroelectric phase is of great importance when using the material in electronics. The choice of this topic is very important because the commonly used in electronics compound zirconate - lead titanate (PZT) in accordance with the directive of the European Union should be withdrawn from use. NBT could be a potential successor to PZT, however, its piezoelectric properties are weaker than PZT. Therefore, the question arose whether changing the conditions for the fabrication of NBT can strengthen these properties. The dissertation presents the results of tests carried out on samples of NBT in form of ceramics, whose production conditions differed from the base sample by: - sintering times, - sintering time, - method of manufacture (conventional and hot pressing). The first part of the work presents theoretical knowledge about ferroelectric materials and testing their properties. Literature data on NBT are also provided. The second part of the work presents the technological conditions in which the tested samples were produced and the results of the tests carried out, including structural, microstructural, mechanical, thermal, electrical. At the end of the work the conclusions of the results obtained are presented, which show that at least part of the discrepancies in the experimental literature data and controversy in their interpretation may result from different technological conditions for obtaining NBT samples. The research allowed to determine that technological conditions affect the crystal structure and microstructure, dielectric, ferroelectric and thermal properties. They also enabled the selection of the most favorable technological conditions for the production of NBT, giving the best material properties. The developed method of producing the tested material improves dielectric and ferroelectric properties and increases the depolarization temperature. Studies have also shown that the previous action of an external electric field has a significant effect on the properties of the ferroelectric phase. So far, NBT discharge currents, charging currents and current-voltage characteristics have not been studied, which was completed as part of this dissertation.