Dobijanje piezoelektrične keramike i tankih filmova na bazi bizmut natrijum titanata

Abstract

Piezoelektrično prikupljanje energije predstavlja jednu od obećavajućih alternativnih tehnologija koje bi mogle doprineti zameni fosilnih goriva i smanjenju njihovog negativnog uticaja na životnu sredinu. Ova tehnologija se zasniva na prikupljanju mehaničke energije iz dostupnih izvora, kao što su pritisak i vibracija, i njihovoj transformaciji u električnu energiju, koja se skladišti i napaja energijom manje potrošače. Piezoelektrični materijali predstavljaju osnovne komponente uređaja za prikupljanje energije, a od početka njihovog razvoja do danas, keramički materijali na bazi olova su prepoznati kao najbolji kandidati za ovu primenu. Otkako je zakonom definisano ograničenje upotrebe olova u elektronskim komponentama, traje intenzivna potraga za materijalima koji mogu da zamene materijale na bazi olova. Bizmut natrijum titanat (Bi0.5Na0.5TiO3) predstavlja obećavajuće rešenje, s obzirom da poseduje sličnu strukturu kao olovo cirkonijum titanat, visoku Kirijevu temperaturu (oko 320 °C) i mogućnost dodatka različitih jona (npr. jona barijuma) kada dolazi do formiranja morfotropne granice faza i visokih vrednosti piezoelektričnog koeficijenta. U ovoj doktorskoj disertaciji su sintetisani prahovi na bazi bizmut natrijum titanata hidrotermalnom metodom, pri čemu je praćen uticaj parametara sinteze na fazni sastav i morfologiju prahova. Prahovi su potom presovanjem oblikovani u tabletice i sinterovani, kako bi se dobila gusta keramika. Ispitan je uticaj termičkog tretmana i dodatka jona barijuma na fazni sastav, gustinu i dielektrična svojstva bizmut natrijum titanata. Takođe, uočeno je formiranje sekundarne faze sa povećanjem udela barijuma u strukturi, te je jedan od ciljeva ovog rada bio optimizacija (1−x)Bi0.5Na0.5TiO3-xBaTiO3 sistema, pri čemu je sekundarna faza eliminisana u potpunosti, što je značajno poboljšalo funkcionalna svojstva materijala. Trend minijaturizacije elektronskih komponenti, koji danas predstavlja neophodan korak u razvoju tehnologije, usmerio je veliki deo istraživanja piezoelektričnih komponenti na tehnologiju razvoja tankih filmova. U ovom radu, pripremljeni su tanki filmovi sintezom iz tečne faze (sol-gel metodom), a prethodna iskustva u sintezi prahova iz tečne faze značajno su doprinela uspešnoj sintezi filmova. Naime, ispitan je uticaj različitih termički tretman. Na ovaj način dobijeni su homogeni nanokristalni filmovi debljine ispod 300 nm, sa dobrom adhezijom na supstrat, željenog faznog sastava i dielektričnih svojstava.

Piezoelectric energy harvesting is one of the most promising alternative technologies that could replace the use of fossil fuels and their negative impact on the environment. This technology is based on the harvesting of mechanical energy from available sources such as pressure and vibration, and its conversion into electrical energy, which is stored and can power smaller energy consumers. Piezoelectric materials arethe key components of the piezoelectric energy harvesters. From the beginning of their development, lead-based materials have been recognized as the main candidates for this purpose due to their superior functional properties. Since the use of lead in electronic components has been regulated by law, there is a need to find suitable materials to replace lead-containing systems. Bismuth sodium titanate is considered as a promising solution, because it has similar crystal structure to lead zirconate titanate, high Curie temperature (about 320 °C) and the possibility of chemical modification of the composition with different ions (e.g. barium) when the morphotropic phase boundary forms, resulting in a significant increase of piezoelectric properties. In this dissertation, bismuth sodium titanate based powders were sintetized by hydrothermal method and the influence of the synthesis parameters on the phase composition and morphology were studied. The obtained powders were pressed into pellets and sintered in order to obtain dense ceramics. The effect of thermal treatment and addition of barium ions on the phase composition, density and dielectric properties of bismuth sodium titanate was investigated. Moreover, the formation of a secondary phase with the increase of barium ion concentration was noticed. Therefore, one of the main objectives of this research was to optimize the processing of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3. The complete elimination of the secondary phase resulted in a significant improvement of the functional properties. The trend toward miniaturization of electronic components, which is one of the necessary steps in the development of technology, has directed one big part of research on piezolectric components towards the development of thin film technology. The experience of powder synthesis by wet chemical method has been of significant importance for the synthesis of thin films. In this research, multilayered Bi0.5Na0.5TiO3 films were prepared by sol-gel technique, and the influence of various synthesis parameters (such as solvents, substrates and thermal treatment) was investigated. Optimization of the processing parameters resulted in homogeneous nanocrystalline films with a thickness below 300 nm, good adhesion to the substrate, the desired phase composition and good dielectric properties.