REPOSITORY > RESULTS

Abstract

In the scope of this thesis, I focused on SrTiO3 (ST)-based dielectric ceramic composites as a lead-free perovskite material, which holds great potential for use in various electronic components. Such materials are large-scale and fabricated under high energy requirements, indicating an increasing need for a more environmentally friendly processing method. In this relation, Room Temperature Fabrication (RTF) offers a potential solution to reduce processing temperatures by using water-soluble inorganic compounds such as Li2MoO4 (LMO), which can be cured and densified at room temperature, resulting in the form of pure ceramic or ceramic composites.
In my doctoral research, I optimized the RTF processing parameters on the LMO-ST composite system to improve the dielectric performance. By using LMO or such inorganic salts as the binding phase between ST ceramic particles, an “upside-down” form of the composite was synthesized, where a high loading of functional ceramic filler and a small amount of binder in the form of a solid and saturated aqueous solution were combined. Densification occurs as the binder deposits on the surface of ST filler particles during pressing and drying.
Furthermore, I varied the composition (LMO binder content), which converted the upside-down composites to traditional 0-3 composites. In addition, alternative binders such as Na2MoO4, Na2WO4, Na2SiO3, and MgSO4 were found to be suitable candidates for RTF systems, which resulted in a relative density of 81-87 %, relative permittivity of 65-130, and dielectric loss tangent values of 0.002-0.05 at 1 MHz and corresponding resonant frequencies in the microwave range (4-6 GHz). In the light of comparison, I utilized BaTiO3 (BT) ceramics in the ceramic-binder upside-down composites and investigated the dielectric properties.
During the research course, all composite materials underwent characterization through microstructural imaging, mechanical testing (B3B), X-ray diffraction, Thermo-gravimetrical analysis, and Fourier-transform infrared analysis.
Additionally, I investigated the influence of residual porosity on the dielectric properties through theoretical modeling, i.e., rules of the mixture. The negative effect of residual porosity was partially mitigated by impregnation with Titanium isopropoxide (TTIP). In addition, OOF2 simulations were used to simulate the polarization and density of electric fields in such composites from the SEM images, and the experimentally observed phenomena were further explained.
Overall, this study's results brought meaningful progress in the field of RTF, which entails almost infinite possibilities of combining different materials for various applications and paves the way to more sustainable electronic production.