DEVELOPMENT OF FERROELECTRIC CERAMICS AND THEIR COMPOSITES FOR ELECTROMAGNETIC APPLICATIONS

Date

2025-1-07

Author

Süer, Başar

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Ferroelectrics like BaTiO3 and BaxSr1-xTiO3 (BST) draw great attention for applications in devices operating at microwave frequencies commonly used for wireless electronic systems. Modern systems necessitate reconfigurable, adaptive, and/or tunable components to maximize performance while efficiently performing in a dynamic environment. With the advancements in ferroelectric materials and processing technologies, it is possible to manufacture low-cost and flexible electronics (powder dispersed polymer matrix composites, such as BST/polymers) which can satisfy the needs of such modern systems. At this point, as material scientists it is critical to understand formation mechanisms and related processes in order to address the dielectric-related properties of BST ceramics. With the help of computer analysis technology, it is possible to simulate such composite structures and analyze the distribution of the BST phases throughout the microstructure. This study includes both production of the BST and their composites. Rietveld analysis, Williamson – Hall, and Boltzmann – Matano approaches were carried out to understand structural properties of BST ceramics. Structural characterizations revealed co-existence of paraelectric cubic and ferroelectric tetragonal phases which indicated that the phase transformation was hindered due to limited kinetics at around room temperature. Moreover, investigations on BaTiO3 – SrTiO3 diffusion couple system showed that the Ba-rich and Sr-rich regions exhibited different diffusion characteristics. A demonstrative electromagnetic application (microstrip patch antenna) was designed using ANSYS HFSS operating at 8 GHz based on the dielectric properties of the synthesized BST ceramics in a BST/PDMS composite substrate. The proposed design was experimentally validated at the resonant frequency (8.15 GHz) with -28 dB reflection loss exhibiting its potential use in such applications that require miniaturized antennas on flexible substrates.

Subject Keywords

Ferroelectric Ceramics, Barium Strontium Titanate and their Composites, Structural Analysis via Rietveld's Method, BST Phase Formation and Kinetics, Microstrip Patch Antenna

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https://hdl.handle.net/11511/113353

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Graduate School of Natural and Applied Sciences, Thesis