The influence of SrTiO₃ addition on the dielectric properties of Ba₂TiSi₂O₈ for high frequency microwave components

Abstract

This thesis investigated the structural, morphological, and dielectric properties of Ba₂TiSi₂O₈ (BTS) with SrTiO₃ (STO) additions (0, 5, 10, 15, and 20 wt%) across both radio frequency (RF, f < 300 MHz) and microwave (MW, 300 MHz < f < 300 GHz) ranges. The ceramic composites were synthesized via the solid-state reaction method, uniaxially pressed at 15.2 MPa into cylindrical disks, and sintered at 1200°C for 4 hours. Morphological analysis via Scanning Electron Microscopy (SEM) revealed distinct microstructural evolution with STO incorporation. X-ray diffraction studies were conducted for phase identification and structural refinement. Complex Impedance Spectroscopy (CIS) analysis correlated dielectric properties with microstructural features, where the Maxwell-Wagner-Sillars model best explained the observed behavior. The ceramic composites exhibited activation energies (Ea) ranging from 1.76 to 1.92 eV. Thermal capacitance coefficients (TCC) for 10-15% STO-added compositions fell within ±1500 ppm·°C⁻¹. Nyquist plots analyzed dielectric behavior, with grain and grain boundary effects modeled using equivalent circuits (CPE). For MW-range analysis, the temperature coefficient of resonant frequency (τf) obtained via the Silva-Fernandes-Sombra (SFS) method indicated optimal thermal stability for 3% STO addition (τf = +9.23 ppm·°C⁻¹), making it ideal for antenna applications. Hakki-Coleman measurements showed improved quality factors (53.64 ≤ Q ≤ 110.50), reduced loss tangents (tan δ), and permittivity (εᵣ) values. Numerical simulations demonstrated >96% electromagnetic efficiency when the composites functioned as antennas.