Propriedades dielétricas da matriz Bi2Mo2O9 com adição de Al2O3 para aplicações em micro-ondas e radiofrequência (RF)

Abstract

In the search for new high-performance materials for microwave and radio-frequency telecommuni- cation systems, with connectivity to various types of technologies, this work investigated the struc- tural and dielectric properties of the monoclinic Bi Mo O (BMO) ceramic matrix modified with 2 2 9

alumina (Al O ) additions at 10, 20, and 33 wt%. BMO powders were synthesized by the conventi 2 3 -

onal solid-state reaction method and calcined at 600 °C. The phases present were confirmed by X- ray diffraction with Rietveld refinement. Cylindrical pressed samples were sintered at 640 °C. Die- lectric characterization was performed in the radiofrequency (RF) and microwave (MW) regimes,

also considering the temperature dependence of the properties for potential application in electronic devices operating within these bands. The main objective was the development of ceramic dielectric components with low relative permittivity, effective porosity control, low dielectric loss, thermal stability, and optimized performance in key parameters such as bandwidth, gain, and efficiency. Using the Hakki–Coleman method, the relative permittivity (εr) showed a maximum value of 33.45 for pure BMO with a relative density of 89%, decreasing systematically with the increase in Al O2 3 mass fraction, down to 12.02 for 33% addition. The dielectric loss tangent (tan δ) increased from 7.14×10-4 to 2.35×10-3 with higher Al O content. Thermal stability was optimized in the compositi 2 3 - on with 10 wt% Al O , presenting a resonant frequency temperature coefficient (τ 2 3 f) of 3.24

ppm·°C-1. Far-field simulations were conducted using HFSS software, demonstrating good agree- ment with the experimental data. The performance of dielectric resonator antennas (DRA) based on

these composites showed high efficiency (> 93%), low reflection coefficients (S11 < -30 dB), and an increase in the HE11δ mode resonant frequency with increasing Al O concentration. The (BMO) 2 3 1-X: (Al O ) 2 3 X composite showed applications in MW and RF devices at 10 and 20 wt% concentrations,

due to its tunable dielectric properties, thermal stability, and thermally activated electrical conducti- on.