Estudo das propriedades Dielétricas da matriz cerâmica SrBi2Nb2O9 (SBN) para uso em dispositivos de RF e microondas

Abstract

The group of ferroelectric materials with bismuth layer (BLSFs) has been extensively studied due to their potential use in random access memories (FeRAMs applications). Layered structures of perovskite bismuth SrBi2Nb2O9 ( SBN ) belong to the Aurivillius family, which has the general formula (Bi2O2)2+(An-1BnO3n+1)2-, where the sites are occupied by the larger cations, whereas the cations with high valence are located in sites B and n is the number of octahedral layers between the layers of bismuth (Bi2O2)2+. The presence of the bismuth layer serves as a buffer to withstand fatigue and polarization preserving the stability of the bismuth layer structured ferroelectrics. In this work, the structural and dielectric properties of SrBi2Nb2O9 (SBN) based on the level of addition of Bi2O3 or La2O3 on radio frequencies (RF) and microwave were studied. The SBN was prepared using the method of solid state reaction with the addition of 3, 5, 10 and 15% of Bi2O3 and La2O3. A single orthorhombic phase was formed after calcination at 900° C for 2h. The analysis by X-ray diffraction (XRD) using the Rietveld refinement confirmed the formation of a single phase compound with a crystal structure (a = 5.5129Å, b = 5.5183Å, c = 25.0819Å, α = β = γ = 90°) . The scanning electron microscopy (SEM) showed the material (nearly round) globular grain morphologies across the surface of the samples. The Curie temperature found for the undoped sample was 400°C. With additions of Bi3+, and the decreased temperature and with additions of La3+ Curie temperature rose significantly above 450°C. In the measurement of the dielectric properties of SBN at room temperature to 10 MHz, the highest values for permittivity SBN5LaP (5% La2O3) were observed, with values of 116.71 and the lowest loss (0.0057) was obtained by SBN15LaP (15% La2O3). In the region of frequency microwave , added Bi2O3 samples showed higher dielectric permittivity that La2O3 samples added, highlight the SBN15BiG (15% Bi2O3) with higher dielectric permittivity in 70.32 (3.4GHz) . The values of dielectric constant are included in the range of 28-71 and the dielectric losses are of the order of 10-2. The samples were investigated for possible applications in RF and microwave components.