High dielectric permittivity in the microwave region of SrBi2Nb2O9 (SBN) added La2O3, PbO and Bi2O3, obtained by mechanical alloying

Abstract

This paper presents the microwave dielectric properties and a structural study of SrBi2Nb2O9 (SBN) added La2O3, PbO or Bi2O3 obtained by a solid state procedure. High-energy mechanical milling was used to reduce the particle size, which allows for a better shaping of the green body and an increased reactivity. The mechanical milling activation process produced a reduced sintering temperature in the material, decreasing the loss of the volatile elements and controlling the growth of the grain that is produced when a high temperature is required to obtain dense ceramics. The incorporation of La3+, or Pb2+, or Bi3+ of different amounts (0, 3, 5, 10 and 15 wt%) was used to improve the densification without changing the crystal structure, since with a low doping content these ions can occupy the A site of the perovskite blocks; they can also occupy the Bi3+ sites in Bi2O3 layers. A single orthorhombic phase was formed after calcination at 800 °C for 2 h. X-ray diffraction, Fourier transformation, infrared and Raman spectroscopy have been carried out in order to investigate the effects of doping on SBN. The dielectric permittivity (ε′r) and loss in the microwave region (2–4 GHz) of SBN ceramics with additions of Bi2O3, La2O3 and PbO were studied. Higher values of permittivity (εr′ = 154.6) have been obtained for the SBN added La (15 wt%); a lower loss (tgδ = 0.01531) was also achieved in the SBN added La (15 wt%) sample with PVA and TEOS, respectively. The samples that showed the highest dielectric permittivities were all lanthanum doped, all with values of permittivity above 90. A comparative study associated with different types of binders was completed (with glycerin, PVA and TEOS). This procedure allowed us to obtain phases at lower temperatures than usually appear in the literature. The microwave dielectric properties (permittivity and loss) in the region 2–4 GHz, were studied for all samples. The structural and microwave dielectric properties of SBN show a high potential for applications in the microwave region for filters, antennas etc.