Estudo das propriedades dielétricas e estruturais das matrizes cerâmicas Na2Nb4O11 (NN) com aditivo de Bi2O3 para aplicações em componentes de rádio frequência e microondas

Abstract

In this present work, Na2Nb4O11, ferroelectric ceramics have been investigated by their monoclinic phase structural and dielectric properties have been enhanced by the addition of 2, 5 and 10 wt% Bismuth. Na2Nb4O11 powders have been produced by conventional solid-state reaction method. Milling process was carried out by using a high energy planetary mill. The calcined powders were thoroughly weighted and pressed using an axial press to make cylinder pellets for sintering. The single-phase Na2Nb4O11 was determined by X-Ray Diffraction (XRD) technique and Rietveld refinement method, while morphology, crystal structure and phase composition were determined via Scattering Electron Microscopy (SEM) where the samples’ crystal structure micrographs show nearly the density measures obtained by Pycnometry technique. Dielectric characterization was carried out over a radiofrequency (RF) and microwave (MW) range. Both cases, we have studied the properties related to temperature variation for likely applications to RF and MW devices. We have focused on obtaining dielectric ceramics with high dielectric permittivity ( r  ), low dielectric loss ( tan ) and near-zero temperature coefficient of resonant frequency ( f  ). Room temperature measures at 25°C have had a high permittivity value ( r  =250.9) for NN10Bi (10% of Bi2O3) at 10 kHz and a dielectric loss, relatively low value ( tan =1.8010-2) for NN2Bi (2% of Bi2O3) at 1MHz. Varying temperature and fixed frequency at 100 kHz, we have obtained a high dielectric permittivity value ( r  = 440.78 at 440°C) for NN2Bi and a dielectric loss about 1,81.10-1 at 280°C for NN10Bi. Near-zero temperature coefficient of resonant frequency ( f  ) has shown possibility of reaching thermal stability ( f  = 0) as increasing Bi2O3 addition level. For NN00 we have obtained f  = - 3378.42 ppm/oC. More Bi2O3 addition provides f  = - 250.04 ppm/oC for NN10Bi. Microwave measures were carried out using Hakki Coleman technique. A numerical simulation was also achieved for each sample for verifying the similarity to experimental data. In this study we have obtained NN10Bi ceramics, applicable for low-gain antenna devices, for satellite communication systems, wireless internet, radar, microwave oven, radio frequency receptor and spacecraft designing. Keywords: Ferroelectricity; dielectric ceramics; Na2Nb4O11.